Pre-straining alters hydrogen-assisted cracking site and local hydrogen diffusivity in a nitrogen-doped duplex steel

Abstract The pre-deformation effects of hydrogen embrittlement on nitrogen-doped duplex stainless steel were investigated using tensile testing. Hydrogen pre-charging and pre-straining were adopted, which increased the yield strength, but decreased the ductility. Silver decoration revealed that diffusible hydrogen was preferentially located in the ferrite or grain boundaries of the undeformed steel, whereas the 22% pre-strained steel had diffusible hydrogen in austenite. When deformed, the preferential plastic deformation path of the steel was in the ferrite; hence, the apparent diffusivity in ferrite decreased, while the austenite had a relatively high apparent hydrogen flux. Pre-straining suppressed macroscopic hydrogen diffusion and local diffusion in ferrite and austenite by increasing the dislocation density. The degree of the suppression of the local diffusion was more significant in ferrite than austenite. The changes in dislocation and hydrogen behaviors associated with pre-straining altered the cracking sites in the austenite and ferrite, and decreased hydrogen embrittlement susceptibility.