Properties Of Austenitic Stainless Steel Research Articles

Two-stage rolling and partial annealing enables heterogeneous structure and strength-ductility enhancement for austenitic stainless steel

Austenitic stainless steels are widely used in civil and defense industries. However, its low yield strength severely limits its fields of application. Under conventional processing routes, uniform grain refinement improves strength but unfortunately sacrifices ductility. In order to achieve the balance of strength and ductility, a new processing route of cold rolling and cryogenic rolling combined with partial annealing was proposed in this work. The results showed that the two-stage rolling and annealing produced dual-phase heterogeneous microstructure containing micron-sized grains (> 1 μm), submicron-sized grains (500-1000 nm), and ultra-fine grains (100-500 nm) arranged in lamellar structures. Compared with the single-stage cold rolled and annealed steel, the tensile strength increased to 1.1 GPa, which was slightly higher than the single-stage cryogenic rolled and annealed steel. Furthermore, the elongation was improved to 25%. The improvement of tensile properties was mainly due to the contribution of persistent hetero-deformation induced (HDI) hardening and twining induced plasticity (TWIP) effect to work hardening. This study not only proposed a simple and effective way to improve the mechanical properties of austenitic stainless steels, but also provided guidance for the design and development of high performance heterostructured materials.

Effect of cold rolling route and annealing on the microstructure and mechanical properties of AISI 316 L stainless steel

Since cross rolling promotes the transformation of austenite to deformation-induced α΄-martensite and increases the dislocation density in the retained austenite, the reversion/recrystallization annealing after cross rolling might be more effective to achieve finer grain sizes in metastable austenitic stainless steels. Accordingly, the effect of cold rolling route and annealing for grain refinement and improvement of mechanical properties of AISI 316 L stainless steel was systematically investigated in the present work. It was found and formulated that by increasing strain, the grain refinement efficiency during annealing is improved, the effect being more pronounced if the cold rolling step is applied by cross rolling instead of unidirectional rolling. The evaluation of tensile properties revealed that all cold rolling and annealing routes lead to significant improvements of mechanical properties in terms of strength and plasticity, the influence of cross rolling being more prominent again. Moreover, the cross rolling and annealing route led to a remarkable strength-ductility balance, which revealed the opportunities that this route can offer for the improvement of mechanical properties of austenitic stainless steels. Accordingly, the results of the present work may shed light on the further utilization of cold rolling route and annealing treatment.

Effects of cutting conditions on materials properties of austenitic stainless steels

Austenitic stainless steel SUS304 is widely used in various engineering applications, including semiconductor manufacturing equipment and food processing machinery, owing to its exceptional material characteristics such as non-magnetic properties, high corrosion resistance, strength, and ductility. However, concerns have arisen in recent years regarding potential alterations in the material properties of austenitic stainless steel after machining processes. As the cutting process was conducted widely to make various engineering applications with different machining conditions, an examination of the effect of machining conditions on the material properties is important. In the present study, the influence of cutting conditions on the microstructure and mechanical of SUS304 was experimentally and numerically investigated, where three types of ball-end mills with rake angles (- 20°, − 3°, and 5°) and different cutting speeds (50 m･min−1 and 100 m･min−1) were conducted with plane and side machining to investigate the cutting properties. Material properties of SUS304 can be changed by the cutting resistance of the above cutting process, in particular the low rake angles under plane machining, where the high cutting resistance makes high dislocation density and strain-induced martensite formation. This occurrence made the low corrosion resistance as well as low ductility. On the contrary, no significant effect of the cutting speeds on the cutting resistance was detected compared to the condition of the rake angle on the plane machining. The reasons behind this will be discussed in detail systematically in this paper. From this approach, it could be clarified to maintain the high material properties of SUS304 even after the cutting process, which could be useful to make design of the engineering applications.

Refinement MRP-135 constitutive equation model for tensile properties of austenitic stainless steel

This study focuses on analyzing and enhancing MRP-135 constitutive models, which are crucial for assessing the tensile properties of irradiated stainless steels in the reactor vessel internals of pressurized water reactors. The newly developed model, named M1, incorporates parameters from MRP-135, while minimizing modifications to ensure high compatibility with existing models. A significant improvement in M1 is the resolution of the inversion phenomenon observed between the yield strength and ultimate tensile strength at low temperatures in Type 316 stainless steel, a challenge previously identified in MRP-135 Rev. 2. M1 integrates the temperature effects from the earlier version, MRP-135 Rev. 1, to address this issue effectively. Additionally, for Type 316, M1 refined the equations to represent the cold work factor more accurately, enabling precise interpolation of strength variations across different levels of cold work from solution-annealed to cold-worked conditions. A comparative analysis of the M1 and the MRP-135 models against actual irradiated tensile test data for Type 304 and 316 stainless steel demonstrated the superior accuracy of M1, as indicated by a lower root-mean-square deviation. This study highlights the importance of continuous improvements in constitutive models, with future work aimed at further refining these models based on comprehensive irradiation test data.

The influence of structure, sensitization and corrosion on the fatigue properties of austenitic steel

The article will be focused on examining and comparing the influence of structure, sensitization and corrosion on the fatigue properties of austenitic stainless steel. The methodology of the experiment includes fatigue tests of samples attacked by intercrystalline corrosion. Therefore, the test samples were subjected to heat treatment for sensitization. Then these samples were subjected to long-term exposure in an aggressive corrosion solution. Experiments deal with microstructural material analysis, fractographic analysis, mechanical and fatigue tests.

The beneficial effect of yttrium microalloying in the solid solution treatment of AISI 321 stainless steel：Grain refinement and inclusions modification

Solid solution treatment is an important means of regulating the microstructure and mechanical properties of austenitic stainless steel, and a suitable solid solution process window is critical for austenitic stainless-steel service. In this paper, the effect of (RE) yttrium and solid solution temperatures on the microstructure and mechanical properties of austenitic stainless steel was investigated by adding trace amounts of RE yttrium to AISI 321 stainless steel with different solid solution temperature treatments. The results show that the austenite grains gradually coarsen with the increase of solid solution temperature, and the addition of RE yttrium effectively inhibits the coarsening of grains and keeps an excellent the comprehensive mechanical properties of AISI 321 stainless steel at 1150 °C for 30 min, this indicates that the addition of RE yttrium broad solid solution process window for AISI 321 stainless steel. In addition, the RE yttrium microalloying has a positive modification effect on the carbonitrides with refinement and spherization, which has a good contribution to the strength and plasticity retention of the material. This research is expected to provide more options for the heat treatment of austenitic stainless steels.

High-Efficient Gas Nitridation of AISI 316L Austenitic Stainless Steel by a Novel Critical Temperature Nitriding Process

To improve the surface properties of austenitic stainless steels, a thick S-phase layer was prepared by using a novel critical temperature nitriding (CTN) process. The properties of the thick S-phase layer were optimized by controlling the process parameters. The microstructures and phase compositions of CTN-treated layers were characterized by the optical microscope, scanning electron microscope and X-ray diffraction, respectively. The surface properties, including corrosion and wear resistance, were systematically investigated by the electrochemical workstation, micro-hardness tester and ball-on-disk tribometer, respectively. The results showed that a thick S-phase layer with a thickness of 18 to 25 μm can be fabricated in a short time by critical temperature nitriding, which represented higher efficiency than conventional low-temperature nitriding. Although the most top surfaces of CTN-treated layers contain massive iron nitrides, there are no precipitates in the inner nitrided layer. The electronic work function calculated by first-principles method has confirmed that those iron nitrides had a slight influence on the corrosion resistance of nitrided layers. The optimized CTN-treated layer exhibited a comparable corrosion resistance and wear resistance as the low-temperature nitrided layer. The CTN process is considered a potentially highly efficient surface modification method for austenitic stainless steels.

Boron as an alloying element for improving mechanical properties of austenitic stainless steels in laser powder bed fusion

Laser powder bed fusion provides freedom for producing complex shapes from a variety of alloys. Moreover, it also gives the possibility to manipulate the chemical composition of material during the printing process to improve its properties. The widely use 316L stainless steel exhibits the good corrosion resistance, high ductility, but comparably low strength characteristics. Various approaches can be applied to relax this limitation. Herein we use boron-containing additives to the feedstock powder for improving the microhardness of 316L stainless steel. Boron was found to reduce the porosity of the printed materials and increases the microhardness from 210 to 350 HV. The ultimate tensile strength doubled to 1045 MPa. Such findings allow using the modified 316L steel for tool printing.

Mechanical Properties of Austenitic Stainless Steel After Exposure to Elevated Temperature

Stainless steel has been widely used in the building industry as load-bearing elements such as beams and columns. Many fire accidents in stainless steel buildings were recorded, but only a few have collapsed entirely. These buildings can be rehabilitated and the undamaged parts can be reused, which reduces the economic losses in buildings exposed to fire. The residual mechanical properties of stainless steel after the fire, are the primary determinant of the validity of the stainless steel structure. In this paper, the effect of high temperatures and the time of exposure and cooling method on the mechanical properties of S304 stainless steel was studied. The specimens were heated to 800°C and 1000°C for different heating times (30, 60,90 and 120 minutes) and cooling methods (air-cooled and water-cooled). Results showed that the post-fire yield stress was reduced by 24% and 18% after heating to 800°C for 120minutes and cooled in water and air respectively. However, heating to 1000°C showed a marginal effect on the yield stress of air-cooled specimens and a clear reduction (29%) in the water-cooled specimens. Elongation capacity increased with heating time for 1000oC specimens but decreased for 800oC specimens in both cooling methods.

Anisotropic response of additively manufactured 316 L stainless steel towards low-temperature gaseous carburization

In order to modify the surface properties of austenitic stainless steel fabricated by Laser Powder Bed Fusion (L-PBF), low-temperature gaseous carburization (LTGC) was employed. During LTGC, a carburized case of expanded austenite forms at the surface, which contains a high surface carbon content (∼2.5 wt%), high nano-hardness (∼12.6 GPa), large compressive residual stresses (from −2.4 GPa to −3.2 GPa), and is free of carbide precipitates. In the expanded austenite zones, different residual stresses were measured with X-ray diffractometry (XRD) for the top plane, i.e. in the plane perpendicular to the build direction, and for the side plane. This anisotropy is suggested to be caused by grain-shape anisotropy for the different specimen planes and inherent to the hierarchical microstructures resulting from L-PBF.

Effects of aging and nitridation on microstructure and mechanical properties of austenitic stainless steel

Understanding the effects of in-service microstructural changes in metal alloys on the mechanical performance and remaining life of equipment is a critical part of integrity management in industrial plants. However, the effects of processes such as carburization or nitridation are not accounted for in industry-standard life assessment methodologies such as those provided in the API 579-1/ASME FFS-1: Fitness-For-Service standard. This is problematic for the austenitic stainless steel Alloy 800H, which typically operates in the creep regime and has been reported to suffer nitriding during high-temperature service in air. Despite this being one of the most common service environments for 800H, the impact of nitriding on in-service performance and implications for remaining life assessment have not been well-studied for this alloy. In this work, we characterize the microstructures of as-received, aged, and nitrided Alloy 800H tube material, and correlate observations with room-temperature tensile properties and high-temperature creep behavior. We show that while the creep properties of aged 800H material can be captured by the widely-used MPC Project Omega creep model and API 579-1 Omega properties for 800H, nitrided material properties fall outside of the expected bounds, and therefore remaining life cannot be reliably predicted using this method without experimental data.

Evolution of the structure, texture and mechanical properties of a cold-swaged austenitic stainless steel during post-deformation annealing

In this work, we studied the effect of annealing temperature on the structure and texture, as well as the mechanical properties of the austenitic stainless steel AISI 316. Initially, the program material was subjected to cold rotary swaging with a reduction of 95%. Studies showed the formation of the structure and texture gradient during preliminary plastic deformation. Annealing at low temperatures (500-600°C) provoked polygonization, while the intensity of the and texture components remained unchanged. After annealing at 700°С, the onset of recrystallization was observed only in the subsurface layers of the rod. As a result of annealing at 800–900°C, static recrystallization occurred over the entire cross section of the rod, which caused dissipation of the texture gradient. Annealing at temperatures of 400–600°C was accompanied by an increase in the strength and hardness characteristics. Meanwhile, ductility also increased with the annealing temperature. Annealing at 700°C resulted in softening of the program material almost to the level of the initial cold-swaged state and a significant increase in ductility up to 16%.

Evolution of the Structure, Texture, and Mechanical Properties of Austenitic Stainless Steel during Annealing after Cold Radial Forging

Evolution of the Structure, Texture, and Mechanical Properties of Austenitic Stainless Steel during Annealing after Cold Radial Forging

Influence of Inclusions in the Corrosion Behavior of Plasma Nitrided Stainless Steel

Plasma nitriding is a well‐established technique to improve hardness and tribological properties of austenitic stainless steel. It is proved that it is also possible to preserve the corrosion resistance after nitriding by controlling the process parameters such as time and temperature, obtaining the so‐called S phase. Herein, the corrosion behavior is evaluated for nitrided layers produced by three different plasma treatments: DC plasma nitriding, plasma immersion ion implantation (PIII), and low‐energy ion implantation (LEII), using different parameters in order to obtain the S‐phase in thickness from 1.2 to about 6 μm without nitride precipitation. The microstructure and chemical composition of the nitrided layers is characterized by means of X‐ray diffraction, secondary‐ion mass spectroscopy, and scanning electron microscopy–focused ion beam. The corrosion behavior is evaluated by means of the cyclic polarization tests in NaCl solution. The morphology of the corrosion attack is studied by optical microscopy and SEM‐FIB, revealing a change from crevice to pitting after the nitriding process. The inclusions are observed to be corrosion initiation sites. Due to this, the thickest nitrided layers (with high N concentration) show better corrosion behavior than the thinner ones.

Effect of Electropolishing Conditions on the Outgassing Properties of Stainless Steel Surface Electropolished by Wiping and Immersion Methods

The effect of electropolishing conditions on the outgassing properties of austenitic stainless steel (SUS316L) electropolished by a wiping method (WiEP) and an immersion method (ImEP) was investigated using thermal desorption spectroscopy. In the case of electropolishing by the WiEP in which the metal surface was wiped with an electrolyte-solution-impregnated felt wiper cathode, the SUS316L surface became smoother and the amount of outgassing decreased as the applied voltage (4-8 V) increased. In the case of electropolishing by the ImEP, the SUS316L surface became smoother and the amount of outgassing decreased as the current density (8-15 A dm−2) increased. After electropolishing by the WiEP at higher applied voltages and the ImEP at higher current densities, diffusible hydrogen desorbed from the SUS316L surface below 723 K was almost completely removed, however most of the non-diffusible hydrogen remained. These results suggest that the migration of diffusible hydrogen to the SUS316L surface is enhanced by the increase in the applied voltage of electropolishing.

Mechanical Properties of σ-Phase and Its Effect on the Mechanical Properties of Austenitic Stainless Steel

In this present paper, the mechanical properties of σ-phase and its effect on the mechanical properties of 304H austenitic stainless steel after servicing for about 8 years at 680–720 °C were studied by nano-indentation test, uniaxial tensile test, and impact test. The results showed that the nano-hardness (H), Young’s modulus (E), strain hardening exponent (n), and yield strength (σy) of σ-phase were 14.95 GPa, 263 GPa, 0.78, and 2.42 GPa, respectively. The presence of σ-phase increased the hardness, yield strength, and tensile strength, but greatly reduced the elongation and impact toughness of the material.

Ti-containing 316L stainless steels with excellent tensile properties fabricated by directed energy deposition additive manufacturing

Additive manufacturing is used to produce complex shapes, and it has been actively investigated. In this study, 316L stainless steels with various amounts of Ti were fabricated using directed energy deposition. The addition of Ti changed the microstructure and significantly improved the tensile properties of austenitic stainless steels. The addition of Ti led to distinct microstructural evolutions, such as changes in the cellular structure, grain size and Ti-rich particle. Microstructural changes such as change in change to equiaxed cellular structure and grain refimenet were due to Ti-rich particles acting as new nucleation sites and suppressing the segregation of solute atoms. In particular, the yield strength, tensile strength, and elongation of the specimen with 2 wt% Ti were 637 MPa, 857 MPa, and 43%, respectively, which were considerably higher than those of 316L stainless steel without Ti. Therefore, the addition of Ti is a suitable strategy for improving the tensile properties of additively manufactured 316L stainless steel.

Complementary transient thermal models and metaheuristics to simultaneously identify linearly temperature-dependent thermal properties of austenitic stainless steels

This paper presents an experimental approach for simultaneously identifying the temperature-dependent thermal conductivity (k) and specific heat (c p ) of 304 austenitic stainless steel (ASS) using complementary transient experiments and metaheuristics. Inverse thermal analysis was based on two heat conducting solids with different geometries. In estimation problems in general, one seeks to obtain as much sensitive data as possible using as few sensors as possible. Single thermocouple data were collected for each thermal model. An objective function fitting these complementary measurements to the corresponding numerical temperatures was minimized using the Lichtenberg algorithm. This metaheuristic algorithm takes advantage of more sensitive information provided by using complementary data, enabling for an accurate inverse solution, even when dealing with wide search ranges. The proposed technique provides a cost-effective and robust property estimation from tests conducted at room temperature. Single-step estimation occurred throughout the whole temperature domain to determine the parameters for linear functions representing the temperature dependence of k and c p . The obtained lines agreed well with curves from the literature. The 95% confidence bounds for the parameters of interest indicated deviations below ± 8.5%. Error analysis considering numerical and experimental processes showed an uncertainty close to ± 3%, applied to all estimated parameters.

Improving mechanical properties of austenitic stainless steel by the grain refinement in wire and arc additive manufacturing assisted with ultrasonic impact treatment

In this study, the ER321 stainless steel is fabricated by wire and arc additive manufacturing (WAAM) assisted with ultrasonic impact treatment (UIT). The mechanical properties and microstructure characterizations of ER321 stainless steel with and without UIT are investigated. It is found that grain structure of ER321 stainless steel is reduced to equiaxed dendrites (with UIT) from coarse columnar dendrites (without UIT). The UIT effectively refines grain sizes that decreases by ∼150% and homogenizes the grain structure of the deposition layers. Simultaneously, the UIT also facilitates the recrystallization that leads to the reduction of dislocation and texture densities. Furthermore, the improvement of grain structure enhances yield strength (∼10.5%), ultimate tensile strength (∼3.7%), microhardness (∼12.5%) and elongation of ER321 stainless steel. The grain boundary strengthening is the main strengthening mechanism, which leads to the yield strength increment of ER321 stainless steel under UIT condition. A way to effectively control grain structure in additive manufacturing-fabricated metal products using an UIT technique is provided in this work.

Fire resistance design of austenitic SUS316 stainless columns subjected to axial compression

To explore the effect of cold-working on the properties of austenitic stainless steel, a material mechanical property test of austenitic SUS316 stainless steel coupons extracted from cold-formed RHS columns at elevated temperatures was conducted. Based on the fire test of 5 austenitic stainless SHS columns subjected to axial compression, a refined finite element model was established. A single parametric analysis of different parameters, cross-sectional area, height-thickness ratio, initial overall imperfection, eccentricity, slenderness ratio, aspect ratio and load ratio was conducted, mainly investigating the effects on the critical temperature and maximum axial displacement. As the effect of the load ratio was the most significant, a multiparameter analysis of the load ratio with other parameters was further conducted. Presently, the design methods in EN 1993–1-2 for carbon steel columns are also applied to stainless steel columns, where section classification is needed. Based on numerous parametric analyses, the design methods in EN 1993–1-2 were assessed and modified. EN 1993–1-2 underestimated the bearing capacity of stainless steel SHS and RHS columns, and the modified method improved the utilization rate of stainless steel. A new method for evaluating the bearing capacity of stainless SHS and RHS columns using the maximum axial displacement was proposed, for which the section classification was not needed. As a preliminary study, the new method was only applicable to stainless SHS and RHS columns with load ratios between 0.2 and 0.6, which was also the most commonly applied scope in engineering.