Effects of residual stress and plastic strain on hydrogen embrittlement of a stretch-formed TRIP-aided martensitic steel sheet

[Display omitted] •Hydrogen embrittlement behavior of a stretch-formed TRIP-aided steel was investigated.•Residual stress and plastic strain were analyzed by means of hard synchrotron X-rays.•Crack initiation took place at the region of the foot of the impression.•High tensile stress was detected at the region from the foot to the hillside.•The crack initiation site corresponded to the region where acted the maximum stress. Hydrogen assisted cracking on hemispherically-stretch-formed specimens of transformation induced plasticity-aided martensitic steel was investigated. Hydrogen charging induced cracking around the foot of the impression formed on the steel sheet, and the cracks propagated along the radial direction toward the hillside and the plains. Distributions of stress, plastic strain and volume fraction of retained austenite were analyzed employing the energy-dispersive X-ray diffraction method utilizing the synchrotron X-ray radiation at SPring-8. It was notable that the crack initiation took place in the region where the measured tensile stress was the highest. Influences of plastic strain and resulted martensitic transformation were also suggested.