Austenitic Stainless Steel Research Articles

Finite Element Simulation and Experimental Analysis of the Thermo-Mechanical Properties of Dissimilar S275 and 316L Austenite Stainless Steels using the RFW Process

This research examines the effect of thermomechanical and microstructural constituents on welding of AISI 316L (austenite stainless steel) and S275 steel. A Finite Element Model (FEM) was constructed using ANSYS 19.1, and an experimental study was conducted using the Rotary Friction Welding (RFW) process. It was determined that there is a genuine correlation between the simulation FEM and the experimental procedure with regard to the thermal profile and ultimate yield strength, particularly when a welding speed of 2,000 rev/min is employed. At that speed, the higher temperature recorded and calculated was 1,450 oC. The discrepancy between the numerical FEM and the experimental temperature profile for the peak temperature calculation was determined to be 2.78%. The mechanical analysis was conducted through tensile force calculations and experiments, the results of which indicated an estimated error of 12%. The calculated error for the ultimate yield strength of the various samples is less than 6% for tensile strength. Upon tensile testing, failure occurred in the S275 sample. The microstructure exhibited increases in Cr and Ni of 1.2% and 1.01%, respectively, in comparison to the base metal of 316L stainless steel.

The ability of austenitic stainless steel (Alloy-28) to withstand corrosion when exposed to a combination of industrial phosphoric acid and an oxidizing agent

The ability of austenitic stainless steel (Alloy-28) to withstand corrosion when exposed to a combination of industrial phosphoric acid and an oxidizing agent

Deposition Strategy on Microstructure Development and Mechanical Properties of Wire Arc Additively Manufactured Austenitic Stainless Steel

Deposition Strategy on Microstructure Development and Mechanical Properties of Wire Arc Additively Manufactured Austenitic Stainless Steel

The Expanded Phases Formed in Stainless Steels by Means of Low-Temperature Thermochemical Treatments: A Corrosion Perspective

Surface engineering of stainless steels using thermochemical treatments at low temperatures has been the subject of intensive research for enhancing the surface hardness of these alloys without impairing their corrosion resistance. By using treatment media rich in nitrogen and/or carbon, it is possible to inhibit chromium compound formation and obtain supersaturated solid solutions, known as expanded phases, such as expanded austenite or S-phase in austenitic stainless steels, expanded ferrite in ferritic grades, and expanded martensite in martensitic grades. These low-temperature treatments produce a significant increase in surface hardness, which improves wear and fatigue resistance. However, the corrosion behavior of the modified surface layers remains of paramount importance. In the international literature, many studies on this topic are reported, but the results are not always univocal, and there are still open questions. In this review, the corrosion behavior of the expanded phases and the modified layers in which they are present is critically analyzed and discussed. The relationships between the phase composition and the microstructure of the modified layers and the corrosion resistance are highlighted while also considering the different test conditions. Furthermore, corrosion test methods are discussed, and suggestions are given for improving the measurements. Finally, perspectives on future directions for investigation are suggested for encouraging further research.

Physics-coupled Data-driven Design of High-Temperature Alloys

We present a materials design loop, which streamlines physics-coupled machine learning (ML) surrogate models to discover new alloy chemistries with improved properties. The efficacy is demonstrated by discovering a high-temperature alumina-forming austenitic (AFA) stainless steel with enhanced creep, followed by experimental validation. The ML models have been trained using a well-curated, highly consistent experimental dataset augmented with synthetic microstructural features from a computational thermodynamic approach. We have populated a large number of hypothetical AFA alloys to explore the high-dimensional composition space and have predicted their creep properties by providing the same synthetic input features obtained from the trained ML models. Uncertainties from the ML training were taken as thresholds for truncating predicted results to identify alloys with improved or deteriorated creep. Individual elemental compositions have been determined via probability density distribution analysis from the group of alloys at the top and bottom of the predicted creep values for further virtual and experimental validations. We anticipate that this workflow can be applied to screen desired conditions, such as chemistry and processing parameters, in high-dimensional space through physics-guided data analytics.

Correlation of mechanics degradation and thermal aging damage defects in Z3CN20.09M cast austenitic stainless steels

Microstructural characterization and mechanical testing were performed on 400℃ thermally aged Z3CN20.09M cast austenitic stainless steels. A quantitative mathematical model is introduced for the relationship between aging defects and mechanical properties. Charpy impact energy was used as a characteristic mechanical parameter, and the short-range order of the Cr element segregation that induced by spinodal decomposition was chosen as the characteristic defect parameters. The macroscopic mechanical properties and the microscopic thermal aging defects was quantitatively correlated in this model, which has a great reference significance in safety assessment and lifetime prediction of the reactor structural materials.

Creep-fatigue interactive behavior and damage mechanism of TP321 stainless steel under hybrid-controlled conditions

In this study, Hybrid-controlled creep-fatigue (HCCF) tests were conducted on TP321 austenitic stainless steel under a variety of test conditions. The effects of strain amplitude, holding time, holding stress and temperature on the creep-fatigue behavior of TP321 austenitic stainless steel were not only analyzed in detail but also revealed the creep-fatigue damage interactive mechanism. The results demonstrated that a rise in test temperature and load holding time markedly induced creep deformation, resulting in a notable reduction in failure life. Additionally, an increase in test temperature led to the cessation of the cyclic hardening phenomenon. Secondly, the analysis of fracture morphology and X-ray computed tomography (X-CT) scanning results demonstrated that the transgranular cracks expanded inwards and connected with the intergranular voids under creep-fatigue interaction, forming a mixed intergranular and transcrystalline fracture mode. The presence of large creep cavities impeded the propagation of fatigue cracks when creep damage was the dominant phenomenon. Subsequently, the damage evolution mechanism was elucidated through microstructural analysis, which revealed that the impact of the slip bands on the triangular grain boundaries and the precipitation of carbides facilitated the nucleation of voids and the internal formation of intergranular microcracks, thereby causing creep-fatigue damage interaction. Finally, the TP321 austenitic stainless steel creep-fatigue damage interactive mechanism diagram was proposed in conjunction with the fracture morphological characteristics and microstructure.

Metallic Bipolar Plates for Polymer Electrolyte Fuel Cell (PEFC) Used in Electric Vehicles using the WSM Method

Metallic Bipolar Plates for Polymer Electrolyte Fuel Cell (PEFC) used in electric vehicles. Electric vehicles use electrolytic polymeric fuel cells (PEFCs) built of bipolar sheet metal. Along with the MEA, One of the most essential components of a PEFC cell is the bipolar plate. since they support the MEA, provide rigidi-ty to the layer, and even allow for gas diffusion. Electrical conductivity is provided by the entire electrode surface. The control of heat and the ejection of product water are two additional benefits of a well-prepared bipolar plate [103-105]. In the PEFC stack, bipolar plates are placed between the MEAs so that each of them offers a link to one end of a MEA and, on the other side, to the cath of an adjacent MEA. Bi-polar panels should be small and thin to reduce For PEMFCs, a variety of metal bipolar plates are now being investigated to suit the demands of lowering costs, increasing stacking size, lowering weight, and raising energy density. The quality of interest strategy was compared to the best answer (TOPSIS) the multi-attribute decision-making approach (MADM) in this work, the optimal substance for a metallic bi-polar plate is selected using (MADM). For electrolyte polymer fuel cells (PEFCs), which can have numer-ous competing objectives? Material designers can choose the best material based on preset criteria with the use of a suggested algorithm tool. The theoretical framework is followed by a case study on the mate-rial selection for a PEFC bipolar plate. A list of all the products that meet the requirements for selection, including production costs, by dividing each of our objectives by a user-supplied weight, we divide our audience into a single goal via the weighted sum approach. One of the most popular methods is this one. When considering overall weights, one concern is determining how much weight to give each goal. The primary goal governs are added with varying weights in the weighed total approach, and the sum is then optimized. The goal that function is optimized while another is constrained to a variable's value in the electrically operated constraint approach you can generate an integrated analysis by combining several inputs and weights using the Total Weight function. In that several raster inputs representing various fac-tors can be easily mixed, mixing weights or relative importance, it is comparable to the Weighted Overlay function. 316 austenitic stainless steel,310 austenitic stainless steel,317l austenitic stainless steel,316l aus-tenitic stainless steel, aluminum (gold plated), aisi 446 ferritic stainless steel, aisi 436 ferritic stainless steel, aisi 444 ferritic stainless stee, aisi 434 ferritic stainless stee,304 austenitic stainless steel, titanium (coated with nitride), a560 (50cr–ni). the density of an object, the tensile strength, the expansions coeffi-cients, conductivity of heat, thermal diffusivity, and fracture toughness are some of the other characteris-tics of bipolar plates that should be considered. From the result it is seen that titanium (coated with ni-tride) is got the first rank whereas is the 310 austenitic stainless steel having the lowest rank. The first ranking titanium (coated with nitride) is obtained with the lowest quality of 310 austenitic stainless steel.

Optimizing laser cutting of stainless steel using latin hypercube sampling and neural networks

Optimizing cutting parameters in fiber laser cutting of austenitic stainless steel is challenging due to the complex interplay of multiple variables and quality metrics. To solve this problem, Latin hypercube sampling was used to ensure a comprehensive and efficient exploration of the parameter space with a smaller number of trials (185), coupled with feedforward neural networks for predictive modeling. The networks were trained with a leave-one-out cross-validation strategy to mitigate overfitting. Different configurations of hidden layers, neurons, and training functions were used. The approach was focused on minimizing dross and roughness on both the top and bottom areas of the cut surfaces. During the testing phase, an average MSE of 0.063 and an average MAPE of 4.68% were achieved by the models. Additionally, an experimental test was performed on the best parameter settings predicted by the models. Initial modelling was conducted for each quality metric individually, resulting in an average percentage difference of 1.37% between predicted and actual results. Grid search was also performed to determine an optimal input parameter set for all outputs, with predictions achieving an average accuracy of 98.34%. Experimental validation confirmed the accuracy and robustness of the model predictions, demonstrating the effectiveness of the methodology in optimizing multiple parameters of complex laser cutting processes.

The Effect of σ Phase Content on the Hot Working Properties of Super Austenitic Stainless Steel Containing 7Mo-0.42N

In the present study, super austenitic stainless steel containing 7Mo-0.42N was isothermally treated at 1100 °C, 1200 °C, and 1250 °C for different times, in order to obtain the samples with different σ precipitate content of 7%, 1.4%, and 0.7%. The effect of σ phase content on the hot working properties of the specimens was investigated under hot compression conditions at 900~1200 °C and strain rates of 0.01~5 s−1. Results show that, with the increase in σ content, the recrystallized grains increase gradually, and the internal stress decreases firstly and then increases. Therefore, the σ phase has two roles in the thermal deformation process. One is that the σ phase promotes recrystallization and the other is that the σ phase hinders dislocation motion. In the hot working diagram of super austenitic stainless steel with different σ phase contents, the distribution of high power consumption and instability regions is significantly different. The sample containing 1.4% σ phase does not show the region where the power dissipation coefficient η is negative, and there is a large number of dynamic recrystallized grains in the high power region, showing good hot working performance. However, the local rheology and cracking in samples containing 0.7% and 7% σ phase after deformation are more serious. Combined with the constitutive equation, hot working diagram, and microstructure, it is found that the optimum hot working property of the super austenitic stainless steel containing 7Mo-0.42N could be obtained when it is deformed at a temperature of 1200 °C with a strain rate of 5 s−1 when the content of σ phase is 1.4%.

Unexpected pitting inhibition of additively-manufactured austenitic stainless steel by electrochemical hydrogen-charging

Pitting of austenitic stainless steel (SS) is intensified under hydrogen environment, resulting in great uncertainty of safety. However, austenitic SS printed by selective laser melting (SLM) after electrochemical hydrogen-charging manifests an unanticipatedly anti-pitting behavior. Pitting resistance is found in all the SLM samples after H-charging, while the original SLM and all the commercial SS samples are composed of corrosive pits on the surfaces. XRD, EBSD and TEM observations of SLM sample after H-charging reveal that nanotwins and ɛ-phase are newly formed interior of the cellular cells, which inhibit martensite transformation and enhance the formation of Cr oxides in passivation film.

Microstructure and wear characteristics of austenitic stainless steel coatings fabricated through various directed energy deposition

Austenitic stainless steels are widely used in automotive and marine environments because of their high toughness, corrosion resistance, and wear resistance. The present comparative study focuses on the microstructure and wear resistance of double-layer austenitic stainless-steel coatings prepared on a ductile iron substrate using circular spot high-speed laser-directed energy deposition (DED) and broad-beam laser-DED. The results indicate that while the deposition process does not alter the physical phase of coating, it does influence the preferred orientation of surface grains. Both coatings exhibit characteristics of hypoeutectic alloys, where the harder eutectic structure serves as a skeleton to resist external pressure. The high-speed laser-DED coating demonstrates higher hardness and wears resistance due to its denser eutectic structure. In addition, its finer microstructure produces smaller wear debris, contributing to the formation of a denser oxide film, thereby enhancing wear resistance.

Additive-Manufacturing-Induced Cell Structure in Stainless Steel 316L: 3D Morphology and Formation Mechanism

AbstractThe 3D morphology of the additive-manufacturing-induced cell structure is characterized and its formation in austenitic stainless steel 316L fabricated by laser powder bed fusion is analyzed. The experimental results demonstrate that the cell structure has a 3D prism-like morphology with a crystallography-dependent spatial orientation. The formation of the cell structure is discussed. It is proposed that both the liquid–solid transformation and thermal strain contribute to the formation: the initial cells form during the liquid–solid transformation, and the final dislocation cell structure is shaped by thermal-stress-induced deformation during cooling and subsequent thermal cycles.

Microstructural characterization, mechanical, and intergranular corrosion of an Inconel 625 - AL6XN super austenitic stainless steel welded joint

Microstructural characterization, mechanical, and intergranular corrosion of an Inconel 625 - AL6XN super austenitic stainless steel welded joint

Acoustic emission for real-time monitoring of interfacial erosion-corrosion of austenitic stainless steel in polluted phosphoric acid environment

Erosion-corrosion is a complex problem causing severe damage of austenitic stainless-steel equipment used in phosphoric acid production. Herein, time-resolved analyses of the acoustic emission (AE) signal together with the corrosion potential and weight loss were performed to online monitor and evaluate the dynamic degradation and depassivation of the 904L stainless steel under the effect of abrasive SiC particles. Important insights into the erosion-corrosion process are gained from the analysis of the AE waveform and its parameters. The characteristic root mean square (RMS) voltage and acoustic energy of AE signals revealed the self-healing difficulty of the passive film, of which the waveform of AE signals showed the appearance of imperfect continuous high intensity waveform, ranging from 0.1 to 0.4 mV. Evaluation of the average frequency spectrum showed that the amount of SiC particles alters the damage mechanism from AE events dominated by ploughing to AE events driven by micro-cutting. This suggests that the imperfect continuous waveform is possibly a precursor to the emergence of new acoustic sources (burst type): sudden jumps of chips from the cutting lips. This response resulted in a quasi-linearity in the mass loss of the alloy with the respective acoustic response at high particle loading (24 g L−1). The non-linear erosion-corrosion behavior suggests that the depassivation-repassivation events are dependent. These results render the combined AE and electrochemical analysis an effective sustainable approach for the online investigation of the synchronously changing erosion and corrosion rates.

Characterizing microstructural changes due to hydrogen embrittlement: Predicting mechanical properties according to hydrogen amount

To prevent the occurrence of severe industrial accidents caused by the hydrogen embrittlement (HE) of austenitic stainless steel, the mechanism of HE based on deformation behavior is identified, and a model equation for predicting the mechanical properties according to hydrogen amount is developed. The mechanical properties included with various amounts of hydrogen are evaluated via a slow strain rate test. Whereas the hydrogen trapping sites remain unchanged regardless of the hydrogen amount, the following vary: the microstructural characterizations formed by HE on the fracture surface, the work-hardening rate behavior with strain-induced martensite, and the phase fraction after fracture. Depending on the amount of hydrogen, either both ductility and brittleness or only brittleness may be observed. Based on these characteristics, the effect of hydrogen on deformation behavior is confirmed. By confirming the two effects of hydrogen on the deformation behavior, the phase fraction after fracture, elongation, and elongation loss are predicted according to the mechanical properties predicted according to hydrogen amount.

Serration-induced plasticity in phase transformative stainless steel 316L upon ultracold deformation at 4.2 K

Eras of hydrogen economy and aerospace have reignited interest in long-used austenitic stainless steel series owing to cost-effective and desirable mechanical properties for cryogenic applications. However, their mechanical response at liquid helium temperature (4.2 K), a critical temperature for liquid hydrogen and aerospace applications, is still arguable, and the associated underlying deformation mechanisms upon such ultracold deformation remain elusive. Here, we investigate the microstructural evolution of stainless steel 316L during ultracold tensile deformation at 4.2 K, showcasing microstructures about how tensile properties conducted at 4.2 K are distinguishable compared to the widely known ones at 77 K and about what deformation mechanism at 4.2 K prevails. We make clear that ultracold tensile deformation of stainless steel 316L enables a large ductility, increasing from 52 % at 77 K to 60 % at 4.2 K, even a drop of loading temperature from 77 K to 4.2 K, and even severe discontinuous plastic serration flow in the strain-stress curves at 4.2 K. Microstructural analysis of 4.2 K-ultracold deformation structure elucidates that simultaneous enhancement in strength and ductility is the consequence of both effects, i.e., the first-order solid-state transformation hardening effect by phase transformation of austenite to highly dislocated ά-martensite microstructure in the earlier plastic strain regime, followed by twinning-induced plasticity effect within the deformation-induced ά-martensitic body-centered cubic (BCC) grains in the later stages of deformation. The advent of deformation twin boundaries in ά-martensite grains acts as robust impediments to dislocation accumulation, resulting in substantial work hardening. Further, our high-resolution transmission electron microscopy analysis, taken from the regions of stress-induced adiabatic shear bands, reveals two significant features: (i) the intersection of plentiful coherent twins imposes atomic-scale stacking faults, nano-incoherent twins, and disconnections into BCC ά-martensite; (ii) at these localized temperature-rise regions, the ordered domain is often observed in the BCC martensite. Our findings can provide both a new paradigm of serration impact on mechanical properties and the origin of serrated yielding in the plastic strain regime at 4.2 K, guiding the twinning-utilized alloy design conformable for ultracold applications.

Buckling Strength of Cold-Formed Austenitic Stainless Steel SHS Columns Subjected to Concentric Axial Load

Buckling Strength of Cold-Formed Austenitic Stainless Steel SHS Columns Subjected to Concentric Axial Load

Plastic flow instability in austenitic stainless steels at room temperature: Macroscopic tests and microstructural analysis

AISI 304 steel experiences plastic flow instability during tension at room temperature if appropriate conditions are applied: a low strain rate and a sufficiently long gauge section of the sample. Then, propagation of the strain-localised band is activated. The electron backscattered diffraction (EBSD) research revealed that the reason is not only the difference in the content of the secondary phase – martensite α’ across the front face, but also the change in the volume fraction of austenite grains with Copper (Cu) and Goss-Brass (GB) orientation. Consequently, there is a division between two areas of high and limited deformation capacity. The tendency to maintain the continuity of deformation fields induces a massive rotation of austenite grains to Cu and GB orientations, which then undergo shearing and phase transformation. As a result, momentary strain accumulation leaves behind a stiffer zone. It is shown that the trapping of austenite grains prone to large deformations, inside the matrix with Cu and GB orientations, makes the formation of a plastic strain front possible. These features improve the ductility and strength of the 304 steel over 316L and 316LN at room temperature. The in-situ EBSD tension studies for the considered grades reveal three developing textures, with their comparison showing a gradual decrease in the preferences of the Cu and GB components. Thus, the appearing bands of the accumulated strains in 316L are limited by the Cu and GB areas, while such blockages do not occur in 316LN. The presented strengthening mechanism is confirmed by the digital image correlation (DIC) measurements. The root-mean-square (RMS) function of strains along the tensile direction, characterising the linear surroundings of the considered point, is introduced as a tool for linking the micro and macro scales. The experimental results provide a basis for explaining discontinuous front propagation at a temperature near 0 K.

Atomistic simulation of primary microstructure formation in metals during crystallization from the melt

Additive manufacturing of metallic parts by Selective Laser Melting (SLM) implies high temperature gradients and small volume of the melt bath. These conditions make the process scales close to those available for state-of-the-art massively parallel atomistic simulations. In the paper, the microscopic mechanisms responsible for the formation of primary microstructure during molten metal solidification are investigated using classical molecular dynamics (CMD). The 316L austenitic stainless steel with face centred cubic lattice, which is widely used in industry including SLM applications was chosen as a material for the CMD simulations. It was shown that solidified material inherits substrate defects and catches new ones, which interact with the solidification front thus producing the primary microstructure. Peculiarities of solidification in different crystallographic directions and solidification front interaction with grain boundaries and newly produced defects (mostly twin boundaries) as well as their formation are under study. Resulting microstructures of virtual samples are compared with those of real samples produced by SLM and analysed by the electron backscatter diffraction (EBSD) method. The comparison shows similarities of EBSD and CMD sample patterns and evidences for the capability of the large-scale atomistic simulations to reproduce main features of the microstructures formed in the metallic SLM additive production.