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A 316 austenitic stainless-steel alloy, with modified alloy composition, manufactured by laser powder bed fusion (L-PBF) has been investigated. The modification of the alloy composition included addition of niobium (Nb), tungsten (W) and copper (Cu), together with a reduction in the amount of molybdenum (Mo) and an increased amount of carbon (C). To find suitable process parameters, a parameter study by varying laser power, hatch distance and scan speed was performed, centered on typical parameters used for normal 316 L. As-built material from a selected parameter configuration was then subjected to different stress relief annealing heat treatments and ageing heat treatments. The effectiveness of the stress annealing was ranked using a deformation-based method. Microstructural characterization, hardness and room temperature tensile testing were done to evaluate the effect of stress relief and aging heat treatments. It was found that a higher volumetric energy was needed to build dense material, about ∼50 % higher compared to the volumetric energy input for normal 316 L. A subsequent aging heat treatment at 725 °C for 3 h increased the strength and hardness of the material. A reinforcement of the cellular microstructure by precipitation of carbides in between the cells is believed to be the main reason for this. To completely alleviate the residual stresses it was necessary to carry out a stress relief annealing process at 950 °C, which resulted in a removal of the cellular structure and a lower strength material., Validerad;2024;Nivå 2;2024-02-26 (joosat);Full text license: CC BYFunder: The Swedish National Space Agency; GKN Aerospace Sweden AB

A 316 austenitic stainless-steel alloy, with modified alloy composition, manufactured by laser powder bed fusion (L-PBF) has been investigated. The modification of the alloy composition included addition of niobium (Nb), tungsten (W) and copper (Cu), together with a reduction in the amount of molybdenum (Mo) and an increased amount of carbon (C). To find suitable process parameters, a parameter study by varying laser power, hatch distance and scan speed was performed, centered on typical parameters used for normal 316 L. As-built material from a selected parameter configuration was then subjected to different stress relief annealing heat treatments and ageing heat treatments. The effectiveness of the stress annealing was ranked using a deformation-based method. Microstructural characterization, hardness and room temperature tensile testing were done to evaluate the effect of stress relief and aging heat treatments. It was found that a higher volumetric energy was needed to build dense material, about ∼50 % higher compared to the volumetric energy input for normal 316 L. A subsequent aging heat treatment at 725 °C for 3 h increased the strength and hardness of the material. A reinforcement of the cellular microstructure by precipitation of carbides in between the cells is believed to be the main reason for this. To completely alleviate the residual stresses it was necessary to carry out a stress relief annealing process at 950 °C, which resulted in a removal of the cellular structure and a lower strength material., Validerad;2024;Nivå 2;2024-02-26 (joosat);Full text license: CC BYFunder: The Swedish National Space Agency; GKN Aerospace Sweden AB

To detect mechanical overloads on the component directly in operation, a metastable material can be used as a load-sensitive sensor when combined with an eddy current testing system. In order to find a suitable metastable sensor material that exhibits microstructural changes at an early stage before fatigue failure, quasi-static tensile tests and cyclic rotating bending tests were carried out with the austenitic stainless steels 1.4301 (2 batches), 1.4305, 1.4541 and 1.4550. For the detection of microstructural changes, electromagnetic testing was used in-situ in the tensile test and ex-situ between the rotating bending test after a pre-defined number of cycles. The investigated materials 1.4301 batch2 and 1.4550 showed the largest signal changes and the lowest austenite stability both in the tensile test and under cyclic bending load. Due to the better mechanical properties, 1.4301 batch2 should be preferred. The order of the austenitic stainless steels tested was similar in terms of transformation behavior in both tests. Thus, the tensile test combined with in-situ electromagnetic testing appears to have potential as a suitable benchmark test for austenite stability. With regard to the cyclic bending stress, an overload of the specimens could be detected for the materials 1.4301 batch2, 1.4305, 1.4541 and for the 1.4550 on the basis of a significant amplitude change. At low bending stresses, uncritical for structural integrity, no increase in amplitude was measured. The results have shown that an early detection of overloads is possible with several materials, however, the potential for detecting overloads varies between materials and also between individual batches. In addition, it has been observed that as the bending stress increases, the gradient of the change in amplitude over the number of cycles increases as well. Thus, with a known number of cycles, it could be possible to classify the previous load spectrum based on the difference in amplitude between two

The emergence of innovative high-performance stainless steels is essential at the forefront of material science. This research highlights the meticulous development of a novel high-Mn-N Ni-free austenitic stainless steel via the powder bed fusion laser–based (PBF-LB) technique. We strategically optimized the laser parameters, achieving ultralow porosity and a refned microstructure with defects under 2%. Comprehensive analysis revealed superior dendritic cellular formations at melt pool boundaries, underlining our method’s precision. Unveiling the strength of this novel steel, sample S11 (scanning speed of 800 mm/s and laser power of 147 W) showed a remarkable tensile strength of 1190±20 MPa and an impressive elongation to fracture of 35±3%. Interestingly, twin formations became evident under external loads, enhancing mechanical resistance while preserving ductility. Advanced quantifcation methods were employed to ensure accuracy, especially for low atomic number elements, overcoming previous measurement constraints. This pioneering study introduces a game-changing austenitic Ni-free stainless steel enriched by Mn and N. It sets a new benchmark in material development and application, synergizing exceptional mechanical attributes with robust ductility., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The work was financially supported by the São Paulo Research Foundation, FAPESP (grants 2021/02926–4 and 2020/09079–2), and the National Council of Scientific and Technological Development, CNPq (grants 304157/2020–1 and 306960/2021–4)., Postprint (published version)

To detect mechanical overloads on the component directly in operation, a metastable material can be used as a load-sensitive sensor when combined with an eddy current testing system. In order to find a suitable metastable sensor material that exhibits microstructural changes at an early stage before fatigue failure, quasi-static tensile tests and cyclic rotating bending tests were carried out with the austenitic stainless steels 1.4301 (2 batches), 1.4305, 1.4541 and 1.4550. For the detection of microstructural changes, electromagnetic testing was used in-situ in the tensile test and ex-situ between the rotating bending test after a pre-defined number of cycles. The investigated materials 1.4301 batch2 and 1.4550 showed the largest signal changes and the lowest austenite stability both in the tensile test and under cyclic bending load. Due to the better mechanical properties, 1.4301 batch2 should be preferred. The order of the austenitic stainless steels tested was similar in terms of transformation behavior in both tests. Thus, the tensile test combined with in-situ electromagnetic testing appears to have potential as a suitable benchmark test for austenite stability. With regard to the cyclic bending stress, an overload of the specimens could be detected for the materials 1.4301 batch2, 1.4305, 1.4541 and for the 1.4550 on the basis of a significant amplitude change. At low bending stresses, uncritical for structural integrity, no increase in amplitude was measured. The results have shown that an early detection of overloads is possible with several materials, however, the potential for detecting overloads varies between materials and also between individual batches. In addition, it has been observed that as the bending stress increases, the gradient of the change in amplitude over the number of cycles increases as well. Thus, with a known number of cycles, it could be possible to classify the previous load spectrum based on the difference in amplitude between two

Over the last few decades, Instrumented Indentation Test (IIT) has evolved into a versatile and convenient method for assessing the mechanical properties of metals. Unlike conventional hardness tests, IIT allows for incremental control of the indenter based on depth or force, enabling the measurement of not only hardness but also tensile properties, fracture toughness, and welding residual stress. Two crucial measures in IIT are the reaction force (F) exerted by the tested material on the indenter and the depth of the indenter (D). Evaluation of the mentioned properties from F–D curves typically involves complex analytical formulas that restricts the application of IIT to a limited group of materials. Moreover, for soft materials, such as austenitic stainless steel SS304L, with excessive pile-up/sink-in behaviors, conducting IIT becomes challenging due to improper evaluation of the imprint depth. In this work, we propose a systematic procedure for replacing complex analytical evaluations of IIT and expensive physical measurements. The proposed approach is based on the well-known potential of Neural Networks (NN) for data-driven modeling. We carried out physical IIT and tensile tests on samples prepared from SS304L. In addition, we generated multiple configurations of material properties and simulated the corresponding number of IITs using Finite Element Method (FEM). The information provided by the physical tests and simulated data from FEM are integrated into an NN, to produce a parametric mapping that can predict the parameters of a constitutive model based on any given F–D curve. Our physical and numerical experiments successfully demonstrate the potential of the proposed approach.

Stainless steel is a corrosion resistant iron alloy with great potential in structural engineering due to its excellent mechanical features, durability and aesthetic properties. Since most of the existing research has concerned the behaviour of the material, the response of individual structural members, or the performance of simple structural systems under monotonic loading, one of the challenges that remains is the evaluation of the cyclic performance of members to promote its use in seismic design and exploit the excellent ductility and strain hardening properties of this material. For this reason, an experimental programme on austenitic stainless steel Rectangular Hollow Section (RHS) specimens was carried out at the Department of Civil Engineering of the Università degli Studi di Salerno in collaboration with the Universitat Politècnica de Catalunya. A total of eight RHS specimens were tested around the minor axis under both monotonic (three specimens) and cyclic (five specimens) loading, in an experimental set-up that followed a cantilever scheme. The main purpose of this study was to acquire information on the cyclic performance of austenitic steel structural members, focusing on the comparison between monotonic and cyclic behaviours. The outcomes of the tests included the load–displacement and the moment–rotation curves, the energy dissipation capacity, and the evaluation of the key rotation capacities of the members. The reported data are essential to enhance the still scarce research on the seismic behaviour of stainless steel structures., The research was supported by the Spanish Ministry for the Economy and Competitiveness through the Project BIA2016–75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a acciones accidentales de sismo y fuego”. The first author would also acknowledge the financial support received from the Spanish Ministry for Science, Innovation and Universities through the FPI-MINECO PhD fellowship Ref. BES-2017–082958., Peer Reviewed, Postprint (author's final draft)

Due to their versatile properties, austenitic stainless steels have a wide application potential, including in specific fields, such as the nuclear power industry. ChN35VT steel is a chromium-nickel-tungsten type of steel stabilized by titanium, and it is suitable for parts subjected to considerable mechanical stress at elevated temperatures. However, the available data on its deformation behavior at elevated/high temperatures is scarce. The core of the presented research was thus the experimental characterization of the deformation behavior of the ChN35VT steel under hot conditions via the determination of flow stress curves, and their correlation with microstructure development. The obtained data was further compared with data acquired for 08Ch18N10T steel, which is also known for its applicability in the nuclear power industry. The experimental results were subsequently used to determine the Hensel-Spittel rheology laws for both the steels. The ChN35VT steel exhibited notably higher flow stress values in comparison with the 08Ch18N10T steel. This difference was more significant the lower the temperature and the higher the strain rate. Considering the peak stress values, the lowest difference was similar to 8 MPa (1250 degrees C and 0.01 s(-1)), and the highest was similar to 150 MPa (850 degrees C and 10 s(-1)). These findings also corresponded to the microstructure developments-the higher the deformation temperature, the more negligible the observed differences as regards the grain size and morphology.

The mechanical properties of three austenitic stainless steels alloys, namely 21-6-9, 316L and a modified 316, fabricated via laser powder bed fusion, have been studied. From the results previously obtained through tensile tests at room and cryogenic temperatures, their strength and ductility were compared against similar conventionally processed materials. The three alloys exhibited a higher or similar strength than their conventional counterparts at both temperatures. In the case of ductility, the additive manufactured 316L was the only alloy that outperformed a conventional 316L at room temperature. At cryogenic temperature, the ductility of the three alloys was either similar or lower. Also, their plastic behavior throughout different stages of deformation was characterized from their microstructure evolution. At room temperature, a two stage, monotonically descending strain hardening rate was observed, similar to F.C.C. medium stacking fault energy materials. At cryogenic temperatures, four stages of strain hardening rates were observed, caused by a martensite transformation induced by plastic deformation, as it happens in TRIP steels., Outgoing

The addition of Si to steels is a well stablished method to delay cementite precipitation, allowing for carbon partitioning from martensite to retained austenite during tempering. It has been argued that carbon enrichment and stabilization of austenite leads to increased ductility and toughness. This has been the main motivation for the development of novel heat treatments, such as quenching and partitioning. High carbon steels can also benefit from improved ductility provided by the presence of stabilized retained austenite. However, the process of carbon partitioning is less understood due to the increased tendency for competitive carbide formation with increasing carbon content. The present work investigates the austenite carbon partitioning and austenite decomposition phenomena in a modified 1.82 wt.% Si hypereutectoid bearing steel during tempering. Dilatometry, in-situ and ex-situ synchrotron X-ray diffraction, 3D atom probe tomography, scanning electron microscopy, and hardness measurements were used. The results are discussed based on different equilibrium states between a' and carbides. It was found that carbon partitioning towards retained austenite occurs for several minutes without significant phase decomposition at temperatures lower than 300 °C. A transition temperature between prevalent austenite carbon enrichment and austenite decomposition occurs at 350 °C. Secondary cementite precipitation inside martensite, and at the a'/¿ interfaces, is observed during tempering at temperatures above 400 °C. Results from constrained carbon equilibrium modeling with carbide presence indicate that homogeneously dispersed spheroidized primary cementite has little influence in the carbon partitioning phenomenon., Peer Reviewed, Postprint (author's final draft)

This research presents the microstructural and mechanical evolution throughout the welded seam of an austenitic stainless steel (ASS) tube. It was found that the main hardness decrement occurred in the fusion zone (FZ), followed by the heat-affected zone (HAZ) and the base material (BM). Optical microscopy indicated a dendritic structure in FZ and heterogeneous austenitic grain size from the HAZ towards the BM, ranging from 100 µm to 10 µm. The welding process generated an intense texture around the FZ and the HAZ, while the BM still showed an extrusion-like texture. In terms of mechanical behavior, the largest austenite grain size in the FZ led to the lowest strength and ductility of all zones due to the earliest strain localization manifested by heterogeneous strain distribution. However, the strain localization in all zones appeared after 0.4 true strain, indicating an overall good ductility of the seam. These high values were related to two microstructure characteristics: (1) the 10% d-ferrite after solidification in the FZ favored by the Creq/Nieq=1.67 relationship that delayed the crack propagation along the austenite grains and (2) the heterogeneous microstructure made up of soft austenite and hard martensite in the HAZ and BM producing multiple strain concentrations. Kernel Average Misorientation (KAM) maps obtained by Electron Back-Scattering Diffraction (EBSD) allowed observing higher internal misorientations in the FZ than in the HAZ due to interconnected walls between the d-ferrite grains. However, the largest KAM values were observed in the BM between ¿-austenite and the deformation-induced a’-martensite phases. X-ray diffraction revealed that the residual stresses in the cross-section of the welded seam were compression-type and then switched to tension-type in the outer surface., Peer Reviewed, Postprint (published version)

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

Samples of the metastable austenitic stainless steel AISI 301LN were subjected to laser treatment with a nanosecond pulsed laser. Scanning speed and laser power were considered as the main process input variables, while the geometrical dimensions of laser tracks (depth and width) and surface roughness were the process responses. The effects of the input parameters on the responses were statistically investigated using analysis of variance (ANOVA). Microstructural characterization of the laser-treated zone was carried out via optical and focus ion beam microscopy, X-ray diffraction, and electron backscattered diffraction, mainly to discern the induced martensitic transformation. Also, tensile tests were performed in specimens with and without laser modification, in order to assess a possible effect on the mechanical response of the steel. The results show that, by increasing the laser power and decreasing the scanning speed, the geometrical dimensions of the laser tracks augment, the surface becomes rougher, and the higher heat input induces more martensitic transformation, whereas tensile properties are not significantly affected., Peer Reviewed, Postprint (author's final draft)

Dissipative zones in buildings allow for the release of energy when a seismic event occurs. The structural analysis of these zones involves the study of the structure at different levels ranging from mechanical properties of materials, adjacent elements, and the whole system. The materials, elements and structures require ductility and strength. Within this framework, austenitic stainless steel (ASS), as a material subjected to cyclic fatigue, shows significant strain hardening and ductility. These promising features require an in-depth analysis when used for dissipative zones. For instance, structures such as eccentrically braced frames (EBFs), whose dissipative zones are placed in links, need that these links achieve the plastic stage first whereas the adjacent elements remain in the elastic stage. The overstrength within the numerical design of structures deserves particular attention, as do the factors involved in the modelling that can affect its assumption. Particularly, a study of the way of cyclic hardening parameters are used can influence the overstrength ASS was carried out. Three ways were considered: average, single values and the superposition of eight backstresses for kinematic hardening. The last one revealed the most conservative results and a higher influence on the link overstrength. It was found that the designed-assumed cyclic parameters directly influenced the link overstrength. With the designed-assumed that considered several changes to the kinematic hardening, the link overstrength was higher with less energy dissipated. Nonetheless, the link’s ductility and dissipated energy increased when the hardening was regular. The experimental material validation and numerical results of the EBF with ASS links were similar., The authors acknowledge the financial support provided by the Project BIA2016-75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a acciones accidentales de sismo fuego”, funded by the Spanish Ministry of Economic Affairs and Digital Transformation (MINECO). The first author acknowledges the financial support from the Peruvian Government Beca Generación del Bicentenario., Peer Reviewed, Postprint (published version)

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

Laser surface modification treatments have been applied to samples of a metastable austenitic stainless steel AISI 301LN. The amount of residual stresses and the presence of induced a´-martensite phase on the surface and subsurface of the samples, as a consequence of laser modification, have been investigated in this study. X-ray diffraction has been used to measure these values, which is a non-destructive method. Laser modification has been applied as parallel lines at a distance of 40 µm, using a laser intensity of 4 A and scanning speeds of 1, 3, and 5 bits/ms, frequency had a constant value of 1000 Hz. The results of the phase analysis show an increase in the a´-martensite present in the surface modified by the laser and that the sample corresponding to the lowest laser speed has the highest martensite fraction. Also, high tensile residual stresses were generated, more pronounced for the lowest laser scanning speed., Peer Reviewed, Postprint (published version)

Metastable austenitic stainless steels (MASS) are widely used in various industrial applications due to their exceptional compromise between mechanical properties and corrosion resistance. However, the mechanical properties of these materials can be further enhanced by surface treatments. This paper reviews various surface treatment methodologies used to improve the mechanical properties of MASS, with particular attention to laser treatments. The effects of these surface treatments on the microstructure and chemical composition in the thermal affected zone of the MASS are discussed, and their impact on the material’s mechanical properties, such as hardness, tensile strength, and fatigue life, are investigated in detail. Additionally, the paper highlights the limitations of these surface treatments and points out some areas where further research is needed. The findings presented can be used to guide the selection of appropriate surface treatment techniques for specific applications, ultimately improving the performance and lifespan of MASS in various industrial settings., Peer Reviewed, Postprint (published version)

Creep tests at very low stresses are often terminated before the stationary stage is reached, which makes it essential to use a model for primary creep to assess the results. Such a model was developed in a recent paper by the author. The model is applied to creep at very low stresses where dislocation creep is the controlling mechanism. Two cases are investigated. i) Aluminium at very high temperatures. This is usually referred to as Harper-Dorn creep. ii) The austenitic stainless steel 316H at 700oC. Most aluminium data for the considered case can be modelled assuming stationary conditions, but some data has to be represented with the primary creep model giving stress exponents down to 1. Contrary to the case for aluminium, the data for 316H at low stresses are very far from stationary conditions. The model results give in agreement with observations a stress exponent of 1 and stress strain curves consistent with the & phi; (phi) model, i.e. an exponentially decreasing strain rate with increasing time. The consistency with the & phi; model verifies that dislocation creep is the controlling mechanism in spite of the fact that the Coble model gives a higher strain rate for diffusion creep., QC 20230810

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation., QC 20230626

The mechanical properties of three austenitic stainless steel alloys, namely 21-6-9, 316L and a modifed 316, fabricated via laser powder bed fusion, have been studied. From the results previously obtained through tensile tests at room and cryogenic temperatures, their strength and ductility were compared against similar conventionally processed materials. The three alloys exhibited a higher or similar strength than their conventional counterparts at both temperatures. In the case of ductility, the additive manufactured 316L was the only alloy that outperformed a conventional 316L at room temperature. At cryogenic temperature, the ductility of the three alloys was either similar or lower. Also, their plastic behavior throughout di˙erent stages of deformation was characterized from their microstructure evolution. At room temperature, a two stage, monotonically descending strain hardening rate was observed, similar to FCC medium stacking fault energy materials. At cryogenic temperatures, four stages of strain hardening rates were observed, caused by a martensite transformation induced by plastic deformation, as it happens in TRIP steels.

Additive manufacturing (AM) techniques are being studied for their application in the aerospace industry. Numerous benefits come from the already in shape final piece, which needs reduced amount of prime material for its production and can have its shape numerically optimized for weight reduction. Austenitic stainless steels (AuSS) are widely used in aerospace and their manufacturing through AM is a popular research topic in order to accelerate their effective incorporation in air-crafts and spaceships. The special microstructures of AM has been observed with characterization techniques. The present work studies the high temperature stability of three AuSS (316L, MOD-316 and 21-6-9) considering two approaches; surface corrosion and microstructure evolution. First, for high temperature corrosion, thermogravimetric analysis has been performed from 850°C to 1150°C. From the results, kinetic analysis were performed and the activation energy was extracted from Arrhenius fits. Two mechanism were found for alloy 316L (first 435.41 kJ/mol and second 593.24 kJ/mol) and MOD-316 (first 740.01 kJ/mol and second 495.58 kJ/mol). Further SEM observations on the scales have shown Ni diffusion through the chromia scale in MOD-316 alloy, which could explain the higher oxidation rates at 1150°C. Alloy 21-6-9 has the best passivation behaviour with an activation energy of 190.47 kJ/mol. Secondly, long heat treatment (HT) at 725°C in air atmosphere has been performed, for 24 and 240h. Samples were initially as-built or annealed (900°C for 1h), to compare the effect of the HT on the microstructure evolution and precipitates formation. LOM observation showed preferable nucleation in grain boundaries (GB), an increment of the number of precipitates and a growth towards elongated shapes following GB with increased time. It was also observed a reduction in precipitates number with the annealing HT for all the alloys. XRD, SEM and EDS analysis has been carried out to identify the structure an, SeSSA

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

Additive manufacturing (AM) techniques are being studied for their application in the aerospace industry. Numerous benefits come from the already in shape final piece, which needs reduced amount of prime material for its production and can have its shape numerically optimized for weight reduction. Austenitic stainless steels (AuSS) are widely used in aerospace and their manufacturing through AM is a popular research topic in order to accelerate their effective incorporation in air-crafts and spaceships. The special microstructures of AM has been observed with characterization techniques. The present work studies the high temperature stability of three AuSS (316L, MOD-316 and 21-6-9) considering two approaches; surface corrosion and microstructure evolution. First, for high temperature corrosion, thermogravimetric analysis has been performed from 850°C to 1150°C. From the results, kinetic analysis were performed and the activation energy was extracted from Arrhenius fits. Two mechanism were found for alloy 316L (first 435.41 kJ/mol and second 593.24 kJ/mol) and MOD-316 (first 740.01 kJ/mol and second 495.58 kJ/mol). Further SEM observations on the scales have shown Ni diffusion through the chromia scale in MOD-316 alloy, which could explain the higher oxidation rates at 1150°C. Alloy 21-6-9 has the best passivation behaviour with an activation energy of 190.47 kJ/mol. Secondly, long heat treatment (HT) at 725°C in air atmosphere has been performed, for 24 and 240h. Samples were initially as-built or annealed (900°C for 1h), to compare the effect of the HT on the microstructure evolution and precipitates formation. LOM observation showed preferable nucleation in grain boundaries (GB), an increment of the number of precipitates and a growth towards elongated shapes following GB with increased time. It was also observed a reduction in precipitates number with the annealing HT for all the alloys. XRD, SEM and EDS analysis has been carried out to identify the structure an, SeSSA

The mechanical properties of three austenitic stainless steel alloys, namely 21-6-9, 316L and a modifed 316, fabricated via laser powder bed fusion, have been studied. From the results previously obtained through tensile tests at room and cryogenic temperatures, their strength and ductility were compared against similar conventionally processed materials. The three alloys exhibited a higher or similar strength than their conventional counterparts at both temperatures. In the case of ductility, the additive manufactured 316L was the only alloy that outperformed a conventional 316L at room temperature. At cryogenic temperature, the ductility of the three alloys was either similar or lower. Also, their plastic behavior throughout di˙erent stages of deformation was characterized from their microstructure evolution. At room temperature, a two stage, monotonically descending strain hardening rate was observed, similar to FCC medium stacking fault energy materials. At cryogenic temperatures, four stages of strain hardening rates were observed, caused by a martensite transformation induced by plastic deformation, as it happens in TRIP steels.

Due to their versatile properties, austenitic stainless steels have a wide application potential, including in specific fields, such as the nuclear power industry. ChN35VT steel is a chromium-nickel-tungsten type of steel stabilized by titanium, and it is suitable for parts subjected to considerable mechanical stress at elevated temperatures. However, the available data on its deformation behavior at elevated/high temperatures is scarce. The core of the presented research was thus the experimental characterization of the deformation behavior of the ChN35VT steel under hot conditions via the determination of flow stress curves, and their correlation with microstructure development. The obtained data was further compared with data acquired for 08Ch18N10T steel, which is also known for its applicability in the nuclear power industry. The experimental results were subsequently used to determine the Hensel-Spittel rheology laws for both the steels. The ChN35VT steel exhibited notably higher flow stress values in comparison with the 08Ch18N10T steel. This difference was more significant the lower the temperature and the higher the strain rate. Considering the peak stress values, the lowest difference was similar to 8 MPa (1250 degrees C and 0.01 s(-1)), and the highest was similar to 150 MPa (850 degrees C and 10 s(-1)). These findings also corresponded to the microstructure developments-the higher the deformation temperature, the more negligible the observed differences as regards the grain size and morphology.

This study explores pulsed Nd:YLF laser surface modification (LSM) effects on AISI 301LN stainless steel. Laser-treated surfaces underwent SEM characterization, revealing patterns and irregularities. Higher heat input surfaces showed significant microstructural changes, while lower heat input surfaces experienced less alteration. Increased laser spot overlap led to larger exposed areas and higher heat input, influencing groove width, depth, and surface roughness. Three-dimensional reconstructions illustrated the correlation between laser parameters and surface characteristics. XRD (X-ray diffraction analysis) and EBSD (Electron backscatter diffraction) analyses revealed a transformation from austenite to martensite, with an increase in the a’-martensite phase, particularly in patterns with high laser power, attributed to rapid cooling during laser modification. Grain size analysis indicated a 42% reduction post-treatment, enhancing the surface fraction of fine grains. Hardness measurements demonstrated an overall increase in laser-treated samples, linked to fine-grained microstructure formation, induced residual stresses, and the a’-martensitic phase., The authors would like to express their special gratitude to the Outokumpu for supplying the stainless steel and the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) del Departament de Recerca i Universitats de la Generalitat de Catalunya for recognizing the Microstructural Design and Advanced Manufacturing of Materials Group as a consolidated research group (number 2021SGR01053). M. Rezayat acknowledges the AGAUR (FI-SDUR-2020) of the Generalitat de Catalunya for its financial support. H. Besharatloo acknowledges Ministerio de Universidades for the Margarita Salas grant., Peer Reviewed, Postprint (published version)

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

Intrinsic stacking fault energy (SFE) values of gamma-Fe and AISI 304 austenitic stainless steels were determined as a function of carbon and nitrogen content using ab initio calculations. In contrast to previous investigations, the analysis was conducted incorporating the paramagnetic state to account for the magnetic constitution of real austenitic stainless steels. The effect of finite temperature was partially accounted for by performing ab initio calculations at the experimental volumes at room temperature. Including paramagnetism in gamma-Fe increases the SFE of non-magnetic gamma-Fe by similar to 385 mJ.m(-2). Interstitial alloying of non-magnetic gamma-Fe causes a linear increase in intrinsic stacking fault energy with interstitial content. In comparison, interstitial alloying of paramagnetic gamma-Fe increases the SFE at only about half the rate. The SFE of paramagnetic interstitial-free AISI 304 is within the range of -12 to 0 mJ.m(-2) and only deviates slightly from the SFE of paramagnetic gamma-Fe. It follows a similar, albeit flatter linear dependency on the interstitial content compared to gamma-Fe. Both gamma-Fe and gamma-AISI 304 were found to be metastable in their interstitial-free condition and are stabilized by interstitial alloying. The possible effect of short range ordering between interstitials and Cr on the SFE was discussed. The calculated threshold nitrogen content necessary to stabilize austenite in AISI 304 is in good agreement with experimental investigations of deformation microstructures in dependence of the nitrogen content. Finally, the calculated negative SFE values of AISI 304 were reconciled with experimentally determined positive SFE values using a recent method that accounts for the kinetics of stacking fault formation.

In the very high cycle fatigue regime, fatigue crack initiation in high-strength steels is usually correlated to a subsurface inclusion with a fine granular area (FGA). Localized stress-strain concentration at the subsurface inclusion is a critical factor. Fatigue crack initiation with an FGA in the bulk matrix without any defect has rarely been reported. In this paper, a fundamental study on the formation of FGAs in the bulk matrix of an austenitic stainless steel has been carried out using a progressive stepwise load-increasing test with a cycle step of about 108 cycles. FGA formation in the subsurface bulk matrix has been observed. The micro structural damage in the fatigue-tested specimens has been studied using the electron channeling contrast imaging electron microscopy technique. Strain localization and grain fragmentation are the main processes for the formation of FGAs. Local plasticity exhaustion leads to crack initiation due to local stress concentrations. This method can also be used to predict the fatigue damage process, especially the damage rate in individual specimens.

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

A fine granular area, FGA, is a typical phenomenon observed at the very high cycle fatigue fracture crack origin with a subsurface defect in the material. The FGA has been widely investigated, and different mechanisms have been proposed. In this paper, the formation of FGA in a non-defect matrix of one austenitic steel during very high cycle fatigue was studied using a progressive stepwise load-increasing method and electron scanning microscopy/electron channeling contrast imaging (ECCI) technique. A nano rough surface area or FGA at the fatigue crack origin has been observed in the subsurface matrix without any defect. It is a new phenomenon. A mechanism was proposed using the dislocation plasticity theory. The formation of FGA in a non-defect matrix is a localized plasticity exhausting process by strain localization, grain fragmentation, stress concentration and nano crack initiation and propagation along low-angle grain boundaries.

The AUSTANDING project proposes the design and additive manufacturing of a new stainless steel with special characteristics that possesses the right combination of strength, ductility and toughness while maintaining high levels of corrosion resistance. This innovative manufacturing process, based on layer-by-layer 3D printing, enables the production of steel parts with the aforementioned high performance and complex geometries that could not be achieved until now, which will be applied to the production of next-generation heat exchangers, devices widely used and demanded by multiple industrial sectors. The nature of the processes used in the manufacture of this steel will contribute to moving towards a zero net carbon steel industry model. On the other hand, as it is a manufacturing process that seeks materials with the simplest possible chemical composition and minimises the use of scarce metals, the project fulfils the mission of the circular economy., El proyecto AUSTANDING propone el diseño y la fabricación aditiva de un nuevo acero inoxidable con características especiales que posea una combinación adecuada de resistencia, ductilidad y tenacidad y a la vez mantenga altos niveles de resistencia a la corrosión. Este innovador proceso de fabricación, basado en la impresión 3D capa a capa, permite la elaboración de piezas de acero con las altas prestaciones mencionadas y geometrías complejas que no han podido lograrse hasta ahora, lo cual se aplicará a la producción de intercambiadores de calor de próxima generación, unos dispositivos ampliamente usados y demandados por múltiples sectores industriales. La naturaleza de los procesos empleados en la fabricación de este acero contribuirá a avanzar hacia un modelo de industria siderúrgica con cero emisiones netas de carbono. Por otro lado, al ser una fabricación que busca materiales con una composición química lo más simple posible y que minimiza la utilización de metales escasos, el proyecto cumple con la misión de la economía circular.

Laser surface modification treatments have been applied to samples of a metastable austenitic stainless steel AISI 301LN. The amount of residual stresses and the presence of induced a´-martensite phase on the surface and subsurface of the samples, as a consequence of laser modification, have been investigated in this study. X-ray diffraction has been used to measure these values, which is a non-destructive method. Laser modification has been applied as parallel lines at a distance of 40 µm, using a laser intensity of 4 A and scanning speeds of 1, 3, and 5 bits/ms, frequency had a constant value of 1000 Hz. The results of the phase analysis show an increase in the a´-martensite present in the surface modified by the laser and that the sample corresponding to the lowest laser speed has the highest martensite fraction. Also, high tensile residual stresses were generated, more pronounced for the lowest laser scanning speed., Postprint (author's final draft)

Since 2021, cobalt (Co) is in Europe classified as carcinogen in quantities exceeding 0.1 wt-%. This affects nickel-rich stainless steels, which contain about 0.2 wt-% Co impurities. Previous findings show the bioaccessibility of Co in stainless steel to be primarily determined by the corrosion resistance. It has been unclear whether Co is distributed heterogeneously in the alloy and the outermost surface and whether a specific location would pose a risk for Co release under specific exposure conditions. This study aimed at locating Co in stainless steel 316L (0.2 wt-% Co) surfaces prior to and after exposure to different synthetic body fluids for 24 h at 37 °C. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICPMS) investigated the location of Co in the surface oxide and extent of release along with other metals (iron, chromium, nickel, and manganese) into synthetic biological fluids (gastric fluid, pH 1.5; lysosomal fluid, pH 4.5; phosphate buffered saline-PBS, pH 7.4). Co was homogeneously distributed along with metallic nickel beneath the surface oxide and co-released with other metals upon surface reformation and passivation. Exposure in PBS resulted in the incorporation of both Co and phosphate in the oxide., Not duplicate with DiVA 1611076QC 20221125

Although fundamental models have been developed for time extrapolation of creep rupture data, empirical methods are still dominating. One limitation with the empirical methods is that no systematic way of estimating the error in the results has been available. To remove this limitation, formulae for error estimates are developed in the present paper. Error estimates are first established for single creep rupture curves. Then error estimates are formulated for creep data at several test temperatures assessed with Time-Temperature Parameters (TTPs). A new requirement is introduced in the optimization, namely that the first and second derivatives of the rupture curve should be negative, referred to as constrained. The constrained optimization significantly reduces the error in the extrapolated values. The constrained procedure is applied to the austenitic steel Sanicro 25. The procedure gives quite a stable result, and the post-assessment tests developed by ECCC are satisfied automatically for five common TTPs tested., QC 20221109

For modern creep-resistant steels, ductility is primarily controlled by cavitation, since brittle rupture is dominating during long-term service. In recent years, the present authors have formulated fundamental models for nucleation and growth of cavities that have been verified to be able to describe experiments for austenitic stainless steels. These equations, together with models for dislocation creep, are used in this paper to present basic modelling results for the creep ductility of austenitic stainless steels for the first time. New results are also presented for ductile rupture, where the elongation values are mainly governed by plastic instability and necking. The Hart criterion is used to identify the strain where the instability forms. Modelling shows that the instability grows very slowly and that its size is not significant until close to rupture. These facts are used to demonstrate that ductility during ductile rupture can be predicted from necking behaviour., QC 20221118

To advance the understanding of metallic materials for structural components at cryogenictemperatures, a review of previous studies on the mechanical properties of austenitic stainlesssteels, titanium alloys, aluminum alloys, and copper alloys is presented herein. In particular,the evaluation of strength and toughness balance intends to clarify key differences betweenthese alloys to facilitate better alloy design and potentially bolster further alloy development.Several key points on cryogenic mechanical tests are also introduced. Temperature control,testing tools, and test conditions should be properly calibrated to avoid experimental errors.Furthermore, substantial progress for subsurface crack initiation in high-cycle fatigue at cryogenictemperatures is presented, in which the mechanism of subsurface crack generation ishighlighted as a key design consideration in microstructure of high-strength alloys.

Nanotwin formation is observed during laser powder bed fusion (LPBF) of austenitic stainless steels fabricated with various process parameters. Transmission electron microscopy was employed to reveal the nature of such twins, which are formed due to the high strain rapid solidification inherent to LPBF. Dynamic recrystallization (DRX) was also activated during LPBF, and induced by the deformation nanotwins. A thermostatistical model is proposed to determine the critical conditions for twinning-induced DRX; the model is validated with the reported experimental results. This modelling approach offers a method to microstructurally engineer austenitic stainless steels for potential applications needing high strength and ductility.

The effects of different thermochemical post-processing treatments on the microstructure and properties of additively manufactured austenitic stainless steel were investigated. If the nitrogen content in the as-built condition is high, austenitization in vacuum causes a reduction in nitrogen content near the surface. This can be remedied by applying a small amount of nitrogen in the gas during austenitization. Using high temperature solution nitriding, the surface hardness could be effectively raised by deliberate nitrogen ingress, while maintaining a very fine structure inside the primary austenite grains. The excellent combination of strength and ductility of the as-built condition is accompanied by a low degree of work-hardening. This condition showed elastic and plastic anisotropy. The vertically built condition exhibits a lower strength and an early initiation of yielding as compared to the horizontally built conditions. High temperature treatments were able to efficiently reduce the mechanical anisotropy exhibited in the as-built condition. A combination of high- and low temperature surface hardening was investigated using nitriding, carburizing and nitrocarburizing. In all cases expanded austenite developed on the surface, which created a strong hardness increase.

Low-temperature carburizing dramatically enhances the inherently low wear resistance of austenitic stainless steels due to the formation of a carbon-supersaturated solid solution, i.e. expanded austenite. The formation of expanded austenite from low-temperature carburizing has been intensively investigated. However, the influence of chemical composition of the stainless steel on the carburizing response has not received the same interest. This contribution addresses the effect of the chemical composition on low-temperature carburizing in terms of carbon solubility, decomposition of expanded austenite upon exceeding the solubility limit and the elasto-plastic accommodation of the carbon-induced lattice expansion. The results demonstrate that the carbon solubility increases with an increasing Cr-equivalent and that higher Cr- and Ni-equivalents favor the formation of Cr-based M7C3 over Fe-based Hägg (M5C2) carbide.

In this paper, an experimental program on cyclic loading of austenitic stainless steel specimens is presented. The program encompasses a series of forty specimens subjected both cyclic (low and extremely low) and arbitrary loading (following certain rules). These protocols include companion, multiple-step and a set of arbitrary earthquake-like strain history, which represents a novelty in the material understanding. Stainless steel exhibits strain hardening as a key feature for structural applications. This feature is fundamental in the definition of cross-sectional resistance, cross-section classification, ductility and energy dissipation. In recent years, the strategic use of stainless steel as a potential structural material in dissipative zones of earthquake-resistant elements is under consideration. When it comes to seismic design, strain-hardening must be known precisely for further characterization of the seismic structural behaviour of the actual system in which stainless steel is used strategically. The use of stainless steel in dissipative zones of earthquake-resistant structures requires research related to cyclic loading at many levels. Thus, its potential use in seismic areas, as well as the performance of existing structures, can be considered. A systematic analysis of the results, which include cyclic hardening, stabilisation and material degradation, is presented. In addition, these results are used for the further numerical implementation of cyclic hardening in non-linear models., The authors acknowledge the financial support provided by the Project BIA2016-75678-R, AEI/FEDER, UE “Comportamiento estructural de pórticos de acero inoxidable. Seguridad frente a acciones accidentales de sismo y fuego”, funded by the Spanish Ministry of Economic Affairs and Competitiveness (MINECO). The first author acknowledges the financial support from the Peruvian Government Beca Generación del Bicentenario., Peer Reviewed, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura, Postprint (author's final draft)

Computational materials design has made significant progress lately. However, one underexploited opportunity lies in the combination of physically based modelling and machine learning (ML). In the present work we exploit this combination for modelling of strain-induced martensitic phase transformation (SIMT) in austenitic steels. A fully predictive model for SIMT, responsible for the TRIP effect in many steels, is devised. An experimental dataset correlating SIMT with composition, temperature and strain is collected from the open literature firstly. Secondly, the Olson-Cohen model is applied to make physically based predictions on temperature and strain dependence of SIMT in order to expand the database to the final size of 16,500 entries relating the features and the target. Thirdly, ensemble ML methods are applied to model the data and the final model is validated on a holdout dataset, including also dual-phase alloys. The final model provides accurate predictions of SIMT in a temperature range from −196 to 100 °C and from 0 to 1 in strain. The model can readily be extended to consider further factors such as strain rate and stress state. Moreover, it can be used together with thermodynamic and kinetic calculations, or thermomechanical simulations, for the design of steels and components, respectively., QC 20210205

Abrasive water jet machining is a proficient alternative for cutting difficult-to-machine materials with complex geometries, such as austenitic stainless steel 304L (AISI304L). However, due to differences in machining responses for varied material conditions, the abrasive waterjet machining experiences challenges including kerf geometric inaccuracy and low material removal rate. In this study, an abrasive waterjet machining is employed to perform contour cutting of different profiles to investigate the impacts of traverse speed and material thickness in achieving lower kerf taper angle and higher material removal rate. Based on experimental investigation, a trend of decreasing the level of traverse speed and material thickness that results in minimum kerf taper angle values of 0.825° for machining curvature profile and 0.916° for line profiles has been observed. In addition, higher traverse speed and material thickness achieved higher material removal rate in cutting different curvature radii and lengths in line profiles with obtained values of 769.50 mm3/min and 751.5 mm3/min, accordingly. The analysis of variance revealed that material thickness had a significant impact on kerf taper angle and material removal rate, contributing within the range of 69–91% and 62–69%, respectively. In contrast, traverse speed was the least factor measuring within the range of 5–18% for kerf taper angle and 27–36% for material removal rate.

Present work investigates the effect of heat input (controlled by welding current, welding voltage andwelding speed) on tensile strength, micro-hardness and microstructure elements produced by shielded metal arc welding (SMAW). From the experimental results it was found that the increase in heat input affects the micro-constituents of base metal, and heat affected zone (HAZ). Tensile strength decreaseswith increase in heat input and from scanning electron microscopy of tensile test fractured surfaces exhibited ductile & brittle failure. From micro hardness data values it was observed that hardness of material increases with increase in heat input in weld pool and decreases in HAZ zone. Optical microscopy shows that smaller dendrite sizes and lesser inter-dendritic spacing were observed in the fusion zone at low heat input.

Present work investigates the effect of heat input (controlled by welding current, welding voltage andwelding speed) on tensile strength, micro-hardness and microstructure elements produced by shielded metal arc welding (SMAW). From the experimental results it was found that the increase in heat input affects the micro-constituents of base metal, and heat affected zone (HAZ). Tensile strength decreaseswith increase in heat input and from scanning electron microscopy of tensile test fractured surfaces exhibited ductile & brittle failure. From micro hardness data values it was observed that hardness of material increases with increase in heat input in weld pool and decreases in HAZ zone. Optical microscopy shows that smaller dendrite sizes and lesser inter-dendritic spacing were observed in the fusion zone at low heat input.

Present work investigates the effect of heat input (controlled by welding current, welding voltage andwelding speed) on tensile strength, micro-hardness and microstructure elements produced by shielded metal arc welding (SMAW). From the experimental results it was found that the increase in heat input affects the micro-constituents of base metal, and heat affected zone (HAZ). Tensile strength decreaseswith increase in heat input and from scanning electron microscopy of tensile test fractured surfaces exhibited ductile & brittle failure. From micro hardness data values it was observed that hardness of material increases with increase in heat input in weld pool and decreases in HAZ zone. Optical microscopy shows that smaller dendrite sizes and lesser inter-dendritic spacing were observed in the fusion zone at low heat input.

Present work investigates the effect of heat input (controlled by welding current, welding voltage andwelding speed) on tensile strength, micro-hardness and microstructure elements produced by shielded metal arc welding (SMAW). From the experimental results it was found that the increase in heat input affects the micro-constituents of base metal, and heat affected zone (HAZ). Tensile strength decreaseswith increase in heat input and from scanning electron microscopy of tensile test fractured surfaces exhibited ductile & brittle failure. From micro hardness data values it was observed that hardness of material increases with increase in heat input in weld pool and decreases in HAZ zone. Optical microscopy shows that smaller dendrite sizes and lesser inter-dendritic spacing were observed in the fusion zone at low heat input.