Investigation into the strengthening and toughening mechanisms of G13Cr4Mo4Ni4V steel

Heat treatments utilizing varying quenching temperatures were applied to G13Cr4Mo4Ni4V martensitic steel. The investigation focused on the microstructural evolution and its influence on the strength and toughness under different heat treatments of the steel using scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). An analysis of the underlying strengthening and toughening mechanisms was conducted. The results demonstrate that the steel can achieve superior overall properties when quenched at 1100 °C. The prior austenite grain size, martensitic packet size and block width all increase with the increasing quenching temperature. In contrast, the width of the martensitic laths remains largely unaffected. Among the contributing strengthening mechanisms, solid solution strengthening accounts for the highest proportion. Second phase strengthening is most significant at the quenching temperature of 1100 °C correlating with the peak yield strength. The yield strength and impact toughness show stronger correlation with characteristic sizes of the martensitic block and packet, respectively. Furthermore, the heterogeneous distribution of aggregated nano-sized carbides induces local strain concentration leading to a reduction in impact energy. The formation of ferrite slightly enhances strength due to strain hardening but drastically diminishes impact energy. This embrittlement is attributed to microcracks initiation at the ferrite-matrix interfaces.