SUS316L Stainless Steel Research Articles

Indentation-Free Resistance Spot Welding of SUS301L Stainless Steel

Paint-free bodywork has become an attractive alternative for rail vehicles, in the direction of easy maintainability and low manufacturing costs. However, conventional resistance spot welding inevitably leaves indentation marks to detrimentally reduce the optical homogeneity of the paint-free bodywork. In light of this, indentation-free resistance spot welding is proposed for joining SUS301L stainless steel sheets in order to achieve superior surficial integrity. A tiny SUS301L steel ball with a diameter of 1.5 mm was chosen as the intermediate filler between two steel sheets to avoid the formation of surficial indentation. The influence of welding current and welding time on the mechanical properties of joints was studied. The optimal parameters of the mechanical properties were obtained when the welding current was 8.0 kA, the welding time was 150 ms, the electrode pressure was 0.35 MPa, and the electrodes were cylindrical planar electrodes, which was determined by comparing the tensile shear test results. The surficial indentation depth was less than 1% of the plate thickness, and no observable indentations were seen on the surface of the optimized welding spots.

The effect of oxide scale on the corrosion resistance of SUS301L stainless steel welding joints

The effect of thermal oxidates on the corrosion of SUS301L stainless steel welded joint was investigated using electrochemical corrosion test and TEM microstructure observation. Activation dissolution behavior without passive region was found in the potentiodynamic polarization curves on the welding zone and heat affected zone. The activation corrosion is related to the preferential dissolution of the NiFe layer at the interface between chromium oxide and substrate. However, the passive region in the polarization curve reappears after the unstable NiFe dissolves in the salt-frog test. The passivation behavior due to microstructure evolution beneath the thermal oxide film was discussed during the corrosion process.

A semi-empirical life-prediction model for multiaxial ratchetting-fatigue interaction of SUS301L stainless steel tubular welded joint

Based on the strain measured in the SUS301L stainless steel tubular welded joint in the asymmetrically stress-controlled multiaxial low-cycle fatigue tests by using the digital image correlation (DIC) method, the dependence of fatigue life on the loading level and loading path is well explained by discussing the multiaxial ratchetting-fatigue interaction in the fatigue failure zone of welded joint. To reflect the contribution of mean stress to the non-proportionality of loading path, a new non-proportionality factor is defined. And then the path-dependent damage parameters of pure fatigue damage and additional ratchetting one are proposed in a strain form and validated. Finally, a multiaxial life-prediction model is constructed through addressing the concurrent efforts of additional ratchetting damage and pure fatigue one to predict the multiaxial fatigue life of welded joint. The results demonstrate that the predicted multiaxial fatigue lives are well expected and all life data fall in the twice error bands regarding to the experimental ones.

Effect of Rotational Velocity on Mechanical and Corrosion Properties of Friction Stir-Welded SUS301L Stainless Steel.

Friction stir welding was utilized to obtain high-quality SUS301L stainless steel joints, whose mechanical and corrosion properties were thoroughly evaluated. Sound joints were obtained with a wide range of rotational velocities from 400 to 700 rpm. The microstructures of the stir zone primarily consisted of austenite and lath martensite without the formation of detrimental phases. The ultimate tensile strength of the welded joints improved with higher rotational velocities apart from 400 rpm. The ultimate tensile strength reached 813 ± 16 MPa, equal to 98.1 ± 1.9% of the base materials (BMs) with a rotational velocity of 700 rpm. The corrosion resistance of the FSW joints was improved, and the corrosion rates related to uniform corrosion with lower rotational velocities were one order of magnitude lower than that of the BMs, which was attributed to the lower martensite content. However, better anti-pitting corrosion performance was obtained with a high rotational velocity of 700 rpm, which was inconsistent with the uniform corrosion results. It could be speculated that a higher martensitic content had a negative effect on the uniform corrosion performance, but had a positive effect on the improvement of the anti-pitting corrosion ability.

Microstructural evolution and corrosion responses of friction stir welded SUS301L stainless steel

As a typical manifestation of elemental segregation of stainless steel, chromium depletion was often brought about by welding, leading to undesirable corrosion resistance. In light of this, we employed friction stir welding through WC-W composite welding tools to achieve sound joints of SUS301L stainless steel, with corrosion resistance exceeding that of the base material (BM). A higher austenite fraction of 20.8% enhanced corrosion resistance since the corrosion potential of austenite is nobler than that of martensite. Austenite was not decomposed into harmful σ-phases due to the shorter holding time at the elevated temperature, thus enhancing the homogeneity of the microstructure. The ultimate tensile strength of the welded joints reached 820 MPa, which was equal to 98.9% of BM. The pitting potential of the joint was increased by 0.078 V, indicating that the stability of the passive films was improved, and the ability to resist the corrosive medium was strengthened. Chromium depletion was eliminated, resulting in no sensitivity to intergranular corrosion.

Chloride-Induced Stress Corrosion Cracking of Friction Stir-Welded 304L Stainless Steel: Effect of Microstructure and Temperature

Dry storage canisters of used nuclear fuels are fabricated using SUS 304L stainless steel. Chloride-induced stress corrosion cracking (CISCC) is one of the major failure modes of dry storage canisters. The cracked canisters can be repaired by friction stir welding (FSW), a low-heat input ‘solid-phase’ welding process. It is important to evaluate the ClSCC resistance of the friction stir welded material. Stress corrosion cracking (SCC) studies were carried out on mill-annealed base materials and friction stir welded 304L stainless U-bend specimens in 3.5% NaCl + 5 N H2SO4 solution at room temperature and boiling MgCl2 solution at 155 °C. The engineering stress on the outer fiber of the FSW U-bend specimen was ~60% higher than that of the base metal (BM). In spite of the higher stress level of the FSW, both materials (FSW and BM) showed almost similar SCC failure times in the two different test solutions. The SCC occurred in the thermo-mechanically affected zone (TMAZ) of the FSW specimens in the 3.5% NaCl + 5 N H2SO4 solution at room temperature, while the stirred zone (SZ) was relatively crack-free. The failure occurred at the stirred zone when tested in the boiling MgCl2 solution. Hydrogen reduction was the cathodic reaction in the boiling MgCl2 solution, which promoted hydrogen-assisted cracking of the heavily deformed stirred zone. The emergence of the slip step followed by passive film rupture and dissolution of the slip step could be the SCC events in the 3.5% NaCl + 5 N H2SO4 solution at room temperature. However, the slip step height was not sufficient to cause passivity breakdown in the fine-grained SZ. Therefore, the SCC occurred in the partially recrystallized softer TMAZ. Overall, the friction-stirred 304L showed higher tolerance to ClSCC than the 304L base metal.

Electrochemical polymerization of PEDOT:PSS with graphene oxide and silver nanoparticles for antibacterial coating and SERS detection

This study involved the use of electrochemical polymerization to coat poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS) and graphene oxide (GO) onto SUS316L stainless steel substrates, aiming to produce PEDOT:PSS and GO@PEDOT:PSS films. Following this, Ag@PEDOT:PSS and GO/Ag@PEDOT:PSS films were developed through the electrochemical deposition of silver nitrate. Electrochemical impedance spectroscopy (EIS) indicated that adding GO increased the impedance of film, while AgNPs deposition decreased it, thereby enhancing conductivity. Films with AgNPs showed surface enhanced Raman scattering (SERS) effects, as assessed using malachite green (MG). Compared to films without GO, the GO/Ag@PEDOT:PSS films exhibit enhanced conductivity and SERS detection performance due to the negatively charged functional groups on the GO surface forming a continuous layer of AgNPs. Moreover, antibacterial capabilities were evaluated through bacterial attachment and inhibition zone assays. Both Ag@PEDOT:PSS and GO/Ag@PEDOT:PSS films were effective in inhibiting bacterial adhesion, achieving up to 99.4 % and 99.0 % inhibition, respectively. In the inhibition zone assays, the GO/Ag@PEDOT:PSS film showed a 1.33 times increase in antibacterial efficacy compared to Ag@PEDOT:PSS. Furthermore, the effectiveness of electrodepositing antibiotics on these substrates was investigated, confirming optimal antibacterial performance. This efficacy is attributed to the synergistic interaction between silver nanoparticles and antibiotics, potentially reducing the need for antibiotics. The findings of this study highlight its significant potential for applications in antibacterial treatments and biomedical detection.

Effects of Al Addition and Annealing on Microstructure and Properties of Ni-Ti Coatings Synthesized on SUS 316L Stainless Steel Substrates Using Mechanical Alloying Method

Effects of Al Addition and Annealing on Microstructure and Properties of Ni-Ti Coatings Synthesized on SUS 316L Stainless Steel Substrates Using Mechanical Alloying Method

Numerical Study on a Ductile Fracture Model in Pre-Cracked Tension Tests of SUS304L.

The effectiveness of a ductile fracture model in accurately predicting fracture initiation has been demonstrated. In this study, we concentrate on applying the ductile fracture model to pre-cracked structures constructed from SUS304L stainless steel with experimental and numerical analyses. The Swift hardening law was employed to extend the plastic behavior beyond the onset of necking. Additionally, the Hosford-Coulomb model, integrated with a damaged framework, was utilized to predict ductile fracture behavior, particularly under non-proportional loading conditions. Tension tests were conducted on various specimens designed to illustrate various fracture modes resulting from geometric effects. Numerical analyses were conducted to explore the loading histories, utilizing an optimization process to calibrate fracture model parameters. The proposed fracture model is validated against pre-cracked structures detailed in a reference paper. The results convincingly demonstrate that the fracture model effectively predicts both fracture initiation and propagation in pre-cracked structures.

Antibiofilm Property and Biocompatibility of Siloxane-Based Polymer Coatings Applied to Biomaterials

Biofilm infections sometimes occur on biomaterials inserted into the body because biomaterials can block the attack of immune cells such as macrophages, promoting biofilm formation by invading bacteria. Owing to their use in antifouling applications, including biofilm formation, siloxane-based polymer coatings are considered a promising method to prevent biofilm formation on the surface of biomaterials. In this study, we explored the antibiofilm property and biocompatibility of siloxane-based polymer coatings. Biofilm formation and cytotoxicity tests were performed using Escherichia coli and Staphylococcus epidermidis to quantify the biofilms while U937 cells were used to measure the time course of viable cell concentration and viability, respectively. In both the biofilm formation and cytotoxicity tests, stainless steel SUS316L plates and titanium plates coated with the siloxane-based polymer and sterilized in an autoclave were used as the biomaterials. The amount of biofilm formed on the polymer-coated titanium plate was substantially higher than that on a noncoated titanium plate in the case of S. epidermidis. The viable cell concentration and viability of U937 cultured on the polymer-coated titanium plate were lower than those of U937 cultured on the noncoated titanium plate. The same trend was observed between polymer-coated and noncoated SUS316L plates. These results indicate that the siloxane-based polymer coatings need additional treatment to achieve a satisfactory antibiofilm property and that they are sensitive to autoclave treatment, resulting in cytotoxicity.

Deposition Silver Based Thin Film on Stainless Steel 316l as Antimicrobial Agent Using Electrophoretic Deposition Method

SUS316L stainless steel has been widely used in medical applications. However, some germs frequently adhere to the device surface, resulting in infections following implantation surgery. Unfortunately, the material lacks antibacterial characteristics that prevent microorganisms from adhering to the surface. This study aims to use electrophoretic deposition to deposit chitosan/silver (Ag) as an antibacterial agent on stainless steel 316L. The antimicrobial effects of chitosan and silver are well established. During the deposition, the rectifier voltage was adjusted to a constant 10 volts with a suspension pH range of 2.7 to 5.1. The effect of varying the pH of the suspension on the physical, mechanical, and antibacterial properties of chitosan/Ag thin films was investigated. The materials’ structure and morphology were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier- transform infrared spectroscopy (FTIR). The antimicrobial inhibition was examined using the Kirby-Bauer antimicrobial test. The results reveal that increasing the pH of the suspension causes an increase in the thickness, size, and aggregation of the chitosan/Ag thin film. The highest thickness achieved during deposition with a pH 5.1 suspension is 5.265 𝜇m. The best antibacterial agent is achieved at a pH 3.5 suspension sample with an inhibitory zone diameter of 4 mm

Investigations of Tungsten Inert Gas and Metal Active Gas Joints of SUS301L Stainless Steel: Electron Backscatter Diffraction Characterization and Fatigue Performance

Investigations of Tungsten Inert Gas and Metal Active Gas Joints of SUS301L Stainless Steel: Electron Backscatter Diffraction Characterization and Fatigue Performance

Investigation of Foreign Particles in Moderna COVID-19 Vaccine

Particular batches of Moderna mRNA Coronavirus Disease 2019 (COVID-19) vaccine were recalled after foreign particles were found in some vaccine vials at the vaccination site in Japan in August 2021. We investigated the foreign particles at the request of the Ministry of Health, Labour and Welfare. Energy dispersive X-ray spectroscopy analysis suggested that the foreign particles found in the vials recalled from the vaccination sites were from stainless steel SUS 316L, which was in line with the findings of the root cause investigation by the manufacturer. The sizes of the observed particles ranged from <50 μm to 548 μm in the major axis. Similar foreign particles were also detected in 2 of the 5 vaccine vials of the same lot stored by the manufacturer, indicating that the foreign particles have already been administered to some people via vaccine. Observation of the vials of the same lot by digital microscope found smaller particles those were not detected by visual inspection, suggesting that more vials were affected. Contrarily, visual inspection and subvisible particulate matter test indicated no foreign particles in the vials of normal lots. Possible root cause and strategies to prevent such a deviation were discussed from technical and regulatory aspects.

Microstructure evolution and mechanical properties of SUS301L stainless steel sheet welded joint in ultrasonic vibration assisted laser welding

Ultrasonic assisted laser welding (ULW) is a newly developed welding method. In this paper, a new kind of ultrasonic assisted laser welding method, which is named trailing ultrasonic assisted laser welding (T-ULW) is proposed. First, the welding temperature fields as well as the weld pool temperature evolution in trailing ultrasonic assisted laser welding (T-ULW) and conventional laser welding (LW) are numerically simulated, and the shapes of the molten pools during T-ULW and LW are observed by a high-speed camera monitoring system. Both the simulation and monitoring results show that ultrasonic can reduce the temperature gradient of the weld pool and prolong the solidification time. Then, such three kinds of welding methods as T-ULW, common fixed-position ultrasonic assisted laser welding (F-ULW) and LW are used to weld SUS301 stainless steel sheet with a thickness of 0.6 mm respectively, and their performances are comparatively investigated by analyzing the experimentally-obtained macro morphologies, microstructures of welded joints. Macro morphology analysis results show that ultrasonic vibration not only elongates the molten pool, but also changes the cross-sectional shapes of the welds in such a way that decreases the top width and increases the bottom width. Microstructure analysis results indicate that the fusion zone of the welds obtained by T-ULW is uniformly distributed mainly by the refined equiaxed grains. Subsequently, the crystal refinement mechanisms of the welds in ultrasonic-assisted laser welds of SUS301 stainless steel are theoretically analyzed and experimentally verified, which show that due to ultrasonic disturbance, the temperature gradient of the molten pool is decreased, a stress field is generated in the welds and a so-called ultrasonic cavitation effect is produced in the molten pool. Such three mechanisms play very important roles in refining crystals in different ways that the decreased temperature gradient provides a good nucleation condition for the growth of equiaxed dendrite, and both the generated stress and ultrasonic cavitation cause the grain boundary to fracture, thereby form more new grain boundary, which finally lead to form fine and uniform grains in the welds. Finally, the mechanical properties of the joints are measured, and the results demonstrated that ultrasonic assisted laser welding especially T-ULW enables not only to increase the tensile strength of the welds, but also to improve the ductility of the welds.

Nanomechanical Analysis of SUS304L Stainless Steel with Bimodal Distribution in Grain Size

An improved combination of strength and ductility is generally a trade-off relationship, and it remains a major research topic in the field of structural materials. A bimodal grained microstructure, consisting of a coarse-grained region “core” and a surrounding fine-grained region “shell”, exhibits a good balance between strength and ductility. Therefore, the exact reason for the strengthening mechanism needs to be investigated. In the present study, we conducted nanomechanical characterization to evaluate the individual strengthening factors, including matrix strength (σ0), and grain boundary effect (k), in the Hall–Petch model for each region of the core and shell to clarify the strengthening mechanism in the bimodal grained microstructure. The nanoindentation technique was applied locally in the “grain interior” to evaluate σ0, and “on grain boundary” and “near grain boundary” to assess the grain boundary effect associated with the k value. The grain interior nanohardness was found to be higher in the core region than that in the shell, which is explained by the higher pre-existing dislocation density in the core region. The nanomechanical characterization of the “on grain boundary” and the “near grain boundary” regions show a higher barrier effect due to the grain boundary in the shell than that in the core, which is presumably dominated by the higher internal strain at the shell grain boundary. Furthermore, a Hall–Petch plot was constructed using nanohardness, Vickers hardness, and grain size to estimate the k value. The plot showed a higher k value in the shell, which is consistent with the higher strengthening effect of the shell grain boundary that is evaluated independently in the local region. Therefore, the macroscopic strength of the shell region is significantly affected by both grain boundary effect as well as fine grain size.

Effect of Zn interlayer on friction stir butt welding of A1100 and SUS316L stainless steel

The effect of Zn interlayer on the microstructure and mechanical properties of dissimilar A1100 and SUS316L friction stir welded (FSW) butt joints was investigated. The results showed that Zn could improve the joint’s tensile strength. However, a complete dissolution of the Zn interlayer was necessary to achieve a sound joint. During the FSW process, the stirring action of the tool dispersed the Zn into the A1100 matrix forming a solid solution of Zn. A direct relationship was found between the tool rotational speed and the Zn dissolution rate. Also, the addition of Zn inhibited the Al–Fe IMCs growth, which played a positive role in the obtained tensile strength.

Dry passivation of austenitic SUS 301L stainless steel against pitting corrosion in marine atmospheric environment

Dry passivation of austenitic SUS 301L stainless steel against pitting corrosion in marine atmospheric environment

Keyhole dynamic status and spatter behavior during welding of stainless steel with adjustable-ring mode laser beam

A novel adjustable-ring mode laser (ARM) welding of SUS304L stainless steel sheet was investigated in this work. The ARM laser consists of two parts: ring laser beam as outer part; circular laser beam as center part. A Phantom high-speed camera with image processing algorithm was used to monitor the keyhole dynamic behavior. The spatter ejection, molten pool, and keyhole status were observed from the top view position. The characteristics of spatters were monitored from the side position of the camera. Experimental results showed that the pure circular laser beam (regular Gaussian beam) generated a periodic opening and collapsing keyhole with plenty of spatters in the welding process. However, the pure ring laser beam generated a continuously opening keyhole-inlet in the welding process. Because of the ring laser on welding, the dual-mode ring/circular laser (ARM laser) maintained a relatively opening keyhole with a smaller number of spatters comparing to pure circular laser welding. This work provided a full understanding of the process mechanism regarding the welding with shaped laser beam. The adjustable-ring mode laser is expected to be applied in a high-quality industrial manufacturing process.

Temperature Field in MIG Welding of Thin Plate of Stainless Steel

This paper studies the butt welded joint of SUS316L stainless steel. The butt joint is not beveled, has a gap and is welded in one pass by MIG welding process. First, the welding parameters of this weld are determined through calculation and test welding for the butt joint of two plates of 3 mm in thickness. Then these welding parameters are used as input data to calculate and determine the temperature field by two methods: the calculation method based on the theory of heat transfer process and the numerical simulation method of welding processes that relies on SYSWELD software on the basis of the finite element method. The calculation results of the two methods were compared with each other and tested by experiment to show the reliability of calculation and simulation results.

Strain effect on microstructural properties of SUS 304L joint by PAW+GTAW

JIS SUS 304L stainless steel was joined by a combination welding process of plasma arc welding and gas tungsten arc welding (PAW+GTAW). Then pre-strain treatment on 304L welded joint of 9 % was carried out using uniaxial quasi-static tensile at room temperature. Effect of strain on microstructure evolution in joint was analyzed by field emission scanning electron microscope (FESEM) and on mechanical properties was also studied. The results indicated that the pre-strain rate of 304L joint showed inhomogeneity including 3 % in the weld metal and 13 % in the heat-affected zone (HAZ), which induced martensitic transformation occurring in HAZ. Tensile strength of the joint increased from 700 MPa as welded to 804 MPa after pre-strain treatment at room temperature, and it reached 1700 MPa from 1480 MPa as welded at low temperature of −196 °C. Impact energy in the HAZ was the least among the whole 304L weld, but it was still 94 J at −196 °C after pre-strain. The fracture morphology showed large numbered of cleavage steps with elongated parabolic dimples.