The influence of the Cu-rich nanoprecipitates structure on the hydrogen embrittlement behavior of 17–4PH stainless steel in a high-pressure hydrogen environment

Abstract

This study investigates the effect of Cu-rich precipitates formed at different aging temperatures on the hydrogen embrittlement (HE) behavior of 17–4PH stainless steel through mechanical tests and microstructure analysis. The result shows that as the aging temperature increased from 480°C to 620°C, the material strength gradually decreases, and the HE resistance first increases and then decreases. Among them, the material aged at 580°C exhibits the lowest HE susceptibility (about 9.96 %). The fracture morphology changes from a cleavage fracture to an intergranular fracture and then to a quasi-cleavage fracture. This is mainly related to the microstructure transformation of the Cu-rich precipitates. The diffuse Cu precipitated at 480°C strongly pins the dislocations, thereby triggering cleavage fracture based on the hydrogen-enhanced decohesion mechanism (HEDE) model. When the precipitated phase transforms into BCC-Cu (520°C), local deformation at the grain boundaries causes intergranular cracking based on the HEDE model and hydrogen-enhanced decohesion mechanism (HELP) model. Moreover, when the aging temperature increases to 580°C, 9R-Cu with a lower distribution density forms. It can generate a large number of dislocation clusters through the Orowan mechanism, thereby inhibiting the segregation of dislocations and hydrogen, and delaying cracking. however, the FCC-Cu formed at 620°C cannot effectively hinder the movement of dislocations, resulting in dislocation segregation caused by the effect of hydrogen, which leads to premature fracture at a relatively low strength. This study suggests that appropriate precipitate phase structure and distribution can enhance the material's resistance to HE by reducing dislocation aggregation and weakening interfacial stress.