The effect of rapid resistance heating on microstructure and hydrogen embrittlement of ultra-high-strength hot stamping steel

Abstract

The rapid resistance heating (RH) method, which is recognized for its time-saving and energy efficiency, shows potential for producing hot stamping ultra-high-strength steels. However, its impact on mechanical properties, particularly hydrogen embrittlement (HE), has not yet been comprehensively investigated. This study reveals that although RH enhances the mechanical properties of steels, it also leads to an increase in HE sensitivity, which can be alleviated through a baking treatment. Compared to conventional furnace heating (FH), RH significantly shorten the heating duration, refines the prior austenite grain (PAG) size, and increases dislocation density. The finer PAG size enhances the variant selectivity during martensitic transformation, while dislocation strengthening contributed to improved strength and ductility. However, RH specimens exhibited more severe hydrogen-induced deterioration in mechanical performance, with fracture surfaces characterized by distinct intergranular fracture even under short-duration hydrogen charging. Then, the baking treatment was proven effective in reducing HE sensitivity by impeding hydrogen transport via dislocation slip to PAG boundaries, thereby mitigating hydrogen-induced boundary decohesion and delaying the onset of intergranular cracking. Furthermore, the weakened variant selectivity of martensite promotes the formation of low-angle PAG boundary segments, which act to hinder crack propagation. These findings provide a faster and more efficient heating method for producing ultra-high-strength steels with improved performance and reduced HE sensitivity.