EFFECT OF HYDROGEN PRESSURE ON HYDROGEN EMBRITTLEMENT BEHAVIOR OF 23Cr2Ni4MoV HIGH STRENGTH STEEL

In this paper, effects of gaseous hydrogen pressure on the mechanical properties and fracture morphology of the 23Cr2Ni4MoV steel were analyzed by modified slow strain rate tensile (MSSRT) test and scanning electron microscope (SEM). The results show that the plasticity of 23Cr2Ni4MoV is significantly influenced in hydrogen environment with respect to that in nitrogen environment, rather than the yield strength and ultimate tensile strength. The elongation (EL) and the reduction in area (RA) are degraded by 79% and 68% in 35 MPa gaseous hydrogen with respect to the results in 35 MPa gaseous nitrogen. The crack initiates at the surface of the sample in the hydrogen, and the initiation depths influenced by hydrogen are 100 mu m, 300 mu m, and 700 mu m in 1 MPa, 10 MPa and 35 MPa hydrogen environment, respectively. In the nitrogen environment, the microstructure of the crack-initiated region is dimple; while in the hydrogen environment, it is cleavage and rock-sugar like. In addition, in the hydrogen environment, circumferential cracks appear at the surfaces near the fracture of 23Cr2Ni4MoV steel.