Strengthening mechanisms of nanoprecipitates at elevated temperature in secondary hardening steel

Abstract

This study systematically investigated the effects of tempering temperature on the microstructural evolution, carbide precipitation behavior, and high-temperature mechanical properties of a newly developed 30Cr2Ni3Mo3V secondary hardening steel using SEM, TEM, XRD, and high-temperature tensile testing. The results show that the high-temperature strength initially increased and then decreased with increasing tempering temperature. The tensile strength reached a peak value of 405 MPa at 700 °C for samples tempered at 600 °C. When the tempering temperature was raised to 700 °C, carbides significantly coarsened, and the dislocation density decreased, resulting in a tensile strength drop to 338 MPa. During high-temperature tensile testing, the dispersed precipitation of nanoscale MC carbides (3–5 nm) effectively hindered dislocation motion via the Orowan mechanism, exhibiting superior thermal stability compared to M₂₃C₆. This study revealed that the high-temperature strength of 30Cr2Ni3Mo3V steel originates from the strengthening mechanism induced by the dispersion of nanoscale MC carbides during high-temperature deformation.