Effect of microstructure on the hydrogen embrittlement behavior of DP and FB steels

Abstract

High-strength steels are increasingly used in automobile industry. However, susceptibility of hydrogen embrittlement is also markedly increased, resulting in the deterioration of mechanical properties. This thesis presents a comparative study of hydrogen embrittlement (HE) and resistance to HE of dual-phase (DP) and ferrite-bainite (FB) steels, which are most widely used steels in automobile parts. Hydrogen was infiltrated into the steel by an electrochemical method, then a slow strain rate test(SSRT) and thermal desorption spectrometry(TDS) tests were conducted. DP steel absorbed more hydrogen than FB steel. Consequently DP steel showed much lower fracture strength than FB steel implying that FB steel was more resistant than DP steel to HE. The results were attributed to the high dislocation density of the DP steel and the fine grain size of the FB steel.