Metallurgical evidence of stress induced hydrogen diffusion and corresponding crack nucleation behaviors of high-strength ferritic steel used in sour environment

Owing to the difficulty in obtaining experimental evidence of stress-facilitated hydrogen-diffusion/trapping behavior, previous studies focused on numerical analyses of electrochemical permeation measurements. To address the weak points of the theoretical approaches and provide strong supporting evidence, the nascent facture surface of an initial crack formed only under an applied stress was examined. This paper presents two metallurgical findings of clusters comprised of 2nd phase particles and traces of grain/lath boundaries observed in the crack nucleation site of high-strength ferritic steel under an applied tensile stress in elastic range.