• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.4
• /
• pp.460-466
• /
• 2004

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained teaming data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Transactions of Materials Processing
• /
• v.31 no.6
• /
• pp.394-403
• /
• 2022

In the automotive industry, cold-drawn austenitic stainless steel is commonly used to handle high fuel pressures in gasoline direct injection (GDI) engines. In this study, we analyzed the effects of main process variables such as cross-sectional shape, drawing speed and friction coefficient on the microstructure, hardness and residual stress of the drawn material in the two-step cold drawing process. By changing the cross-sectional shape in the first-step cold drawing, the possibility of improving the shape accuracy or physical properties of the finally cold-drawn fuel rail pressure sensor product was investigated.

• Structural Engineering and Mechanics
• /
• v.87 no.6
• /
• pp.601-614
• /
• 2023

In this study, the uniaxial ratcheting effect of Z2CND18.12N austenitic stainless steel at room and elevated temperatures is firstly simulated based on the Ahmadzadeh-Varvani hardening rule (A-V model), which is embedded into the finite element software ABAQUS by writing the user material subroutine UMAT. The results show that the predicted results of A-V model are lower than the experimental data, and the A-V model is difficult to control ratcheting strain rate. In order to improve the predictive ability of the A-V model, the parameter γ2 of the A-V model is modified using the isotropic hardening criterion, and the extended A-V model is proposed. Comparing the predicted results of the above two models with the experimental data, it is shown that the prediction results of the extended A-V model are in good agreement with the experimental data.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.19 no.2
• /
• pp.171-178
• /
• 2023

For the phase boundary crack found in the gasket made of cast austenitic stainless steel in the nuclear power plant, the oxide layers were analyzed through SEM and TEM. The results showed that cracks initiated and propagated along the austenite/δ-ferrite phase boundary, the propagation path was changed to penetrate the inside of the phase. The oxide layer located at the periphery of the crack along the phase boundary was identified as a complex multi-layered spinel structure, and Cr-rich carbides were also detected in the oxide. The cracks that propagated inside the austenite matrix were attributed to the presence of high external stresses and impurities.

• Journal of Mechanical Science and Technology
• /
• v.15 no.1
• /
• pp.26-34
• /
• 2001

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.15 no.2
• /
• pp.9-18
• /
• 2019

The objective of this study is to investigate the feasibility of simulating the mechanical properties of irradiatied austenitic stainless steels by cold-working. In this study, the tensile properties, cyclic hardening behaviors and fracture toughness of cold-worked TP316L stainless steel were compared with those of austenitic stainless steels irradiated by neutrons. It showed that cold-working can properly simulate the increase in strength and the decrease in ductility and fracture resistance of austenitic stainless steels by neutron irradiation, even though it could not perfectly simulate the microstructures of irradiated austenitic stainless steels. Also, cold-working can appropriately simulate the hardening behaviors of neutron irradiated austenitic stainless steels under monotonic and cyclic loading conditions.

• Journal of Welding and Joining
• /
• v.16 no.3
• /
• pp.111-120
• /
• 1998

To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

• Steel and Composite Structures
• /
• v.49 no.1
• /
• pp.1-17
• /
• 2023

Based on Ahmadzadeh-Varvani hardening rule (A-V model), multiaxial ratcheting effect of Z2CND18.12N austenitic stainless steel is simulated by ABAQUS with user subroutine UMAT. The results show that the predicted results of the origin multiaxial A-V model are lower than the experimental data, and it is difficult to control ratcheting strain rate. In order to improve the predicted capability of A-V model, the A-V model is modified. In this study. Moreover, under the assumption of the von Mises yield criterion and normal plasticity flow rule, we develop a numerical algorithm of plastic strain with the improved model to implement the finite element calculation of the model. Internal iteration in the numerical algorithm was implemented with the Euler backward method, which calculated the trial strain for each equilibrium iteration using the consistent tangent matrix. With a user subroutine, the proposed model is programmed into ABAQUS for a user - executable version. By simulating the uniaxial ratcheting of a round bar made of Z2CND18.12N austenitic stainless steel, we observe that the predicted results simulated by ABAQUS with UMAT are compared with the experimental data. The predicted results of the improved multiaxial A-V model are consistent well with the experimental data.

• Journal of the Korean Society for Heat Treatment
• /
• v.22 no.5
• /
• pp.298-306
• /
• 2009

Gas nitriding and post oxidation were performed on stainless steels and SACM 645 steel. With increasing gas nitriding time, the increasing rate of nitrided layer was most rapid on SACM 645 steel and the nitriding depth of nitrided layer was most narrow on STS 304 steel among three steels. Corrosion resistance was increased with post oxidation on stainless steels and with increasing time the effect of corrosion resistance was decreased to compare with relatively short gas nitriding time. An improvement effect of corrosion resistance was consisted of predominantly on austenitic stainless steel by post oxidation after gas nitriding among three steels and it was relatively less influenced on martensitic stainless steel.

• Corrosion Science and Technology
• /
• v.9 no.2
• /
• pp.98-103
• /
• 2010

In order to further reduce the cost without reducing the corrosion resistance, a high-manganese austenitic alloy for sink roll or stabilizer roll in continuous hot-dip coating lines was developed. A systematic study of corrosion behavior of the high-manganese austenitic alloy in pure zinc bath at $490^{\circ}C$ was carried out. The results shows that, the high-manganese austenitic alloy shows better corrosion resistance than 316L steel. The corrosion rate of the high-manganese austenitic alloy in pure zinc bath is calculated to be approximately $6.42{\times}10^{-4}g{\cdot}cm^{-2}{\cdot}h^{-1}$, while the 316L is $1.54{\times}10^{-3}g{\cdot}cm^{-2}{\cdot}h^{-1}$. The high-manganese austenitic alloy forms a three-phase intermetallic compound layer morphology containing ${\Gamma$}, ${\delta}$ and ${\zeta}$ phases, while the 316L is almost ${\zeta}$ phase. The ${\Gamma}$ and ${\delta}$ phases of the high-manganese austenitic alloy contain about 8.5 wt% Cr, the existence of Cr improve the stabilization of phases, which slow down the reaction of Fe and Zn, improve the corrosion resistance of the high-manganese austenitic alloy. So substitute the nickel with the manganese to manufacture the high-manganese austenitic alloy of low cost is feasible.