Hydrogen Embrittlement Evaluation Methods for Ultra-high Strength Steel Sheets for Automobiles

In order to apply ultra-high strength steel sheets with tensile strength of 980MPa or higher to automobiles, it is necessary to ensure the safety of steel parts against hydrogen embrittlement (HE). HE is influenced by hydrogen content and stress and strain introduced in parts by various forming processes. In this paper, the critical HE conditions for 1180MPa grade steels were investigated with specimens formed by bending and drawing. The critical hydrogen contents of the HE regions induced by both forming modes decreased with increasing equivalent strain. The critical HE conditions were also compared.