SUS304 Austenitic Stainless Steel Research Articles

Solid‐State Bonding of Iron or Steel with Stainless Steels by Spark Plasma Sintering Bonding

In this study, pure iron, S45C carbon steel (Fe–0.45mass%C), carburized iron, and nitrided iron are bonded with two types of stainless steels, i.e., SUS304 austenitic stainless steel (Fe–18mass%Cr–8mass%Ni) with face center cubic structure or SUS430 ferritic stainless steel (Fe–18mass%Cr) with body center cubic structure by a spark plasma sintering (SPS) machine. Bonding experiments are carried out by SPS bonding. It is found that the bonding temperature of the S45C/SUS samples is lower than that of Fe/SUS samples, and carbon atoms in the S45C play important role on the bonding performance. The bonding temperature for SUS304/SUS430 sample is more than 30 °C higher than those for the Fe/SUS and S45C/SUS samples. The presence of thin chromium oxides on both stainless steels reduces the bonding performance of SUS304/SUS430 sample. Better bonding performance is found for the carburized and nitrided iron for bonding with stainless steels. However, continuous single‐phase layer on the surface leads to reduce the bonding performance. It is concluded that not only the concentration of carbon and nitrogen but also the phase configuration in the iron at interface strongly influences the bonding performance between iron alloys and stainless steels by SPS bonding.

Application of small punch test to estimate mechanical behaviour of SUS304 austenitic stainless steel

The small punch test with an application of a relatively small specimen has recently become a reliable material mechanics testing method. In this study, the small punch test is set up based on the conventional mechanical testing machine for SUS304 stainless steel to evaluate the mechanical properties of SUS304 steel at different displacement rates of the punch in quasi-static loading condition in the case of with and without heat treatment. Although heat treatment has an insignificant effect on the microstructure and hardness of the material, the mechanical properties of the material in the small punch test are greatly reduced after heat treatment. Both cases with and without heat treatment have a similar tendency for the rate - sensitivity of the applied force - displacement curve. A higher value of force is applied to obtain the same value of displacement at a low displacement rate in the stable plastic deformation zone. Meanwhile, the maximum value of applied force is higher at a higher displacement rate in the stage that initiation of crack might appear. In the examined range of displacement rate, a positive rate - sensitivity of displacement at the maximum force. Therefore, a correlation between equivalent fracture strain and fracture toughness of the material can be achieved.

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.

Hardness Prediction of the Heat-Affected Zone in Multilayer Welded SUS316 Stainless Steel Based on Dislocation Density Change Behavior

The effects of strain hardening and recovery/recrystallization on the hardness of the heat-affected zone (HAZ) in multilayer welded austenitic stainless steel SUS316 were investigated in this study. The results revealed that strain hardening due to welding strain and softening due to recovery/recrystallization were the dominant factors affecting the hardness change in the HAZ during multilayer welding process. Furthermore, the relationship between the strain and dislocation density and that between the recovery/recrystallization and dislocation density were quantitatively investigated using positron annihilation lifetime spectroscopy. Based on these results, a new hardness prediction method based on the change in dislocation density in the HAZ during multilayer welding was proposed. The hardness values in the HAZ after the multilayer welding were predicted based on the simulated strain and thermal history, and the calculated hardness values agreed well with the measured results. This indicates that the newly proposed hardness prediction method based on the dislocation density change behavior in the HAZ during multilayer welding is valuable and effective for selecting the appropriate welding conditions before actual welding.

Modeling of welding residual stress in a dissimilar metal butt-welded joint between P92 ferritic steel and SUS304 austenitic stainless steel

In this study, a butt-welded joint between P92 ferritic steel and SUS304 austenitic stainless steel was fabricated with a nickel-based filler material. Based on Sysweld software, three-dimensional thermal-metallurgical-mechanical coupled finite element analyses were performed to investigate the hardness and welding residual stress in the welded joint. In the material behavior model, various factors influencing the formation and distribution of hardness and welding residual stress were carefully considered, including the austenitic transformation, martensitic transformation, and the tempering of martensite in P92 steel; the isotropic strain hardening, annealing effect, and melting effect of all materials; and the differential thermal expansion between dissimilar metals. The neutron diffraction method and hole-drilling strain gauge method were applied to measure the profiles of residual stress of the welded joint, respectively. Hardness mapping was performed on a weld cross-section specimen. The predicted results of welding residual stress and hardness are in good agreement with the measurements, respectively. The peak residual stresses in longitudinal and transverse directions are above 600 MPa in P92 steel. There are high tensile residual stress and significant cold work near the weld root in SUS304 stainless steel. The solid-state phase transformation induces compressive longitudinal residual stress in the heat-affected zone, high tensile transverse residual stress near the weld toe in P92 steel, and a significant stress gradient. The tempering effect can reduce the hardness and tensile residual stress in the heat-affected zone of P92 steel. The formation mechanism of welding-induced residual stress was illustrated based on the Satoh test. The effects of peak temperature, internal restraint, and differential thermal expansion are found to be decisive for the formation of residual stress. Large tensile residual stress can be generated with internal restraints, which promote the stress increase and lead to material yielding. A restraint factor was proposed for the quantitative assessment of stress evolution.

Improved Wear and Corrosion Resistance in TiC-Reinforced SUS304 Stainless Steel

Herein, the vacuum arc-melting process is applied to incorporate various amounts of Ti and C into SUS304 austenitic stainless steel based on the high-entropy alloy concept to obtain wear- and corrosion-resistant alloys with in situ carbide reinforcements. Five compositions containing the equivalent of 5, 10, 15, 20, and 25 volume percentages of TiC in SUS304 stainless steel, named A1, A2, A3, A4, and A5, respectively, were designed, melted, and solidified by the arc-melting method. Microstructural analyses, hardness measurements, immersion tests in four corrosive solutions, electrochemical measurements in a 3.5 wt % NaCl(aq) solution, and tribological tests were conducted to determine the properties and explain the relevant mechanisms. A1 exhibited a eutectic structure between FCC dendrites, while A2, A3, A4, and A5 possessed proeutectic dendritic TiC, FCC dendrites enveloping the TiC dendrites, and a eutectic structure. A5 represents the optimal composition. Its hardness, wear resistance, and corrosion resistance are 2, 14, and 4 times higher than those of SUS304, respectively. Additionally, its wear resistance is 2.5 times that of high-chromium cast iron. Consequently, A5 could have a 2.5-fold longer lifetime in wear operation. Therefore, A5 could be potentially applied in corrosive and abrasive environments, such as rotary shafts, rotors, bearings, and structural parts in food, chemical, and optoelectronic industries.

Improvement of fretting fatigue strength by carbon monoxide and catalyst activation under chemomechanical effects of fretting

It is known that the fretting fatigue strength in hydrogen (H2) gas is lower than that in air. The objective of this study is to mitigate the hydrogen effect during the fretting fatigue test in H2 gas by adding carbon monoxide (CO) to the H2 environment. The expected CO effect was reduction in the hydrogen uptake into the material following deactivation of the catalytic surface where H2 molecules dissociate into H atoms. However, an unexpected result, which was unique in fretting, was obtained. The fretting fatigue test using JIS SUS304 austenitic stainless steel was performed in H2, argon (Ar), 2 vol% CO mixed H2, and 2 vol% CO mixed Ar gases. The fretting fatigue strengths in the CO-mixed gases were significantly improved. For instance, the fretting fatigue life at σa = 240 MPa was 8.8 × 105 cycles in the H2 and 107 cycles or longer in the CO mixed H2. The cause of the improved fretting fatigue strength was the formation of amorphous carbon between the contacting surfaces during the fretting. The carbon reduced the tangential force coefficient between the contacting surfaces from around 0.6 in the H2 to 0.2 or less in the CO mixed H2. The reduced tangential force resulted in improvement of the fretting fatigue strength. Although the detailed mechanisms of the carbon deposition were unclear, it is plausible that the catalytic action of the metal surface for the CO decomposition into C and O was activated by the effect of fretting, such as removal of the surface oxide layer and other chemomechanical effects.

A new numerical model to predict welding-induced sensitization in SUS304 austenitic stainless steel joint

In this paper, a SUS304/P92 dissimilar metal butt-welded joint was fabricated, and the welding-induced sensitization of SUS304 austenitic stainless steel in this joint was investigated via the numerical simulation and experiment. In the proposed new numerical model, the time–temperature-precipitation diagram and the time–temperature-sensitization diagram were used to simulate the region and the degree of sensitization, respectively. The predicted degree of sensitization (DOS) in the weld decay zone matched the electrochemical measurements well. Based on the simulation results, the evolution of DOS at the austenitic stainless steel side during the multi-pass welding process was examined in detail. The obtained results can help evaluate the material susceptibility to stress corrosion cracking in austenitic stainless steel joints.

Monitoring of high-speed laser welding process based on vapor plume

The increase of welding speed can improve the productivity of laser welding. The behavior of vapor plume is an important indicator reflecting the state of the laser welding process. However, the behavior of vapor plume in high-speed laser welding (whose welding speed is higher than 10 m/min) has not been studied adequately. In this research, images of the vapor plume in high-speed laser welding of SUS304 austenitic stainless steel are captured through high-speed imaging for the monitoring of the welding process. Characteristics of the vapor plume are extracted with image processing, and the influences of laser power and welding speed on these characteristics are analyzed. The relationships between the behavior of vapor plume and melt pool are discussed, and three ejection regimes of the vapor plume are proposed. In order to predict the occurrence of humping, which is a typical defect in high-speed laser welding, samples are built by applying a time sliding window and then a classification model is built with the random forest. In addition, the importance of features in the classification is analyzed. The test results show that the proposed method can predict the humping defect in high-speed laser welding accurately.

Development of impact small punch test for investigating energy absorption

Energy absorption of steel with Transformation-induced Plasticity (TRIP) under bending deformation needs to be carefully examined at very high strain rates for its new applications in the automotive industries. Energy absorption members made of the steel can suppress severe damages by traffic accidents. However, it is difficult to apply three-point bending test based on the split Hopkinson pressure bar (SHPB) method because a use of a thick pre-cracked specimen is required for such materials with high toughness. In contrast, if the impact small punch test, which dominant deformation mode of a relatively-small specimen is bending, is established, its experimental arrangement might become simpler and the SHPB technique is applicable. In this study, a novel and reliable impact small punch testing method based on SHPB technique with high accuracy is developed for an investigation on impact energy absorption of the steel with TRIP. Besides, its design, feasibility and validity are confirmed by finite element simulation for austenitic stainless steel SUS304, a representative of steel with TRIP. The obtained experimental as well as computational results show that the developed testing apparatus for impact small punch test based on SHPB technique is reliable and reasonable for the investigation on impact energy absorption of the high toughness material including steel with TRIP.

Duplex treatment of active screen plasma nitriding and amorphous hydrogenated carbon coating

Active screen plasma nitriding (ASPN) has recently emerged as an alternative nitriding technology with the potential to eliminate problems such as edge effect, arcing, and hollow cathode effects, associated with conventional direct current plasma nitriding technology. Amorphous hydrogenated carbon (a-C:H) is a thin film characterized by high hardness, a low friction coefficient, and superior wear resistance. However, the high residual stress of the a-C:H leads to poor adhesion between the a-C:H film and substrate. This study's objective was to investigate the properties of samples obtained by a duplex treatment (i.e., ASPN and a-C:H coating) of SUS304 austenitic stainless steel. The ASPN treatment was performed in 25% N2 + 75% H2 atmosphere for 5 h at 673 K under 600 Pa. An a-C:H film was coated using RF plasma-enhanced chemical vapor deposition in the presence of methane for 90 min. The results indicated that an a-C:H film with an S-phase interlayer formed after the duplex treatment of ASPN and a-C:H coating. Moreover, this treatment improved the adhesion and wear properties of the resulting sample.

Study on the Grain Boundary Misorientation Change and Texture Evolution in SUS304 Austenitic Stainless Steel at Low Cold‐Rolling Reductions

To study the grain boundary misorientation change and texture evolution in austenitic stainless steel at low cold‐rolling reductions, SUS304 austenitic stainless steel samples with a cold‐rolling reduction of 5%, 8%, 10%, 15%, 20%, and 23% are prepared. The electron backscatter diffraction analysis reveals that with the increase in the cold‐rolling reduction, the proportions of low‐angle grain boundary (LAGB) and high‐angle grain boundary (HAGB) gradually increase and decrease, respectively. The decrease in HAGB reduces the toughness of the material. With the increase in cold‐rolling reduction, the strain area inside the material increases, which enhances the toughness and strength of the steel plate. Austenite textures at different cold‐rolling reductions are composed of Brass, Goss, S, and shear texture {011}<122>. The intensity of the Brass‐type texture increases with the increasing cold‐rolling reduction. The martensite texture mainly consists of R‐Cube, Brass, shear texture {111}<110>, {111}<112>, and {332}<113>. When the cold‐rolling reduction is less than 15%, the Brass texture appears in the α′‐martensite phase. In addition, the intensity of the R‐Cube texture increases with the increasing cold‐rolling reduction. The martensite phase texture is affected by the austenite phase texture, and its formation can be attributed to the Kurdjumov–Sachs orientation relationship.

Comparative Investigation of the Mechanical and Wear Properties of Multilayer Si-DLC/DLC Films

In this study, multilayer diamond-like carbon films 1 µm thick with different numbers of multilayer repetitions were deposited onto austenitic stainless steel SUS304 substrates using different source gases. The influence of the gas and the difference in the number of multilayer repetitions on the adhesion strength and wear resistance of the films was subsequently investigated. The samples were subjected to cross-sectional microstructure observations, elemental analysis by glow-discharge optical emission spectroscopy, nano-indentation tests, Rockwell indentation tests, friction and wear tests, and delamination tests. The nano-indentation tests showed that the films prepared using C2H2 gas were harder than those prepared using CH4 gas. In addition, irrespective of the gas used, the film hardness was improved when four layers rather than two layers were deposited. However, the hardness of the eight layers film decreased. The Rockwell indentation tests showed no improvement in adhesiveness when the gas or the number of multilayer repetitions was varied. The wear tests revealed that the friction coefficient of the films prepared using C2H2 gas was smaller than that of films prepared using CH4 gas. No difference was observed with increasing number of multilayer repetitions. The delamination tests showed that the distance until delamination of the films prepared using C2H2 gas was longer than that of the films prepared using CH4 gas. In addition, the distance until delamination was improved by changing the number of multilayer repetitions from two layers to four layers for both gases but decreased when the number of repetitions was extended to eight layers. In this study, the value of H/E (hardness/Young’s modulus) increased and various characteristics improved with increasing number of multilayer repetitions.

Effects of Helium Production and Displacement Damage on Microstructural Evolution and Mechanical Properties in Helium-Implanted Austenitic Stainless Steel and Ferritic/Martensitic Steel

The effects of helium concentration and displacement damage on microstructural evolution at low dpa and low helium concentration were mainly investigated in specimens of austenitic stainless steel 316FR or SUS304 and a high chromium martensitic steel (HCM12A). The 316FR and HCM12A specimens were implanted uniformly with helium at 823 K up to 30 appm-He or 50 appm-He by 50 MeV cyclotron accelerator using energy degraders. After the helium implantation, the microstructures were examined by a transmission electron microscopy and positron annihilation lifetime measurements. Irradiation hardening behaviors were analyzed using SUS304 and HCM12A steels at 823 K implanted with He ion up to 100 appm with different He/dpa ratios in the HIT ion irradiation experiments and the hardening behaviors were examined by nano indentation method. In the irradiation and annealing specimens, these mechanical properties and microstructures were examined to understand the effects of helium production, displacement damage and annealing on microstructural development, and kinetic Monte Carlo (kMC) simulations were also performed to understand the microstructural development, and the results were compared with the results of TEM observation and positron annihilation lifetime measurements. Important some differences in the microstructural developments such as cavity formation and growth between austenitic stainless steel and martensitic steel were observed in low dpa and low helium concentration conditions.

Effect of Hydrogen on Creep Properties of SUS304 Austenitic Stainless Steel

The objective of this study is to derive mechanistic insight into the degradation of metals in high-temperature hydrogen in order to enable the safety of evolving hydrogen technologies that operate at elevated temperature. Creep testing was performed in argon and hydrogen gases under absolute pressure of 0.12 MPa at 873 K. The material was JIS SUS304 austenitic stainless steel. Results revealed that the creep life (time to failure) and creep ductility (strain to failure) of the SUS304 in hydrogen gas and in argon displayed opposite trends. While the creep life (time to failure) of the SUS304 in hydrogen gas was significantly shorter than that in argon, creep ductility (strain to failure) was higher in hydrogen. Associated with the relatively higher creep ductility, evidence of transgranular microvoid coalescence was more prevalent on fracture surfaces produced in hydrogen compared to those produced in argon. In addition, analysis of the steady-state creep relationships in hydrogen and argon indicated that the same creep mechanism operated in the two environments, which was deduced as dislocation creep. Regarding the mechanisms governing reduced creep life in hydrogen, the effects of decarburization, carbide formation, and the hydrogen-enhanced localized plasticity mechanism were investigated. It was confirmed that these effects were not responsible for the reduced creep life in hydrogen, at least within the creep life range of this study. Alternately, the plausible role of hydrogen was to enhance the vacancy density, which led to magnified lattice diffusion (self-diffusion) and associated dislocation climb. As a consequence, hydrogen accelerated the creep strain rate and shortened the creep life.

An experimental study on strain-induced martensitic transformation behavior in SUS304 austenitic stainless steel during higher strain rate deformation by continuous evaluation of relative magnetic permeability

In the past, it is experimentally revealed that the stacking fault energy (SFE) for the strain-induced martensitic transformation (SIMT) in metastable austenitic stainless steels is positively dependent on the strain rate, especially at impact strain rate; however, a conflicting view is recently reported that it is independent on the strain rate. To solve the conflict on the rate sensitivity of SFE, a non-destructive method to determine the martensitic volume fraction precisely under quasi-static tensile loading is effective and a method for measuring the relative magnetic permeability using AC voltage has been previously developed. However, this technique overestimates magnetic permeability during impact testing due to the eddy current generated at high frequencies, which can be avoided by applying DC voltage to the primary coil. In this work, quasi-static and impact tensile tests are performed on commercial SUS304 metastable austenitic stainless steel at various strain rates to determine its relative magnetic permeability during deformation. The obtained experimental data are utilized to investigate the SIMT behavior of SUS304 steel under quasi-static and impact tensions. As a result, it successfully captures the SIMT behavior in SUS304, especially during high strain rate deformation and the role of SFE on SIMT at higher strain rate is discussed.

Effects of Nanometric Control in Tool Cutting Edge Sharpness on Micropunching of Austenitic Stainless Steel SUS304

Effects of Nanometric Control in Tool Cutting Edge Sharpness on Micropunching of Austenitic Stainless Steel SUS304

非熔透激光搭接焊SUS304奥氏体不锈钢无焊缝侧变形机理

非熔透激光搭接焊SUS304奥氏体不锈钢无焊缝侧变形机理

Fatigue strength assessment of SUS316 by small bulge fatigue (SBF) test

A new fatigue test apparatus with a small disk-type specimen (8 mm in diameter) was developed in the authors’ group. This testing technique was termed “Small Bulge Fatigue (SBF) test”. Unlike the small punch (SP) test, a hydraulic bulging method was adopted for avoiding problems attributable to the contact or the friction between ball and specimen. A cyclic oil pressure could be alternatively applied to both specimen surfaces at the frequency of 10 Hz. The specimen thickness of central region (gauge area) was relatively reduced to avoid cracking at the edge of specimen, and the characteristic small disk-type specimen with flat and concave surfaces was proposed considering machinability and handleability. Austenitic stainless steel SUS316 was subjected to the preliminary test using this newly developed testing technique. The obtained results indicated that this SBF test had a potential for fatigue strength assessment.

Dissolution Behavior of Iron and Steel Materials in Liquid Magnesium

The dissolution of metallic elements from Fe and steel materials into pure liquid Mg was investigated with the aim of improving control of impurities in Mg during processes such as Mg-alloy production and Ti smelting. Pure Mg was melted between 1073 and 1323 K (800 and 1050 °C) for 24 to 96 hours in closed crucibles made of pure Fe, low-carbon steel, or austenitic stainless steel SUS316. From the experiments using the pure Fe crucible, the relationship between the solubility of Fe in liquid Mg [Csol,Fe (mass pct)] and temperature [T (K)] was determined to be log(Csol,Fe) = − 3.67 × 103/T + 2.48 (± 0.06), from which the standard Gibbs energy of Fe dissolution in liquid Mg was evaluated. The amount of Fe dissolved from low-carbon steel was the same as that from pure Fe. From SUS316, not only Fe but also Cr and Ni dissolved into liquid Mg; the Fe and Cr concentrations in liquid Mg did not change significantly over time, whereas the Ni concentration increased monotonically. Preferential Ni dissolution resulted in a Ni-poor layer on the SUS316 surface. Finally, using the experimental data of Fe dissolution from low-carbon steel, the Fe contamination route in the current Ti smelting process, where a large amount of Mg is used as a reducing agent, is discussed.