Study on Vacuum Gas Nitriding Process and Surface Properties of AISI 430 Stainless Steel

Study on Vacuum Gas Nitriding Process and Surface Properties of AISI 430 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 Article Study on Vacuum Gas Nitriding Process and Surface Properties of AISI 430 Stainless Steel 嘉隆 左, 文权 王, 新戈 张 This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7535140/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract AISI 430 stainless steel is widely used in engineering applications due to its low cost and excellent corrosion resistance. Vacuum gas nitriding is a commonly used surface modification technique, and in industrial production, it is necessary to prepare a thick and uniform nitrided layer. To comprehensively analyze the microstructure, phase composition, mechanical properties and diffusion kinetics of the nitrided layer, vacuum gas nitriding experiments were conducted on AISI 430 stainless steel. The results showed that the nitriding layer thickness increased with rising temperature. At 620°C, the nitriding layer thickness after 6 hours of nitriding was 56.7 µm, with a surface hardness of 912 HV0.025; however, its surface ductility and toughness were poor. It was found that within a certain nitriding time range, the nitrided layer thickness increased with time. At 560°C, nitriding for 18 hours resulted in the maximum nitrided layer thickness of 123.6 µm and a surface hardness of 1440 HV0.025, but its wear resistance decreased. Compared to AISI 430 stainless steel, specimens treated with 14 hours of vacuum gas nitriding at 560°C achieved a nitrided layer thickness of 115.9 µm, with surface hardness increased by 8–9 times and wear loss reduced by 83%. The nitrided layer primarily consists of iron-nitride phases, with a small amount of chromium-nitride phases contributing to hardness enhancement. AISI430 vacuum gas nitriding diffusion kinetics friction wear volume nitriding parameters Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction Ferritic stainless steel plays a crucial role in people's daily lives and industrial production due to its low cost, excellent corrosion resistance and good ductility. To meet the diverse application requirements across various industries, an increasing number of researchers are conducting studies on the strength, surface hardness, wear resistance, tensile strength and fatigue strength of ferritic stainless steel[ 1 – 4 ]. Research has shown that ferritic stainless steel can form hard and dense nitrides at higher temperatures after nitriding treatment. Nitriding, as a chemical heat treatment process, has widespread applications in surface engineering and material strengthening. Nitriding significantly increases the nitrogen content on the material surface, altering the surface structure and phase composition, thereby enhancing its strength, wear resistance, corrosion resistance and service life. Based on recent research reports in the field of stainless steel nitriding, it has been found that research on stainless steel nitriding primarily focuses on austenitic steel, martensitic steel and duplex steel, with nitriding technologies mainly concentrated on traditional gas nitriding and low-temperature plasma nitriding. Bo Wang et al. [ 5 ]altered the phase fractions of different phases in duplex stainless steel 2205 through annealing treatment to investigate the effect of austenite and ferrite phase fractions on nitriding kinetics. The study found that a relatively high ferrite phase fraction results in finer grains. Eugenia L. Dalibon et al. [ 6 ]subjected AISI 420 martensitic stainless steel to low-temperature plasma nitriding treatment. The specimens treated at 440°C exhibited better wear resistance and corrosion resistance. The reason for this may be related to the presence of carbonitrides and the thickness of the nitrided layer. Xiangpeng Chang et al. [ 7 ] conducted gas nitriding treatment on industrial pure iron to investigate the nitriding behavior in the austenitic region. They found that the diffusion coefficient of nitrogen increases with rising temperature, leading to an increase in nitriding layer thickness. Thus, compared with other nitriding technologies, vacuum nitriding has certain advantages. Vacuum nitriding technology effectively addresses surface oxidation issues encountered in traditional gas nitriding processes and results in a more uniform and dense compound structure in the diffusion layer, further enhancing the surface properties of the workpiece[ 8 – 9 ]. This study investigates the vacuum gas nitriding process applied to AISI 430 stainless steel, focusing on the development of a nitrided layer with a uniform microstructure and significant thickness. The influence of nitriding temperature and time on the microstructure, hardness and wear resistance of the nitrided layer is systematically explored. Experimental results reveal the critical role of process parameters in controlling the quality and performance of the nitrided layer. The findings provide a theoretical basis for optimizing the vacuum gas nitriding process for AISI 430 stainless steel, which can be applied to enhance the material's surface properties for industrial applications. 2 Experimental The test material selected was AISI 430 stainless steel, with a chromium (Cr) content exceeding 16%. Chromium is a strong nitride-forming element that readily reacts with nitrogen during nitriding, thereby limiting nitrogen diffusion[ 10 ]. The chemical composition (mass fraction, %) is shown in Table 1 . Table 1 AISI430 Chemical composition of stainless steel(wt%) C Cr Mn Si Ti V P S Fe 0.065 16.520 0.351 0.351 0.003 0.093 0.026 0.002 Bal. Use an electric discharge wire cutting machine to cut the material into square thin sheets measuring 10 mm × 10 mm × 0.6 mm for subsequent nitriding treatment and performance testing. The material nitriding process is shown in Fig. 1 . Before vacuum gas nitriding, the specimen surface is degreased and polished. The experiments were conducted in a vacuum tube furnace provided by Qingdao Fengdong Heat Treatment Company. Before heating the nitriding chamber, high-pressure argon gas was used to evacuate the air inside the chamber. The furnace was then evacuated to below 1×10⁻² Pa, after which the vacuum pump was shut off. High-purity ammonia gas at 0.5 MPa was introduced into the chamber, maintaining an ammonia atmosphere of at least 99% inside the furnace. After nitriding, the furnace was cooled to room temperature, and the specimens were removed for testing. For AISI 430 stainless steel, according to the national standard for vacuum gas nitriding GB/T 18177 − 2000, the commonly used temperature range for vacuum gas nitriding is 480°C to 680°C[ 11 ]. Therefore, three different temperatures were selected within the nitriding temperature range: 500°C, 560°C and 620°C. The nitriding time was selected within the range of 6 to 18 hours. The specific nitriding process is shown in Table 2 . Grind the surface using metallographic sandpaper ranging from 240 # to 2000 # to remove the passivation layer, followed by degreasing treatment. After nitriding, remove the specimen and cool it in air. The specimens after vacuum gas nitriding were cut, then ground using sandpaper with grit sizes ranging from 300 # to 7000 #, polished with W0.1 diamond polishing paste, and etched with a 5% nitric acid alcohol solution. The microstructure of the specimen cross-section was observed using a Scope Axio ZEISS optical microscope; the microstructure of the specimen was examined using a TESCAN scanning electron microscope, and elemental composition was determined using an Aztec X-Max50 energy dispersive spectrometer; The microstructure of the grinding marks was observed using an Olympus OLS3000 laser scanning confocal microscope; the phase composition was analyzed using a DmaxPC-2500 X-ray diffractometer with a Cu Kα target (40 kV, 200 mA), a scanning range of 20°–90°, and a scanning speed of 4° per minute. The hardness distribution of the diffusion layer is measured using an MH-3 microhardness tester, with a load of 100 g and a loading time of 15 seconds; The surface wear resistance of the specimens is tested using a UMT TriboLab multifunctional friction and wear tester, using a 2 mm diameter GCr15 counterball; The mass before and after the wear test is measured using an analytical balance. To ensure measurement accuracy, each specimen is measured three times, and the average value is taken. Table 2 Nitriding process parameters Specimen number Processing method Temperature/℃ Time/h S1 Vacuum gas nitriding 500 6 S2 560 6 S3 620 6 S4 560 10 S5 14 S6 18 3 Results and discussion 3.1 Study on Nitriding Temperature of AISI 430 3.1.1 Microstructural analysis Figure 2 shows the microstructure of the cross-section of AISI 430 stainless steel after nitriding at different temperatures. (a) represents AISI 430 stainless steel that has not undergone vacuum gas nitriding treatment, while (b), (c) and (d) represent specimens treated at nitriding temperatures of 500°C, 560°C and 620°C for 6 hours, respectively. As shown in Fig. 2 (a), the grain size and microstructure of AISI 430 stainless steel are relatively uniform. It can be observed that the original microstructure of AISI 430 stainless steel without vacuum gas nitriding treatment exhibits a relatively regular polygonal shape, with straight grain boundaries, characteristic of typical ferritic grain structure. As shown in Fig. 2 (b), after 6 hours of vacuum gas nitriding treatment at 500°C, due to the relatively low nitriding temperature, ammonia gas was unable to decompose sufficient active nitrogen atoms to participate in the nitriding process, resulting in the absence of a uniform and continuous nitrided layer. However, it can be observed that the grain size of the substrate is finer compared to the untreated specimen. As shown in Fig. 2 (c), the interfaces between the bright layer, the nitride layer and the substrate can be clearly distinguished. The increased nitriding temperature promotes the decomposition of ammonia gas, accelerating the rate at which active nitrogen atoms penetrate the steel substrate. Once a certain concentration is reached, a stable iron-nitrogen phase is formed[ 12 – 13 ].As shown in Fig. 2 (d), the diffusion layer thickness of this specimen is greater than that of the other two specimens treated at lower temperatures in a vacuum gas nitriding process. However, it exhibits an abnormal region at the boundary of the diffusion layer. It can be observed that the diffusion layer contains relatively coarse grains, and numerous black nitride precipitates have formed along the grain boundaries. This may be due to the fact that after vacuum gas nitriding at 620°C, the key corrosion-resistant element Cr escapes, causing Cr to segregate at the grain boundaries and combine with N to form CrN. This reduces the Cr content, leading to poorer corrosion resistance at the grain boundaries. Under the same corrosion treatment, the grain boundaries exhibit darker colors and more severe corrosion[ 14 ]. Nitriding is the process of nitrogen atoms diffusing into the interior of stainless steel. According to the Arrhenius equation, when the nitriding temperature in a vacuum is low, the decomposition rate of ammonia is low, and the temperature gradient between layers is small, resulting in insufficient diffusion driving force for nitrogen, leading to shallow nitrogen diffusion depth; as the temperature increases, the decomposition rate of ammonia gas increases, and the temperature gradient between layers also increases, thereby enhancing the diffusion driving force and increasing the diffusion depth of nitrogen. As the temperature continues to rise, the decomposition rate of ammonia gas in the nitriding process continues to increase, but the nitrogen potential gradually decreases, leading to a reduction in nitrogen content. This results in certain areas of the nitrided layer having relatively higher thickness, while the interface between the nitrided layer and the substrate becomes uneven[ 15 ].In general, for AISI 430 stainless steel, increasing the nitriding temperature within a certain temperature range can significantly increase the thickness of the nitrided layer. However, a higher nitriding temperature is not always better. Nitriding is the process of nitrogen atoms diffusing into stainless steel, described by the Arrhenius equation : $$\:\text{D}={\text{D}}_{0}\text{e}\text{x}\text{p}\left(-\frac{\text{Q}}{\text{R}\text{T}}\right)$$ In the equation: D is the diffusion coefficient; D0 is the diffusion constant; R is the ideal gas constant; Q is the activation energy per mole of atoms; T is the thermodynamic temperature. The decomposition formula for ammonia is shown in : $$\:2N{H}_{3}=3{H}_{2}+2\left[N\right]$$ When the nitriding temperature increases, the diffusion coefficient increases according to the Arrhenius equation, and more ammonia decomposes into active nitrogen atoms, which diffuse into the stainless steel to form a solid solution. 3.1.2 Mechanical properties analysis The effective hardened layer thickness refers to the vertical distance from the surface of the part to a point 50 HV higher than the base material hardness[ 16 ]. The base hardness of AISI 430 stainless steel is 165 HV. According to this standard, after vacuum gas nitriding at different temperatures, the effective hardened layer thicknesses were 95.4, 107.6 and 113.3 µm, respectively. These results were all higher than the nitrided layer values measured from the cross-sectional metallographic images. As shown in Fig. 2 (c), the bright layer, nitride layer and base material can be easily distinguished. However, in Figs. 2 (b) and (d), the diffusion layer boundaries are not uniformly clear, and the diffusion layer thickness can only be roughly estimated, with the corresponding thicknesses at the thickest points of the nitrided layer being 8.86 and 56.7 µm, respectively. As the layer depth increases, the hardness of the nitride layer gradually increases, but simultaneously, its brittleness gradually increases, leading to a gradual decrease in the ductility and impact resistance of the diffusion layer. According to the Arrhenius equation, under the condition of constant nitriding time and pressure, the highest vacuum gas nitriding temperature yields the deepest diffusion layer, which is consistent with the experimental results. Table 3 Characteristics of the diffusion layer of AISI 430 stainless steel treated at different process temperatures Specimen number Surface hardness/HV Permeable layer thickness/µm Effective hardened layer thickness/µm AISI 430 165 S1 231 8.86 36.4 S2 875 44.5 107.6 S3 912 56.7 113.3 As shown in Fig. 2 and Table 3 , the surface hardness value of the specimen is highest after vacuum gas nitriding treatment at 620°C. Since CrN is the hardest compound that can be formed in ferritic stainless steel, the higher hardness indicates that a higher proportion of chromium has been converted to CrN[ 17 ]. CrN is more stable than the iron nitride phase. Therefore, under certain nitrogen concentrations, for AISI 430 stainless steel, chromium is the element with the second highest content after iron, and nitrogen atoms are more likely to combine with chromium to form compounds[ 18 ]. Therefore, after vacuum gas nitriding of ferritic stainless steel, a chromium nitride phase appears on the surface layer. The relatively low surface hardness indicates that the proportion of iron-nitrogen compounds in the generated phase is higher. The high surface hardness is mainly due to the formation of fine and uniform CrN-type bonded chromium nitride precipitates[ 19 ]. As shown in Fig. 3 , the average hardness value of the AISI 430 stainless steel substrate is approximately 167 HV. After vacuum gas nitriding treatment, the hardness values of the specimens all exhibit varying degrees of increase. This is because the ferritic stainless steel is exposed to a high-temperature active nitrogen atmosphere for an extended period, and according to the diffusion law, active nitrogen atoms gradually penetrate into the stainless steel substrate, thereby achieving the effect of vacuum gas strengthening. As the vacuum gas nitriding treatment temperature decreases from high to low, the hardness values also decrease accordingly. For specimens treated at 500°C, the near-surface layer hardness values at a depth of 5–15 µm from the surface are around 225 HV, representing a 34.7% increase compared to the base material, while the hardness values near the core decrease to values close to the base material hardness. Specimens treated at 560°C and 620°C exhibit hardness values of approximately 900 HV at the cross-section, which is 5–6 times that of the substrate; the hardness decreases sharply from the surface toward the substrate, reaching the substrate hardness at approximately 200 µm from the surface, after which it remains relatively constant. According to diffusion laws, nitrogen atoms diffuse from regions of higher concentration into the stainless steel matrix with lower concentration, from the surface inward. The amount of nitrogen penetration decreases in a gradient, and the degree of lattice distortion caused by nitrogen atoms entering the iron lattice decreases, leading to a reduction in hardness values[ 20 ]. The design principle of the vacuum gas nitriding process is to form a nitrided layer with excellent comprehensive performance on the surface of components while ensuring the integrity of the base material. The hardness value of the specimen surface can be determined by comparing the size of the indentations, and the brittleness level can be determined by observing the Vickers hardness indentation state of the specimen[ 21 ].The indentation marks on the specimens after vacuum gas nitriding treatment are shown in Fig. 4 . It can be seen that the specimens treated at 500°C and 560°C have good surface indentation morphology and clear edges, while the specimens treated at 620°C show a certain degree of deformation around the surface indentation marks, with higher brittleness and lower toughness. After undergoing nitriding treatment at 620°C, the surface of the workpiece will form a compound layer of a certain thickness with high hardness. Under service conditions involving impact or heavy loads, an excessively thick compound layer is prone to local cracking or even peeling due to its high brittleness, leading to component failure[ 22 ]. Based on the above research, the morphology of the S2 diffusion layer is good, with a uniform and continuous interface between the nitrided layer and the substrate. Both surface hardness and effective hardened layer thickness show significant improvements compared to the substrate. While the hardness values are similar to those of S3, the surface toughness of S2 is relatively better. Therefore, for vacuum gas nitriding treatment of AISI 430 stainless steel, 560°C is selected as the optimal nitriding temperature for the next phase of vacuum gas nitriding treatment, to investigate the effects of different nitriding times on the microstructure and properties of the nitrided layer of AISI 430 stainless steel. 3.2 Study on Nitriding Time of AISI 430 Stainless Steel 3.2.1 Microstructural morphology and phase analysis As shown in Fig. 5 , after being exposed to the corrosive agent, all specimens treated at 560°C with different nitriding times exhibited distinct layering phenomena and formed uniform needle-like structures. The microstructure of the AISI 430 stainless steel substrate transformed from a single ferritic phase to a mixed phase of ferrite and other precipitates. In all four groups of specimens, a bright white, high-hardness diffusion layer was observed in the region 15–30 µm from the surface. This layer exhibited a uniform and dense microstructure with a clear interface at the boundary with the nitriding layer. Additionally, the density of the nitrided layer is influenced by the nitriding duration. At 6, 10 and 14 hours of nitriding, the nitrided layer was relatively dense and uniform. At 18 hours of nitriding, the nitrided layer began to exhibit black punctate and diffuse substances, along with loose pores, making it prone to peeling. The specimens processed using the 560°C nitriding for 18 hours process parameters exhibit a more severe degree of porosity in the nitrided layer compared to other specimens. As shown in Fig. 5 , by observing the microstructure morphology, it can be seen that the thickness of the nitrided layer varies significantly at different treatment times under 560°C. The nitrided layer thickness formed after 6 hours of treatment is approximately 60 µm. At 10, 14 and 18 hours of treatment, the nitrided layer thickness exhibits a small-range steep increase trend, followed by a relatively gradual increase trend. In general, at the same temperature, the thickness of the nitrided layer of AISI 430 stainless steel is directly proportional to the nitriding time. The specimen treated for 18 hours has the thickest nitrided layer, approximately 123 µm. Analyzing the overall growth trend in Fig. 6 , the thickness of the nitrided layer generally increases after nitriding, forming a hardened layer that protects the AISI 430 stainless steel substrate. As shown in Fig. 6 , comparing specimens 1, 2, and 3, increasing the nitriding temperature enhances the nitriding layer thickness; as shown in Fig. 6 , comparing specimens 4, 5 and 6, the nitriding time has a more pronounced promotional effect on the growth of the nitriding layer thickness of AISI 430 stainless steel. The XRD patterns of the specimen surfaces of AISI 430 stainless steel after different durations of vacuum gas nitriding at 560°C are shown in Fig. 7 . The XRD analysis probe has a detection limit depth of 2.2 µm, with the detection area covering the specimen surface and the nitrided layer near the surface. As clearly shown in the figure, the diffraction peaks of AISI 430 stainless steel are sharp and distinct, with no diffraction peaks from other phases detected, indicating that the crystal structure of the specimen is relatively simple and no other phases such as austenite or pearlite are present. By analyzing the XRD diffraction peaks of specimens treated at the same nitriding temperature but with different nitriding times, it was found that the surface phase structure of the nitrided layer changes with increasing nitriding time. At 560°C for 10 hours of nitriding, the surface diffraction peaks of the nitrided layer showed iron nitride phases Fe₃N and Fe₄N; at 560°C for 14 hours of nitriding, the surface diffraction peaks of the nitrided layer showed the CrN phase, with the diffraction peaks of the iron nitride phases relatively weakened; At 560°C for 18 hours, the XRD diffraction peaks of the iron nitride phase on the surface of the nitrided layer showed a slight shift, while the CrN phase diffraction peaks gradually strengthened. Through analysis of the XRD diffraction peaks, it can be observed that as the nitriding time increases, the diffraction peaks of the iron-nitrogen phase gradually shift to the left at small angles, indicating that the crystal lattice of the iron-nitrogen phase has expanded. The lattice expansion indicates that nitrogen atoms have diffused into the interstitial spaces of the lattice. This suggests that as the nitriding time increases, nitrogen atoms reach a supersaturated state and cause changes in the lattice parameters. The CrN phase appears on the surface of the S6 nitrided layer. Combined with the diffuse distribution of precipitates in the bright white layer shown in Fig. 5 , it can be concluded that chromium nitride mainly forms in the shallow surface layer with high nitrogen concentration during vacuum gas nitriding, and is dispersed in the bright white layer in the form of small precipitates. CrN precipitates begin to form along grain boundaries and internal defects within grains, specifically along dislocation lines or twin boundaries throughout the entire layer. Regions near the surface are more prone to nucleation than deeper regions near the substrate interface, as nitrogen has been enriched in these areas earlier, and chromium atom diffusion is more likely to facilitate the growth of these precipitates. Due to the influence of grain boundaries or local stress fields, the activation energy required to transport nitrogen atoms through more active regions is lower than that required for the formation of primary precipitates. 3.2.2 Hardness and wear resistance analysis As shown in Fig. 8 , under the same temperature conditions, different nitriding treatment times result in varying degrees of hardening effects on the microhardness transition from the nitrided layer to the base material for AISI 430 stainless steel. The microhardness measurement values are a function of depth from the surface, with a sharp decrease occurring around 100 µm from the surface, followed by a gradual decrease in hardness values until reaching the effective nitrided layer thickness, after which the hardness becomes similar to that of the base material. It can be observed that the surface hardness of stainless steel significantly increases after vacuum gas nitriding. The base material hardness of AISI 430 stainless steel is 167 HV. After vacuum gas nitriding at 560°C for 6, 10, 14 and 18 hours, the surface hardness of the specimens was875 ,1345 ,1380 and 1440 HV, respectively, representing a 5- to 9-fold increase compared to the hardness of AISI 430 stainless steel before vacuum gas nitriding. The high surface hardness of the specimens after vacuum gas nitriding treatment is attributed to the significant formation of CrN and Fe₂₋₃N on the stainless steel surface, which markedly enhances the surface's resistance to plastic deformation. At a nitriding temperature of 560°C, a white bright layer with a thickness of approximately 5–20 µm is present at the interface between the vacuum gas nitrided surface and the ferritic matrix of AISI 430 stainless steel. This is consistent with the presence of Fe₃N and Fe₄N as shown in XRD Fig. 7 . Despite varying nitriding times, the diffusion layer boundaries adjacent to the AISI 430 stainless steel matrix are all continuous, uniform and smooth, representing an ideal boundary state for nitriding treatment of high-chromium alloy steels[ 24 ]. Within a certain range of nitriding time, the hardness value increases as the nitriding time is extended, followed by a slight decrease. This is because chromium nitride is the compound with the highest hardness value. Higher hardness indicates a greater proportion of chromium reacting with nitrogen to form chromium nitride. While CrN has high hardness, it also exhibits significant brittleness, meaning it may be prone to cracking or fracturing under external forces, particularly in the absence of toughness enhancement[ 25 ]. As the nitriding time increases, more compounds are formed between active nitrogen atoms and chromium atoms. Regarding the depth of the nitrided layer, it is related to the diffusion function, and diffusion increases with increasing nitriding temperature and nitriding time. This means that a longer nitriding treatment time allows for more thorough diffusion, resulting in a deeper nitrided layer, consistent with the micrograph of the specimen in Fig. 3.5[ 26 ]. The surface wear patterns and laser confocal wear depth maps of the original AISI 430 stainless steel specimens and those treated with vacuum gas nitriding are shown in Fig. 9 . As shown in Figure (a), the surface of the original specimen exhibits parallel grooves aligned with the direction of ball movement and minor flake-like spalling after wear. This indicates that the wear mechanism of AISI 430 stainless steel involves adhesive wear and abrasive wear. The presence of grooves may be attributed to the friction between the harder GCr15 balls and the softer AISI 430 stainless steel substrate[ 27 ]. Hard particles are pressed into the friction surface under the action of a vertical force, and subsequently leave plow-like grooves on the surface during reciprocating linear motion, indicating that the friction surface has low hardness and good ductility. No obvious plow grooves were observed in Figures (b), (c), (d), and (e), as the nitrided layer on the surface of AISI 430 stainless steel after vacuum gas nitriding has a high hardness, making it difficult for hard particles to be pressed into the specimen surface under the same vertical force. Experimental results indicate that the duration of vacuum gas nitriding significantly affects the friction characteristics of the nitrided specimens. The wear marks on the vacuum gas nitriding specimens exhibit small pits and scratches, indicating that the primary wear mechanism is adhesive wear. As shown in the figure, as the vacuum gas nitriding time increases, the number of pits in Figures (b), (c) and (d) gradually decreases, and the morphology of the scratches also weakens. Combining the three-dimensional morphology of the wear marks on the specimens obtained using laser confocal microscopy, the Z-axis is set with the same scale, and the depth of the wear marks is indicated by changes in color intervals. It can be observed that the width of the wear marks in Figures (g), (h) and (i) gradually narrows, and the depth of the wear marks gradually decreases. This may be attributed to the formation of a high-hardness iron nitride phase on the surfaces of the S3 and S4 specimens, which enhances surface hardness while improving wear resistance; the S5 specimen exhibits a small amount of CrN phase, resulting in a reduced content of iron nitride phase. The CrN phase is a stable phase with higher hardness than the iron-nitride phase, resulting in superior performance of S5 in the abrasion test. This indicates that under the same vacuum gas nitriding temperature, within a certain nitriding time range, the wear resistance of the AISI 430 stainless steel specimen surface can be enhanced[ 28 ].Figure (e) shows that part of the inner layer surface is deep black, and the scratches are deeper than those in Figures (b), (c) and (d), indicating that local spalling has occurred. The reason for this phenomenon is that the S6 specimen generates more CrN, which has higher surface hardness but is more brittle, and undergoes slight fragmentation under the action of hard particles. The fine particles generated by the peeling of the hardened layer are incorporated into the reciprocating linear motion of the grinding balls, causing secondary damage to the specimen surface[ 29 ]. After being treated at 560°C for 6 hours, 10 hours, 14 hours and 18 hours, respectively, the wear volume of the AISI 430 stainless steel specimens is shown in Fig. 10 . The wear volume of a metal surface sliding against another metal surface is inversely proportional to hardness and directly proportional to the wear coefficient, applied load, and sliding distance[ 30 ]. Since the applied load and sliding distance were the same in the tests conducted, surfaces with high hardness and deep penetration layers exhibit the best wear resistance, and the research results confirm this. From the wear volume, it can be seen that due to the low surface hardness of AISI 430 stainless steel, the wear volume is relatively large, at 0.335 mm³. However, the wear volume of the S3-6 specimen treated with vacuum gas nitriding is significantly reduced, indicating that vacuum gas nitriding can improve the wear resistance of the surface of AISI 430 stainless steel. As the nitriding time increases, the wear volume follows a pattern of first decreasing and then increasing. The wear volume of the S3 specimen decreased by 43% compared to AISI 430 stainless steel, but it remains higher than that of the S4-6 specimen, which underwent longer vacuum gas nitriding. This phenomenon may be attributed to the presence of only Fe₂₋₃N and Fe₄N phases in S2, while other processed specimens contain CrN[ 31 ]. Chromium nitride phases exhibit higher hardness and wear resistance than iron nitride phases, resulting in S2 having inferior wear resistance compared to the other three specimens with longer vacuum gas nitriding times, and thus exhibiting greater wear volume. After 18 hours of vacuum gas nitriding treatment, the wear volume of the specimens increased slightly. CrN is a chromium-nitrogen phase with high hardness but poor ductility. The S6 specimen has a higher CrN content in its surface phase composition. A possible reason is that during friction with the harder GCr15 grinding balls, under the combined effects of normal stress and transverse shear stress, CrN particles peel off and become hard particles that participate in subsequent friction, causing the wear mechanism to shift to abrasive wear and resulting in reduced wear resistance. The friction coefficient curves of the S3-6 nitrided specimens and the original specimens over time are shown in Fig. 3.11. As can be seen from the figure, the friction coefficient is related to the nitriding time, and there are certain differences in the friction coefficients of the specimens treated under different nitriding times. The friction coefficient of AISI 430 stainless steel specimens exhibits significant fluctuations in the initial stage, rapidly rising to approximately 0.5 and exhibiting pronounced fluctuations in the curve. This is because during the initial wear-in process, the passivation film on the stainless steel surface is damaged, exposing the fresh, soft surface to wear against the hard GCr15 balls. The wear balls must overcome adhesive resistance, leading to adhesive wear, which causes the friction coefficient to surge sharply. From the 2nd minute onwards, the coefficient of friction gradually stabilizes, indicating that the AISI 430 stainless steel requires a break-in period to enter a stable phase. From the friction coefficients of the specimens, it can be seen that the break-in stage generally occurs around 2 minutes, followed by a stable wear state. The friction coefficients of the 565°C + 10, 14and 18 h nitrided specimens eventually stabilized at approximately 0.4, 0.38, and 0.5, respectively, with minimal variation. The coefficient of friction for specimen S3 sharply increased to 0.5 and then underwent another rise phase for about 2 minutes. Subsequently, during the subsequent friction and wear process, the coefficient of friction increased at a relatively slow rate and finally stabilized at around 0.68. The reason for the continuous fluctuations in the curve may be that the nitriding layer formed by short-term nitriding is relatively thin. When the counterball wears away the nitriding layer, the counterball comes into contact with particles of the nitriding layer mixed with the base material, causing significant fluctuations in the friction coefficient curve. When the friction coefficient enters the stable wear phase, its fluctuations are significant, indicating that a large amount of wear debris is generated through friction and wear, and the debris is not removed in a timely manner, leading to the phenomenon of severe fluctuations in the friction coefficient curve[ 32 ].S4-6 initially rises and then stabilizes within approximately 1 minute. Subsequently, it is influenced by a combination of factors, including the surface roughness and hardness of the specimen's penetration layer, as well as the debris generated during the wear process, causing the friction coefficient curve to decline to a certain extent. Afterward, the friction coefficient stabilizes at around 0.4 and 0.5, respectively, until the wear process concludes. After the friction coefficient curve stabilizes, the amplitude of its fluctuations is relatively small, indicating that excessive wear particles were not generated during the friction and wear process. 4 Conclusion Under a constant nitriding time of 6 hours, both the nitriding layer thickness and surface hardness increase progressively with rising nitriding temperature. The maximum nitriding layer thickness reaches 56.7 µm, while the surface hardness attains 912 HV. However, an increase in temperature leads to a reduction in surface plasticity and toughness. At a constant nitriding temperature of 560°C, the thickness of the nitriding layer increases with the extension of nitriding time. The experimental results indicate that, when the nitriding temperature is maintained constant, the nitriding time has a significant effect on promoting the growth of the nitriding layer thickness in AISI 430 stainless steel. For AISI 430 stainless steel, nitriding at a temperature of 560°C for 14 hours yields the best overall surface performance. The nitrided layer thickness can reach 115.9 µm, with a surface hardness of 1380 HV, which is 8.26 times higher than that of the original AISI 430 stainless steel specimen. Wear loss weight is reduced by 83% and the material exhibits good ductility and toughness. Declarations Author Contribution Professor Wang Wenquan provided guidance and recommendations for the design and implementation of the research plan, leveraging his deep expertise in surface technology.Professor Zhang Xinge assisted in resolving technical challenges during the experiments, ensuring their smooth execution.Throughout the research process, both professors offered invaluable insights and suggestions for the manuscript. Their professional guidance and technical support played a crucial role in enhancing the overall quality of the paper.Zuo Jialong served as the primary executor of this research. He was responsible for experimental implementation, operational execution, and data collection and organization. Additionally, Zuo Jialong undertook the writing of the paper, including drafting the text content and preparing and formatting the figures and tables. References LUO H, et al. 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1","display":"","copyAsset":false,"role":"figure","size":75919,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the nitriding process\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/c708688facf8ec6775c6e8fb.jpg"},{"id":92014881,"identity":"7c504538-9a90-4fa7-be03-581b1a0b46ba","added_by":"auto","created_at":"2025-09-23 16:20:47","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82990,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional morphology of AISI 430 stainless steel and specimens treated with nitriding at different temperatures：a) AISI430 stainless steel；b)500℃+6h；c)560℃+6h；d)620℃+6h\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/93728fe5c21251d4bd173080.jpg"},{"id":92015583,"identity":"6383a0a5-ecba-46bf-956e-a5a2ae7917c5","added_by":"auto","created_at":"2025-09-23 16:28:47","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":38159,"visible":true,"origin":"","legend":"\u003cp\u003eMicrohardness distribution of AISI 430 stainless steel cross-section after nitriding at different temperatures\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/fa63991c002034eefdb73035.jpg"},{"id":92014878,"identity":"13200702-ce5a-487a-9581-5dc5b3198d7d","added_by":"auto","created_at":"2025-09-23 16:20:47","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":28968,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of brittleness at different temperatures: (a) 500 °C (b) 560 °C (c) 620 °C\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/fad06815a444318d0555476b.jpg"},{"id":92016939,"identity":"13331e9a-7a85-4b4e-9a74-48ffa1ea7db8","added_by":"auto","created_at":"2025-09-23 16:44:47","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":74888,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional morphology of specimens treated at 560°C for different nitriding times: a)560 ℃+6 h; b)560 ℃+10 h; c)560 ℃+14 h; d)560 ℃+18 h\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/d72246f63ea428586fce29c1.jpg"},{"id":92015875,"identity":"2e333d5f-3247-4d61-a2ee-70949c8d4598","added_by":"auto","created_at":"2025-09-23 16:36:47","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":31427,"visible":true,"origin":"","legend":"\u003cp\u003eNitriding layer thickness of each specimen under different nitriding times\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/4eb3da7903cb9e1f4f7c3b95.jpg"},{"id":92014882,"identity":"203a57a0-493e-4e1e-bdb9-78fe9f1007b0","added_by":"auto","created_at":"2025-09-23 16:20:47","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":42266,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of nitrided layers of specimens treated at 560 °C for different nitriding times\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/9c5ff228fd3e41654f82477f.jpg"},{"id":92014887,"identity":"dbd5867e-bb55-4c88-9167-f8da5c30dd3e","added_by":"auto","created_at":"2025-09-23 16:20:47","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":50332,"visible":true,"origin":"","legend":"\u003cp\u003eHardness distribution curves of specimens with different nitriding times\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/5d2e5b75a0655e742bdfa7e1.jpg"},{"id":92015879,"identity":"d3450d0b-1139-4798-932d-7c23631b83d2","added_by":"auto","created_at":"2025-09-23 16:36:47","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":220351,"visible":true,"origin":"","legend":"\u003cp\u003eScratch morphology and laser confocal scratch depth map of AISI 430 stainless steel and specimens subjected to vacuum gas nitriding for different durations:（a）AISI430 stainless steel；（b）560℃+6h；（c）560℃+10h；（d）560℃+14h；（e）560℃+18h\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/7a6a848b6223aaa50cd18b1e.jpg"},{"id":92017171,"identity":"6f0c4f96-93d6-4857-aa0e-f22f17ee8b94","added_by":"auto","created_at":"2025-09-23 16:52:47","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":33745,"visible":true,"origin":"","legend":"\u003cp\u003eWear volume of specimens at different nitriding times\u003c/p\u003e","description":"","filename":"Picture10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/4b946cc07ec1fed361d7f60f.jpg"},{"id":92015592,"identity":"5cc12aa5-da1f-4d64-a1ec-f92290144d1e","added_by":"auto","created_at":"2025-09-23 16:28:47","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":46221,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient curves of specimens with different nitriding times at 560°C\u003c/p\u003e","description":"","filename":"Picture11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/8fe1f85593e509e95779d7ab.jpg"},{"id":92063106,"identity":"19f8808b-27a0-475d-ab28-129d936eead9","added_by":"auto","created_at":"2025-09-24 08:36:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1356221,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7535140/v1/1a2c3c75-8f87-46dd-81cc-9973aed4beb6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on Vacuum Gas Nitriding Process and Surface Properties of AISI 430 Stainless Steel","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eFerritic stainless steel plays a crucial role in people's daily lives and industrial production due to its low cost, excellent corrosion resistance and good ductility. To meet the diverse application requirements across various industries, an increasing number of researchers are conducting studies on the strength, surface hardness, wear resistance, tensile strength and fatigue strength of ferritic stainless steel[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eResearch has shown that ferritic stainless steel can form hard and dense nitrides at higher temperatures after nitriding treatment. Nitriding, as a chemical heat treatment process, has widespread applications in surface engineering and material strengthening. Nitriding significantly increases the nitrogen content on the material surface, altering the surface structure and phase composition, thereby enhancing its strength, wear resistance, corrosion\u003c/p\u003e\u003cp\u003eresistance and service life.\u003c/p\u003e\u003cp\u003eBased on recent research reports in the field of stainless steel nitriding, it has been found that research on stainless steel nitriding primarily focuses on austenitic steel, martensitic steel and duplex steel, with nitriding technologies mainly concentrated on traditional gas nitriding and low-temperature plasma nitriding. Bo Wang et al. [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]altered the phase fractions of different phases in duplex stainless steel 2205 through annealing treatment to investigate the effect of austenite and ferrite phase fractions on nitriding kinetics. The study found that a relatively high ferrite phase fraction results in finer grains. Eugenia L. Dalibon et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]subjected AISI 420 martensitic stainless steel to low-temperature plasma nitriding treatment. The specimens treated at 440\u0026deg;C exhibited better wear resistance and corrosion resistance. The reason for this may be related to the presence of carbonitrides and the thickness of the nitrided layer. Xiangpeng Chang et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] conducted gas nitriding treatment on industrial pure iron to investigate the nitriding behavior in the austenitic region. They found that the diffusion coefficient of nitrogen increases with rising temperature, leading to an increase in nitriding layer thickness. Thus, compared with other nitriding technologies, vacuum nitriding has certain advantages. Vacuum nitriding technology effectively addresses surface oxidation issues encountered in traditional gas nitriding processes and results in a more uniform and dense compound structure in the diffusion layer, further enhancing the surface properties of the workpiece[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study investigates the vacuum gas nitriding process applied to AISI 430 stainless steel, focusing on the development of a nitrided layer with a uniform microstructure and significant thickness. The influence of nitriding temperature and time on the microstructure, hardness and wear resistance of the nitrided layer is systematically explored. Experimental results reveal the critical role of process parameters in controlling the quality and performance of the nitrided layer. The findings provide a theoretical basis for optimizing the vacuum gas nitriding process for AISI 430 stainless steel, which can be applied to enhance the material's surface properties for industrial applications.\u003c/p\u003e"},{"header":"2 Experimental","content":"\u003cp\u003eThe test material selected was AISI 430 stainless steel, with a chromium (Cr) content exceeding 16%. Chromium is a strong nitride-forming element that readily reacts with nitrogen during nitriding, thereby limiting nitrogen diffusion[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. The chemical composition (mass fraction, %) is shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\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\u003eAISI430 Chemical composition of stainless steel(wt%)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\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=\"left\" 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\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCr\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMn\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eTi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eV\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eP\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eFe\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e0.065\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e16.520\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.351\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.351\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.093\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.026\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eBal.\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\u003eUse an electric discharge wire cutting machine to cut the material into square thin sheets measuring 10 mm \u0026times; 10 mm \u0026times; 0.6 mm for subsequent nitriding treatment and performance testing. The material nitriding process is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Before vacuum gas nitriding, the specimen surface is degreased and polished. The experiments were conducted in a vacuum tube furnace provided by Qingdao Fengdong Heat Treatment Company. Before heating the nitriding chamber, high-pressure argon gas was used to evacuate the air inside the chamber. The furnace was then evacuated to below 1\u0026times;10⁻\u0026sup2; Pa, after which the vacuum pump was shut off. High-purity ammonia gas at 0.5 MPa was introduced into the chamber, maintaining an ammonia atmosphere of at least 99% inside the furnace. After nitriding, the furnace was cooled to room temperature, and the specimens were removed for testing. For AISI 430 stainless steel, according to the national standard for vacuum gas nitriding GB/T 18177\u0026thinsp;\u0026minus;\u0026thinsp;2000, the commonly used temperature range for vacuum gas nitriding is 480\u0026deg;C to 680\u0026deg;C[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Therefore, three different temperatures were selected within the nitriding temperature range: 500\u0026deg;C, 560\u0026deg;C and 620\u0026deg;C. The nitriding time was selected within the range of 6 to 18 hours. The specific nitriding process is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eGrind the surface using metallographic sandpaper ranging from 240 # to 2000 # to remove the passivation layer, followed by degreasing treatment. After nitriding, remove the specimen and cool it in air. The specimens after vacuum gas nitriding were cut, then ground using sandpaper with\u003c/p\u003e\u003cp\u003egrit sizes ranging from 300 # to 7000 #, polished with W0.1 diamond polishing paste, and etched with a 5% nitric acid alcohol solution. The microstructure of the specimen cross-section was observed using a Scope Axio ZEISS optical microscope; the microstructure of the specimen was examined using a TESCAN scanning electron microscope, and elemental composition was determined using an Aztec X-Max50 energy dispersive spectrometer; The microstructure of the grinding marks was observed using an Olympus OLS3000 laser scanning confocal microscope; the phase composition was analyzed using a DmaxPC-2500 X-ray diffractometer with a Cu Kα target (40 kV, 200 mA), a scanning range of 20\u0026deg;\u0026ndash;90\u0026deg;, and a scanning speed of 4\u0026deg; per minute. The hardness distribution of the diffusion layer is measured using an MH-3 microhardness tester, with a load of 100 g and a loading time of 15 seconds; The surface wear resistance of the specimens is tested using a UMT TriboLab multifunctional friction and wear tester, using a 2 mm diameter GCr15 counterball; The mass before and after the wear test is measured using an analytical balance. To ensure measurement accuracy, each specimen is measured three times, and the average value is taken.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eNitriding process parameters\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecimen number\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eProcessing method\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eTemperature/℃\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTime/h\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003eVacuum gas nitriding\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e500\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e560\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e620\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003e560\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e14\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e18\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Study on Nitriding Temperature of AISI 430\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1 Microstructural analysis\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the microstructure of the cross-section of AISI 430 stainless steel after nitriding at different temperatures. (a) represents AISI 430 stainless steel that has not undergone vacuum gas nitriding treatment, while (b), (c) and (d) represent specimens treated at nitriding temperatures of 500\u0026deg;C, 560\u0026deg;C and 620\u0026deg;C for 6 hours, respectively. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a), the grain size and microstructure of AISI 430 stainless steel are relatively uniform. It can be observed that the original microstructure of AISI 430 stainless steel without vacuum gas nitriding treatment exhibits a relatively regular polygonal shape, with straight grain boundaries, characteristic of typical ferritic grain structure. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b), after 6 hours of vacuum gas nitriding treatment at 500\u0026deg;C, due to the relatively low nitriding temperature, ammonia gas was unable to decompose sufficient active nitrogen atoms to participate in the nitriding process, resulting in the absence of a uniform and continuous nitrided layer. However, it can be observed that the grain size of the substrate is finer compared to the untreated specimen. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c), the interfaces between the bright layer, the nitride layer and the substrate can be clearly distinguished. The increased nitriding temperature promotes the decomposition of ammonia gas, accelerating the rate at which active nitrogen atoms penetrate the steel substrate. Once a certain concentration is reached, a stable iron-nitrogen phase is formed[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d), the diffusion layer thickness of this specimen is greater than that of the other two specimens treated at lower temperatures in a vacuum gas nitriding process. However, it exhibits an abnormal region at the boundary of the diffusion layer. It can be observed that the diffusion layer contains relatively coarse grains, and numerous black nitride precipitates have formed along the grain boundaries. This may be due to the fact that after vacuum gas nitriding at 620\u0026deg;C, the key corrosion-resistant element Cr escapes, causing Cr to segregate at the grain boundaries and combine with N to form CrN. This reduces the Cr content, leading to poorer corrosion resistance at the grain boundaries. Under the same corrosion treatment, the grain boundaries exhibit darker colors and more severe corrosion[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNitriding is the process of nitrogen atoms diffusing into the interior of stainless steel. According to the Arrhenius equation, when the nitriding temperature in a vacuum is low, the decomposition rate of ammonia is low, and the temperature gradient between layers is small, resulting in insufficient diffusion driving force for nitrogen, leading to shallow nitrogen diffusion depth; as the temperature increases, the decomposition rate of ammonia gas increases, and the temperature gradient between layers also increases, thereby enhancing the diffusion driving force and increasing the diffusion depth of nitrogen. As the temperature continues to rise, the decomposition rate of ammonia gas in the nitriding process continues to increase, but the nitrogen potential gradually decreases, leading to a reduction in nitrogen content. This results in certain areas of the nitrided layer having relatively higher thickness, while the interface between the nitrided layer and the substrate becomes uneven[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].In general, for AISI 430 stainless steel, increasing the nitriding temperature within a certain temperature range can significantly increase the thickness of the nitrided layer. However, a higher nitriding temperature is not always better.\u003c/p\u003e\u003cp\u003eNitriding is the process of nitrogen atoms diffusing into stainless steel, described by the Arrhenius equation :\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\text{D}={\\text{D}}_{0}\\text{e}\\text{x}\\text{p}\\left(-\\frac{\\text{Q}}{\\text{R}\\text{T}}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn the equation: D is the diffusion coefficient; D0 is the diffusion constant; R is the ideal gas constant; Q is the activation energy per mole of atoms; T is the thermodynamic temperature. The decomposition formula for ammonia is shown in :\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:2N{H}_{3}=3{H}_{2}+2\\left[N\\right]$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eWhen the nitriding temperature increases, the diffusion coefficient increases according to the Arrhenius equation, and more ammonia decomposes into active nitrogen atoms, which diffuse into the stainless steel to form a solid solution.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2 Mechanical properties analysis\u003c/h2\u003e\u003cp\u003eThe effective hardened layer thickness refers to the vertical distance from the surface of the part to a point 50 HV higher than the base material hardness[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The base hardness of AISI 430 stainless steel is 165 HV. According to this standard, after vacuum gas nitriding at different temperatures, the effective hardened layer thicknesses were 95.4, 107.6 and 113.3 \u0026micro;m, respectively. These results were all higher than the nitrided layer values measured from the cross-sectional metallographic images. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c), the bright layer, nitride layer and base material can be easily distinguished. However, in Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b) and (d), the diffusion layer boundaries are not uniformly clear, and the diffusion layer thickness can only be roughly estimated, with the corresponding thicknesses at the thickest points of the nitrided layer being 8.86 and 56.7 \u0026micro;m, respectively. As the layer depth increases, the hardness of the nitride layer gradually increases, but simultaneously, its brittleness gradually increases, leading to a gradual decrease in the ductility and impact resistance of the diffusion layer. According to the Arrhenius equation, under the condition of constant nitriding time and pressure, the highest vacuum gas nitriding temperature yields the deepest diffusion layer, which is consistent with the experimental results.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCharacteristics of the diffusion layer of AISI 430 stainless steel treated at different process temperatures\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=\"left\" 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\u003eSpecimen number\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eSurface hardness/HV\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePermeable layer thickness/\u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eEffective hardened layer thickness/\u0026micro;m\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eAISI 430\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e165\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eS1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e231\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e8.86\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eS2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e875\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e44.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e107.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u003cp\u003eS3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e912\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e56.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e113.3\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\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the surface hardness value of the specimen is highest after vacuum gas nitriding treatment at 620\u0026deg;C. Since CrN is the hardest compound that can be formed in ferritic stainless steel, the higher hardness indicates that a higher proportion of chromium has been converted to CrN[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. CrN is more stable than the iron nitride phase. Therefore, under certain nitrogen concentrations, for AISI 430 stainless steel, chromium is the element with the second highest content after iron, and nitrogen atoms are more likely to combine with chromium to form compounds[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Therefore, after vacuum gas nitriding of ferritic stainless steel, a chromium nitride phase appears on the surface layer. The relatively low surface hardness indicates that the proportion of iron-nitrogen compounds in the generated phase is higher. The high surface hardness is mainly due to the formation of fine and uniform CrN-type bonded chromium nitride precipitates[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the average hardness value of the AISI 430 stainless steel substrate is approximately 167 HV. After vacuum gas nitriding treatment, the hardness values of the specimens all exhibit varying degrees of increase. This is because the ferritic stainless steel is exposed to a high-temperature active nitrogen atmosphere for an extended period, and according to the diffusion law, active nitrogen atoms gradually penetrate into the stainless steel substrate, thereby achieving the effect of vacuum gas strengthening. As the vacuum gas nitriding treatment temperature decreases from high to low, the hardness values also decrease accordingly. For specimens treated at 500\u0026deg;C, the near-surface layer hardness values at a depth of 5\u0026ndash;15 \u0026micro;m from the surface are around 225 HV, representing a 34.7% increase compared to the base material, while the hardness values near the core decrease to values close to the base material hardness. Specimens treated at 560\u0026deg;C and 620\u0026deg;C exhibit hardness values of approximately 900 HV at the cross-section, which is 5\u0026ndash;6 times that of the substrate; the hardness decreases sharply from the surface toward the substrate, reaching the substrate hardness at approximately 200 \u0026micro;m from the surface, after which it remains relatively constant. According to diffusion laws, nitrogen atoms diffuse from regions of higher concentration into the stainless steel matrix with lower concentration, from the surface inward. The amount of nitrogen penetration decreases in a gradient, and the degree of lattice distortion caused by nitrogen atoms entering the iron lattice decreases, leading to a reduction in hardness values[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe design principle of the vacuum gas nitriding process is to form a nitrided layer with excellent comprehensive performance on the surface of components while ensuring the integrity of the base material. The hardness value of the specimen surface can be determined by comparing the size of the indentations, and the brittleness level can be determined by observing the Vickers hardness indentation state of the specimen[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].The indentation marks on the specimens after vacuum gas nitriding treatment are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It can be seen that the specimens treated at 500\u0026deg;C and 560\u0026deg;C have good surface indentation morphology and clear edges, while the specimens treated at 620\u0026deg;C show a certain degree of deformation around the surface indentation marks, with higher brittleness and lower toughness.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAfter undergoing nitriding treatment at 620\u0026deg;C, the surface of the workpiece will form a compound layer of a certain thickness with high hardness. Under service conditions involving impact or heavy loads, an excessively thick compound layer is prone to local cracking or even peeling due to its high brittleness, leading to component failure[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eBased on the above research, the morphology of the S2 diffusion layer is good, with a uniform and continuous interface between the nitrided layer and the substrate. Both surface hardness and effective hardened layer thickness show significant improvements compared to the substrate. While the hardness values are similar to those of S3, the surface toughness of S2 is relatively better. Therefore, for vacuum gas nitriding treatment of AISI 430 stainless steel, 560\u0026deg;C is selected as the optimal nitriding temperature for the next phase of vacuum gas nitriding treatment, to investigate the effects of different nitriding times on the microstructure and properties of the nitrided layer of AISI 430 stainless steel.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Study on Nitriding Time of AISI 430 Stainless Steel\u003c/h2\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1 Microstructural morphology and phase analysis\u003c/h2\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, after being exposed to the corrosive agent, all specimens treated at 560\u0026deg;C with different nitriding times exhibited distinct layering phenomena and formed uniform needle-like structures. The microstructure of the AISI 430 stainless steel substrate transformed from a single ferritic phase to a mixed phase of ferrite and other precipitates. In all four groups of specimens, a bright white, high-hardness diffusion layer was observed in the region 15\u0026ndash;30 \u0026micro;m from the surface. This layer exhibited a uniform and dense microstructure with a clear interface at the boundary with the nitriding layer. Additionally, the density of the nitrided layer is influenced by the nitriding duration. At 6, 10 and 14 hours of nitriding, the nitrided layer was relatively dense and uniform. At 18 hours of nitriding, the nitrided layer began to exhibit black punctate and diffuse substances, along with loose pores, making it prone to peeling. The specimens processed using the 560\u0026deg;C nitriding for 18 hours process parameters exhibit a more severe degree of porosity in the nitrided layer compared to other specimens.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, by observing the microstructure morphology, it can be seen that the thickness of the nitrided layer varies significantly at different treatment times under 560\u0026deg;C. The nitrided layer thickness formed after 6 hours of treatment is approximately 60 \u0026micro;m. At 10, 14 and 18 hours of treatment, the nitrided layer thickness exhibits a small-range steep increase trend, followed by a relatively gradual increase trend. In general, at the same temperature, the thickness of the nitrided layer of AISI 430 stainless steel is directly proportional to the nitriding time. The specimen treated for 18 hours has the thickest nitrided layer, approximately 123 \u0026micro;m. Analyzing the overall growth trend in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the thickness of the nitrided layer generally increases after nitriding, forming a hardened layer that protects the AISI 430 stainless steel substrate. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, comparing specimens 1, 2, and 3, increasing the nitriding temperature enhances the nitriding layer thickness; as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, comparing specimens 4, 5 and 6, the nitriding time has a more pronounced promotional effect on the growth of the nitriding layer thickness of AISI 430 stainless steel.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe XRD patterns of the specimen surfaces of AISI 430 stainless steel after different durations of vacuum gas nitriding at 560\u0026deg;C are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The XRD analysis probe has a detection limit depth of 2.2 \u0026micro;m, with the detection area covering the specimen surface and the nitrided layer near the surface. As clearly shown in the figure, the diffraction peaks of AISI 430 stainless steel are sharp and distinct, with no diffraction peaks from other phases detected, indicating that the crystal structure of the specimen is relatively simple and no other phases such as austenite or pearlite are present. By analyzing the XRD diffraction peaks of specimens treated at the same nitriding temperature but with different nitriding times, it was found that the surface phase structure of the nitrided layer changes with increasing nitriding time. At 560\u0026deg;C for 10 hours of nitriding, the surface diffraction peaks of the nitrided layer showed iron nitride phases Fe₃N and Fe₄N; at 560\u0026deg;C for 14 hours of nitriding, the surface diffraction peaks of the nitrided layer showed the CrN phase, with the diffraction peaks of the iron nitride phases relatively weakened; At 560\u0026deg;C for 18 hours, the XRD diffraction peaks of the iron nitride phase on the surface of the nitrided layer showed a slight shift, while the CrN phase diffraction peaks gradually strengthened. Through analysis of the XRD diffraction peaks, it can be observed that as the nitriding time increases, the diffraction peaks of the iron-nitrogen phase gradually shift to the left at small angles, indicating that the crystal lattice of the iron-nitrogen phase has expanded. The lattice expansion indicates that nitrogen atoms have diffused into the interstitial spaces of the lattice. This suggests that as the nitriding time increases, nitrogen atoms reach a supersaturated state and cause changes in the lattice parameters.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe CrN phase appears on the surface of the S6 nitrided layer. Combined with the diffuse distribution of precipitates in the bright white layer shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, it can be concluded that chromium nitride mainly forms in the shallow surface layer with high nitrogen concentration during vacuum gas nitriding, and is dispersed in the bright white layer in the form of small precipitates. CrN precipitates begin to form along grain boundaries and internal defects within grains, specifically along dislocation lines or twin boundaries throughout the entire layer. Regions near the surface are more prone to nucleation than deeper regions near the substrate interface, as nitrogen has been enriched in these areas earlier, and chromium atom diffusion is more likely to facilitate the growth of these precipitates. Due to the influence of grain boundaries or local stress fields, the activation energy required to transport nitrogen atoms through more active regions is lower than that required for the formation of primary precipitates.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2 Hardness and wear resistance analysis\u003c/h2\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, under the same temperature conditions, different nitriding treatment times result in varying degrees of hardening effects on the microhardness transition from the nitrided layer to the base material for AISI 430 stainless steel. The microhardness measurement values are a function of depth from the surface, with a sharp decrease occurring around 100 \u0026micro;m from the surface, followed by a gradual decrease in hardness values until reaching the effective nitrided layer thickness, after which the hardness becomes similar to that of the base material. It can be observed that the surface hardness of stainless steel significantly increases after vacuum gas nitriding. The base material hardness of AISI 430 stainless steel is 167 HV. After vacuum gas nitriding at 560\u0026deg;C for 6, 10, 14 and 18 hours, the surface hardness of the specimens was875 ,1345 ,1380 and 1440 HV, respectively, representing a 5- to 9-fold increase compared to the hardness of AISI 430 stainless steel before vacuum gas nitriding. The high surface hardness of the specimens after vacuum gas nitriding treatment is attributed to the significant formation of CrN and Fe₂₋₃N on the stainless steel surface, which markedly enhances the surface's resistance to plastic deformation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAt a nitriding temperature of 560\u0026deg;C, a white bright layer with a thickness of approximately 5\u0026ndash;20 \u0026micro;m is present at the interface between the vacuum gas nitrided surface and the ferritic matrix of AISI 430 stainless steel. This is consistent with the presence of Fe₃N and Fe₄N as shown in XRD Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. Despite varying nitriding times, the diffusion layer boundaries adjacent to the AISI 430 stainless steel matrix are all continuous, uniform and smooth, representing an ideal boundary state for nitriding treatment of high-chromium alloy steels[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWithin a certain range of nitriding time, the hardness value increases as the nitriding time is extended, followed by a slight decrease. This is because chromium nitride is the compound with the highest hardness value. Higher hardness indicates a greater proportion of chromium reacting with nitrogen to form chromium nitride. While CrN has high hardness, it also exhibits significant brittleness, meaning it may be prone to cracking or fracturing under external forces, particularly in the absence of toughness enhancement[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. As the nitriding time increases, more compounds are formed between active nitrogen atoms and chromium atoms. Regarding the depth of the nitrided layer, it is related to the diffusion function, and diffusion increases with increasing nitriding temperature and nitriding time. This means that a longer nitriding treatment time allows for more thorough diffusion, resulting in a deeper nitrided layer, consistent with the micrograph of the specimen in Fig.\u0026nbsp;3.5[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe surface wear patterns and laser confocal wear depth maps of the original AISI 430 stainless steel specimens and those treated with vacuum gas nitriding are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. As shown in Figure (a), the surface of the original specimen exhibits parallel grooves aligned with the direction of ball movement and minor flake-like spalling after wear. This indicates that the wear mechanism of AISI 430 stainless steel involves adhesive wear and abrasive wear. The presence of grooves may be attributed to the friction between the harder GCr15 balls and the softer AISI 430 stainless steel substrate[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Hard particles are pressed into the friction surface under the action of a vertical force, and subsequently leave plow-like grooves on the surface during reciprocating linear motion, indicating that the friction surface has low hardness and good ductility. No obvious plow grooves were observed in Figures (b), (c), (d), and (e), as the nitrided layer on the surface of AISI 430 stainless steel after vacuum gas nitriding has a high hardness, making it difficult for hard particles to be pressed into the specimen surface under the same vertical force. Experimental results indicate that the duration of vacuum gas nitriding significantly affects the friction characteristics of the nitrided specimens.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe wear marks on the vacuum gas nitriding specimens exhibit small pits and scratches, indicating that the primary wear mechanism is adhesive wear. As shown in the figure, as the vacuum gas nitriding time increases, the number of pits in Figures (b), (c) and (d) gradually decreases, and the morphology of the scratches also weakens. Combining the three-dimensional morphology of the wear marks on the specimens obtained using laser confocal microscopy, the Z-axis is set with the same scale, and the depth of the wear marks is indicated by changes in color intervals. It can be observed that the width of the wear marks in Figures (g), (h) and (i) gradually narrows, and the depth of the wear marks gradually decreases. This may be attributed to the formation of a high-hardness iron nitride phase on the surfaces of the S3 and S4 specimens, which enhances surface hardness while improving wear resistance; the S5 specimen exhibits a small amount of CrN phase, resulting in a reduced content of iron nitride phase. The CrN phase is a stable phase with higher hardness than the iron-nitride phase, resulting in superior performance of S5 in the abrasion test. This indicates that under the same vacuum gas nitriding temperature, within a certain nitriding time range, the wear resistance of the AISI 430 stainless steel specimen surface can be enhanced[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].Figure (e) shows that part of the inner layer surface is deep black, and the scratches are deeper than those in Figures (b), (c) and (d), indicating that local spalling has occurred. The reason for this phenomenon is that the S6 specimen generates more CrN, which has higher surface hardness but is more brittle, and undergoes slight fragmentation under the action of hard particles. The fine particles generated by the peeling of the hardened layer are incorporated into the reciprocating linear motion of the grinding balls, causing secondary damage to the specimen surface[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAfter being treated at 560\u0026deg;C for 6 hours, 10 hours, 14 hours and 18 hours, respectively, the wear volume of the AISI 430 stainless steel specimens is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The wear volume of a metal surface sliding against another metal surface is inversely proportional to hardness and directly proportional to the wear coefficient, applied load, and sliding distance[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Since the applied load and sliding distance were the same in the tests conducted, surfaces with high hardness and deep penetration layers exhibit the best wear resistance, and the research results confirm this. From the wear volume, it can be seen that due to the low surface hardness of AISI 430 stainless steel, the wear volume is relatively large, at 0.335 mm\u0026sup3;. However, the wear volume of the S3-6 specimen treated with vacuum gas nitriding is significantly reduced, indicating that vacuum gas nitriding can improve the wear resistance of the surface of AISI 430 stainless steel. As the nitriding time increases, the wear volume follows a pattern of first decreasing and then increasing. The wear volume of the S3 specimen decreased by 43% compared to AISI 430 stainless steel, but it remains higher than that of the S4-6 specimen, which underwent longer vacuum gas nitriding. This phenomenon may be attributed to the presence of only Fe₂₋₃N and Fe₄N phases in S2, while other processed specimens contain CrN[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Chromium nitride phases exhibit higher hardness and wear resistance than iron nitride phases, resulting in S2 having inferior wear resistance compared to the other three specimens with longer vacuum gas nitriding times, and thus exhibiting greater wear volume.\u003c/p\u003e\u003cp\u003eAfter 18 hours of vacuum gas nitriding treatment, the wear volume of the specimens increased slightly. CrN is a chromium-nitrogen phase with high hardness but poor ductility. The S6 specimen has a higher CrN content in its surface phase composition. A possible reason is that during friction with the harder GCr15 grinding balls, under the combined effects of normal stress and transverse shear stress, CrN particles peel off and become hard particles that participate in subsequent friction, causing the wear mechanism to shift to abrasive wear and resulting in reduced wear resistance.\u003c/p\u003e\u003cp\u003eThe friction coefficient curves of the S3-6 nitrided specimens and the original specimens over time are shown in Fig.\u0026nbsp;3.11. As can be seen from the figure, the friction coefficient is related to the nitriding time, and there are certain differences in the friction coefficients of the specimens treated under different nitriding times. The friction coefficient of AISI 430 stainless steel specimens exhibits significant fluctuations in the initial stage, rapidly rising to approximately 0.5 and exhibiting pronounced fluctuations in the curve. This is because during the initial wear-in process, the passivation film on the stainless steel surface is damaged, exposing the fresh, soft surface to wear against the hard GCr15 balls. The wear balls must overcome adhesive resistance, leading to adhesive wear, which causes the friction coefficient to surge sharply. From the 2nd minute onwards, the coefficient of friction gradually stabilizes, indicating that the AISI 430 stainless steel requires a break-in period to enter a stable phase. From the friction coefficients of the specimens, it can be seen that the break-in stage generally occurs around 2 minutes, followed by a stable wear state. The friction coefficients of the 565\u0026deg;C\u0026thinsp;+\u0026thinsp;10, 14and 18 h nitrided specimens eventually stabilized at approximately 0.4, 0.38, and 0.5, respectively, with minimal variation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe coefficient of friction for specimen S3 sharply increased to 0.5 and then underwent another rise phase for about 2 minutes. Subsequently, during the subsequent friction and wear process, the coefficient of friction increased at a relatively slow rate and finally stabilized at around 0.68. The reason for the continuous fluctuations in the curve may be that the nitriding layer formed by short-term nitriding is relatively thin. When the counterball wears away the nitriding layer, the counterball comes into contact with particles of the nitriding layer mixed with the base material, causing significant fluctuations in the friction coefficient curve. When the friction coefficient enters the stable wear phase, its fluctuations are significant, indicating that a large amount of wear debris is generated through friction and wear, and the debris is not removed in a timely manner, leading to the phenomenon of severe fluctuations in the friction coefficient curve[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].S4-6 initially rises and then stabilizes within approximately 1 minute. Subsequently, it is influenced by a combination of factors, including the surface roughness and hardness of the specimen's penetration layer, as well as the debris generated during the wear process, causing the friction coefficient curve to decline to a certain extent. Afterward, the friction coefficient stabilizes at around 0.4 and 0.5, respectively, until the wear process concludes. After the friction coefficient curve stabilizes, the amplitude of its fluctuations is relatively small, indicating that excessive wear particles were not generated during the friction and wear process.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003eUnder a constant nitriding time of 6 hours, both the nitriding layer thickness and surface hardness increase progressively with rising nitriding temperature. The maximum nitriding layer thickness reaches 56.7 \u0026micro;m, while the surface hardness attains 912 HV. However, an increase in temperature leads to a reduction in surface plasticity and toughness.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAt a constant nitriding temperature of 560\u0026deg;C, the thickness of the nitriding layer increases with the extension of nitriding time. The experimental results indicate that, when the nitriding temperature is maintained constant, the nitriding time has a significant effect on promoting the growth of the nitriding layer thickness in AISI 430 stainless steel.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eFor AISI 430 stainless steel, nitriding at a temperature of 560\u0026deg;C for 14 hours yields the best overall surface performance. The nitrided layer thickness can reach 115.9 \u0026micro;m, with a surface hardness of 1380 HV, which is 8.26 times higher than that of the original AISI 430 stainless steel specimen. Wear loss weight is reduced by 83% and the material exhibits good ductility and toughness.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eProfessor Wang Wenquan provided guidance and recommendations for the design and implementation of the research plan, leveraging his deep expertise in surface technology.Professor Zhang Xinge assisted in resolving technical challenges during the experiments, ensuring their smooth execution.Throughout the research process, both professors offered invaluable insights and suggestions for the manuscript. Their professional guidance and technical support played a crucial role in enhancing the overall quality of the paper.Zuo Jialong served as the primary executor of this research. He was responsible for experimental implementation, operational execution, and data collection and organization. Additionally, Zuo Jialong undertook the writing of the paper, including drafting the text content and preparing and formatting the figures and tables.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLUO H, et al. Electrochemical and passive behaviour of tin alloyed ferritic stainless steel in concrete environment[J]. Appl Surf Sci, 2018, 439(1): 232\u0026ndash;239. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.apsusc.2017.12.243\u003c/span\u003e\u003cspan address=\"10.1016/j.apsusc.2017.12.243\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXIE L A, WANG X Q, HAN Z J, et al. Post-fire stress\u0026ndash;strain response of structural ferritic stainless steels[J]. 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Coatings, 2023, 13(10): 1708. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/coatings13101708\u003c/span\u003e\u003cspan address=\"10.3390/coatings13101708\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"surface-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Surface Science and Technology](https://link.springer.com/journal/44251)","snPcode":"44251","submissionUrl":"https://submission.springernature.com/new-submission/44251/3","title":"Surface Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"AISI430, vacuum gas nitriding, diffusion kinetics, friction wear volume, nitriding parameters","lastPublishedDoi":"10.21203/rs.3.rs-7535140/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7535140/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAISI 430 stainless steel is widely used in engineering applications due to its low cost and excellent corrosion resistance. Vacuum gas nitriding is a commonly used surface modification technique, and in industrial production, it is necessary to prepare a thick and uniform nitrided layer. To comprehensively analyze the microstructure, phase composition, mechanical properties and diffusion kinetics of the nitrided layer, vacuum gas nitriding experiments were conducted on AISI 430 stainless steel. The results showed that the nitriding layer thickness increased with rising temperature. At 620\u0026deg;C, the nitriding layer thickness after 6 hours of nitriding was 56.7 \u0026micro;m, with a surface hardness of 912 HV0.025; however, its surface ductility and toughness were poor. It was found that within a certain nitriding time range, the nitrided layer thickness increased with time. At 560\u0026deg;C, nitriding for 18 hours resulted in the maximum nitrided layer thickness of 123.6 \u0026micro;m and a surface hardness of 1440 HV0.025, but its wear resistance decreased. Compared to AISI 430 stainless steel, specimens treated with 14 hours of vacuum gas nitriding at 560\u0026deg;C achieved a nitrided layer thickness of 115.9 \u0026micro;m, with surface hardness increased by 8\u0026ndash;9 times and wear loss reduced by 83%. The nitrided layer primarily consists of iron-nitride phases, with a small amount of chromium-nitride phases contributing to hardness enhancement.\u003c/p\u003e","manuscriptTitle":"Study on Vacuum Gas Nitriding Process and Surface Properties of AISI 430 Stainless Steel","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-23 16:20:42","doi":"10.21203/rs.3.rs-7535140/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-08T09:33:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-24T13:16:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"121778766854765390370627209399158057528","date":"2025-09-24T04:50:05+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"331496346054369164795041132536229910149","date":"2025-09-22T11:19:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"200612867774275427894705819619784905540","date":"2025-09-17T01:45:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-15T01:34:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-10T06:25:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-10T06:24:02+00:00","index":"","fulltext":""},{"type":"submitted","content":"Surface Science and Technology","date":"2025-09-04T10:23:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"surface-science-and-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Surface Science and Technology](https://link.springer.com/journal/44251)","snPcode":"44251","submissionUrl":"https://submission.springernature.com/new-submission/44251/3","title":"Surface Science and Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Open","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"df04fff6-a035-4cd1-ac89-eecf0d207ce6","owner":[],"postedDate":"September 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-11-07T02:23:10+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-23 16:20:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7535140","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7535140","identity":"rs-7535140","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}