Intercritical annealing temperature dependence of hydrogen embrittlement behavior of cold-rolled Al-containing medium-Mn steel

Abstract

The present investigation attempts to evaluate the influence of intercritical annealing temperature (TIA) on the hydrogen embrittlement (HE) of a cold-rolled Al-containing medium-Mn steel (Fe-0.2C-4.88Mn-3.11Al-0.62Si) by using electrochemical hydrogen-charging, slow strain rate tensile test and scanning electron microscope. The results show that an excellent combination of strength and ductility (the product of ultimate tensile strength and total elongation) up to ∼53 GPa·% was obtained for the specimen intercritically annealed at an intermediate temperature of 730 °C, whereas the HE index increases significantly with an increase in TIA up to 850 °C. Being different from the typical dimple ductile fracture for the uncharged specimen, the hydrogen-charged specimen exhibits a mixed brittle interface decohesion and ductile intragranular fracture mode in the crack initiation region and the brittle fracture fraction increases with increasing TIA. Both the stability and amount of austenite play a critical role in governing the HE behavior of TRIP-assisted medium-Mn steel. Thus, it is suggested that suitable TIA should be explored to guarantee the safety service of automotive parts made of this type of steel in addition to acquiring excellent mechanical properties.