Hydrogen-induced delayed cracking in the AISI 301 unstable austenitic steel sheet

This work aims to study the hydrogen-induced delayed cracking related to the martensitic transformation in the AISI 301 unstable austenitic stainless steel. It happens because the metastable austenite is substantially transformed into image-martensite due to the deformation occurring during the clamp-forming operation. To understand this phenomenon, morphological and chemical analyses have been made. The martensite fraction in the inside bend radius was measured by X-ray Diffraction (XRD) and the breaking patterns were observed using a Scanning Electron Microscope (SEM). The clamps breaking patterns observed after delayed cracking show a brittle intergranular fracture in the bend radius. Under laboratory conditions and after hydrogen-charged clamps, delayed cracking occurred. The main fractographic feature observed in cracked clamps is the intergranular Hydrogen Embrittlement (HE). This brittle behavior is intensified by the high heterogeneous stress state in the material and the high content of martensite.