Critical hydrogen concentration for the brittle fracture of AISI 430 stainless steel

The introduction of hydrogen to AISI 430 stainless steel by electrochemical charging was studied. Tensile tests were employed to elucidate the mechanical behavior of the alloy responding to the effect of aging after cathodic charging, dynamic charging, and interrupted charging. The fractography was investigated by scanning electron microscopy. It was found that the hydrogen embrittlement of AISI 430 stainless steel was mainly due to the trapping of hydrogen at dislocations, and its fracture type is mainly transgranular with a small fraction of intergranular fracture. Through mathematical modeling, with the diffusivity and surface concentration of hydrogen obtained by permeation measurements, the critical concentration of hydrogen required to change the fracture mode from ductile microvoid coalescence to brittle transgranular cracking was determined to he 1.45 x 10(-5) mol/cm(3).