Abstract
Strain-induced martensite transformation (SIMT) commonly exists around a crack tip of metastable austenite stainless steels. The influence of the volume expansion of the SIMT on the hydrogen diffusion was investigated by hydrogen diffusion modeling around a crack tip in type 304L austenite stainless steel. The volume expansion changed the tensile stress state into pressure stress state at the crack tip, resulting in a large stress gradient along the crack propagation direction. Compared to the analysis without considering the volume expansion effect, this volume expansion further accelerated the hydrogen transport from the inner surface to a critical region ahead of the crack tip, and further increased the maximum value of the hydrogen concentration at the critical position where the strain-induced martensite fraction approximates to 0.1, indicating that the volume expansion of the SIMT further increased the hydrogen embrittlement susceptibility.
Highlights
Due to the high resistance to hydrogen embrittlement (HE) and low hydrogen diffusivity, austenite stainless steels (ASSs) have been widely used in hydrogen-containing environments
Sofronis and McMeeking [8] established the basis of hydrogen diffusion near a blunting crack tip, where the maximum lattice hydrogen concentration is at the distance of the peak site of the hydrostatic stress from the crack tip
The martensite fraction distributions around the crack tip were similar in both calculations, indicating that the volume expansion has less effect on the SIMT, as well as plastic strain
Summary
Due to the high resistance to hydrogen embrittlement (HE) and low hydrogen diffusivity, austenite stainless steels (ASSs) have been widely used in hydrogen-containing environments. ASSs, such as type 301, 304(L) and 316, usually undergo suitable cold work process to reach higher strength and better resistance to HE and stress corrosion cracking [1,2]. Excessive cold work reverses this effect due to the over-occurrence of strain-induced martensite (α’-martensite and ε-martensite) transformation (SIMT) [3], since the strain-induced martensite is much more sensitive than austenite to hydrogen [4,5]. Investigating the hydrogen diffusion around a crack tip is critical to predict and prevent the hydrogen assisted crack. Sofronis and McMeeking [8] established the basis of hydrogen diffusion near a blunting crack tip, where the maximum lattice hydrogen concentration is at the distance of the peak site of the hydrostatic stress from the crack tip. Yokobori et al [9] constructed a physical and numerical analysis to describe the hydrogen concentration evolution around a crack tip Metals 2019, 9, 977; doi:10.3390/met9090977 www.mdpi.com/journal/metals
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