Specific features of separations in fracture after CTOD tests of low-carbon microalloyed offshore steel S460MLO

Specific features of separations in fracture after CTOD tests of low-carbon microalloyed offshore steel S460MLO | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Specific features of separations in fracture after CTOD tests of low-carbon microalloyed offshore steel S460MLO Eugene Goli-Oglu, Marco Palombo, Andrei Filatov This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4583102/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Using the results of testing industrial batches of 23 mm steel heavy plates after thermomechanical rolling and subsequent post-weld heat treatment, the patterns of fatigue cracks formation in the fracture specimens during CTOD (Crack Tip Opening Displacement) testing for fracture toughness are investigated. Visual, microstructural, and fractographic studies of the nature of fracture formation and the surface of the secondary separations have been conducted. The probable causes of the manifestation of the potential «pop-in» effect on the load-displacement diagrams of the notch opening displacement are described, as well as its potentially negative impact on the interpretation of test results low-carbon steel heavy plate fatigue crack opening displacement fracture toughness separations pop-in effect CTOD Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction For the production of steel constructions for the Northern and Arctic regions, designed for high levels of cyclic loads with varying amplitudes, only high-quality heavy plate steel with enhanced requirements for low-temperature toughness and fracture toughness is used. Illustrative examples of structures subjected to variable forces are offshore fixed platforms in the energy sector, where primary cyclic loads are generated by marine currents, wind, waves, and sometimes ice floes, resulting in complex stress diagrams at various points of contact. As an example, Figure 1 shows the wind direction frequency characteristics and hourly wind speed index (with an average speed of 9.6 m/s) near the Horns Rev2 offshore wind farm in the North Sea, close to the Danish shore. These graphs clearly demonstrate the nature and degree of asymmetry in the environmental impacts on offshore platform operation and, consequently, reasonable variability in the degree and direction of asymmetric cyclic loads. Under such aggressive environmental conditions, the most stressed structural components may experience rapid failure due to internal defects or fatigue cracks forming in localized areas of high stress. Consequently, Annex F has been added to the latest revision of the offshore standard EN 10225-1:2019 [ 2 ] to regulate the procedure for pre-qualification testing of heavy plate steel for fixed offshore structures operating in the Northern and Arctic regions. The regulation includes evaluating the steel's fracture toughness, for which CTOD (crack tip opening displacement) tests are conducted according to ISO 12135 [ 3 ]. These tests to measure the maximum opening of a pre-induced fatigue crack before the critical moment of its opening at temperatures ranging from -10 to -40 °C. These tests enable the determination of several crucial steel properties, including the critical crack tip opening δ (in mm), the J-integral, and the stress intensity coefficients Kc under plane strain and KIc of the 1st strain mode [ 4 , 5 ]. The experience received in conducting and analyzing CTOD test results of steels produced by thermomechanical processing (TMCP) shows that in some cases the interpretation of CTOD test results could be more complicated due to the need to examine the fracture surface of samples to identify the so-called "pop-in" effects on the strain curves. According to existing BS, ASTM, ISO standards, such an occurrence can be deemed like critical. At the same time, the fracture of the tested specimen shows the formation of transverse (secondary) splits in the direction of the plate thickness without significant crack propagation in the plane of the pre-induced fatigue crack. In the case of TMCP steels, the appearance of short-term spikes in the fracture diagrams, similar to a potential “pop-in” effect, does not always indicate a brittle fracture mechanism of the steel and may depend on extraneous factors [ 6 ]. One such factor is related to the specifics of the formation of the microstructural state and crystallographic texture of the steel oriented along the deformation direction [ 7 , 8 ], especially during low-temperature thermomechanical processing of heavy plates of thickness groups below 25 mm, where the level of low-temperature deformation riveting is high. In case of high purity of TMCP steel on non-metallic inclusions, the mechanism of separations may also be due to the anisotropy of critical tearing stresses in the plane of the plates and in the Z-direction [ 9 ]. The objective of the article is to identify the type and nature of secondary separations in CTOD samples through macro-, micro-, and fractographic studies, as well as to evaluate the relationship between the fracture characteristics and the test results with the occurrence of potential "pop-in" effects on the fracture diagrams of low-carbon microalloyed heavy plate steel S460MLO for offshore applications, produced by the thermomechanical control process. Materials and Methods Basic oxygen furnace (BOF) cast into slabs with a thickness of 355 mm were used as the examined material. The chemical composition of the steels under investigation is provided in Table 1. Two types of microalloying were employed: Nb-V-Ti and Nb-Ti. Slabs were rolled on a reversible hot rolling mill 4200 [ 10 ] according to the technology of low-temperature two-stage thermomechanical rolling for the final plate thickness of 23 mm with the end of deformation in the γ+α-region. The level of basic mechanical properties corresponds to heavy plates of quality grade S460MLO according to EN 10225-1:2019. Table 1. Chemical composition of the investigated steels, wt. % Steel Microalloying C Mn Si S P N Ni С eq A Nb-V-Ti 0,06 1,45 0,24 0,001 0,005 0,004 0,25 0,33 B Nb-Ti 0,04 1,44 0,18 0,001 0,008 0,005 0,25 0,31 From the rolled plates, series of samples were selected for mechanical testing. Half of the samples underwent additional heat treatment, including controlled heating from a temperature of 400°C at a rate of 55°C/hour to 580±3°C, holding for 60 minutes, and controlled cooling to 400°C at a rate of 55°C/hour. These specified process parameters simulate the heat treatment of critical joints of structures after assembly or repair welding (PWHT). The investigated steels have a homogeneous ferritic-pearlitic microstructure with light bending ( Fig. 2 ) and elongated ferrite grains. The average conditional ferrite grain diameter in the surface layers is approximately 4.3 µm, in the quarter ~ 5.7 µm, and in the center ~ 6 µm. The average mechanical characteristics of the investigated steels in the initial state are as follows: yield strength R eH : 514 MPa and 509 MPa, tensile strength Rm: 566 MPa and 545 MPa, elongation A 200 = 25% and 22%, respectively for Steel A and Steel B. The values of the impact energy KVТ -40 are in the range of 285-305 J (Steel A) and 138-292 J (Steel B). Ultrasonic testing in both cases showed S 3 E 4 results according to EN 10160 standard. After additional heat treatment for Steel A, the average values are as follows: R eH = 504 MPa, R m = 556 MPa, A 200 = 27%, KVL -40 = 211-307 J. For Steel B: R eH = 489 MPa, R m = 535 MPa, A 200 = 25%, KVL- 40 = 111-128 J. Fracture toughness and fatigue tests were conducted on a universal testing system with freely moving outer rollers Zwick/Roell Z600 for single edge notch bending (SENB) samples, which were made of base metal and had dimensions of 20×40×185 mm, in accordance with ISO 12135 requirements. After applying a 17 mm notch on the specimens, a fatigue crack was grown to the nominal specified depth of 0.5ao/W, so that the total initial length of the notch with the fatigue crack was in the range of a (0.45-0.55W). The pre-crushing force was Pm = 9.9 kN, and the span (distance between supports) was S = 160 mm. Test temperatures: -10, -20, -30, -40 °C. The critical value of CTOD was determined using formulas (1) and (2), taking into account the thickness (B) and height (W = 2B) of the specimen, the span of the testing machine (S), the size of the induced fatigue crack (a o ), the distance from the measurement point of the notch opening above the specimen surface (z, a value of z = 0 was used), the yield strength at the testing temperature (σ YS ), test temperature, force (F), displacement (V), Young's modulus (E), and Poisson's ratio (ν). Microstructural investigations and fractographic analysis of the structure and fracture zones were conducted using an optical microscope (OM) Carl Zeiss Axio Observer 7 MAT and a scanning electron microscope (SEM) Tescan MIRA3. Discussion The values of critical crack tip opening displacement (δ, mm) obtained after serial tests for the steels under investigation in the TMCP and TMCP+PWHT states are presented in Table 2. Overall, the investigated steels demonstrated a sufficient level of fracture toughness across the entire temperature range of the tests. The crack opening value did not drop below 1.00 mm. Steel A exhibited approximately 10% higher overall relative fracture toughness than Steel B in the initial condition and approximately 30% higher when PWHT was applied. The application of the PWHT resulted in lower CTOD values and an increased probability of short-term shear and load reduction, characterised as a potential “pop-in” effect. ( Fig. 3b ). The nature of such shifts along the contour of the short-term stress drop (sharp jump transition) and the moment of appearance (close to the section of transition from elastic to plastic deformation) resembles the yield point in tensile stress-strain diagrams during tensile tests in the plane of rolling direction. Table 2. Results of serial CTOD tests of the studied steels for fracture toughness № Crack tip opening displacement, δ (mm) TMCP TMCP+PWHT 580±3 °C, 60 min -10 °C -20 °C -30 °C -40 °C -10 °C -20 °C -30 °C -40 °C Steel A 1 1.48 1.66 1.73 2.01 1.58 1.41 1.61 1.99 2 1.65 1.59 1.69 1.59 1.64 1.73 1.15 1.93 3 1.66 1.72 1.58 1.90 1.75 1.68 1.86 1.81 Steel a 1 1.62 1.70 1.90 1.23 1.10 1.34 1.26 1.06 2 1.54 1.32 1.75 1.21 1.09 1.29 1.23 1.07 3 1.15 1.59 1.90 1.04 1.07 1.12 1.30 1.35 Examining the fracture diagrams after CTOD tests (see Fig. 3 ), several typical zones can be identified. The initial zone, characterized by a linear relationship between displacement and applied force, corresponds to the stage of elastic deformation. Then, the slope of the curve changes, and with increasing load within the fatigue crack, plastic deformation develops. Analysis of the logarithmic odds ratio (χ2 = 7.23, p = 0.057) showed that there was no statistically significant relationship (significance level α = 0.05) between test temperature and the occurrence of short-term shear with load drop at the diagrams. Therefore, the probability of the occurrence of shear (potential “pop-in” effect) can be considered as a statistically random variable. In [ 11 ] the significance and mechanism of separations during various mechanical tests of pipe steels are investigated in detail. The authors suggest not to take into account such short-term load reduction as a critical “pop-in” effect in determining the CTOD value, and to put the main emphasis on the macroscopic appearance of the fracture surface. Consider the mechanisms and regularities of separations formation in the obtained fractures after CTOD tests. Visual fracture analysis The characteristic visual appearance of the samples selected after testing at different temperatures is given for Steel A in Fig. 4a and for Steel B in Fig. 4b . After PWHT, the fracture structure is shown in Fig. 4c and Fig. 4d . Regardless of chemical composition and final treatment, all samples are characterised by a high number of transverse separations. In case of registration of potential “pop-in” spikes on the diagrams ( Fig. 3b ), the secondary separations observed in the fractures ( Fig. 4 b, d ) extend into the induced crack region and propagate in it for a length of 0.5-0.9 mm. The number of spikes on the diagram corresponds to the number of separations that have entered the induced crack zone. The further the separations have propagated into the induced crack region, the more clearly the potential “pop-in” spikes is discernible on the diagram. It is with this feature, noted on individual samples, that the authors attribute the manifestation of the potential “pop-in” effect. It can be assumed that the appearance of secondary splits is due to the action of transverse forces directed along the thickness of the plate, when these forces act on elongated microstructural elements perpendicular to the main fracture plane and serving as the crack initiation point, separations can occur. This type of fracture occurs due to the coincidence of crystallographic planes with reduced layer bonding energy [ 12 ]. One of the main reasons for shear detection may be the parallel arrangement of elongated microstructural or crystallographic elements along the thickness of the plate. Also beside above mentioned separations could be related to the texture of the material [9]. Visually, the investigated separations are split perpendicular to the direction of the main crack development in planes parallel to the surface of the plate. The separations are observed along the entire thickness direction, indicating that this is not a single-layer effect, as can occur when opening along the center line of segregation. Rather, plastic tightening of the sample along the edges leads to an increase in the stress state close to the plane strain state, when the connectivity of layers in the rolling direction decreases, which is directly related to the features of the formed microstructure. Heating the steels to 580±3 °C and holding for 60 minutes resulted in a general increase in the number of delaminations visible on the surface of the fractures, which, in turn, increased the probability of separations coming to the surface of the preliminary notch zone. Microstructural analysis of separations The microstructural condition of the examined samples was investigated in the TMCP ( Fig. 2 ) and TMCP+PWHT condition. To identify the nature of separations, the microstructure at crack nucleation and propagation was analyzed and compared with the microstructure of the base metal. The microstructure in the regions adjacent to the separations exhibits greater elongation along the deformation direction of the separations. Several main crack morphologies were identified at the termination points of visible separation boundaries. In the case of potential “pop-in” separations ( Fig. 5a ), the crack ends along the boundary of the elongated deformed ferrite grain, does not propagate deep and has no side branches. The relief of the walls is smooth with a small number of rounded depressions on one side and protrusions on the opposite side. The protrusions and depressions are nearly symmetrical and have angles close to 90°. When medium and smaller separations are observed, the cracks do not always propagate to the surface of the investigated grinding plane. In such cases, intense plastic flow of the metal is observed in the vicinity of the separations ( Fig. 5b ). The homogeneity absence in the bending strain bands along the metal cross-section can be explained by the alternation of adjacent regions with pronounced plastic flow during local bending [ 13 ]. This phenomenon is characteristic of the microstructural condition of the steel, which is defined by elongated ferrite grains formed through heavy deformation below the Ar 3 temperature. Morphological analysis of separations The morphological analysis was conducted following similar principles for describing the fracture nature after the drop weight tear test (DWTT) regulated by EN 10274 and API RP 5L3, which categorize separations into two types. The first type propagates parallel to the plate plane and terminates in a sharp crack ( Fig. 6a ). Such separations are not considered brittle characteristics and are referred to as “Separations”. The second type is termed “Cleavage”, and the separations in this case have a blunted termination ( Fig. 6b ) and are oriented at a slight angle to the sheet surface. This type should be classified as a brittle component. In the case of separations of the first type, their formation occurs during plastic deformation preceding fracture, while separations of the second type result from fatigue crack propagation [ 14 ]. Visually, it is not always straightforward to determine the type of separations, both in samples after DWTT and CTOD tests, as significant differences can be observed only on cross-sections of the fracture surface [ 15 ] and in fractographic studies. The macroscopic analysis showed that after completing the CTOD tests, all fractures of the samples can be classified into the following areas ( Fig. 4b ): the pre-induced fatigue crack zone, fracture zone, zone of fracture before complete sample failure, and fracture retraction zone [ 16 ]. Two large separations were observed on the cross-section: the first measured 11.3 mm in length with an opening of up to 3.5 mm, while the second measured 9.2 mm and 3 mm, respectively. Medium-sized separations exhibited openings of up to 2.8 mm, while smaller separations were evident within the gaps among the larger ones. The retraction area comprised approximately 15% (abs.) of the total, with a minimum retraction width of 16.1 mm. Additionally, the sample subjected to PWHT two large separations in the central portion of the fracture, with length-to-opening ratios of approximately 13 mm/2.9 mm for the first separation and 14.9 mm/2.6 mm for the second. Furthermore, there were 5 medium separations with openings of up to 2 mm, along with numerous elongated smaller separations. The retraction area accounted for roughly 11% of the total, with a minimum retraction width of 17 mm. The panoramic photographs of the sample surface cross-section were graphically processed so that the outline of separations was clearly visible ( Fig. 7 ). Analysis of the cross-section of the fractures allowed for determining the nature of propagation and the depth of the separations. The deep separations, which define the potential “pop-in” spike in the diagram for the initial state, reach 5.7 mm, while for the PWHT condition, they reach 5.6 mm. The ends of the separations appear as single openings or multiple thin cracks. The opening angles at the endpoints are sharp and oriented perpendicular to the fracture surface. Fractographic analysis of separations The detailed scanning electron microscopy studies are illustrated using an example of the sample after CTOD tests at -40°C. Following visual ( Fig. 4d ) and macroscopic ( Fig. 8a ) analyses, 4 regions ( Fig. 8b ) have been chosen to describe the nature of fracture propagation within separations. Area 1 ( Fig. 8b.1 ) is located at the edge of the largest separation, opposite to the direction of fatigue crack propagation. At low magnifications (×200) in this zone, only a ductile type of fracture is discernible, but at ×500 and ×2000, small areas with a mixed fracture character can be distinguished. Nevertheless, the ductile component prevails in this area, and the area of fracture by brittle mechanism is small. Area 2 ( Fig. 8b.2 ), located on the inner side of the same separation, also exhibits predominantly ductile fracture, as confirmed by the presence of dimple fracture structure. For area 3 ( Fig. 8b.3 ), where the separation extends into the induced crack zone, causing the potential “pop-in” spike, a mixed type of fracture is characteristic. Individual local brittle areas of instantaneous fracture are detected in the form of streamlet-let relief (quasi-cleavage), likely occurring in areas with a pearlitic component. Area 4 ( Fig. 8b.4 ), free from separations and located in the zone of initial fracture, is characterized by the presence of typical dimples typical of ductile fracture [ 17 ]. It is likely that the formation of separations occurs by facilitating delamination through chipping of planes along the rolling direction, resulting in the formation of a certain number of separations in the plastically deformed fracture zone ahead of the growing crack front. If separations formed by this mechanism exhibit a potential «pop-in» spike, then they probably should not be considered as the final event during the test, unlike cases where the spike is caused by the propagation of the main fatigue crack deep into the sample through brittle mechanism. Summarizing the conducted studies, it can be noted that the areas of the surface of the examined separations are predominantly characterized by ductile fracture. Therefore, such metal can be considered as a multilayer material, where strength and ductility are determined by the energy of crack propagation occurring at each transition from one layer to another. Conclusion Low-carbon microalloyed 23 mm thick steel heavy plates of quality grade EN10225-1:2019 S460MLO was CTOD tested in TMCP and TMCP+PWHT conditions. Investigating the relationship between fracture types, fracture characteristics, and CTOD test results in test temperature range -10 … -40 °C authors determined that: - all fractures of the samples are characterized by a high number of secondary splittings. The examined splittings belong to the type I separations according to the classification of EN 10274, API 5L3, with a predominant ductile fracture mechanism. - an individual peculiarity of fracture with CTOD specimens splits is the presence of statistically random short-term bursts with load reduction, registered on the diagrams “load – crack opening displacement” as a potential “pop-in” effect. The appearance of such short-term spikes in the investigated cases is attributed to the emergence of individual separations from the fracture zone into the primary induced fatigue crack zone. In this case, the fracture also occurs by a ductile mechanism, and the main fracture toughness indicator δ (mm) remains at a high level (more than 1.0 mm), indicating that such short-term spikes could not be considered like critical events during the CTOD test of the investigated steel type. - application of additional heat treatment to the investigated TMCP steel increases the likelihood of potential “pop-in” spikes appearing on the fracture diagram. This is likely due to relaxation between microstructural layers and simplification of conditions for the occurrence of a greater number and depth of separations. The results of the research have been used successfully in passing the certification tests of heavy plate products of quality categories S460MLO, S420MLO, S355MLO according to the standards EN10225-1:2019 and NORSOK M-120, including pre-qualification for operation in Arctic areas. Declarations Author Contribution E.O. wrote the main manuscriptM.P. reviewed the manuscript, analysed the data and produced table 2, figure 3 and figure 4A.F. prepared the other figures and tables. References Official web recourse The Global Wind Atlas by DTU and Co-Developers. https://globalwindatlas.info (date of reference 2024-03-13). European Standard EN 10225-1. Weldable Structural Steels for Fixed Offshore Structures – Technical Delivery Conditions – Part 1: Plates. Brussels. 2019. 62 p. ISO 12135:2021. Metallic materials — Unified method of test for the determination of quasistatic fracture toughness. Edition 3. 2021. Moore P., Pisarski H. CTOD and Pipelines: The past, present, and future / The Journal of Pipeline Engineering. 2013. Vol. 12. Issue 3. P. 237–244. Zhu X.-K. Review of fracture toughness test methods for ductile materials in low-constraint conditions // Int. J. Pressure Vessels Piping. 2016. No. 139–140. P. 173–183. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4583102","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":321387236,"identity":"30e2ed52-05b8-4ea7-8f72-0c9d561e4231","order_by":0,"name":"Eugene Goli-Oglu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA80lEQVRIie3QMQrCMBSA4VcC6RJ1k0pBrxAROgkOXiRd6iZCQToWhHQRnJ08g4tzRXASwVFc4g1066BoEl1TOgrmHxIK76NJAGy2X01QubjgCPVRB1yBMEUQILVJUImAJtirRBrgngSbQLszJEFy5zDGzT2DItkYSSslMZUH63V3JDgvOcTYj3JnfrgYCc1J5DH6CtczElxqHELuj1LkcDMZfAhoEj+rEAruXpMVIoGcVCTKS4m3I0jfhSIct+ZHTxG2LbtLI8uu4vaQL5bN1rdi2g8XftQVRWImgAj9vsPnr3rNzfMqV+itk5aP2Ww22x/3BhL/Sggir+0jAAAAAElFTkSuQmCC","orcid":"","institution":"NLMK DanSteel","correspondingAuthor":true,"prefix":"","firstName":"Eugene","middleName":"","lastName":"Goli-Oglu","suffix":""},{"id":321387237,"identity":"e8872dc8-d501-4dbf-977c-a01d6fc37f37","order_by":1,"name":"Marco Palombo","email":"","orcid":"","institution":"Istituto Italiano della Saldatura","correspondingAuthor":false,"prefix":"","firstName":"Marco","middleName":"","lastName":"Palombo","suffix":""},{"id":321387239,"identity":"fa173570-cfdc-4e61-8b38-3a25b9f8b339","order_by":2,"name":"Andrei Filatov","email":"","orcid":"","institution":"NLMK DanSteel","correspondingAuthor":false,"prefix":"","firstName":"Andrei","middleName":"","lastName":"Filatov","suffix":""}],"badges":[],"createdAt":"2024-06-14 15:45:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4583102/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4583102/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59487964,"identity":"65d91945-383e-4ebe-a6b0-19cdcba5d877","added_by":"auto","created_at":"2024-07-02 11:29:43","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":81458,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency characteristics of wind direction (a) and hourly wind speed index (b) [\u003csup\u003e1\u003c/sup\u003e] near the Horns Rev2 offshore wind farm in the North Sea\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/3df98aa2c2182290d851acb9.png"},{"id":59489245,"identity":"4137ee13-c5c4-4610-a484-29f6cc8570d4","added_by":"auto","created_at":"2024-07-02 11:45:43","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":641107,"visible":true,"origin":"","legend":"\u003cp\u003eTypical microstructure of 23 mm plate from Steel A with deformation ending in the γ+α region, magnification ×200\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/d05bab3a1651cd7b8750d83a.png"},{"id":59488622,"identity":"6452919d-8068-440c-bab7-3b6bd908e82f","added_by":"auto","created_at":"2024-07-02 11:37:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":114944,"visible":true,"origin":"","legend":"\u003cp\u003eSerial curves of CTOD tests for the Steel A: a – after TMCP, b – after TMCP+PWHT; note the curves were shifted of 1 mm along the [mm] axis.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/b7ea1e353c17270d912155e2.png"},{"id":59489246,"identity":"54e21bd7-6d7f-46f5-8e2e-f554089a4d84","added_by":"auto","created_at":"2024-07-02 11:45:43","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":772687,"visible":true,"origin":"","legend":"\u003cp\u003eCharacteristic structure of fractures after CTOD tests of 23 mm thick rolled products: a - Steel A after TMCP, b - Steel B in TMCP condition, c - Steel A in TMCP+PWHT, d - Steel B after TMCP+PWHT\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/509fab85ceb17c435504528e.png"},{"id":59487969,"identity":"aea2fe99-ff46-40b9-97c2-61e160db5fa8","added_by":"auto","created_at":"2024-07-02 11:29:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1025924,"visible":true,"origin":"","legend":"\u003cp\u003eMicrostructure of Steel B samples after CTOD tests at -40° C: a - large separations, b - medium and small separations\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/45ae958aa8f4908af85c0454.png"},{"id":59487967,"identity":"5869f4d2-8058-4267-97d5-70e166428974","added_by":"auto","created_at":"2024-07-02 11:29:43","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":68063,"visible":true,"origin":"","legend":"\u003cp\u003eTypes of separations according to API 5L3 in fractures: a - morphology of type I separations, b - morphology of type II separations.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/20b93cdab321d8c46448847a.png"},{"id":59488625,"identity":"c8ae4f93-a63b-40d5-9882-0ca5be7e4dd2","added_by":"auto","created_at":"2024-07-02 11:37:43","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":29838,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional profile of Steel A sample after CTOD tests: a – after TMCP, b afterTMCP + PWHT\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/afbd36264c0175e83467b81e.png"},{"id":59487970,"identity":"dbd27d59-c18a-43a7-9fd7-c5f3d386d9c1","added_by":"auto","created_at":"2024-07-02 11:29:43","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":612374,"visible":true,"origin":"","legend":"\u003cp\u003eFractographic view of the fracture of the sample after CTOD tests at -40°C in the TMCP + PWHT condition with potential “pop-in” effect: a - study area, b - nature of fracture of selected areas\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/5ede664e8d296062181ffdd6.png"},{"id":60178697,"identity":"9f3a8b0a-555f-4590-9053-5166f027e017","added_by":"auto","created_at":"2024-07-12 16:44:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3601163,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4583102/v1/f7298a53-6365-419e-86bb-53a3776319bf.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Specific features of separations in fracture after CTOD tests of low-carbon microalloyed offshore steel S460MLO","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFor the production of steel constructions for the Northern and Arctic regions, designed for high levels of cyclic loads with varying amplitudes, only high-quality heavy plate steel with enhanced requirements for low-temperature toughness and fracture toughness is used. Illustrative examples of structures subjected to variable forces are offshore fixed platforms in the energy sector, where primary cyclic loads are generated by marine currents, wind, waves, and sometimes ice floes, resulting in complex stress diagrams at various points of contact. As an example, \u003cstrong\u003eFigure 1\u003c/strong\u003e shows the wind direction frequency characteristics and hourly wind speed index (with an average speed of 9.6 m/s) near the Horns Rev2 offshore wind farm in the North Sea, close to the Danish shore. These graphs clearly demonstrate the nature and degree of asymmetry in the environmental impacts on offshore platform operation and, consequently, reasonable variability in the degree and direction of asymmetric cyclic loads.\u003c/p\u003e\n\u003cp\u003eUnder such aggressive environmental conditions, the most stressed structural components may experience rapid failure due to internal defects or fatigue cracks forming in localized areas of high stress. Consequently, Annex F has been added to the latest revision of the offshore standard EN 10225-1:2019 [\u003csup\u003e2\u003c/sup\u003e] to regulate the procedure for pre-qualification testing of heavy plate steel for fixed offshore structures operating in the Northern and Arctic regions. The regulation includes evaluating the steel\u0026apos;s fracture toughness, for which CTOD (crack tip opening displacement) tests are conducted according to ISO 12135 [\u003csup\u003e3\u003c/sup\u003e]. These tests to measure the maximum opening of a pre-induced fatigue crack before the critical moment of its opening at temperatures ranging from -10 to -40 \u0026deg;C. These tests enable the determination of several crucial steel properties, including the critical crack tip opening \u0026delta; (in mm), the J-integral, and the stress intensity coefficients Kc under plane strain and KIc of the 1st strain mode [\u003csup\u003e4\u003c/sup\u003e, \u003csup\u003e5\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003eThe experience received in conducting and analyzing CTOD test results of steels produced by thermomechanical processing (TMCP) shows that in some cases the interpretation of CTOD test results could be more complicated due to the need to examine the fracture surface of samples to identify the so-called \u0026quot;pop-in\u0026quot; effects on the strain curves. According to existing BS, ASTM, ISO standards, such an occurrence can be deemed like critical. At the same time, the fracture of the tested specimen shows the formation of transverse (secondary) splits in the direction of the plate thickness without significant crack propagation in the plane of the pre-induced fatigue crack. In the case of TMCP steels, the appearance of short-term spikes in the fracture diagrams, similar to a potential \u0026ldquo;pop-in\u0026rdquo; effect, does not always indicate a brittle fracture mechanism of the steel and may depend on extraneous factors [\u003csup\u003e6\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003eOne such factor is related to the specifics of the formation of the microstructural state and crystallographic texture of the steel oriented along the deformation direction [\u003csup\u003e7\u003c/sup\u003e, \u003csup\u003e8\u003c/sup\u003e], especially during low-temperature thermomechanical processing of heavy plates of thickness groups below 25 mm, where the level of low-temperature deformation riveting is high. In case of high purity of TMCP steel on non-metallic inclusions, the mechanism of separations may also be due to the anisotropy of critical tearing stresses in the plane of the plates and in the Z-direction [\u003csup\u003e9\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThe objective of the article\u003c/strong\u003e is to identify the type and nature of secondary separations in CTOD samples through macro-, micro-, and fractographic studies, as well as to evaluate the relationship between the fracture characteristics and the test results with the occurrence of potential \u0026quot;pop-in\u0026quot; effects on the fracture diagrams of low-carbon microalloyed heavy plate steel S460MLO for offshore applications, produced by the thermomechanical control process.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eBasic oxygen furnace (BOF) cast into slabs with a thickness of 355 mm were used as the examined material. The chemical composition of the steels under investigation is provided in Table 1. Two types of microalloying were employed: Nb-V-Ti and Nb-Ti. Slabs were rolled on a reversible hot rolling mill 4200 [\u003csup\u003e10\u003c/sup\u003e] according to the technology of low-temperature two-stage thermomechanical rolling for the final plate thickness of 23 mm with the end of deformation in the γ+α-region. The level of basic mechanical properties corresponds to heavy plates of quality grade S460MLO according to EN 10225-1:2019.\u003c/p\u003e\n\u003cp\u003eTable 1. Chemical composition of the investigated steels, wt.\u0026nbsp;%\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003eSteel\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.791666666666668%\"\u003e\n \u003cp\u003eMicroalloying\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003eP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eNi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eС\u003csub\u003eeq\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.791666666666668%\"\u003e\n \u003cp\u003eNb-V-Ti\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e1,45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,004\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e0,25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.791666666666668%\"\u003e\n \u003cp\u003eNb-Ti\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e1,44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.375%\"\u003e\n \u003cp\u003e0,005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e0,25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003e0,31\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eFrom the rolled plates, series of samples were selected for mechanical testing. Half of the samples underwent additional heat treatment, including controlled heating from a temperature of 400°C at a rate of 55°C/hour to 580±3°C, holding for 60 minutes, and controlled cooling to 400°C at a rate of 55°C/hour. These specified process parameters simulate the heat treatment of critical joints of structures after assembly or repair welding (PWHT).\u003c/p\u003e\n\u003cp\u003eThe investigated steels have a homogeneous ferritic-pearlitic microstructure with light bending (\u003cstrong\u003eFig. 2\u003c/strong\u003e) and elongated ferrite grains. The average conditional ferrite grain diameter in the surface layers is approximately 4.3 µm, in the quarter ~ 5.7 µm, and in the center ~ 6 µm.\u003c/p\u003e\n\u003cp\u003eThe average mechanical characteristics of the investigated steels in the initial state are as follows: yield strength R\u003csub\u003eeH\u003c/sub\u003e: 514 MPa and 509 MPa, tensile strength Rm: 566 MPa and 545 MPa, elongation A\u003csub\u003e200\u003c/sub\u003e = 25% and 22%, respectively for Steel A and Steel B. The values of the impact energy KVТ\u003csub\u003e-40\u003c/sub\u003e are in the range of 285-305 J (Steel A) and 138-292 J (Steel B). Ultrasonic testing in both cases showed S\u003csub\u003e3\u003c/sub\u003eE\u003csub\u003e4\u003c/sub\u003e results according to EN 10160 standard. After additional heat treatment for Steel A, the average values are as follows: R\u003csub\u003eeH\u003c/sub\u003e = 504 MPa, R\u003csub\u003em\u003c/sub\u003e = 556 MPa, A\u003csub\u003e200\u003c/sub\u003e = 27%, KVL\u003csub\u003e-40\u003c/sub\u003e = 211-307 J. For Steel B: R\u003csub\u003eeH\u003c/sub\u003e = 489 MPa, R\u003csub\u003em\u003c/sub\u003e = 535 MPa, A\u003csub\u003e200\u003c/sub\u003e = 25%, KVL-\u003csub\u003e40\u003c/sub\u003e = 111-128 J.\u003c/p\u003e\n\u003cp\u003eFracture toughness and fatigue tests were conducted on a universal testing system with freely moving outer rollers Zwick/Roell Z600 for single edge notch bending (SENB) samples, which were made of base metal and had dimensions of 20×40×185 mm, in accordance with ISO 12135 requirements. After applying a 17 mm notch on the specimens, a fatigue crack was grown to the nominal specified depth of 0.5ao/W, so that the total initial length of the notch with the fatigue crack was in the range of a (0.45-0.55W). The pre-crushing force was Pm = 9.9 kN, and the\u0026nbsp;span\u0026nbsp;(distance between supports) was S = 160 mm. Test temperatures: -10, -20, -30, -40 °C.\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003eThe critical value of CTOD was determined using formulas (1) and (2), taking into account the thickness (B) and height (W = 2B) of the specimen, the span of the testing machine (S), the size of the induced fatigue crack (a\u003csub\u003eo\u003c/sub\u003e), the distance from the measurement point of the notch opening above the specimen surface (z, a value of z = 0 was used), the yield strength at the testing temperature (σ\u003csub\u003eYS\u003c/sub\u003e), test temperature, force (F), displacement (V), Young's modulus (E), and Poisson's ratio (ν).\u003c/p\u003e\n\u003cp\u003eMicrostructural investigations and fractographic analysis of the structure and fracture zones were conducted using an optical microscope (OM) Carl Zeiss Axio Observer 7 MAT and a scanning electron microscope (SEM) Tescan MIRA3.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe values of critical crack tip opening displacement (\u0026delta;, mm) obtained after serial tests for the steels under investigation in the TMCP and TMCP+PWHT states are presented in Table 2. Overall, the investigated steels demonstrated a sufficient level of fracture toughness across the entire temperature range of the tests. The crack opening value did not drop below 1.00 mm. Steel A exhibited approximately 10% higher overall relative fracture toughness than Steel B in the initial condition and approximately 30% higher when PWHT was applied. The application of the PWHT resulted in lower CTOD values and an increased probability of short-term shear and load reduction, characterised as a potential \u0026ldquo;pop-in\u0026rdquo; effect. (\u003cstrong\u003eFig. 3b\u003c/strong\u003e). The nature of such shifts along the contour of the short-term stress drop (sharp jump transition) and the moment of appearance (close to the section of transition from elastic to plastic deformation) resembles the yield point in tensile stress-strain diagrams during tensile tests in the plane of rolling direction.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 2. Results of serial CTOD tests of the studied steels for fracture toughness\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.11111111111111%\" rowspan=\"3\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.080808080808081%\" rowspan=\"3\"\u003e\n \u003cp\u003e№\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"80.8080808080808%\" colspan=\"8\"\u003e\n \u003cp\u003eCrack tip opening displacement,\u0026nbsp;\u0026delta;\u0026nbsp;(mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"50%\" colspan=\"4\"\u003e\n \u003cp\u003eTMCP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"50%\" colspan=\"4\"\u003e\n \u003cp\u003eTMCP+PWHT\u0026nbsp;580\u0026plusmn;3 \u0026deg;C, 60\u0026nbsp;min\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-10\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-20\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-30\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-40\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-10\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-20\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-30\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.5%\"\u003e\n \u003cp\u003e-40\u0026nbsp;\u0026deg;C\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.11111111111111%\" rowspan=\"3\"\u003e\n \u003cp\u003eSteel\u0026nbsp;A\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.080808080808081%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e2.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.99\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"9.090909090909092%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.93\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"9.090909090909092%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.11111111111111%\" rowspan=\"3\"\u003e\n \u003cp\u003eSteel\u0026nbsp;a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.080808080808081%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.1010101010101%\"\u003e\n \u003cp\u003e1.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"9.090909090909092%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.07\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"9.090909090909092%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.363636363636363%\"\u003e\n \u003cp\u003e1.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eExamining the fracture diagrams after CTOD tests (see \u003cstrong\u003eFig. 3\u003c/strong\u003e), several typical zones can be identified. The initial zone, characterized by a linear relationship between displacement and applied force, corresponds to the stage of elastic deformation. Then, the slope of the curve changes, and with increasing load within the fatigue crack, plastic deformation develops.\u003c/p\u003e\n\u003cp\u003eAnalysis of the logarithmic odds ratio (\u0026chi;2 = 7.23, p = 0.057) showed that there was no statistically significant relationship (significance level \u0026alpha; = 0.05) between test temperature and the occurrence of short-term shear with load drop at the diagrams. Therefore, the probability of the occurrence of shear (potential \u0026ldquo;pop-in\u0026rdquo; effect) can be considered as a statistically random variable.\u003c/p\u003e\n\u003cp\u003eIn [\u003csup\u003e11\u003c/sup\u003e] the significance and mechanism of separations during various mechanical tests of pipe steels are investigated in detail. The authors suggest not to take into account such short-term load reduction as a critical \u0026ldquo;pop-in\u0026rdquo; effect in determining the CTOD value, and to put the main emphasis on the macroscopic appearance of the fracture surface. Consider the mechanisms and regularities of separations formation in the obtained fractures after CTOD tests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eVisual fracture analysis\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe characteristic visual appearance of the samples selected after testing at different temperatures is given for Steel A in \u003cstrong\u003eFig. 4a\u003c/strong\u003e and for Steel B in \u003cstrong\u003eFig. 4b\u003c/strong\u003e. After PWHT, the fracture structure is shown in \u003cstrong\u003eFig. 4c\u003c/strong\u003e and \u003cstrong\u003eFig. 4d\u003c/strong\u003e. Regardless of chemical composition and final treatment, all samples are characterised by a high number of transverse separations. In case of registration of potential \u0026ldquo;pop-in\u0026rdquo; spikes on the diagrams (\u003cstrong\u003eFig. 3b\u003c/strong\u003e), the secondary separations observed in the fractures (\u003cstrong\u003eFig. 4 b, d\u003c/strong\u003e) extend into the induced crack region and propagate in it for a length of 0.5-0.9 mm. The number of spikes on the diagram corresponds to the number of separations that have entered the induced crack zone. The further the separations have propagated into the induced crack region, the more clearly the potential \u0026ldquo;pop-in\u0026rdquo; spikes is discernible on the diagram. It is with this feature, noted on individual samples, that the authors attribute the manifestation of the potential \u0026ldquo;pop-in\u0026rdquo; effect.\u003c/p\u003e\n\u003cp\u003eIt can be assumed that the appearance of secondary splits is due to the action of transverse forces directed along the thickness of the plate, when these forces act on elongated microstructural elements perpendicular to the main fracture plane and serving as the crack initiation point, separations can occur. This type of fracture occurs due to the coincidence of crystallographic planes with reduced layer bonding energy [\u003csup\u003e12\u003c/sup\u003e]. One of the main reasons for shear detection may be the parallel arrangement of elongated microstructural or crystallographic elements along the thickness of the plate. Also beside above mentioned separations could be related to the texture of the material [9].\u003c/p\u003e\n\u003cp\u003eVisually, the investigated separations are split perpendicular to the direction of the main crack development in planes parallel to the surface of the plate. The separations are observed along the entire thickness direction, indicating that this is not a single-layer effect, as can occur when opening along the center line of segregation. Rather, plastic tightening of the sample along the edges leads to an increase in the stress state close to the plane strain state, when the connectivity of layers in the rolling direction decreases, which is directly related to the features of the formed microstructure. Heating the steels to 580\u0026plusmn;3 \u0026deg;C and holding for 60 minutes resulted in a general increase in the number of delaminations visible on the surface of the fractures, which, in turn, increased the probability of separations coming to the surface of the preliminary notch zone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMicrostructural analysis of separations\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe microstructural condition of the examined samples was investigated in the TMCP (\u003cstrong\u003eFig. 2\u003c/strong\u003e) and TMCP+PWHT condition. To identify the nature of separations, the microstructure at crack nucleation and propagation was analyzed and compared with the microstructure of the base metal. The microstructure in the regions adjacent to the separations exhibits greater elongation along the deformation direction of the separations. Several main crack morphologies were identified at the termination points of visible separation boundaries. In the case of potential \u0026ldquo;pop-in\u0026rdquo; separations (\u003cstrong\u003eFig. 5a\u003c/strong\u003e), the crack ends along the boundary of the elongated deformed ferrite grain, does not propagate deep and has no side branches. The relief of the walls is smooth with a small number of rounded depressions on one side and protrusions on the opposite side. The protrusions and depressions are nearly symmetrical and have angles close to 90\u0026deg;.\u003c/p\u003e\n\u003cp\u003eWhen medium and smaller separations are observed, the cracks do not always propagate to the surface of the investigated grinding plane. In such cases, intense plastic flow of the metal is observed in the vicinity of the separations (\u003cstrong\u003eFig. 5b\u003c/strong\u003e). The homogeneity absence in the bending strain bands along the metal cross-section can be explained by the alternation of adjacent regions with pronounced plastic flow during local bending [\u003csup\u003e13\u003c/sup\u003e]. This phenomenon is characteristic of the microstructural condition of the steel, which is defined by elongated ferrite grains formed through heavy deformation below the Ar\u003csub\u003e3\u003c/sub\u003e temperature.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMorphological analysis of separations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe morphological analysis was conducted following similar principles for describing the fracture nature after the drop weight tear test (DWTT) regulated by EN 10274 and API RP 5L3, which categorize separations into two types. The first type propagates parallel to the plate plane and terminates in a sharp crack (\u003cstrong\u003eFig. 6a\u003c/strong\u003e). Such separations are not considered brittle characteristics and are referred to as \u0026ldquo;Separations\u0026rdquo;. The second type is termed \u0026ldquo;Cleavage\u0026rdquo;, and the separations in this case have a blunted termination (\u003cstrong\u003eFig. 6b\u003c/strong\u003e) and are oriented at a slight angle to the sheet surface. This type should be classified as a brittle component. In the case of separations of the first type, their formation occurs during plastic deformation preceding fracture, while separations of the second type result from fatigue crack propagation [\u003csup\u003e14\u003c/sup\u003e]. Visually, it is not always straightforward to determine the type of separations, both in samples after DWTT and CTOD tests, as significant differences can be observed only on cross-sections of the fracture surface [\u003csup\u003e15\u003c/sup\u003e] and in fractographic studies.\u003c/p\u003e\n\u003cp\u003eThe macroscopic analysis showed that after completing the CTOD tests, all fractures of the samples can be classified into the following areas (\u003cstrong\u003eFig. 4b\u003c/strong\u003e): the pre-induced fatigue crack zone, fracture zone, zone of fracture before complete sample failure, and fracture retraction zone [\u003csup\u003e16\u003c/sup\u003e]. Two large separations were observed on the cross-section: the first measured 11.3 mm in length with an opening of up to 3.5 mm, while the second measured 9.2 mm and 3 mm, respectively. Medium-sized separations exhibited openings of up to 2.8 mm, while smaller separations were evident within the gaps among the larger ones. The retraction area comprised approximately 15% (abs.) of the total, with a minimum retraction width of 16.1 mm. Additionally, the sample subjected to PWHT two large separations in the central portion of the fracture, with length-to-opening ratios of approximately 13 mm/2.9 mm for the first separation and 14.9 mm/2.6 mm for the second. Furthermore, there were 5 medium separations with openings of up to 2 mm, along with numerous elongated smaller separations. The retraction area accounted for roughly 11% of the total, with a minimum retraction width of 17 mm.\u003c/p\u003e\n\u003cp\u003eThe panoramic photographs of the sample surface cross-section were graphically processed so that the outline of separations was clearly visible (\u003cstrong\u003eFig. 7\u003c/strong\u003e). Analysis of the cross-section of the fractures allowed for determining the nature of propagation and the depth of the separations. The deep separations, which define the potential \u0026ldquo;pop-in\u0026rdquo; spike in the diagram for the initial state, reach 5.7 mm, while for the PWHT condition, they reach 5.6 mm. The ends of the separations appear as single openings or multiple thin cracks. The opening angles at the endpoints are sharp and oriented perpendicular to the fracture surface.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFractographic analysis of separations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe detailed scanning electron microscopy studies are illustrated using an example of the sample after CTOD tests at -40\u0026deg;C. Following visual (\u003cstrong\u003eFig. 4d\u003c/strong\u003e) and macroscopic (\u003cstrong\u003eFig. 8a\u003c/strong\u003e) analyses, 4 regions (\u003cstrong\u003eFig. 8b\u003c/strong\u003e) have been chosen to describe the nature of fracture propagation within separations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eArea 1 (\u003cstrong\u003eFig. 8b.1\u003c/strong\u003e) is located at the edge of the largest separation, opposite to the direction of fatigue crack propagation. At low magnifications (\u0026times;200) in this zone, only a ductile type of fracture is discernible, but at \u0026times;500 and \u0026times;2000, small areas with a mixed fracture character can be distinguished. Nevertheless, the ductile component prevails in this area, and the area of fracture by brittle mechanism is small. Area 2 (\u003cstrong\u003eFig. 8b.2\u003c/strong\u003e), located on the inner side of the same separation, also exhibits predominantly ductile fracture, as confirmed by the presence of dimple fracture structure. For area 3 (\u003cstrong\u003eFig. 8b.3\u003c/strong\u003e), where the separation extends into the induced crack zone, causing the potential \u0026ldquo;pop-in\u0026rdquo; spike, a mixed type of fracture is characteristic. Individual local brittle areas of instantaneous fracture are detected in the form of streamlet-let relief (quasi-cleavage), likely occurring in areas with a pearlitic component. Area 4 (\u003cstrong\u003eFig. 8b.4\u003c/strong\u003e), free from separations and located in the zone of initial fracture, is characterized by the presence of typical dimples typical of ductile fracture [\u003csup\u003e17\u003c/sup\u003e].\u003c/p\u003e\n\u003cp\u003eIt is likely that the formation of separations occurs by facilitating delamination through chipping of planes along the rolling direction, resulting in the formation of a certain number of separations in the plastically deformed fracture zone ahead of the growing crack front. If separations formed by this mechanism exhibit a potential \u0026laquo;pop-in\u0026raquo; spike, then they probably should not be considered as the final event during the test, unlike cases where the spike is caused by the propagation of the main fatigue crack deep into the sample through brittle mechanism. Summarizing the conducted studies, it can be noted that the areas of the surface of the examined separations are predominantly characterized by ductile fracture. Therefore, such metal can be considered as a multilayer material, where strength and ductility are determined by the energy of crack propagation occurring at each transition from one layer to another.\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eLow-carbon microalloyed 23 mm thick steel heavy plates of quality grade EN10225-1:2019 S460MLO was CTOD tested in TMCP and TMCP+PWHT conditions. Investigating the relationship between fracture types, fracture characteristics, and CTOD test results in test temperature range -10 \u0026hellip; -40 \u0026deg;C authors determined that:\u003c/p\u003e\n\u003cp\u003e- all fractures of the samples are characterized by a high number of secondary splittings. The examined splittings belong to the type I separations according to the classification of EN 10274, API 5L3, with a predominant ductile fracture mechanism.\u003c/p\u003e\n\u003cp\u003e- an individual peculiarity of fracture with CTOD specimens splits is the presence of statistically random short-term bursts with load reduction, registered on the diagrams \u0026ldquo;load \u0026ndash; crack opening displacement\u0026rdquo; as a potential \u0026ldquo;pop-in\u0026rdquo; effect. The appearance of such short-term spikes in the investigated cases is attributed to the emergence of individual separations from the fracture zone into the primary induced fatigue crack zone. In this case, the fracture also occurs by a ductile mechanism, and the main fracture toughness indicator \u0026delta; (mm) remains at a high level (more than 1.0 mm), indicating that such short-term spikes could not be considered like critical events during the CTOD test of the investigated steel type.\u003c/p\u003e\n\u003cp\u003e- application of additional heat treatment to the investigated TMCP steel increases the likelihood of potential \u0026ldquo;pop-in\u0026rdquo; spikes appearing on the fracture diagram. This is likely due to relaxation between microstructural layers and simplification of conditions for the occurrence of a greater number and depth of separations.\u003c/p\u003e\n\u003cp\u003eThe results of the research have been used successfully in passing the certification tests of heavy plate products of quality categories S460MLO, S420MLO, S355MLO according to the standards EN10225-1:2019 and NORSOK M-120, including pre-qualification for operation in \u0026nbsp;Arctic areas.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eE.O. wrote the main manuscriptM.P. reviewed the manuscript, analysed the data and produced table 2, figure 3 and figure 4A.F. prepared the other figures and tables.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eOfficial web recourse The Global Wind Atlas by DTU and Co-Developers. https://globalwindatlas.info (date of reference 2024-03-13).\u003c/li\u003e\n\u003cli\u003eEuropean Standard EN 10225-1. Weldable Structural Steels for Fixed Offshore Structures \u0026ndash; Technical Delivery Conditions \u0026ndash; Part 1: Plates. Brussels. 2019. 62 p. \u003c/li\u003e\n\u003cli\u003eISO 12135:2021. Metallic materials \u0026mdash; Unified method of test for the determination of quasistatic fracture toughness. Edition 3. 2021. \u003c/li\u003e\n\u003cli\u003eMoore P., Pisarski H. CTOD and Pipelines: The past, present, and future / The Journal of Pipeline Engineering. 2013. Vol. 12. Issue 3. P. 237\u0026ndash;244.\u003c/li\u003e\n\u003cli\u003eZhu X.-K. Review of fracture toughness test methods for ductile materials in low-constraint conditions // Int. J. Pressure Vessels Piping. 2016. No. 139\u0026ndash;140. P. 173\u0026ndash;183.\u003c/li\u003e\n\u003cli\u003eSang-Ho K., Woo Kil J., Kyong Ho L., Hyung Hong S. Toughness of Steel Plates For Offshore Structures Manufactured By TMCP // The Eighteenth International Offshore and Polar Engineering Conference, Vancouver, Canada, July 2008.\u003c/li\u003e\n\u003cli\u003eConde F.F., Pinto H.C., Masoumi M., Avila, J.A.. Effect of textures and microstructures on the occurrence of delamination during and after fracture toughness tests of API X80 steel plates // In Strength of Materials. IntechOpen. 2019. P. 27-48.\u003c/li\u003e\n\u003cli\u003eYamashita Yo., Kanna S.. Assessment of Pop-in Significance in Heterogeneous Weld Heat-affected Zone Using Finite Element Analyses // Procedia Materials Science. Vol. 3. 2014. P. 991-996.\u003c/li\u003e\n\u003cli\u003eMa Y., Su L., Shen C., Fletcher L.; Li H., Sun L., Zheng L., Zhang C. Improving the Weld Heat-Affected-Zone (HAZ) Toughness of High-Strength Thick-Walled Line Pipes. Metals 2023. Vol. 13. No. 12. 30 p.\u003c/li\u003e\n\u003cli\u003e23. Sarkits I., Bokachev Y., Goli-Oglu E. Production of heavy plates on the rolling mill 4200 NLMK-DanSteel A/S // Stahl und Eisen. 2014. №4. P. 57 \u0026ndash; 61.\u003c/li\u003e\n\u003cli\u003eScholl S., Schneider A., Schwinn V. Significance of separations occurring in mechanical testing of thermomechanical rolled pipeline steels // Journal of Pipeline Science and Engineering. 2022. Vol. 2, Issue 3. P. 27-34.\u003c/li\u003e\n\u003cli\u003eBerejnoi C., Perez-Ipi\u0026ntilde;a J., Llorente C. Reproducibility of pop-ins in laboratory testing of welded joints // Materials Research. 2010. Vol. 3 No. 4. P. 139-146.\u003c/li\u003e\n\u003cli\u003eSung H.K., Sohn S.S., Shin S.Y., Lee S, Kim N.J., Chon S.H., et al. Effects of finish rolling temperature on inverse fracture occurring during drop weight tear test of API X80 pipeline steels // Materials Science and Engineering A. 2012. Vol. 541 p. 181\u0026ndash;189.\u003c/li\u003e\n\u003cli\u003eShah S. Determination of fracture parameters (KsIC and CTODc) of plain concrete using three-point bend tests // Materials and Structures. 1990. No.23. P. 457-460.\u003c/li\u003e\n\u003cli\u003ePemov I., Morozov Yu., Goli-Oglu E., Lyuchkov A., Mashinson I., Shebanits E., Zernitskii D.. Relationship of failure energy and amount of ductile component in a fracture during the DWTT for rolled plate prepared by controlled rolling // Metallurgist. 2012. Vol. 56. No. 1-2. P. 52-58.\u003c/li\u003e\n\u003cli\u003eHoyos J.J., Masoumi M., Pereira V.F., etc. Influence of hydrogen on the microstructure and fracture toughness of friction stir welded plates of API 5L X80 pipeline steel // International Journal of Hydrogen Energy. 2019. Vol. 44. Issue 41. P. 23458-23471.\u003c/li\u003e\n\u003cli\u003eGoli-Oglu E. A., Filatov A. N.. Fractographic Studies of Destruction Nature of Plate Steel S420MLO After Fatigue Tests CTOD // Steel in Translation. 2023. Vol. 53. No. 5. P. 473-478.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"low-carbon steel, heavy plate, fatigue, crack opening displacement, fracture toughness, separations, pop-in effect, CTOD","lastPublishedDoi":"10.21203/rs.3.rs-4583102/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4583102/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Using the results of testing industrial batches of 23 mm steel heavy plates after thermomechanical rolling and subsequent post-weld heat treatment, the patterns of fatigue cracks formation in the fracture specimens during CTOD (Crack Tip Opening Displacement) testing for fracture toughness are investigated. Visual, microstructural, and fractographic studies of the nature of fracture formation and the surface of the secondary separations have been conducted. The probable causes of the manifestation of the potential «pop-in» effect on the load-displacement diagrams of the notch opening displacement are described, as well as its potentially negative impact on the interpretation of test results","manuscriptTitle":"Specific features of separations in fracture after CTOD tests of low-carbon microalloyed offshore steel S460MLO","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-02 11:29:38","doi":"10.21203/rs.3.rs-4583102/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bdf9d8f0-511a-4736-9770-ba76b6004772","owner":[],"postedDate":"July 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-12T16:36:32+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-02 11:29:38","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4583102","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4583102","identity":"rs-4583102","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}