Microstructure characteristic of hot formed 22MnB5 steel and its relationship with delayed hydride cracking property

Abstract

Hydrogen-induced delayed cracking is an important factor leading to the failure of ultra-high strength steels during service, thus in this study, the mechanical properties and hydrogen trapping of hot formed 22MnB5 steel considering different content of V (0, 0.05, 0.09 wt.%) and corresponding microstructure were investigated. Slow strain rate tensile tests (SSRT) were applied to obtain the tensile strength and elongation of samples under different medium conditions (air, HCl immersion and electrolytic hydrogen charging). Besides, microstructure and atomic distribution morphology of the samples were detected and analyzed by transmission electron microscope (TEM) and atomic probe tomography (APT) technique. Results showed that both resistances of hydrogen-induced delayed cracking in MnB-V5 and MnB-V9 samples were obviously better than that in MnB-V0 sample, besides, the delayed cracking resistances of MnB-V9 and MnB-V5 samples did not improve with the increase of V content, but basically remained the same. Lamellar residual austenite was found in all samples, but no hydrogen was grasped in the same area according to APT result. There was intragranular cementite in all samples, and it has grasped H in the same position. The carbides formed by V, Ti and other alloying elements were found in MnB-V5 and MnB-V9 and were considered to be an important factor in improving the anti-hydrogen delayed cracking performance of the steel.