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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)

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)

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)

In the current research, a complex microstructure and crystallographic data were developed through quenching and partitioning (Q&P) process to improve tensile properties of commercial pearlitic carbon-silicon steel. Two-stage Q&P process, including full austenitization, quenching at 220 °C, followed by two different partitioning temperatures, was applied to the as-received specimen to generate a complex microstructure composed of tempered martensite, bainite, ultrafine carbides/martensite-austenite/retained austenite particles. Microstructure and crystallographic data were investigated by scanning electron microscopy, electron backscattered diffraction (EBSD), and X-ray diffraction techniques. Then, hardness and tensile properties were evaluated to confirm the improvement of mechanical properties. Dilatation-temperature curves exhibited the kinetics of martensitic and bainitic transformation during quenching and isothermal partitioning stages. The presence of nano-carbide particles inside athermal martensite was confirmed by electron microscopy due to the pre-formed martensite carbon depletion during the partitioning stage coupled with bainitic transformation. The formation of preferential atomic-compact <111> direction in BCC (martensite/bainite) plates characterized by EBSD, could enhance ductility by providing adequate slip systems. Point-to-point misorientation analyses demonstrated a slight dominance of low angle boundaries proportion in bainitic dominance structure in Q&P-220-375 specimen, which could be used in phase characterization. Results revealed that the development of nanoscale carbide dispersed in refined bainite/martensite matrix boosted the yield and ultimate tensile strength by over 100% and 110% compared to the initial pearlitic microstructure. However, ductility reduced to half value in Q&P-220-325 and Q&P-220-375 specimens., Peer Reviewed, Postprint (published version)

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)

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)

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)

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)