This study investigated the hydrogen embrittlement behavior of 316 austenitic stainless steel subjected to hydrogen charging at different temperatures, using slow strain-rate testing and acoustic emission (AE) techniques. Compared to the noncharged specimen, the specimen H-charged at 25 °C exhibited similar elongation and a ductile fracture mode, while hydrogen charging at 60 °C led to a pronounced reduction in elongation accompanied by quasi-cleavage fracture. This degradation may be associated with enhanced hydrogen transport and redistribution at the elevated charging temperature, which could increase the effective hydrogen activity at microstructural sites, known to be critical to crack initiation and propagation. Feritscope measurements indicated a relative increase in strain-induced martensite formation in the hydrogen-charged specimens. Specifically, the H-charged at 25 °C specimen showed a localized increase in martensite near the fracture surface, and the H-charged at 60 °C specimen exhibited a high martensite fraction over the measured region of the gauge section. AE analysis showed that the cumulative number of AE events decreased after hydrogen charging, while the cumulative absolute energy increased, particularly for the H-charged at 60 °C specimen. These results suggest a relative change in fracture behavior under hydrogen-charged conditions, from ductile fracture involving numerous low-energy AE events to more abrupt fracture behavior characterized by fewer but more energetic AE events. This study suggests that AE analysis can serve as a complementary tool for characterizing deformation and the fracture behavior associated with hydrogen embrittlement in austenitic stainless steels.

Ridge regression is known to be an effective algorithm for regression problems. However, the algorithm has some drawbacks with highly non-linear datasets. In this research, the hot deformation flow stress of 321 stainless steel was modeled using the kernel ridge regression algorithm. For modeling the flow stress in this research, the tensile test data for 321 stainless steel under temperatures of 700℃, 800℃, and 900℃ at strain rates of 0.0002/s, 0.002/s, and 0.02/s were used. To overcome the drawbacks of the traditional ridge regression algorithm, the algorithm was enhanced by a kernel-type function to handle the non-linear dataset. The predicted data by the kernel ridge regression was accurate. After that, the predicted values were studied in terms of their distribution. The kernel ridge regression algorithm was found to be accurate and stable in predicting the flow stress of hot deformation.

This study investigated the hot deformation behavior and microstructural evolution of PH13-8Mo precipitation-hardening stainless steel. Hot compression tests were performed at temperatures ranging from 900 to 1,200 °C and strain rates of 0.01 to 10 s-1. Constitutive equations based on the Zener-Hollomon parameter were established by considering the compensation of strain, where the material constants were fitted with 6th-order polynomials. The established model showed high predictability with a correlation coefficient of 0.994 and an average absolute relative error of 4.39 %. A hot processing map was developed based on the Dynamic Materials Model, identifying unstable regions characterized by negative instability criteria under low-temperature/high-strain-rate conditions, as well as specific moderate-rate zones. Electron backscatter diffraction (EBSD) integrated analysis [inverse pole figure (IPF), kernel average misorientation (KAM), and grain orientation spread (GOS)] revealed that while dynamic recrystallization promoted grain refinement through necklace structures at 900 °C and 0.01 s-1, high-temperature deformation at 1,200 °C led to significant grain coarsening and high transformation-induced stress. Furthermore, regions of instability were confirmed to cause flow localization and strain hotspots, detrimental to structural integrity. Consequently, the moderate temperature region around 1,100 °C with a low strain rate is proposed as the optimal window for achieving uniform and stable prior austenite grain structures.

This research presents a GRNN(General regression neural network) approach for modeling the high temperature deformation flow behavior of 316L stainless steel under 800℃, 900℃ and 1000℃ and strain rates of 0.0002/s, 0.002/s and 0.02/s. There are many machine learning approaches of modeling the hot deformation of metallic alloys. Among them, the neural network approach is one of the most popular. However, the neural network approach takes a relatively long time and effort to compose and optimize the final model. In this research, GRNN is applied to study its applicability for modeling the hot deformation flow stress behavior. The prediction results were studied by calculating various types of error and observing the distribution of prediction error. The predicted results by the GRNN were very accurate and the GRNN was found to be highly applicable to modeling the flow stress of the hot deformation of 316L stainless steel.

This study compares pure Ni coatings deposited on type 316H stainless steel using high-velocity oxy-fuel (HVOF) and directed energy deposition (DED) processes. Microstructural analysis showed that DED produced more uniform claddings with fewer pores, while HVOF resulted in incomplete melting and cracks. Elemental diffusion of Cr and Fe from the substrate into the cladding was evident in DED samples, especially at higher laser power, but minimal in HVOF due to low heat input. Vickers hardness testing revealed that DED claddings had higher hardness near the interface, which was attributed to solid solution strengthening and reduced porosity. Although HVOF better suppressed diffusion, it exhibited inferior mechanical properties due to internal defects. Overall, the DED process demonstrated superior coating quality and mechanical performance, suggesting its suitability for corrosion-resistant applications requiring both structural integrity and thermal stability, such as molten salt reactors.

The pipes are connected by welding the ends so that they face each other, or, to enhance the assembly, a disc-shaped flange is welded to the end of each pipe, and then the flanges are brought into contact with each other and connected so that they can be separated using bolts and nuts. The ends of pipes with an inner diameter of ∅20 to 50 are plastically processed into a flange shape. This allows for the forming of a flange integral with the pipe, and ensures versatility. When forming a flange on a pipe, it can reduce wear due to friction, improve product quality, and increase the life of the device.

This study investigated the ultra-low-temperature (4.2 K) tensile properties and deformation mechanisms of stainless steel 304L manufactured via laser powder bed fusion (LPBF). The tensile properties of LPBF 304L were compared to those of conventional 304L to assess its suitability for cryogenic applications. The results revealed that LPBF 304L exhibited a significantly higher yield strength but lower ultimate tensile strength and elongation than conventional 304L at 4.2 K. The temperature dependence of the yield strength also favored LPBF 304L. Microstructural analysis demonstrated that LPBF 304L features a high density of dislocation cells and nano-inclusions, contributing to its greater strength. Furthermore, strain-induced martensitic transformation was observed as a key deformation mechanism at cryogenic temperatures, where austenite transformed into both hexagonal-closed packed (HCP) and body-centered cubic (BCC) martensite. Notably, BCC martensite nucleation occurred within a single HCP band. These findings provide critical insights into the mechanical behavior of LPBF 304L at cryogenic temperatures and its potential for applications in extreme environments.

Metal additive manufacturing (AM) facilitates the production of complex geometries with enhanced functionality. Among various AM techniques, laser powder bed fusion (LPBF) is distinguished by its precision and exceptional mechanical properties achieved via laser fusion deposition. Recent advancements in AM have focused on combining LPBF with post-processing methods such as cold rolling, high-pressure torsion, and forming processes. Therefore, understanding the forming behavior of LPBF-processed materials is essential for industrial adoption. This study investigates the stretch-flangeability of LPBF-fabricated 316L stainless steel, emphasizing its anisotropic microstructure and mechanical properties. Hole expansion tests were employed to assess stretch-flangeability in comparison to wrought 316L stainless steel. The results demonstrate that LPBF-processed samples exhibit significant anisotropic behavior, demonstrating the influence of microstructural evolution on formability. These findings contribute valuable insights into optimizing LPBF materials for industrial forming applications.

For the commercialization of bipolar plates, several properties must be considered together. Electrical conductivity, corrosion resistance, contact resistance, mechanical strength, and light weight are essential evaluation factors, with corrosion resistance and durability being significant for unitized regenerative fuel cells (URFCs), which must operate in electrolysis and fuel cell mode. However, improving both properties is challenging, since corrosion resistance is largely inversely proportional to conductivity. In this study, to improve both properties together, composites composed of Pb and Zn with excellent conductivity and corrosion resistance were prepared with graphite powder and formed as a coating layer on the surface of 304 stainless steel (SS304) and evaluated for electrical conductivity and corrosion resistance. Among the ZnPb/C composites prepared at various ratios, Zn8Pb2/C exhibited the lowest transmittance resistance of 1.566 Ω, and improved electrical conductivity and durability compared to bare SS304.

The International Maritime Organization (IMO) is promoting the transition to eco-friendly fuels such as hydrogen and ammonia, with the goal of achieving net-zero greenhouse gas emissions in the shipping sector by 2050. Hydrogen does not emit greenhouse gases, but it must be stored at an extremely low temperature of -253°C when stored as a liquid. 316L stainless steel is mainly used as a tank material to store liquid hydrogen. FCAW (Flux Cored Arc Welding) is known for its excellent weldability with 316L stainless steel, and it is particularly suited for welding thick metals efficiently, making it an ideal choice for storage tank welding. Finite Element Method (FEM) analysis can simulate the thermal and mechanical deformations occurring during welding with high precision, allowing for accurate prediction of deformation patterns and the derivation of optimal welding conditions. This ensures the stability and quality of the structure while reducing costs. In this study, FCAW butt welding was performed on 316L stainless steel, followed by cross-sectional observation and deformation measurement of the weld area. Based on the cross-sectional observation, a 3D FE model was designed, and heat transfer analysis was conducted. Subsequently, thermo-mechanical analysis was carried out to predict welding deformation.

Super-duplex stainless steels are in great demand in various industrial fields such as chemical processing and seawater desalination due to their excellent pitting corrosion resistance. However, detrimental phases can easily form during fabrication, and even minor additions of alloying elements can significantly impact their microstructure and properties. This study investigated the effects Cu or Ti additions on a super-duplex stainless steel. First, the effects of annealing time at 950 °C on the microstructure and corrosion characteristics were investigated. It was found that as the annealing time increased, the fraction of sigma phase increased; however, the corrosion resistance in the electrochemical test using a 3.5 % NaCl electrolyte showed only a slight improvement. The microstructure of duplex stainless steel with added Cu or Ti did not differ significantly from that of the base steel. However, the overall corrosion resistance showed improvement, and in particular, an observed increase in pitting potential. Investigating the characteristics of the passive film on the alloy surface revealed that the stability of the passive film was higher in alloys with added Cu or Ti compared to the standard alloy. Among these, the alloy with Cu addition had the thickest film, while the Ti-added alloy had the highest Cr concentration and a film thickness greater than that of the standard alloy.

Molten salt reactors represent a promising advancement in nuclear technology due to their potential for enhanced safety, higher efficiency, and reduced nuclear waste. However, the development of structural materials that can survive under severe corrosion environments is crucial. In the present work, pure Ni was deposited on the surface of 316H stainless steel using a directed energy deposition (DED) process. This study aimed to fabricate pure Ni alloy layers on an STS316H alloy substrate. It was observed that low laser power during the deposition of pure Ni on the STS316H substrate could induce stacking defects such as surface irregularities and internal voids, which were confirmed through photographic and SEM analyses. Additionally, the diffusion of Fe and Cr elements from the STS316H substrate into the Ni layers was observed to decrease with increasing Ni deposition height. Analysis of the composition of Cr and Fe components within the Ni deposition structures allows for the prediction of properties such as the corrosion resistance of Ni.

원자력 발전소에서 배관 시스템은 냉각수 및 오염수를 운반하고 생성된 증기를 터빈으로 이동시켜 에너지를 생산하는 중요한 설비이다. 국내에 건설된 원자력 발전소의 가동연수가 증가함에 따라 배관 시스템의 물리적, 기계적 성질의 열화현상은 발생할 수 있으며 이를 경년열화로 정의한다. 배관 시스 템의 경년열화는 재료의 피로, 부식(국부감육), 마모 등과 같은 메커니즘을 통해 발생할 수 있으며 재 료의 강도 및 시스템의 성능 저하와 균열을 야기할 수 있다. 지속적이고 안정적인 에너지 생산을 위해 경제성과 정확도를 고려한 원전 배관 시스템의 손상 감시 기술은 필요하다. 따라서 본 연구는 원전 배 관 시스템의 손상 감시 기술을 개발하기 위한 기초적인 연구로써 배관 시스템의 취약요소로 판단되는 elbow의 국부적인 감육에 따른 거동의 변화를 분석하고자 한다.

The microstructure and mechanical properties of the heat-affected zone welded using the GTAW process on SDSS material used in offshore structures were analyzed. The chemical composition of the specimen material was analyzed using XRF. The microstructure of the heat-affected zone where the plate was welded was examined by SEM, and the ferrite volume fraction was assessed using the point count method of ASTM E562. A lot of ferrite was formed in the overheated weldment region, and In the weld cap where the cooling rate was fast, ferrite was not converted back to austenite and the microstructure was not uniform. From the ferrite phase fraction, it was shown that it can be applied to the pitting resistance equivalent numbers through changes in mechanical properties according to welding conditions.

This study aims to evaluate the structural safety of a structural thermal barrier, installed inside the structure of a building and performed the role of a load-bearing element and an insulation simultaneously, contributing to the realization of net-zero buildings. To ensure the reliability of the analysis model, the analysis results derived from LS-DYNA were compared with the experimental results. Based on the results shown through the flexural experiment, the reliability of the thermal cross-section insulation structure model for slabs was validated. In addition, the effect of the UHPC block on the load support performance and its contribution to vertical deflection was verified.