Numerical Simulation on Effect of Microstructure on Hydrogen-induced Cracking Behavior in Duplex Stainless Steel Weld Metal

Abstract

Duplex stainless steels and their deposited weld metal have ferrite and austenite microstructure, which have material properties that are different. In addition, the microstructure of the base metal and weld metal are clearly different; therefore, it affects the hydrogen diffusion and accumulation, and hydrogen-induced cracking behavior at the microstructural scale. In this study, the influence of the microstructure on hydrogen-induced cracking behavior of duplex stainless steel weld metal was investigated. Specimens of duplex stainless steel weld metal were prepared and slow strain rate tensile test was performed after hydrogen charging. Cracks were observed at boundaries of ferrite and austenite phases. In order to clarify the stress and hydrogen concentration distribution at the microstructural scale, a microstructure-based finite element simulation was performed. A finite element model based on a cross sectional observation of the microstructure was designed to calculate the stress and hydrogen concentration distribution. The simulation result showed that the hydrogen accumulation occurs at ferrite/austenite boundaries, which corresponded to the locations where cracks were observed in the experiment. On the other hand, the hydrogen concentration at the accumulation site in the weld metal was low compared to that in the base metal. Therefore, the influence of the phase fraction and the stress-strain curves of the ferrite and austenite phases on the hydrogen concentration was investigated by the proposed numerical simulation. It was demonstrated that both the phase fraction and stressstrain curves have significant influence on the microscopic distribution of hydrogen concentration.

Numerical Simulation on Effect of Microstructure on Hydrogen-induced Cracking Behavior in Duplex Stainless Steel Weld Metal

“…Figure 2 shows the microstructure of the fabricated multi-pass weld metal. Unlike the layered microstructure of the base metal in the previous report, 1) the ferrite and austenite phases were randomly distributed. Crystal orientation analysis by electron backscatter diffraction (EBSD) method was performed with a step size of 0.5 μm after polishing with colloidal silica.…”

“…Gen OGITA, 1,2) Koki MATSUMOTO, 1) Masahito MOCHIZUKI, 1) Yoshiki MIKAMI 3) * and Kazuhiro ITO 3) 1) Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871 Japan.…”

“…The results were then compared with those of the base metal. 1) In addition, the effect of the ferrite and austenite phase ratio and their respective material properties were also investigated.…”

“…However, several reports noted that this results to hydrogen cracking. 1) Stress and strain distribution 2) and its corresponding hydrogen diffusion behavior are strongly influenced by the microstructure morphology 3,4) of duplex stainless steels with heterogeneous structures composed of ferrite and austenite phases with different mechanical properties, hydrogen solubility, and hydrogen diffusion coefficient. However, stress and diffusible hydrogen concentration distribution are influenced by the microstructure and their effects on hydrogen cracking have not been sufficiently studied.…”

Evaluation of Hydrogen-induced Cracking Behavior in Duplex Stainless Steel by Numerical Simulation of Stress and Diffusible Hydrogen Distribution at the Microstructural Scale

“…A similar study was conducted for the weld metal, and the results are described in another paper. 26)…”