Effect of Deformation Microstructures on Hydrogen Embrittlement Sensitivity and Failure Mechanism of 304 Austenitic Stainless Steel: The Significant Role of Rolling Temperature

Metastable austenitic stainless steels (ASSs) have excellent ductility but low strength, so that their usage as load-bearing components is significantly limited. Rolling is an effective method of increasing strength, whereas the effect of rolling temperature on microstructural evolution, the hydrogen embrittlement (HE) sensitivity and fracture mechanisms is still unclear. In present study, the effect of cold/warm rolling on detailed microstructural characteristics of 304 ASS was quantitatively investigated, and the corresponding HE sensitivity was evaluated via slow strain rate test. The results suggest that cold-rolling led to high strength but poor plasticity and deteriorated HE sensitivity, while warm-rolled samples provided combination of high strength and ductility and also superior HE resistance. Compared with 18% α′-martensite in cold -rolled steel, warm-rolled specimens consisted of complete austenite, less twins and lower dislocation density，moreover, the favorable {112} ND and {110} ND textures replaced the harmful {001} ND texture. Based on in-situ EBSD observation during SSRT, the HE sensitivity was governed by the combined effect of pre-deformation microstructures and the dynamic microstructural evolution. Advanced method of time-of-flight secondary ion mass spectrometry was used to observe the distribution of hydrogen, and the hydrogen content of specimens was determined by the gas chromatograph thermal desorption analysis method. An exceedingly small amount of hydrogen entered the warm-rolled samples, while a large amount of hydrogen was trapped at grain boundaries of cold-rolled sample, leading to complete intergranular fracture. Therefore, warm rolling is an effective pathway for obtaining high combination of strength and ductility together with excellent HE sensitivity.