Effect of α′ Martensite Content Induced by Tensile Plastic Prestrain on Hydrogen Transport and Hydrogen Embrittlement of 304L Austenitic Stainless Steel

Yanfei Wang,Weijie Wu,Xuanpei Wu

doi:10.3390/met8090660

Yanfei Wang, Weijie Wu + Show 1 more

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https://doi.org/10.3390/met8090660

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Abstract

Effects of microstructural changes induced by prestraining on hydrogen transport and hydrogen embrittlement (HE) of austenitic stainless steels were studied by hydrogen precharging and tensile testing. Prestrains higher than 20% at 20 °C significantly enhance the HE of 304L steel, as they induce severe α′ martensite transformation, accelerating hydrogen transport and hydrogen entry during subsequent hydrogen exposure. In contrast, 304L steel prestrained at 50 and 80 °C and 316L steel prestrained at 20 °C exhibit less HE, due to less α′ after prestraining. The increase of dislocations after prestraining has a negligible influence on apparent hydrogen diffusivity compared with pre-existing α′. The deformation twins in heavily prestrained 304L steel can modify HE mechanism by assisting intergranular (IG) fracture. Regardless of temperature and prestrain level, HE and apparent diffusivity ( D app ) increase monotonously with α′ volume fraction ( f α ′ ). D app can be described as log D app = log ( D α ′ s α ′ / s γ ) + log [ f α ′ / ( 1 − f α ′ ) ] for 10 % < f α ′ < 90 % , with D α ′ is diffusivity in α′, s α ′ and s γ are solubility in α′ and austenite, respectively. The two equations can also be applied to these more typical duplex materials containing both BCC and FCC phases.

Highlights

Many studies have focused on the effects of microstructural changes induced by prior plastic deformations on the hydrogen embrittlement (HE) and hydrogen transport of austenite stainless steels (ASSs) [1,2,3,4,5,6,7,8,9,10,11], considering that ASS components often suffer from some degrees of plastic deformations during manufacturing processes before hydrogen exposure
The results of α content and OM images are shown in Figures 1–3 Almost no α was detected in un‐prestrained 304L and 316L steels, Figures 1 and 2, indicating that both steels without prestraining un-prestrained 304L and 316L steels, Figures 1 and 2, indicating that both steels without prestraining were fully austenitic
As expected, the 304L steel prestrained at 20 ◦ C exhibit α0, at prestrains higher than 20%, as shown by Feritscope readings, Figure 1, and the presence of (110), at prestrains higher than 20%, as shown by Feritscope readings, Figure 1, and the presence of (110), (200), and (211) α′

Summary

Introduction

Many studies have focused on the effects of microstructural changes induced by prior plastic deformations on the hydrogen embrittlement (HE) and hydrogen transport of austenite stainless steels (ASSs) [1,2,3,4,5,6,7,8,9,10,11], considering that ASS components often suffer from some degrees of plastic deformations during manufacturing processes before hydrogen exposure. Some studies have demonstrated that α0 platelets induced by prior deformations (pre-existing α0 ). Perng and Altstetter [1] showed that the apparent hydrogen diffusivity and permeability in 301 and 304 steels were greatly increased by pre-existing α0. In 316L steel, Metals 2018, 8, 660; doi:10.3390/met8090660 www.mdpi.com/journal/metals

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