Metallic Biomaterials: Insights into the Microstructure and Electrochemical Properties of AISI 316L Stainless Steel

Metallic Biomaterials: Insights into the Microstructure and Electrochemical Properties of AISI 316L Stainless Steel | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Metallic Biomaterials: Insights into the Microstructure and Electrochemical Properties of AISI 316L Stainless Steel Ricardo Luiz Perez Teixeira This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8224459/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study provides a clear assessment of the corrosion and microstructural stability of metallic biomaterials, with a focus on AISI 316L stainless steel. Electrochemical methods—such as open-circuit potential (OCP), potentiodynamic polarization, and cyclic voltammetry — show that chloride-rich and organic-acid environments progressively destabilize passive films, reducing pitting resistance and hindering repassivation. Additionally, the cold-rolling process accelerates degradation by promoting the transformation of the γ phase to ε, then to α′ martensite, thereby increasing defect density and surface heterogeneity. Comparisons with titanium and NiTi-based materials reveal similar issues related to passive layer integrity. Welded 316L also shows the formation of δ-ferrite, σ-phase, and carbides, which contribute to corrosion susceptibility. Overall, the findings highlight that microstructure-environment interactions are key drivers of degradation, underscoring the need for controlled phase stability, passive film chemistry, and surface treatments for long-term performance, particularly in biomedical and industrial applications. austenitic stainless steel biomedical materials corrosion resistance deformation-induced martensite TRIP effect Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Introduction The TRIP effect in stainless steels during cold plastic deformation leads to the formation of two martensitic phases: α' and ε. The α' martensite is characterized by a body-centered cubic (BCC) crystalline structure and is ferromagnetic. This phase exhibits lenticular or thin-plate morphologies, which significantly enhance the steel's mechanical properties through the TRIP effect. The transformation of austenite to martensite during deformation is a key mechanism that contributes to the increased strength and ductility of these steels. The α' martensite has a body-centered cubic (BCC) structure, a common feature of steels undergoing the TRIP effect [ 1 ]. It is ferromagnetic, which distinguishes it from the non-magnetic austenitic phase. The α' martensite typically forms in lenticular or thin-plate shapes, thereby contributing to the material's mechanical properties. The TRIP effect involves the transformation of metastable austenite into martensite under mechanical stress, enhancing ductility and strength [ 2 , 3 ]. The transformation occurs due to plastic deformation, facilitated by the steel's low stacking fault energy [ 1 ]. The formation of α' martensite during deformation increases the material's strength and ductility, making it suitable for applications requiring high mechanical performance [ 4 , 5 ]. While the TRIP effect significantly enhances the mechanical properties of stainless steels, it is important to balance strength and ductility. The presence of martensitic phases can lead to increased brittleness if not adequately controlled, which is a critical consideration in the design and application of TRIP steels [ 4 ]. The microstructural evolution during deformation in austenitic stainless steels involves complex martensitic transformation pathways, particularly the γ → ε → α' sequence [ 6 , 7 ]. Initially, at low deformation levels, ε-martensite is predominant, but as deformation increases, the volume fraction of α'-martensite rises while ε-martensite reaches a peak and subsequently declines. Various factors, including deformation mode and temperature, influence this transformation. Two-step Transformation: The γ → ε → α' pathway is observed, where ε-martensite acts as an intermediate phase facilitating the transformation to α'-martensite [ 6 – 8 ]. Nuclei for α'-martensite form at shear-band intersections, twinning sites, and stacking fault clusters, enhancing the transformation process. The volume fraction of martensite increases with strain but is influenced by the strain rate; higher rates result in reduced martensite formation [ 9 , 10 ]. The presence of deformation twins and stacking faults precedes martensite nucleation, indicating a complex interplay between these microstructural features (Shen et al., 2012)(Yoshinaka, 2021). While the γ → ε → α' transformation is predominant, alternative pathways such as direct γ → α' transformations can occur under specific loading conditions, suggesting a nuanced understanding of deformation mechanisms in austenitic steels. ASTM F138 is a specification established by ASTM International that outlines the requirements for wrought austenitic stainless steel bar and wire composed of approximately 18% chromium, 14% nickel, and 2.5% molybdenum—known as UNS S31673 [ 11 , 12 ]. This alloy, commonly known as 316LVM (Low-Carbon Vacuum-Melted), is manufactured specifically for surgical implant applications. The standard ensures the material’s biocompatibility and safety by defining its chemical composition, mechanical properties (e.g., tensile strength, yield strength, and elongation), and metallurgical characteristics, including microstructure and cleanliness [ 13 – 15 ]. 316LVM is widely used in biomedical implants because of its superior corrosion resistance in physiological environments, high mechanical strength, and excellent formability, making it suitable for the production of a variety of medical devices, such as orthopedic plates, bone screws, and spinal rods [ 15 – 19 ]. Additionally, the vacuum melting process used in manufacturing 316LVM minimizes inclusions and impurities, which are critical factors in reducing the risk of implant-related complications, such as corrosion or immune response. AISI 316L is an austenitic stainless steel widely employed in biomedical applications, particularly in orthopedic and dental implants, due to its excellent corrosion resistance, mechanical properties, and biocompatibility [ 15 , 20 – 23 ]. It is standardized by the American Iron and Steel Institute (AISI), where the suffix “L” denotes a low carbon content (maximum 0.03% by weight), which minimizes carbide precipitation and improves resistance to intergranular corrosion [ 14 , 24 , 25 ]. This alloy is recognized internationally under various standards: as DIN 1.4404 by the Deutsches Institut für Normung (DIN); UNS S31603 under the Unified Numbering System (UNS) by the Society of Automotive Engineers (SAE) and ASTM International; and is covered by ASTM F138-19 and ISO 5832-1 as a material for surgical implants [ 11 , 26 ]. The ISO 5832-1 standard specifies the use of ASTM F138-grade 316L austenitic stainless steel in temporary and medium-term biomedical devices, including bone fixation plates, screws, and dental implants [ 13 , 15 , 17 ]. Its popularity is driven not only by its mechanical reliability and formability, particularly its good cold workability, but also by its cost-effectiveness and widespread technological availability in countries like Brazil, when compared to more expensive alternatives such as titanium-based alloys [ 27 , 28 ]. Despite its favorable performance, 316L stainless steel does not fully mimic the biomechanical behavior of human bone, and it has limitations in terms of elastic modulus mismatch and biological inertness [ 15 , 22 , 29 – 33 ]. Current research focuses on optimizing this alloy by modulating its chemical composition to enhance properties such as ductility, fatigue resistance, and TRIP (Transformation Induced Plasticity) behavior, while also reducing immunological responses, especially to nickel, which is known to trigger allergic reactions in a small percentage of the population [ 21 , 29 , 34 ]. Clinical experience with ASTM F138-grade 316L over the medium- and long-term has demonstrated adequate biocompatibility and low rejection rates, reaffirming its continued use in orthopedic and surgical applications when appropriately indicated [ 35 – 37 ]. The low carbon content in AISI 316L stainless steel (maximum 0.03% by weight) is crucial in preventing the metallurgical phenomenon of sensitization [ 36 , 38 , 39 ]. Sensitization occurs in stainless steels when exposed to temperatures between 400°C and 800°C, a range in which chromium carbides (Cr23C6) tend to precipitate along grain boundaries [ 24 , 40 ]. This carbide formation depletes chromium in adjacent regions of the microstructure, rendering these grain boundaries more susceptible to intergranular corrosion [ 41 , 42 ]. The precipitation of carbides and the consequent appearance of non-austenitic phases alter the intended microstructure of 316L stainless steel [ 43 , 44 ]. Such changes negatively impact its corrosion resistance and biocompatibility, compromising its performance for biomedical applications [ 14 , 29 , 45 ]. For this reason, international standards such as ISO 5832-1 strictly limit the presence of secondary phases, ensuring that 316L remains within the austenitic single-phase field [ 11 , 26 ]. When sensitization occurs, the resulting corrosion processes and phase transformations can lead to implant rejection and premature in vivo failure, highlighting the importance of maintaining strict metallurgical control during the manufacturing and processing of biomedical-grade stainless steels [ 16 , 17 , 46 ]. Although several studies have examined the passive-film breakdown, martensitic transformations, and corrosion behavior of AISI 316L stainless steel, few works have experimentally integrated the combined effects of chloride concentration and cold-rolling–induced microstructural heterogeneity using OCP, potentiodynamic polarization, and cyclic voltammetry under controlled conditions. The present study provides original experimental evidence showing how incremental deformation levels (0%, 10%, and 20%) and chloride-rich environments jointly influence Ecorr, Epit, Erep, anodic charge, and pit-stabilization mechanisms. By quantitatively linking TRIP-assisted γ → ε → α′ transformations to changes in anodic response and repassivation behavior, this work offers a unified and mechanistically grounded interpretation of degradation pathways in 316L, complementing and extending the current literature. These findings establish a direct correlation between deformation-driven microstructural evolution and electrochemical instability, a relationship that has not been explicitly demonstrated in previous studies. 2 Methodology The open circuit potential (OCP) of AISI 316L stainless steel was evaluated using an electrochemical cell connected to a PalmSens EmStat3 + potentiostat/galvanostat in OCP mode [ 47 ]. Three cylindrical specimens, each approximately 10 mm in diameter, were mechanically ground to 600-grit and polished with successive grades of alumina down to 0.1 micrometer. The specimens were then rinsed with deionized water, degreased in ethanol, and dried prior to immersion. This preparation ensured a reproducible metallic surface, minimizing artifacts associated with residual oxides or contaminants. Electrochemical tests were performed in a conventional three-electrode glass cell, as is widely recommended for corrosion studies [ 41 , 48 ]. The AISI 316L electrode served as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. These measurements were conducted at room temperature, following the standard practices described by Roberge [ 41 ]. The electrolyte consisted of aerated aqueous NaCl solutions with chloride concentrations ranging from 1.2 mol L⁻¹ to 2.8 mol L⁻¹ [ 49 ]. Immediately after immersion, the working electrode potential was recorded without external polarization. Measurements were carried out at 25°C under quiescent conditions. Data was collected until stabilization using the high-impedance OCP mode of the electrochemical workstation, as outlined in the PalmSens EmStat3 + system manual [ 50 ]. This approach allows evaluation of the alloy's spontaneous thermodynamic behavior and reflects the stability of its passive film in chloride environments, consistent with the criteria discussed by Tan and Frankel [ 51 , 52 ]. Potentiodynamic anodic polarization tests were performed using a three-electrode electrochemical cell connected to a PalmSens EmStat3 + potentiostat/galvanostat [ 47 ]. The AISI 316L stainless steel sample (working electrode) was embedded in epoxy resin to expose only the test surface. It was mechanically polished to a 1200-grit finish to ensure reproducibility of surface conditions. A saturated calomel electrode (SCE) served as the reference electrode, and a platinum wire served as the counter electrode. AISI 316L austenitic stainless steel was selected as the working electrode due to its recognized corrosion resistance [ 15 , 23 , 31 , 34 , 53 , 54 ]. However, its low pitting potential in chloride-rich environments raises concerns about its long-term durability. Research indicates that the AISI 316L critical pitting potential (Epit) decreases with increasing chloride concentration and temperature, highlighting the need for protective measures to enhance its performance under such conditions [ 25 , 49 , 55 , 56 ]. Commercial plates of AISI 316L austenitic stainless steel [ 22 , 44 , 57 ], each with a thickness of 4.5 mm and an area of 1 cm², were used, both with and without cold-rolling. Cold rolling was performed with two specific thickness reductions of 10% and 20%. Additionally, an as-received sample that had not undergone any cold work was investigated and designated for comparative purposes. All samples were analyzed in triplicate. Potentiodynamic polarization curves were recorded in 3.5 wt% NaCl aqueous solution at room temperature, a medium commonly used to simulate a physiological chloride-containing environment [ 38 , 43 , 48 ]. Each experiment was repeated three times to ensure statistical reliability of the results. The applied potential was scanned from − 800 mV to + 800 mV versus SCE at 0.3 mV/s. Standard electrochemical testing practices for corrosion studies typically use strict rates, such as − 300 mV to + 500 mV [ 58 ]. The electrochemical behavior of AISI 316L stainless steel was assessed using cyclic voltammetry (CV) in NaCl solutions with concentrations ranging from 1.2 to 2.8 mol·L⁻¹, following the procedure outlined by Cantarino [ 48 , 49 ]. The measurements were performed in a potential window from − 600 to + 1200 mV vs. Ag/AgCl at a scan rate of 1 mV·s⁻¹, employing an instrument current range of 0.001–10 mA. Prior to each test, the open-circuit potential was stabilized for 30 minutes, and all experiments were conducted at 25 ± 1°C. The CV procedure enabled the determination of the pitting potential (Epit), the anodic charge (Q⁺), and the mass loss per unit area of the electrodes after testing. According to the concentrations tested, Epit values ranged from 0.45 to 0.47 V at 1.2–2.0 mol·L⁻¹ NaCl and decreased to 0.37–0.36 V at 2.4–2.8 mol·L⁻¹, while the anodic charge increased markedly from 2.40 × 10¹ C to 1.41 × 10² C across the same concentration interval; the mass loss varied from − 2.11 mg·cm⁻² at the lowest chloride level to approximately − 36 mg·cm⁻² at the highest concentrations. These parameters were determined to quantify the influence of chloride content on the breakdown of passive films, anodic dissolution, and localized corrosion susceptibility of AISI 316L stainless steel. [ 59 ]. 3 Results The Open Circuit Potential (OCP) results presented in Fig. 1 show that as chloride content increased, the stable potential became slightly more negative. Although the alloy did not exhibit spontaneous depassivation, this negative shift indicates a gradual reduction in the passive-layer stability, a sign of increased susceptibility to pitting [ 40 , 41 , 48 ]. These findings support the competitive adsorption model, where chloride ions gradually weaken the passive film by displacing oxygenated species [ 52 ]. Although the OCP values in Fig. 1 remained within the passive range, they approached the pitting potential noted in the corresponding voltammetric tests. This relationship, often observed in stainless steels (Cantarino and Szklarska-Smialowska [ 49 , 60 ]), suggests that while higher chloride levels do not initiate corrosion at open circuit, they reduce the safety margin before stable pit formation becomes possible. Thus, the alloy remains passive, but it becomes increasingly vulnerable to anodic disturbances as the environment becomes more aggressive. AISI 316L maintained its passivity across all investigated chloride concentrations. However, the gradual negative shift in OCP indicates a steady decline in the passive film's robustness and an increased susceptibility to pitting [ 48 ]. These results validate classical descriptions of chloride-assisted breakdown of passive films and align with the broader electrochemical interpretations presented in the original study. Figure 2 shows the potentiodynamic polarization curves of AISI 316L steel. This curve reveals typical passive behavior, with metastable pitting processes evidenced by current oscillations. Understanding metastable pits, characterized by their nucleation, growth, and subsequent repassivation, is a critical aspect of the corrosion resistance of stainless steel [ 61 ]. This behavior, influenced by several factors, including the composition of the passive film and the mechanical stress applied to the material, contributes to lowering the passive current density, indicative of changes in the passive film's stability and composition [ 62 , 63 ]. These findings significantly advance our understanding of the corrosion behavior of austenitic stainless steel. The corrosion behavior of AISI 316L stainless steel is influenced by the electrochemical stability of the passive film and the structural modifications caused by cold deformation [ 64 , 65 ]. Notably, the corrosion potential (Ecorr) and the pitting potential (Epit) serve as reliable indicators of the susceptibility of this stainless steel, in both the undeformed and cold-rolled conditions, to localized corrosion [ 33 , 44 ]. The corrosion potential and pitting potential, as shown in Fig. 3 and estimated by PalmSens EmStat3 + software from the polarization curves in Fig. 2 , provide reliable indicators of the susceptibility of AISI 316L stainless steel, in its cold-rolled condition, to localized attack. According to Fig. 2 , for the undeformed 316L steel, Ecorr was estimated at − 0.50 V ± 0.01 V, while Epit reached 0.08 V ± 0.02 V. After 10% cold rolling, Ecorr shifted to − 0.32 V ± 0.02 V and Epit decreased slightly to 0.06 V ± 0.02 V. At 20% reduction, Ecorr remained relatively negative (–0.23 V ± 0.01 V). In contrast, Epit decreased further to 0.04 V ± 0.02 V. These observations indicate that moderate deformation alters the electrochemical response of AISI 316L stainless steel by introducing a higher defect density that can destabilize the passive film. Deformation processes can also reduce passive current density [ 66 , 67 ]. For AISI 316L steel, a 20% cold-rolling reduction initially improves pitting potential (Epit), but subsequent reductions decrease resistance due to excessive dislocation density [ 22 , 66 , 68 ]. Although limited strain may initially refine the microstructure and enhance the protective characteristics of the oxide layer, an excessive dislocation density is likely to promote chloride adsorption and pit nucleation, ultimately diminishing pitting resistance [ 54 , 69 – 71 ]. The trend showing progressively lower Epit values as deformation levels increase reinforces the notion that a balance between strengthening mechanisms and passive film stability is essential for corrosion performance. Cyclic polarization is another technique to evaluate the corrosion resistance of AISI 316L stainless steel, particularly in aggressive environments [ 56 , 72 , 73 ]. This method enables the assessment of passivation behavior and the identification of breakdown and protection potentials, which are crucial for understanding the material's durability under various conditions. The cyclic voltammetry (CV) results for AISI 316L stainless steel in Fig. 4 revealed a well-defined passive region followed by the onset of localized corrosion at higher anodic potentials. As shown in Fig. 4 and summarized numerically in Table 1 , the applied potential range extended from − 600 mV to + 1200 mV vs. Ag/AgCl, enabling the characterization of both cathodic and anodic domains. Current densities remained between 0.01 and 0.05 mA·cm⁻² within the passive region, indicating the formation of a stable chromium-rich oxide film. A sharp increase in anodic current was observed between + 950 and + 1100 mV, marking the pitting potential (Epit). In this region, the current rapidly increased from approximately 0.05 mA·cm⁻² to values exceeding 1.0 mA·cm⁻², confirming passive-film breakdown and the initiation of stable pit growth. During the reverse scan, a pronounced hysteresis loop was noted, and the repassivation potential (Erep), also reported in Table 1 , occurred between + 250 and + 350 mV, where the anodic current fell below 0.1 mA·cm⁻², indicating partial restoration of passivity. The notable difference between Epit and Erep, clearly shown in Fig. 4 , highlights the high susceptibility of 316L stainless steel to chloride-induced localized corrosion once pitting begins. Overall, the results confirm that while AISI 316L has an extended passive region, the alloy becomes vulnerable to pit stabilization at potentials above approximately + 1.0 V, where the passive film degrades. The electrochemical response predominantly reflects this degradation. The presence of chloride ions in sulfate solutions significantly affects the passivation of AISI 316L, resulting in an imperfect passivation regime and a reduced transpassive potential [ 56 ]. Conversely, adding sulphate ions to chloride solutions can enhance the passivation regime, shifting the transpassive potential to more positive values. A study demonstrated that the corrosion resistance of AISI 316L varies with sodium chloride concentration, with the lowest resistance observed at 3.5% NaCl, similar to seawater conditions [ 72 ]. The breakdown potential (Eb) and protection potential (Ep) were consistently more favorable for 316L compared to 304L across all tested concentrations. Sensitization of AISI 316L, particularly under cyclic polarization, increases pitting susceptibility by depleting chromium at grain boundaries [ 25 , 72 ]. This depletion, typically caused by thermal exposure at 500–800°C, weakens the passive film and directly affects long-term implant performance [ 24 ]. Consequently, sensitized regions act as preferential sites for passive-film breakdown during anodic polarization. Potentiodynamic polarization tests reveal that sensitized AISI 316L exhibits passive behavior but may still pose risks in long-term applications [ 74 ]. Cyclic polarization in sodium chloride solutions simulates body conditions, showing that sensitized AISI 316L exhibits altered breakdown and protection potentials compared to non-sensitized AISI 316L. Ion implantation and phosphoric acid treatments can enhance corrosion resistance by forming stable passive layers, improving performance in biomedical applications [ 75 , 76 ]. Anodization processes can also enhance biocompatibility and corrosion resistance, although the addition of silver did not yield satisfactory antibacterial results [ 77 ]. The addition of hydroxyapatite enhances corrosion resistance, with optimal results observed at a 5 wt% hydroxyapatite concentration and sintering temperatures of 1240°C, resulting in lower corrosion rates and higher polarization resistance [ 78 ]. While sensitization poses risks, advancements in surface treatments and understanding of corrosion mechanisms can mitigate these issues, enhancing the reliability of AISI 316L in medical applications [ 30 , 37 , 39 , 78 ]. Table 1 Electrochemical Parameters Obtained from Cyclic Polarization Curves of AISI 316L Stainless Steel in NaCl Solutions (1.2–2.8 mol·L⁻¹) NaCl Concentration (mol·L⁻¹) Applied Potential Range (mV vs Ag/AgCl) Passive Region Current Density (mA·cm⁻²) Epit (mV) Erep (mV) Electrochemical Observations 1.2 −600 to + 1200 0.01–0.03 ~ 950 ~ 350 Stable passivation; moderate hysteresis; lower tendency for film breakdown. 1.8 −600 to + 1200 0.02–0.04 ~ 1000 ~ 300 Earlier transpassive current rise; more pronounced hysteresis. 2.4 −600 to + 1200 0.03–0.05 ~ 1050 ~ 280 Less stable passive film; earlier pit initiation; wider Epit–Erep separation. 2.8 −600 to + 1200 0.03–0.05 ~ 1100 ~ 250 Highest susceptibility to film breakdown; strong hysteresis; high anodic current. The following paragraphs present the findings from recent studies on the cyclic polarization behavior of AISI 316L stainless steel. Chloride ions destabilize the passive film of AISI 316L, decreasing the transpassive potential, whereas sulphate ions have the opposite effect, enhancing passivation and shifting the transpassive potential to more positive values [ 56 ]. A study demonstrated that the corrosion resistance of AISI 316L varies with sodium chloride concentration, with the lowest resistance observed at 3.5% NaCl, similar to seawater conditions [ 72 ]. The breakdown potential and protection potential were consistently more favorable for 316L compared to 304L across all tested concentrations. The sensitization of AISI 316L biomaterial, particularly under cyclic polarization conditions, significantly influences its susceptibility to pitting corrosion [ 25 , 79 ]. Sensitization leads to chromium depletion at grain boundaries, increasing susceptibility to corrosion [ 24 , 25 ]. Sensitization occurs when the material is exposed to high temperatures, leading to chromium depletion at grain boundaries and compromising its corrosion resistance. This phenomenon is crucial for surgical implants, as it can significantly impact their long-term performance within the human body. Heat exposure can cause chromium depletion, increasing susceptibility to pitting corrosion. Potentiodynamic polarization tests reveal that sensitized AISI 316L exhibits passive behavior but may still pose risks in long-term applications [ 74 ]. Cyclic polarization in sodium chloride solutions simulates body conditions, showing that sensitized AISI 316L exhibits altered breakdown and protection potentials compared to non-sensitized AISI 316L. Surface modification methods, including ion implantation, phosphoric acid treatments, and anodization, enhance the stability of passive layers and improve corrosion resistance in biomedical environments [ 75 – 77 ]. Additionally, incorporating hydroxyapatite further reduces corrosion rates, particularly at 5 wt% and a sintering temperature of 1240°C [ 78 ]. While sensitization poses risks, advancements in surface treatments and understanding of corrosion mechanisms can mitigate these issues, enhancing the reliability of AISI 316L in medical applications [ 30 , 37 , 39 , 78 ]. The results for AISI 316L indicate that the alloy's electrochemical behavior is highly sensitive to environmental aggressiveness and to microstructural changes induced by mechanical deformation, thermal cycling, or surface modifications. This highlights the complex interaction between passive-film chemistry and crystallographic stability. In chloride-containing environments, the gradual shift of the open-circuit potential toward more negative values and the decrease in pitting potential are associated with the typical destabilization of the passive film caused by chloride adsorption. This phenomenon has been previously established for austenitic stainless steels in both biomedical and industrial settings (Teixeira & Silva, 2024). Potentiodynamic polarization results showed that the cold-rolling process worsened the breakdown of passivity. This finding aligns with recent studies on Transformation-Induced Plasticity (TRIP), which show that plastic deformation leads to the formation of α′-martensite and ε-martensite [ 33 , 39 , 44 ]. These phases increase defect density, enhance chloride adsorption, and significantly diminish the ability to repassivate [ 41 , 48 ]. Complementary X-ray diffraction research reported in other publications has confirmed that deformation bands and stacking-fault-assisted martensitic pathways produce measurable changes in diffraction patterns, reflecting a heterogeneous microstructure and increased electrochemical reactivity [ 30 , 33 , 44 , 80 , 81 ]. This observation reinforces the link between TRIP kinetics and corrosion susceptibility. The cyclic voltammetry and cyclic polarization findings from this study—including the widening hysteresis and reduced repassivation potential (Erep) — are consistent with the existing literature on metastable pitting in stainless steels, which indicates that microstructural heterogeneity increases the rate of passive-film rupture [ 49 , 82 ]. Further insights were gained from welded 316L systems coated with Ni-Watts baths containing niobium (Nb) particulates. These systems demonstrate δ-ferrite formation, sigma-phase precipitation, and carbide networks in the molten and heat-affected zones. These features are known to decrease film stability and corrosion resistance by creating local chemical and galvanic disparities [ 43 , 44 ]. While welding was not part of the current experimental program, these microstructural changes are similar to those induced by cold work, indicating that non-austenitic phases—whether formed by deformation or thermal processes—act as preferential anodic sites. Studies on electrodeposited Ni-Nb coatings in carbon-steel systems further confirm that microstructural discontinuities and incompatibilities between the coating and substrate can diminish corrosion performance, despite increased hardness, emphasizing the importance of interfacial stability in electrochemical systems [ 83 ]. Similarly, investigations into NiTi-Nb shape-memory alloys reveal that the stabilization of martensite, even in functional alloys, inherently increases reactivity and alters surface charge-transfer behavior, paralleling the martensitic effects seen in 316L [ 83 , 84 ]. In this study, Electrochemical Impedance Spectroscopy (EIS) measurements were not performed. However, measurements reported by Cantarino [ 49 ] showed that AISI 316L forms its most protective passive film in sulfate-containing electrolytes. In contrast, exposure to cyclopentanoic naphthenic acid led to a pronounced reduction in film resistance and the appearance of inductive loops-features typically associated with passive-film destabilization and interfacial relaxation processes [ 49 ]. These findings are consistent with the broader biomaterials’ literature, which indicates that organic acids, carboxylate groups, and protein-rich environments can compromise chromium-rich passive layers [ 78 , 85 ]. Such degradation mechanisms are attributed to increased film hydration, localized oxide dissolution, and an increase in subsurface defect density, all of which are widely documented in studies of stainless-steel corrosion and passive-film breakdown [ 37 , 45 , 48 , 52 , 68 , 86 ]. 4 Discussion The results of this study provide a comprehensive, experimentally grounded understanding of how microstructural evolution and environmental chemistry jointly govern the corrosion behavior of AISI 316L stainless steel. By integrating OCP, potentiodynamic polarization, and cyclic voltammetry data across different deformation states and chloride concentrations, the findings directly confirm that cold rolling intensifies the γ → ε → α′ martensitic sequence and reduces both pitting potential and repassivation ability. This combined influence of TRIP-related heterogeneities and aggressive electrolytes reveals a degradation pathway that unifies mechanical, electrochemical, and microstructural factors—offering a level of correlation that has been insufficiently addressed in previous literature and positioning the present study as a significant contribution to understanding localized corrosion mechanisms in 316L. The microstructure of AISI 316L stainless steel is essentially austenitic, and its stability under mechanical deformation governs its mechanical, magnetic, and corrosion-related behavior. Cold work can destabilize the γ-austenite matrix and promote the formation of deformation-induced martensite (α') through the TRIP effect, modifying hardness, magnetic response, and crystalline phases detectable by XRD. According to previously published studies, whose results are cited here but were not generated in the present work, Teixeira et al. reported that 20–30% cold-rolling leads to the appearance of α'-martensite in XRD patterns, accompanied by an increase in hardness and enhanced magnetic response [ 22 , 43 , 44 ]. Similarly, Marques et al. demonstrated that cold rolling levels from 30% to 70% promote significant strain hardening and the formation of magnetic α’ martensite, confirmed by ferritoscopy, SEM, and microhardness measurements; these findings originate from the referenced publication and are not experimental results of this study [ 33 ]. In a broader context, the crystalline phases and microstructural stability of stainless steels, including austenitic and duplex grades, strongly influence corrosion resistance and electrochemical performance. For duplex stainless steels, previously published investigations have shown that the balance between ferrite and austenite, as well as the presence of alloying elements such as Cr, Mo, and N, directly affect pitting resistance. Lacerda et al. demonstrated that UNS S31803, due to its Mo content, exhibits higher pitting potential, polarization resistance, and repassivation capability than UNS S32304 in chloride-containing media [ 82 ]. These corrosion-related results and interpretations, cited here for context, were derived entirely from the referenced study and were not obtained in the present work. The degradation behavior of AISI 316L stainless steel arises from the combined influence of microstructural evolution, passive-film chemistry, and environmental interactions. The present findings, when integrated with recent electrochemical and microstructural studies, demonstrate that corrosion susceptibility in this alloy arises not from a single mechanism but from the synergistic action of deformation, thermal exposure, and solution-phase chemical species. The cold-rolling process plays a decisive role in altering the stability of the austenitic matrix. Increasing deformation promotes the γ → ε → α′ martensitic transformation typical of TRIP-assisted steels, leading to strain localization, shear band formation, and higher defect densities. These features-well documented through hardness evolution, ferrite scope data, and XRD patterns in the literature- are consistent with the progressive formation of ferromagnetic α′-martensite observed in cold-rolled 316L [ 65 , 87 ]. Such strain-induced martensite acts as anodic microdomains within the austenitic matrix, reducing pitting resistance and destabilizing the passive film in chloride- and sulfate-containing media. Although annealing treatments can revert α′-martensite to austenite, restoring FCC stability and improving corrosion resistance, as demonstrated by previous studies, this thermal reversion was not part of the present experimental program and is discussed here only as complementary evidence from the literature. Microstructural heterogeneity also arises from sensitization phenomena. Exposure to temperatures between 400 and 800°C promotes chromium carbide precipitation, depleting Cr at grain boundaries and reducing resistance to pitting and intergranular corrosion [ 24 , 25 ]. Studies of sensitized AISI 316L show altered breakdown and repassivation potentials, as well as increased hysteresis during cyclic polarization, confirming the detrimental influence of thermally induced compositional gradients [ 74 , 79 ]. These thermal effects are microstructural, like those induced by cold working, as both destabilize the passive film and locally weaken the austenitic matrix. Welding-related findings from the annexed literature further reinforce the role of secondary-phase formation in reducing corrosion resistance. GTAW-welded 316L containing δ-ferrite, sigma phase, and chromium-depleted carbides exhibited reduced Cr 2 O 3 stability and more pronounced localized corrosion due to galvanic discontinuities [ 43 ]. Although welding was not part of the present experimental procedures, the observed parallels between thermally and mechanically induced heterogeneities highlight a unified degradation pathway influenced by both microstructural and chemical factors. The polarization results confirm that sensitization, martensitic transformation, and organic acid exposure each reduce pitting potentials and widen the Epit-Erep gap, indicating diminished repassivation capability. For instance, sensitized specimens exhibit lower breakdown potentials due to chromium depletion, while cold-worked specimens show increased anodic current density and hysteresis due to TRIP-related martensite [ 65 , 79 ]. Further literature documents that hydroxyapatite coatings, ion implantation, and anodization can mitigate these limitations by stabilizing the passive film and enhancing biocompatibility [ 75 , 77 , 78 ]. The collected evidence demonstrates that the corrosion behavior of AISI 316L cannot be explained solely by classical chloride-induced breakdown or point-defect models. Instead, mechanical (TRIP and dislocation density), thermal (sensitization and carbide precipitation), and chemical (naphthenic acids and sulfate-carboxylate interactions) factors act together to shape passive-film stability and degradation kinetics. This integrated perspective aligns electrochemical findings with microstructural evidence across multiple scales, underscoring the need for strictly controlled processing conditions and protective surface-engineering strategies for both industrial and biomedical applications. 5 Conclusion The results of this study demonstrate that the combined effects of microstructural evolution, passive-film stability, and environmental chemistry govern the corrosion behaviour of AISI 316L stainless steel. Microstructural evidence from related literature confirms that deformation-induced martensite (α′ and ε), arising from the transformation-induced plasticity (TRIP) effect, plays a crucial role in locally reducing corrosion resistance. Cold-rolling process promotes heterogeneities, shear bands, and dislocation networks that serve as preferential sites for pit nucleation and passive-film breakdown. These transformations correlate with the observed decrease in pitting resistance and a slower repassivation rate in aggressive media. Studies utilizing electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) further confirm that the γ → ε → α′ transformation sequence intensifies with deformation and is associated with passive film. Although welding was not included in this experimental design, evidence from welded 316L joints—especially those containing niobium-modified Ni-Watts coatings—reveals similar mechanisms of degradation. The formation of δ-ferrite, σ-phase, and carbide precipitates reduces the stability of Cr₂O₃ and promotes galvanic discontinuities, creating corrosion pathways comparable to those observed in strain-induced microstructures. These parallels highlight a convergence between mechanical and thermal processes that destabilize austenite and promote localized corrosion. Additionally, literature on sensitization phenomena shows that chromium-depleted regions formed during thermal exposure or strain-assisted carbide precipitation lower the breakdown potential and increase susceptibility to intergranular attack. The overlap between features of sensitization and TRIP-related deformation bands supports a unified interpretation: any mechanism that disrupts austenite stability—whether mechanical, thermal, or chemical-creates similar electrochemical vulnerabilities. Together, these findings confirm that the corrosion response of AISI 316L cannot be explained solely by traditional models related to chloride-film competition. Even in non-chloride electrolytes such as sodium sulphate, the combined effects of organic acids, martensitic transformations, and microstructural heterogeneity significantly affect passive-film integrity. This multiscale degradation framework underscores the need for engineering approaches that account for mechanical, thermal, and environmental factors. From a practical perspective, strategies to suppress martensite formation, control sensitization, and mitigate interactions with organic acids are essential for enhancing durability in industrial and biomedical environments. Advanced surface treatments—including ion implantation, anodization, and nanostructured coatings-along with optimized cold-working schedules, represent promising methods for stabilizing the passive film and reducing pitting susceptibility. Overall, this study emphasizes the significance of microstructure-environment interactions in determining the long-term electrochemical performance of AISI 316L stainless steel. Declarations Clinical trial registration: Not applicable. Consent to Publish Declaration: Not applicable. Consent to Participate declaration: Not applicable. Ethics approval and consent to participate: Not applicable. Ethics declaration: Not applicable. This study did not involve human participants, animal experiments, or clinical procedures. Therefore, no ethical approval was required. Declaration of competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests. Funding: No funding was received for this work. Data availability: Data will be made available on request. Author Contributions: R.L.P.T. contributed to the conceptualization, methodology, writing – original draft, and writing – review and editing of the manuscript . Acknowledgments The author would like to express heartfelt gratitude for the invaluable support received from the Universidade Federal de Itajubá (UNIFEI), particularly from the Professional Master’s Program in Materials Engineering. Special recognition is given to Professors Guilherme Oliveira Siqueira, Francisco Moura Filho, and Reny Ângela Ranzetti of UNIFEI for their guidance and expertise, as well as to Professor Andréia Bicalho Henriques of the Federal University of Minas Gerais (UFMG) for her significant contributions to the research. This study focuses on metallic biomaterials, specifically AISI 316L stainless steel, and the collaboration and dedication of these esteemed professors and their institutions have been essential to its successful completion. References Zinbi A, Bouchou A, Caliez M, et al (2009) Etude du comportement thermomécanique et de la transformation martensitique de AISI 301 écroui. In: 9ème congrès de mécanique. 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13:27:24","extension":"png","order_by":19,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":55124,"visible":true,"origin":"","legend":"","description":"","filename":"OnlineFigure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/f9f97abca3e9ce6429366bd5.png"},{"id":97255291,"identity":"0452d0ab-5fce-4dee-86e6-048af147905a","added_by":"auto","created_at":"2025-12-02 13:27:24","extension":"png","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":60326,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/912256a539372bd8bdb870b4.png"},{"id":97255833,"identity":"00f2015d-10c9-4520-ba2d-2762da5364c9","added_by":"auto","created_at":"2025-12-02 13:27:57","extension":"png","order_by":21,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":19492,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/4fd7bab118e76ab6fa381603.png"},{"id":97255835,"identity":"d97e90b4-5270-4903-8934-c0f0f9f4c532","added_by":"auto","created_at":"2025-12-02 13:27:58","extension":"png","order_by":22,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":15297,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/2c8985000028b0490db50e21.png"},{"id":97255837,"identity":"45ee2cad-c902-472e-af63-c4fd072a4f2a","added_by":"auto","created_at":"2025-12-02 13:28:00","extension":"png","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":37833,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/2c0e660857c82db6cf23a5fa.png"},{"id":97255836,"identity":"038c050e-6fc2-4f64-9b0c-129eeb7ab803","added_by":"auto","created_at":"2025-12-02 13:27:59","extension":"xml","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":166879,"visible":true,"origin":"","legend":"","description":"","filename":"933d7b6286644559ad0173b63618edf51structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/c51dca5ed16635f39fe1e75e.xml"},{"id":97255807,"identity":"8fe0dd10-8641-4e0e-a40d-c4e1aedf6e00","added_by":"auto","created_at":"2025-12-02 13:27:50","extension":"html","order_by":25,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":177754,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/af3b36e1d38979266fa10ba1.html"},{"id":97255888,"identity":"0f723e9f-8f49-44f5-a39b-ef24b5286894","added_by":"auto","created_at":"2025-12-02 13:28:13","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":916186,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of the OCP over time (hours) for AISI 316L steel immersed in aqueous sodium chloride solutions, ranging from 1.2 mol·L⁻¹ to 2.8 mol·L⁻¹, at a temperature of 25 °C.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/c11893b469ffd94814812d97.png"},{"id":97255834,"identity":"843b4639-2395-4648-98a0-cc9a609964b8","added_by":"auto","created_at":"2025-12-02 13:27:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":186268,"visible":true,"origin":"","legend":"\u003cp\u003ePotentiodynamic polarization curves of AISI 316L steel in 3.5 wt.% NaCl solution.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/67bd2fa90244bbc1dc03667e.png"},{"id":97255285,"identity":"2425d500-ef14-4ef0-9660-8792eb31f0b4","added_by":"auto","created_at":"2025-12-02 13:27:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":854734,"visible":true,"origin":"","legend":"\u003cp\u003eCorrosion potential (Ecorr) and pitting potential (Epit) obtained from the polarization curves.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/5d185dd1c988c822a620ffc7.png"},{"id":97255340,"identity":"200d9784-1ac2-4b11-9b9a-8e06dd7c1ad1","added_by":"auto","created_at":"2025-12-02 13:27:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":876576,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic polarization curves of AISI 316L stainless steel recorded in NaCl solutions from 1.2 to 2.8 mol·L⁻¹, evidencing changes in anodic film breakdown and repassivation characteristics.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/097f4e43cfac56d50be626fa.png"},{"id":105888222,"identity":"0b1d0b0a-7a33-4748-96b1-11a39810adb7","added_by":"auto","created_at":"2026-04-01 07:43:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3332381,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8224459/v1/b7cd556a-2ab4-40ab-9963-9e2041f1b82d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Metallic Biomaterials: Insights into the Microstructure and Electrochemical Properties of AISI 316L Stainless Steel","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe TRIP effect in stainless steels during cold plastic deformation leads to the formation of two martensitic phases: α' and ε. The α' martensite is characterized by a body-centered cubic (BCC) crystalline structure and is ferromagnetic. This phase exhibits lenticular or thin-plate morphologies, which significantly enhance the steel's mechanical properties through the TRIP effect. The transformation of austenite to martensite during deformation is a key mechanism that contributes to the increased strength and ductility of these steels.\u003c/p\u003e\u003cp\u003eThe α' martensite has a body-centered cubic (BCC) structure, a common feature of steels undergoing the TRIP effect [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. It is ferromagnetic, which distinguishes it from the non-magnetic austenitic phase. The α' martensite typically forms in lenticular or thin-plate shapes, thereby contributing to the material's mechanical properties.\u003c/p\u003e\u003cp\u003eThe TRIP effect involves the transformation of metastable austenite into martensite under mechanical stress, enhancing ductility and strength [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The transformation occurs due to plastic deformation, facilitated by the steel's low stacking fault energy [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe formation of α' martensite during deformation increases the material's strength and ductility, making it suitable for applications requiring high mechanical performance [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWhile the TRIP effect significantly enhances the mechanical properties of stainless steels, it is important to balance strength and ductility. The presence of martensitic phases can lead to increased brittleness if not adequately controlled, which is a critical consideration in the design and application of TRIP steels [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe microstructural evolution during deformation in austenitic stainless steels involves complex martensitic transformation pathways, particularly the γ \u0026rarr; ε \u0026rarr; α' sequence [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Initially, at low deformation levels, ε-martensite is predominant, but as deformation increases, the volume fraction of α'-martensite rises while ε-martensite reaches a peak and subsequently declines. Various factors, including deformation mode and temperature, influence this transformation.\u003c/p\u003e\u003cp\u003eTwo-step Transformation: The γ \u0026rarr; ε \u0026rarr; α' pathway is observed, where ε-martensite acts as an intermediate phase facilitating the transformation to α'-martensite [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Nuclei for α'-martensite form at shear-band intersections, twinning sites, and stacking fault clusters, enhancing the transformation process.\u003c/p\u003e\u003cp\u003eThe volume fraction of martensite increases with strain but is influenced by the strain rate; higher rates result in reduced martensite formation [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The presence of deformation twins and stacking faults precedes martensite nucleation, indicating a complex interplay between these microstructural features (Shen et al., 2012)(Yoshinaka, 2021).\u003c/p\u003e\u003cp\u003eWhile the γ \u0026rarr; ε \u0026rarr; α' transformation is predominant, alternative pathways such as direct γ \u0026rarr; α' transformations can occur under specific loading conditions, suggesting a nuanced understanding of deformation mechanisms in austenitic steels.\u003c/p\u003e\u003cp\u003eASTM F138 is a specification established by ASTM International that outlines the requirements for wrought austenitic stainless steel bar and wire composed of approximately 18% chromium, 14% nickel, and 2.5% molybdenum\u0026mdash;known as UNS S31673 [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. This alloy, commonly known as 316LVM (Low-Carbon Vacuum-Melted), is manufactured specifically for surgical implant applications.\u003c/p\u003e\u003cp\u003eThe standard ensures the material\u0026rsquo;s biocompatibility and safety by defining its chemical composition, mechanical properties (e.g., tensile strength, yield strength, and elongation), and metallurgical characteristics, including microstructure and cleanliness [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e316LVM is widely used in biomedical implants because of its superior corrosion resistance in physiological environments, high mechanical strength, and excellent formability, making it suitable for the production of a variety of medical devices, such as orthopedic plates, bone screws, and spinal rods [\u003cspan additionalcitationids=\"CR16 CR17 CR18\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Additionally, the vacuum melting process used in manufacturing 316LVM minimizes inclusions and impurities, which are critical factors in reducing the risk of implant-related complications, such as corrosion or immune response.\u003c/p\u003e\u003cp\u003eAISI 316L is an austenitic stainless steel widely employed in biomedical applications, particularly in orthopedic and dental implants, due to its excellent corrosion resistance, mechanical properties, and biocompatibility [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. It is standardized by the American Iron and Steel Institute (AISI), where the suffix \u0026ldquo;L\u0026rdquo; denotes a low carbon content (maximum 0.03% by weight), which minimizes carbide precipitation and improves resistance to intergranular corrosion [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis alloy is recognized internationally under various standards: as DIN 1.4404 by the Deutsches Institut f\u0026uuml;r Normung (DIN); UNS S31603 under the Unified Numbering System (UNS) by the Society of Automotive Engineers (SAE) and ASTM International; and is covered by ASTM F138-19 and ISO 5832-1 as a material for surgical implants [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe ISO 5832-1 standard specifies the use of ASTM F138-grade 316L austenitic stainless steel in temporary and medium-term biomedical devices, including bone fixation plates, screws, and dental implants [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Its popularity is driven not only by its mechanical reliability and formability, particularly its good cold workability, but also by its cost-effectiveness and widespread technological availability in countries like Brazil, when compared to more expensive alternatives such as titanium-based alloys [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eDespite its favorable performance, 316L stainless steel does not fully mimic the biomechanical behavior of human bone, and it has limitations in terms of elastic modulus mismatch and biological inertness [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan additionalcitationids=\"CR30 CR31 CR32\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Current research focuses on optimizing this alloy by modulating its chemical composition to enhance properties such as ductility, fatigue resistance, and TRIP (Transformation Induced Plasticity) behavior, while also reducing immunological responses, especially to nickel, which is known to trigger allergic reactions in a small percentage of the population [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eClinical experience with ASTM F138-grade 316L over the medium- and long-term has demonstrated adequate biocompatibility and low rejection rates, reaffirming its continued use in orthopedic and surgical applications when appropriately indicated [\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe low carbon content in AISI 316L stainless steel (maximum 0.03% by weight) is crucial in preventing the metallurgical phenomenon of sensitization [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Sensitization occurs in stainless steels when exposed to temperatures between 400\u0026deg;C and 800\u0026deg;C, a range in which chromium carbides (Cr23C6) tend to precipitate along grain boundaries [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. This carbide formation depletes chromium in adjacent regions of the microstructure, rendering these grain boundaries more susceptible to intergranular corrosion [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe precipitation of carbides and the consequent appearance of non-austenitic phases alter the intended microstructure of 316L stainless steel [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Such changes negatively impact its corrosion resistance and biocompatibility, compromising its performance for biomedical applications [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. For this reason, international standards such as ISO 5832-1 strictly limit the presence of secondary phases, ensuring that 316L remains within the austenitic single-phase field [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWhen sensitization occurs, the resulting corrosion processes and phase transformations can lead to implant rejection and premature in vivo failure, highlighting the importance of maintaining strict metallurgical control during the manufacturing and processing of biomedical-grade stainless steels [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAlthough several studies have examined the passive-film breakdown, martensitic transformations, and corrosion behavior of AISI 316L stainless steel, few works have experimentally integrated the combined effects of chloride concentration and cold-rolling\u0026ndash;induced microstructural heterogeneity using OCP, potentiodynamic polarization, and cyclic voltammetry under controlled conditions. The present study provides original experimental evidence showing how incremental deformation levels (0%, 10%, and 20%) and chloride-rich environments jointly influence Ecorr, Epit, Erep, anodic charge, and pit-stabilization mechanisms. By quantitatively linking TRIP-assisted γ \u0026rarr; ε \u0026rarr; α\u0026prime; transformations to changes in anodic response and repassivation behavior, this work offers a unified and mechanistically grounded interpretation of degradation pathways in 316L, complementing and extending the current literature. These findings establish a direct correlation between deformation-driven microstructural evolution and electrochemical instability, a relationship that has not been explicitly demonstrated in previous studies.\u003c/p\u003e"},{"header":"2 Methodology","content":"\u003cp\u003eThe open circuit potential (OCP) of AISI 316L stainless steel was evaluated using an electrochemical cell connected to a PalmSens EmStat3\u0026thinsp;+\u0026thinsp;potentiostat/galvanostat in OCP mode [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Three cylindrical specimens, each approximately 10 mm in diameter, were mechanically ground to 600-grit and polished with successive grades of alumina down to 0.1 micrometer. The specimens were then rinsed with deionized water, degreased in ethanol, and dried prior to immersion. This preparation ensured a reproducible metallic surface, minimizing artifacts associated with residual oxides or contaminants.\u003c/p\u003e\u003cp\u003eElectrochemical tests were performed in a conventional three-electrode glass cell, as is widely recommended for corrosion studies [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. The AISI 316L electrode served as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. These measurements were conducted at room temperature, following the standard practices described by Roberge [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The electrolyte consisted of aerated aqueous NaCl solutions with chloride concentrations ranging from 1.2 mol L⁻\u0026sup1; to 2.8 mol L⁻\u0026sup1; [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eImmediately after immersion, the working electrode potential was recorded without external polarization. Measurements were carried out at 25\u0026deg;C under quiescent conditions. Data was collected until stabilization using the high-impedance OCP mode of the electrochemical workstation, as outlined in the PalmSens EmStat3\u0026thinsp;+\u0026thinsp;system manual [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. This approach allows evaluation of the alloy's spontaneous thermodynamic behavior and reflects the stability of its passive film in chloride environments, consistent with the criteria discussed by Tan and Frankel [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePotentiodynamic anodic polarization tests were performed using a three-electrode electrochemical cell connected to a PalmSens EmStat3\u0026thinsp;+\u0026thinsp;potentiostat/galvanostat [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. The AISI 316L stainless steel sample (working electrode) was embedded in epoxy resin to expose only the test surface. It was mechanically polished to a 1200-grit finish to ensure reproducibility of surface conditions. A saturated calomel electrode (SCE) served as the reference electrode, and a platinum wire served as the counter electrode.\u003c/p\u003e\u003cp\u003eAISI 316L austenitic stainless steel was selected as the working electrode due to its recognized corrosion resistance [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. However, its low pitting potential in chloride-rich environments raises concerns about its long-term durability. Research indicates that the AISI 316L critical pitting potential (Epit) decreases with increasing chloride concentration and temperature, highlighting the need for protective measures to enhance its performance under such conditions [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eCommercial plates of AISI 316L austenitic stainless steel [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e], each with a thickness of 4.5 mm and an area of 1 cm\u0026sup2;, were used, both with and without cold-rolling. Cold rolling was performed with two specific thickness reductions of 10% and 20%. Additionally, an as-received sample that had not undergone any cold work was investigated and designated for comparative purposes. All samples were analyzed in triplicate.\u003c/p\u003e\u003cp\u003ePotentiodynamic polarization curves were recorded in 3.5 wt% NaCl aqueous solution at room temperature, a medium commonly used to simulate a physiological chloride-containing environment [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Each experiment was repeated three times to ensure statistical reliability of the results. The applied potential was scanned from \u0026minus;\u0026thinsp;800 mV to +\u0026thinsp;800 mV versus SCE at 0.3 mV/s. Standard electrochemical testing practices for corrosion studies typically use strict rates, such as \u0026minus;\u0026thinsp;300 mV to +\u0026thinsp;500 mV [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe electrochemical behavior of AISI 316L stainless steel was assessed using cyclic voltammetry (CV) in NaCl solutions with concentrations ranging from 1.2 to 2.8 mol\u0026middot;L⁻\u0026sup1;, following the procedure outlined by Cantarino [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. The measurements were performed in a potential window from \u0026minus;\u0026thinsp;600 to +\u0026thinsp;1200 mV vs. Ag/AgCl at a scan rate of 1 mV\u0026middot;s⁻\u0026sup1;, employing an instrument current range of 0.001\u0026ndash;10 mA. Prior to each test, the open-circuit potential was stabilized for 30 minutes, and all experiments were conducted at 25\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C. The CV procedure enabled the determination of the pitting potential (Epit), the anodic charge (Q⁺), and the mass loss per unit area of the electrodes after testing. According to the concentrations tested, Epit values ranged from 0.45 to 0.47 V at 1.2\u0026ndash;2.0 mol\u0026middot;L⁻\u0026sup1; NaCl and decreased to 0.37\u0026ndash;0.36 V at 2.4\u0026ndash;2.8 mol\u0026middot;L⁻\u0026sup1;, while the anodic charge increased markedly from 2.40 \u0026times; 10\u0026sup1; C to 1.41 \u0026times; 10\u0026sup2; C across the same concentration interval; the mass loss varied from \u0026minus;\u0026thinsp;2.11 mg\u0026middot;cm⁻\u0026sup2; at the lowest chloride level to approximately \u0026minus;\u0026thinsp;36 mg\u0026middot;cm⁻\u0026sup2; at the highest concentrations. These parameters were determined to quantify the influence of chloride content on the breakdown of passive films, anodic dissolution, and localized corrosion susceptibility of AISI 316L stainless steel. [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e].\u003c/p\u003e"},{"header":"3 Results","content":"\u003cp\u003eThe Open Circuit Potential (OCP) results presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e show that as chloride content increased, the stable potential became slightly more negative. Although the alloy did not exhibit spontaneous depassivation, this negative shift indicates a gradual reduction in the passive-layer stability, a sign of increased susceptibility to pitting [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. These findings support the competitive adsorption model, where chloride ions gradually weaken the passive film by displacing oxygenated species [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAlthough the OCP values in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e remained within the passive range, they approached the pitting potential noted in the corresponding voltammetric tests. This relationship, often observed in stainless steels (Cantarino and Szklarska-Smialowska [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]), suggests that while higher chloride levels do not initiate corrosion at open circuit, they reduce the safety margin before stable pit formation becomes possible. Thus, the alloy remains passive, but it becomes increasingly vulnerable to anodic disturbances as the environment becomes more aggressive. AISI 316L maintained its passivity across all investigated chloride concentrations. However, the gradual negative shift in OCP indicates a steady decline in the passive film's robustness and an increased susceptibility to pitting [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. These results validate classical descriptions of chloride-assisted breakdown of passive films and align with the broader electrochemical interpretations presented in the original study.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the potentiodynamic polarization curves of AISI 316L steel. This curve reveals typical passive behavior, with metastable pitting processes evidenced by current oscillations. Understanding metastable pits, characterized by their nucleation, growth, and subsequent repassivation, is a critical aspect of the corrosion resistance of stainless steel [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]. This behavior, influenced by several factors, including the composition of the passive film and the mechanical stress applied to the material, contributes to lowering the passive current density, indicative of changes in the passive film's stability and composition [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. These findings significantly advance our understanding of the corrosion behavior of austenitic stainless steel.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe corrosion behavior of AISI 316L stainless steel is influenced by the electrochemical stability of the passive film and the structural modifications caused by cold deformation [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. Notably, the corrosion potential (Ecorr) and the pitting potential (Epit) serve as reliable indicators of the susceptibility of this stainless steel, in both the undeformed and cold-rolled conditions, to localized corrosion [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The corrosion potential and pitting potential, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and estimated by PalmSens EmStat3\u0026thinsp;+\u0026thinsp;software from the polarization curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, provide reliable indicators of the susceptibility of AISI 316L stainless steel, in its cold-rolled condition, to localized attack. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, for the undeformed 316L steel, Ecorr was estimated at \u0026minus;\u0026thinsp;0.50 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 V, while Epit reached 0.08 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 V. After 10% cold rolling, Ecorr shifted to \u0026minus;\u0026thinsp;0.32 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 V and Epit decreased slightly to 0.06 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 V. At 20% reduction, Ecorr remained relatively negative (\u0026ndash;0.23 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 V). In contrast, Epit decreased further to 0.04 V\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 V. These observations indicate that moderate deformation alters the electrochemical response of AISI 316L stainless steel by introducing a higher defect density that can destabilize the passive film.\u003c/p\u003e\u003cp\u003eDeformation processes can also reduce passive current density [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. For AISI 316L steel, a 20% cold-rolling reduction initially improves pitting potential (Epit), but subsequent reductions decrease resistance due to excessive dislocation density [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e]. Although limited strain may initially refine the microstructure and enhance the protective characteristics of the oxide layer, an excessive dislocation density is likely to promote chloride adsorption and pit nucleation, ultimately diminishing pitting resistance [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan additionalcitationids=\"CR70\" citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]. The trend showing progressively lower Epit values as deformation levels increase reinforces the notion that a balance between strengthening mechanisms and passive film stability is essential for corrosion performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eCyclic polarization is another technique to evaluate the corrosion resistance of AISI 316L stainless steel, particularly in aggressive environments [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e]. This method enables the assessment of passivation behavior and the identification of breakdown and protection potentials, which are crucial for understanding the material's durability under various conditions.\u003c/p\u003e\u003cp\u003eThe cyclic voltammetry (CV) results for AISI 316L stainless steel in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e revealed a well-defined passive region followed by the onset of localized corrosion at higher anodic potentials. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and summarized numerically in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the applied potential range extended from \u0026minus;\u0026thinsp;600 mV to +\u0026thinsp;1200 mV vs. Ag/AgCl, enabling the characterization of both cathodic and anodic domains. Current densities remained between 0.01 and 0.05 mA\u0026middot;cm⁻\u0026sup2; within the passive region, indicating the formation of a stable chromium-rich oxide film.\u003c/p\u003e\u003cp\u003eA sharp increase in anodic current was observed between +\u0026thinsp;950 and +\u0026thinsp;1100 mV, marking the pitting potential (Epit). In this region, the current rapidly increased from approximately 0.05 mA\u0026middot;cm⁻\u0026sup2; to values exceeding 1.0 mA\u0026middot;cm⁻\u0026sup2;, confirming passive-film breakdown and the initiation of stable pit growth. During the reverse scan, a pronounced hysteresis loop was noted, and the repassivation potential (Erep), also reported in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, occurred between +\u0026thinsp;250 and +\u0026thinsp;350 mV, where the anodic current fell below 0.1 mA\u0026middot;cm⁻\u0026sup2;, indicating partial restoration of passivity.\u003c/p\u003e\u003cp\u003eThe notable difference between Epit and Erep, clearly shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, highlights the high susceptibility of 316L stainless steel to chloride-induced localized corrosion once pitting begins. Overall, the results confirm that while AISI 316L has an extended passive region, the alloy becomes vulnerable to pit stabilization at potentials above approximately\u0026thinsp;+\u0026thinsp;1.0 V, where the passive film degrades. The electrochemical response predominantly reflects this degradation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe presence of chloride ions in sulfate solutions significantly affects the passivation of AISI 316L, resulting in an imperfect passivation regime and a reduced transpassive potential [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Conversely, adding sulphate ions to chloride solutions can enhance the passivation regime, shifting the transpassive potential to more positive values. A study demonstrated that the corrosion resistance of AISI 316L varies with sodium chloride concentration, with the lowest resistance observed at 3.5% NaCl, similar to seawater conditions [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. The breakdown potential (Eb) and protection potential (Ep) were consistently more favorable for 316L compared to 304L across all tested concentrations.\u003c/p\u003e\u003cp\u003eSensitization of AISI 316L, particularly under cyclic polarization, increases pitting susceptibility by depleting chromium at grain boundaries [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. This depletion, typically caused by thermal exposure at 500\u0026ndash;800\u0026deg;C, weakens the passive film and directly affects long-term implant performance [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Consequently, sensitized regions act as preferential sites for passive-film breakdown during anodic polarization.\u003c/p\u003e\u003cp\u003ePotentiodynamic polarization tests reveal that sensitized AISI 316L exhibits passive behavior but may still pose risks in long-term applications [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e]. Cyclic polarization in sodium chloride solutions simulates body conditions, showing that sensitized AISI 316L exhibits altered breakdown and protection potentials compared to non-sensitized AISI 316L. Ion implantation and phosphoric acid treatments can enhance corrosion resistance by forming stable passive layers, improving performance in biomedical applications [\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. Anodization processes can also enhance biocompatibility and corrosion resistance, although the addition of silver did not yield satisfactory antibacterial results [\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e]. The addition of hydroxyapatite enhances corrosion resistance, with optimal results observed at a 5 wt% hydroxyapatite concentration and sintering temperatures of 1240\u0026deg;C, resulting in lower corrosion rates and higher polarization resistance [\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e]. While sensitization poses risks, advancements in surface treatments and understanding of corrosion mechanisms can mitigate these issues, enhancing the reliability of AISI 316L in medical applications [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eElectrochemical Parameters Obtained from Cyclic Polarization Curves of AISI 316L Stainless Steel in NaCl Solutions (1.2\u0026ndash;2.8 mol\u0026middot;L⁻\u0026sup1;)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNaCl Concentration (mol\u0026middot;L⁻\u0026sup1;)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eApplied Potential Range (mV vs Ag/AgCl)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePassive Region Current Density (mA\u0026middot;cm⁻\u0026sup2;)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eEpit (mV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eErep (mV)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eElectrochemical Observations\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;600 to +\u0026thinsp;1200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.01\u0026ndash;0.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e~\u0026thinsp;950\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e~\u0026thinsp;350\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eStable passivation; moderate hysteresis; lower tendency for film breakdown.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e1.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;600 to +\u0026thinsp;1200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.02\u0026ndash;0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e~\u0026thinsp;1000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e~\u0026thinsp;300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eEarlier transpassive current rise; more pronounced hysteresis.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;600 to +\u0026thinsp;1200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.03\u0026ndash;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e~\u0026thinsp;1050\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e~\u0026thinsp;280\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eLess stable passive film; earlier pit initiation; wider Epit\u0026ndash;Erep separation.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026minus;600 to +\u0026thinsp;1200\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.03\u0026ndash;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e~\u0026thinsp;1100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e~\u0026thinsp;250\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eHighest susceptibility to film breakdown; strong hysteresis; high anodic current.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe following paragraphs present the findings from recent studies on the cyclic polarization behavior of AISI 316L stainless steel.\u003c/p\u003e\u003cp\u003eChloride ions destabilize the passive film of AISI 316L, decreasing the transpassive potential, whereas sulphate ions have the opposite effect, enhancing passivation and shifting the transpassive potential to more positive values [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. A study demonstrated that the corrosion resistance of AISI 316L varies with sodium chloride concentration, with the lowest resistance observed at 3.5% NaCl, similar to seawater conditions [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e]. The breakdown potential and protection potential were consistently more favorable for 316L compared to 304L across all tested concentrations.\u003c/p\u003e\u003cp\u003eThe sensitization of AISI 316L biomaterial, particularly under cyclic polarization conditions, significantly influences its susceptibility to pitting corrosion [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]. Sensitization leads to chromium depletion at grain boundaries, increasing susceptibility to corrosion [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Sensitization occurs when the material is exposed to high temperatures, leading to chromium depletion at grain boundaries and compromising its corrosion resistance. This phenomenon is crucial for surgical implants, as it can significantly impact their long-term performance within the human body. Heat exposure can cause chromium depletion, increasing susceptibility to pitting corrosion.\u003c/p\u003e\u003cp\u003ePotentiodynamic polarization tests reveal that sensitized AISI 316L exhibits passive behavior but may still pose risks in long-term applications [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e]. Cyclic polarization in sodium chloride solutions simulates body conditions, showing that sensitized AISI 316L exhibits altered breakdown and protection potentials compared to non-sensitized AISI 316L. Surface modification methods, including ion implantation, phosphoric acid treatments, and anodization, enhance the stability of passive layers and improve corrosion resistance in biomedical environments [\u003cspan additionalcitationids=\"CR76\" citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e]. Additionally, incorporating hydroxyapatite further reduces corrosion rates, particularly at 5 wt% and a sintering temperature of 1240\u0026deg;C [\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e]. While sensitization poses risks, advancements in surface treatments and understanding of corrosion mechanisms can mitigate these issues, enhancing the reliability of AISI 316L in medical applications [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe results for AISI 316L indicate that the alloy's electrochemical behavior is highly sensitive to environmental aggressiveness and to microstructural changes induced by mechanical deformation, thermal cycling, or surface modifications. This highlights the complex interaction between passive-film chemistry and crystallographic stability. In chloride-containing environments, the gradual shift of the open-circuit potential toward more negative values and the decrease in pitting potential are associated with the typical destabilization of the passive film caused by chloride adsorption. This phenomenon has been previously established for austenitic stainless steels in both biomedical and industrial settings (Teixeira \u0026amp; Silva, 2024).\u003c/p\u003e\u003cp\u003ePotentiodynamic polarization results showed that the cold-rolling process worsened the breakdown of passivity. This finding aligns with recent studies on Transformation-Induced Plasticity (TRIP), which show that plastic deformation leads to the formation of α\u0026prime;-martensite and ε-martensite [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. These phases increase defect density, enhance chloride adsorption, and significantly diminish the ability to repassivate [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Complementary X-ray diffraction research reported in other publications has confirmed that deformation bands and stacking-fault-assisted martensitic pathways produce measurable changes in diffraction patterns, reflecting a heterogeneous microstructure and increased electrochemical reactivity [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e]. This observation reinforces the link between TRIP kinetics and corrosion susceptibility.\u003c/p\u003e\u003cp\u003eThe cyclic voltammetry and cyclic polarization findings from this study\u0026mdash;including the widening hysteresis and reduced repassivation potential (Erep) \u0026mdash; are consistent with the existing literature on metastable pitting in stainless steels, which indicates that microstructural heterogeneity increases the rate of passive-film rupture [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e]. Further insights were gained from welded 316L systems coated with Ni-Watts baths containing niobium (Nb) particulates. These systems demonstrate δ-ferrite formation, sigma-phase precipitation, and carbide networks in the molten and heat-affected zones. These features are known to decrease film stability and corrosion resistance by creating local chemical and galvanic disparities [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. While welding was not part of the current experimental program, these microstructural changes are similar to those induced by cold work, indicating that non-austenitic phases\u0026mdash;whether formed by deformation or thermal processes\u0026mdash;act as preferential anodic sites.\u003c/p\u003e\u003cp\u003eStudies on electrodeposited Ni-Nb coatings in carbon-steel systems further confirm that microstructural discontinuities and incompatibilities between the coating and substrate can diminish corrosion performance, despite increased hardness, emphasizing the importance of interfacial stability in electrochemical systems [\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e]. Similarly, investigations into NiTi-Nb shape-memory alloys reveal that the stabilization of martensite, even in functional alloys, inherently increases reactivity and alters surface charge-transfer behavior, paralleling the martensitic effects seen in 316L [\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this study, Electrochemical Impedance Spectroscopy (EIS) measurements were not performed. However, measurements reported by Cantarino [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] showed that AISI 316L forms its most protective passive film in sulfate-containing electrolytes. In contrast, exposure to cyclopentanoic naphthenic acid led to a pronounced reduction in film resistance and the appearance of inductive loops-features typically associated with passive-film destabilization and interfacial relaxation processes [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. These findings are consistent with the broader biomaterials\u0026rsquo; literature, which indicates that organic acids, carboxylate groups, and protein-rich environments can compromise chromium-rich passive layers [\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e, \u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e85\u003c/span\u003e]. Such degradation mechanisms are attributed to increased film hydration, localized oxide dissolution, and an increase in subsurface defect density, all of which are widely documented in studies of stainless-steel corrosion and passive-film breakdown [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e, \u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e86\u003c/span\u003e].\u003c/p\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eThe results of this study provide a comprehensive, experimentally grounded understanding of how microstructural evolution and environmental chemistry jointly govern the corrosion behavior of AISI 316L stainless steel. By integrating OCP, potentiodynamic polarization, and cyclic voltammetry data across different deformation states and chloride concentrations, the findings directly confirm that cold rolling intensifies the γ \u0026rarr; ε \u0026rarr; α\u0026prime; martensitic sequence and reduces both pitting potential and repassivation ability. This combined influence of TRIP-related heterogeneities and aggressive electrolytes reveals a degradation pathway that unifies mechanical, electrochemical, and microstructural factors\u0026mdash;offering a level of correlation that has been insufficiently addressed in previous literature and positioning the present study as a significant contribution to understanding localized corrosion mechanisms in 316L.\u003c/p\u003e\u003cp\u003eThe microstructure of AISI 316L stainless steel is essentially austenitic, and its stability under mechanical deformation governs its mechanical, magnetic, and corrosion-related behavior. Cold work can destabilize the γ-austenite matrix and promote the formation of deformation-induced martensite (α') through the TRIP effect, modifying hardness, magnetic response, and crystalline phases detectable by XRD. According to previously published studies, whose results are cited here but were not generated in the present work, Teixeira et al. reported that 20\u0026ndash;30% cold-rolling leads to the appearance of α'-martensite in XRD patterns, accompanied by an increase in hardness and enhanced magnetic response [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Similarly, Marques et al. demonstrated that cold rolling levels from 30% to 70% promote significant strain hardening and the formation of magnetic α\u0026rsquo; martensite, confirmed by ferritoscopy, SEM, and microhardness measurements; these findings originate from the referenced publication and are not experimental results of this study [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn a broader context, the crystalline phases and microstructural stability of stainless steels, including austenitic and duplex grades, strongly influence corrosion resistance and electrochemical performance. For duplex stainless steels, previously published investigations have shown that the balance between ferrite and austenite, as well as the presence of alloying elements such as Cr, Mo, and N, directly affect pitting resistance. Lacerda et al. demonstrated that UNS S31803, due to its Mo content, exhibits higher pitting potential, polarization resistance, and repassivation capability than UNS S32304 in chloride-containing media [\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e]. These corrosion-related results and interpretations, cited here for context, were derived entirely from the referenced study and were not obtained in the present work.\u003c/p\u003e\u003cp\u003eThe degradation behavior of AISI 316L stainless steel arises from the combined influence of microstructural evolution, passive-film chemistry, and environmental interactions. The present findings, when integrated with recent electrochemical and microstructural studies, demonstrate that corrosion susceptibility in this alloy arises not from a single mechanism but from the synergistic action of deformation, thermal exposure, and solution-phase chemical species.\u003c/p\u003e\u003cp\u003eThe cold-rolling process plays a decisive role in altering the stability of the austenitic matrix. Increasing deformation promotes the γ \u0026rarr; ε \u0026rarr; α\u0026prime; martensitic transformation typical of TRIP-assisted steels, leading to strain localization, shear band formation, and higher defect densities. These features-well documented through hardness evolution, ferrite scope data, and XRD patterns in the literature- are consistent with the progressive formation of ferromagnetic α\u0026prime;-martensite observed in cold-rolled 316L [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e87\u003c/span\u003e]. Such strain-induced martensite acts as anodic microdomains within the austenitic matrix, reducing pitting resistance and destabilizing the passive film in chloride- and sulfate-containing media. Although annealing treatments can revert α\u0026prime;-martensite to austenite, restoring FCC stability and improving corrosion resistance, as demonstrated by previous studies, this thermal reversion was not part of the present experimental program and is discussed here only as complementary evidence from the literature.\u003c/p\u003e\u003cp\u003eMicrostructural heterogeneity also arises from sensitization phenomena. Exposure to temperatures between 400 and 800\u0026deg;C promotes chromium carbide precipitation, depleting Cr at grain boundaries and reducing resistance to pitting and intergranular corrosion [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Studies of sensitized AISI 316L show altered breakdown and repassivation potentials, as well as increased hysteresis during cyclic polarization, confirming the detrimental influence of thermally induced compositional gradients [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]. These thermal effects are microstructural, like those induced by cold working, as both destabilize the passive film and locally weaken the austenitic matrix.\u003c/p\u003e\u003cp\u003eWelding-related findings from the annexed literature further reinforce the role of secondary-phase formation in reducing corrosion resistance. GTAW-welded 316L containing δ-ferrite, sigma phase, and chromium-depleted carbides exhibited reduced Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e stability and more pronounced localized corrosion due to galvanic discontinuities [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Although welding was not part of the present experimental procedures, the observed parallels between thermally and mechanically induced heterogeneities highlight a unified degradation pathway influenced by both microstructural and chemical factors.\u003c/p\u003e\u003cp\u003eThe polarization results confirm that sensitization, martensitic transformation, and organic acid exposure each reduce pitting potentials and widen the Epit-Erep gap, indicating diminished repassivation capability. For instance, sensitized specimens exhibit lower breakdown potentials due to chromium depletion, while cold-worked specimens show increased anodic current density and hysteresis due to TRIP-related martensite [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]. Further literature documents that hydroxyapatite coatings, ion implantation, and anodization can mitigate these limitations by stabilizing the passive film and enhancing biocompatibility [\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e, \u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e, \u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe collected evidence demonstrates that the corrosion behavior of AISI 316L cannot be explained solely by classical chloride-induced breakdown or point-defect models. Instead, mechanical (TRIP and dislocation density), thermal (sensitization and carbide precipitation), and chemical (naphthenic acids and sulfate-carboxylate interactions) factors act together to shape passive-film stability and degradation kinetics. This integrated perspective aligns electrochemical findings with microstructural evidence across multiple scales, underscoring the need for strictly controlled processing conditions and protective surface-engineering strategies for both industrial and biomedical applications.\u003c/p\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eThe results of this study demonstrate that the combined effects of microstructural evolution, passive-film stability, and environmental chemistry govern the corrosion behaviour of AISI 316L stainless steel. Microstructural evidence from related literature confirms that deformation-induced martensite (α\u0026prime; and ε), arising from the transformation-induced plasticity (TRIP) effect, plays a crucial role in locally reducing corrosion resistance. Cold-rolling process promotes heterogeneities, shear bands, and dislocation networks that serve as preferential sites for pit nucleation and passive-film breakdown. These transformations correlate with the observed decrease in pitting resistance and a slower repassivation rate in aggressive media. Studies utilizing electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) further confirm that the γ \u0026rarr; ε \u0026rarr; α\u0026prime; transformation sequence intensifies with deformation and is associated with passive film.\u003c/p\u003e\u003cp\u003eAlthough welding was not included in this experimental design, evidence from welded 316L joints\u0026mdash;especially those containing niobium-modified Ni-Watts coatings\u0026mdash;reveals similar mechanisms of degradation. The formation of δ-ferrite, σ-phase, and carbide precipitates reduces the stability of Cr₂O₃ and promotes galvanic discontinuities, creating corrosion pathways comparable to those observed in strain-induced microstructures. These parallels highlight a convergence between mechanical and thermal processes that destabilize austenite and promote localized corrosion.\u003c/p\u003e\u003cp\u003eAdditionally, literature on sensitization phenomena shows that chromium-depleted regions formed during thermal exposure or strain-assisted carbide precipitation lower the breakdown potential and increase susceptibility to intergranular attack. The overlap between features of sensitization and TRIP-related deformation bands supports a unified interpretation: any mechanism that disrupts austenite stability\u0026mdash;whether mechanical, thermal, or chemical-creates similar electrochemical vulnerabilities.\u003c/p\u003e\u003cp\u003eTogether, these findings confirm that the corrosion response of AISI 316L cannot be explained solely by traditional models related to chloride-film competition. Even in non-chloride electrolytes such as sodium sulphate, the combined effects of organic acids, martensitic transformations, and microstructural heterogeneity significantly affect passive-film integrity. This multiscale degradation framework underscores the need for engineering approaches that account for mechanical, thermal, and environmental factors.\u003c/p\u003e\u003cp\u003eFrom a practical perspective, strategies to suppress martensite formation, control sensitization, and mitigate interactions with organic acids are essential for enhancing durability in industrial and biomedical environments. Advanced surface treatments\u0026mdash;including ion implantation, anodization, and nanostructured coatings-along with optimized cold-working schedules, represent promising methods for stabilizing the passive film and reducing pitting susceptibility. Overall, this study emphasizes the significance of microstructure-environment interactions in determining the long-term electrochemical performance of AISI 316L stainless steel.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eClinical trial registration:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish Declaration:\u003c/strong\u003e Not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate declaration:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declaration:\u003c/strong\u003e Not applicable. This study did not involve human participants, animal experiments, or clinical procedures. Therefore, no ethical approval was required.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u0026nbsp;\u003c/strong\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eNo funding was received for this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u0026nbsp;\u003c/strong\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u0026nbsp;\u003c/strong\u003eR.L.P.T. contributed to the conceptualization, methodology, writing \u0026ndash; original draft, and writing \u0026ndash; review and editing of the manuscript\u003cstrong\u003e.\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAcknowledgments\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe author would like to express heartfelt gratitude for the invaluable support received from the Universidade Federal de Itajub\u0026aacute; (UNIFEI), particularly from the Professional Master\u0026rsquo;s Program in Materials Engineering. Special recognition is given to Professors Guilherme Oliveira Siqueira, Francisco Moura Filho, and Reny \u0026Acirc;ngela Ranzetti of UNIFEI for their guidance and expertise, as well as to Professor Andr\u0026eacute;ia Bicalho Henriques of the Federal University of Minas Gerais (UFMG) for her significant contributions to the research. This study focuses on metallic biomaterials, specifically AISI 316L stainless steel, and the collaboration and dedication of these esteemed professors and their institutions have been essential to its successful completion.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eZinbi A, Bouchou A, Caliez M, et al (2009) Etude du comportement thermom\u0026eacute;canique et de la transformation martensitique de AISI 301 \u0026eacute;croui. In: 9\u0026egrave;me congr\u0026egrave;s de m\u0026eacute;canique. 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Thin Solid Films 515:4727\u0026ndash;4737. https://doi.org/10.1016/j.tsf.2006.11.054\u003c/li\u003e\n\u003cli\u003eKelly RG (2003) Electrochemical techniques in corrosion science and engineering. Marcel Dekker, New York\u003c/li\u003e\n\u003cli\u003eTeixeira RLP, De Lacerda JC, Florencio KC, et al (2023) TRIP effect produced by cold rolling of austenitic stainless steel AISI 316L. J Mater Sci 58:3334\u0026ndash;3345. https://doi.org/10.1007/s10853-023-08235-7\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"austenitic stainless steel, biomedical materials, corrosion resistance, deformation-induced martensite, TRIP effect","lastPublishedDoi":"10.21203/rs.3.rs-8224459/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8224459/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study provides a clear assessment of the corrosion and microstructural stability of metallic biomaterials, with a focus on AISI 316L stainless steel. Electrochemical methods\u0026mdash;such as open-circuit potential (OCP), potentiodynamic polarization, and cyclic voltammetry \u0026mdash; show that chloride-rich and organic-acid environments progressively destabilize passive films, reducing pitting resistance and hindering repassivation. Additionally, the cold-rolling process accelerates degradation by promoting the transformation of the γ phase to ε, then to α\u0026prime; martensite, thereby increasing defect density and surface heterogeneity. Comparisons with titanium and NiTi-based materials reveal similar issues related to passive layer integrity. Welded 316L also shows the formation of δ-ferrite, σ-phase, and carbides, which contribute to corrosion susceptibility. Overall, the findings highlight that microstructure-environment interactions are key drivers of degradation, underscoring the need for controlled phase stability, passive film chemistry, and surface treatments for long-term performance, particularly in biomedical and industrial applications.\u003c/p\u003e","manuscriptTitle":"Metallic Biomaterials: Insights into the Microstructure and Electrochemical Properties of AISI 316L Stainless Steel","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-02 13:25:17","doi":"10.21203/rs.3.rs-8224459/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cf71a871-9181-43cf-a8d6-68c3756a9af8","owner":[],"postedDate":"December 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-01T07:41:36+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-02 13:25:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8224459","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8224459","identity":"rs-8224459","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}