Study on Microstructure and Mechanical Properties of Marine 10Ni5CrMoV Steel during Tempering

Abstract

The microstructure and mechanical properties of marine 10Ni5CrMoV steel are systematically investigated at tempering temperatures ranging from 630 to 670 °C. With increasing tempering temperature, several key parameters exhibit notable changes: the volume fraction of reversed austenite decreases from 17.36% to 13.39%. The equivalent grain size increases from 0.91 to 1.09 μm. The equivalent diameter of precipitates increases from 59 to 79 nm. The dislocation density decreases from 0.82 × 10−15 to 0.51 × 10−15 m−2. As the tempering temperature increases, the pinning effect of precipitates on dislocations and martensite laths decreases. This leads to reductions in both dislocation strengthening and precipitation strengthening mechanisms. Consequently, the yield strength of the specimen decreases from 876 to 683 MPa. The increase in the ductile‐brittle transition temperature of the specimens from −116 to −95 °C can be attributed to several factors. First, the increase in precipitate size reduces the critical nucleation stress of cleavage cracks and promotes the nucleation of such cracks. Additionally, the decrease in dislocation density mobility leads to a reduction in the dimple nucleation rate, thereby diminishing the role of dimples in hindering crack propagation.