Hydrogen embrittlement of a cold-rolled Al-containing medium-Mn steel: Effect of pre-strain

It is often unavoidable that automotive steel sheet parts might undergo plastic deformation during forming and service life. The present research explored the effect of pre-strain up to 15% on hydrogen embrittlement (HE) behavior of a cold-rolled and intercritically annealed Al-containing medium-Mn steel by electrochemical hydrogen charging and permeation testing, thermal hydrogen desorption spectrometry and slow strain rate tensile testing. The results show that the primary microstructural changes after pre-strain are the significant increase in dislocation density and the transformation of a slight part of retained austenite into martensite, which cause a decrease in hydrogen diffusion coefficient and a significant increase in absorbed reversible hydrogen concentration. Therefore, the HE susceptibility increases notably with an increase in pre-strain. It is thus concluded that pre-straining not only enhance the strength level but also remarkably increase the HE susceptibility of medium-Mn steel.