Effect of niobium precipitation behavior on microstructure and hydrogen induced cracking of press hardening steel 22MnB5

The effect of different content of Nb on the microstructure, mechanical properties and hydrogen trapping of press hardening steel (PHS) 22MnB5 was investigated. The function of Nb addition on the microstructure was studied by SEM, TEM and XRD, etc. which indicated that the microstructure of the steels containing Nb are finer than that of steel without Nb, what's more, the lath martensite is narrower with the increase of Nb content. Certainly, the tensile strength and elongation of hot-rolled steels, hot stamping steels also were measured. To understand the influence of adsorbed hydrogen on the mechanical property of PHS, Slow Strain Rate Test (SSRT) of smooth specimen was conducted. The results of precipitation behavior and its impact on hydrogen induced cracking manifested that hydrogen embrittlement susceptibility decreased obviously with the addition of Nb content due to reduced hydrogen diffusivity.