• Corrosion Science and Technology
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• 제22권1호
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• pp.55-63
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• 2023

The aim of this study was to propose a multiple linear regression (MLR) equation to predict ultimate tensile strength (UTS) of 316L stainless steel with unspecified pit corrosion. Tensile specimens with pit corrosion were prepared using a potentiostatic acceleration test method. Pit corrosion was characterized by measuring ten factors using a confocal laser microscope. Data were collected from 22 tensile tests. At 85% confidence level, total pit volume, maximum pit depth, mean ratio of surface area, and mean area were significant factors showing linear relationships with UTS. The MLR equation using these three significant factors at a 85% confidence level showed considerable prediction performance for UTS. Determination coefficient (R²) was 0.903 with training and test data sets. The yield strength ratio of 316L stainless steel was found to be around 0.85. All specimens with a pit corrosion presented a yield ratio of approximately 0.85 with R² of 0.998. Therefore, pit corrosion did not affect the yield ratio.

• 한국압력기기공학회 논문집
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• 제13권1호
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• pp.92-100
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• 2017

Due to the presence of ferrite phase in the finished welds, austenitic stainless steel welds (ASSWs) are considered susceptible to the thermal aging embrittlement during long-term service in light water reactor environment. In this study, the thermal aging embrittlement of typical ASSWs, E308 and ER316L welds, were evaluated after the long-term exposure up to 20,000 h at $400^{\circ}C$, which is considered as an accelerated thermal aging condition. After thermal aging, the decrease of tensile ductility and fracture toughness was observed. The microstructure observation with high resolution transmission electron microscopy revealed that spinodal decomposition in ferrite phase of both E308 and ER316L welds would be the main cause of the degradation of mechanical properties. Also, it was shown that the difference of thermal ageing embrittlement between ER316L and E308 welds was significant, such that the reduction of fracture resistance for ER316L weld was much larger than that of E308 weld.

• 방사성폐기물학회지
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• 제18권2호
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• pp.169-177
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• 2020

Here, the stability of stainless steel 316 (SS-316) was investigated to identify its applicability in the oxide reduction process, as a component in related equipment, to produce a complicated gas mixture composed of O₂ and Cl₂ under an argon (Ar) atmosphere. The effects of the mixed gas composition were investigated at flow rates of 30 mL/min O₂, 20 mL/min O₂ + 10 mL/min Cl₂, 10 mL/min O₂ + 20 mL/min Cl₂, and 30 mL/min Cl₂, each at 600℃, during a constant argon flow rate of 170 mL/min. It was found that the corrosion of SS-316 by the chlorine gas was suppressed by the presence of oxygen, while the reaction proceeded linearly with the reaction time regardless of gas composition. Surface observation results revealed an uneven surface with circular pits in the samples that were fed mixed gases. Thermodynamic calculations proposed the combination of Fe and Ni chlorination reactions as an explanation for this pit formation phenomenon. An exponential increase in the corrosion rate was observed with an increase in the reaction temperature in a range of 300 ~ 600℃ under a flow of 30 mL/min Cl₂ + 170 mL/min Ar.

• 동력기계공학회지
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• 제18권3호
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• pp.100-105
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• 2014

This study is to investigate the effect of thermo mechanical treatment on the mechanical properties of 316L stainless steel. ${\alpha}^{\prime}$ and ${\varepsilon}$-martensite was formed by deformation. With increasing number of thermo mechanical treatment, volume fraction of martensite was increased rapidly, and then unchanged. With increasing number of thermo mechanical treatment, hardness and strength was increased rapidly, and then unchanged while elongation was decreased rapidly, and then unchanged. With increasing volume fraction of martensite formed by thermo mechanical treatment, hardness and strength was increased rapidly, elongation was decreased rapidly. Thus, hardness, strength and elongation of thermo mechanical treated 316L stainless steel was strongly affected by martensite formed by thermo mechanical treatment. Good combination of strength and elongation was obtained from thermomechanical treatment.

• 열처리공학회지
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• 제37권5호
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• pp.237-246
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• 2024

In this study, hydrogen embrittlement was investigated for 316L stainless steel (SS316L) and CoCrFeNi medium-entropy alloy (MEA) fabricated by laser-powder bed fusion. The in-situ hydrogen charging tensile tests revealed that the reduction in ductility due to hydrogen was more significant in the CoCrFeNi MEA, compared to the SS316L. In the case of SS316L, hydrogen-assisted cracks (HACs) were observed mainly on the surface, whereas in CoCrFeNi, cracks were found not only at the edges but also in the central region. HACs analysis confirmed that transgranular (TG) cracks were predominant in SS316L, whereas only intergranular cracks were formed in the CoCrFeNi MEA. The difference in hydrogen embrittlement resistance between SS316L and CoCrFeNi was discussed in terms of the differences in deformation microstructure and hydrogen diffusivity, as investigated through electron channeling contrast imaging and nanoindentation.

• 한국재료학회지
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• 제25권6호
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• pp.293-299
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• 2015

In this study, nitrogen ions were implanted into STS 316L austenitic stainless steel by plasma immersion ion implantation (PIII) to improve the corrosion resistance. The implantation of nitrogen ions was performed with bias voltages of -5, -10, -15, and -20 kV. The implantation time was 240 min and the implantation temperature was kept at room temperature. With nitrogen implantation, the corrosion resistance of 316 L improved in comparison with that of the bare steel. The effects of nitrogen ion implantation on the electrochemical corrosion behavior of the specimen were investigated by the potentiodynamic polarization test, which was conducted in a 0.5 M $H_2SO_4$ solution at $70^{\circ}C$. The phase evolution and texture caused by the nitrogen ion implantation were analyzed by an X-ray diffractometer. It was demonstrated that the samples implanted at lower bias voltages, i.e., 5 kV and 10 kV, showed an expanded austenite phase, ${\gamma}_N$, and strong (111) texture morphology. Those samples exhibited a better corrosion resistance.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1357-1368
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• 2021

This paper presents thermal aging effect on fracture toughness properties of GTAW (gas tungsten arc welding) and SMAW (shielded metal arc welding) of 316L stainless steels, and investigates the applicability of the existing three thermal aging models for CASS (cast stainless steels). Thermal aging was carried out at 350 ℃ for up to 15,000h and at 400 ℃ up to 8,000h. After aging, tensile and fracture toughness tests using 0.5T C(T) specimens were carried out at room temperature and at 288 ℃. Comparing with the predictions using three (ANL, French and H3T) thermal aging models for CASS show that the predictions can be very non-conservative at operating temperature, and thus that the existing thermal aging models for CASS cannot be applied to the welded stainless steels.

• 대한금속재료학회지
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• 제47권11호
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• pp.722-727
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• 2009

The bipolar plates are not only the major part of the polymer electrolyte membrane fuel cell (PEMFC) stack in weight and volume, but also a significant contributor to the stack costs. Stainless steels are considered to be good candidates for bipolar plate materials of the PEMFC due to their low cost, high strength and easy machining, as well as corrosion resistance. In this paper, 316L stainless steel with and without nitrogen ion implantation were tested in simulated PEMFC environments for application as bipolar plates. The results showed that the nitride formed by nitrogen ion implantation contributed the decrease of the interfacial contact resistance without degradation of corrosion property. The combination of excellent properties indicated that nitrogen ion implanted stainless steel could be potential candidate materials as bipolar plates in PEMFC. Current efforts have focused on optimizing the condition of ion implantation.

• 대한기계학회논문집A
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• 제26권3호
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• pp.521-527
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• 2002

In this paper, tensile behavior and low cycle fatigue behavior of 316L stainless steel which is currently favored structural material for several high temperature components such as the liquid metal cooled fast breeder reactor (LMFBR) were investigated. Research was performed at 55$0^{\circ}C$, $600^{\circ}C$ and $650^{\circ}C$ since working temperature of 316L stainless steel in a real field is from 40$0^{\circ}C$ to $650^{\circ}C$. From tensile tests performed by strain controls with $1{\times}10^{-3}/s,\; l{\times}10^{ -4}/s \;and\; 1{\times}10/^{ -5}/ s $ strain rates at each temperature, negative strain rate response (that is, strain hardening decreases as strain rate increases) and negative temperature response were observed. Strain rate effect was relatively small compared with temperature effect. LCF tests with a constant total strain amplitude were performed by strain control with a high temperature extensometer at R.T, 55$0^{\circ}C$, $600^{\circ}C$, $650^{\circ}C$ and total strain amplitudes of 0.3%~0.8% were used and test strain rates were $1{times}10^{-2} /s,\; 1{times}10^{-3} /s\; and\; 1{times}10^{-4} /s$. A new energy based LCF life prediction model which can explain the effects of temperature, strain amplitude and strain rate on fatigue life was proposed and its excellency was verified by comparing with currently used models.

• Steel and Composite Structures
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• 제5권5호
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• pp.359-374
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• 2005

This paper presents the experimental and theoretical results of the viscoplastic response and collapse of 316L stainless steel tubes subjected to cyclic bending. The tube bending machine and curvature-ovalization measurement apparatus, which was designed by Pan et al. (1998), were used for conducting the cyclic curvature-controlled experiment. Three different curvature-rates were controlled to highlight the characteristic of viscoplastic response and collapse. Next, the endochronic theory and the principle of virtual work were used to simulate the viscoplastic response of 316L stainless steel tubes under cyclic bending. In addition, a proposed theoretical formulation (Lee and Pan 2001) was used to simulate the relationship between the controlled cyclic curvature and the number of cycles to produce buckling under cyclic bending at different curvature-rates (viscoplastic collapse). It has been shown that the theoretical simulations of the response and collapse correlate well with the experimental data.