To improve the microstructure and mechanical properties of G115 steel fabricated by laser-directed energy deposition (LDED), this study investigated the effects of normalizing cycles on microstructure and mechanical properties, and established a yield strength calculation model to predict the mechanical properties of the steel. The results indicate that compared to single normalizing and tempering, secondary normalizing and tempering significantly decreases the dislocation density, slightly increases the block size, increases the volume fraction of precipitates, and reduces their size. In terms of mechanical properties, after secondary normalizing and tempering, the tensile strength at room temperature, tensile strength at 650 °C, and hardness of G115 steel decreased by 2.13%, 11.24% and 2.90%, respectively. However, the elongation at room temperature, elongation at 650 °C and impact toughness increased by 1.11 times, 1.92 times and 1.8 times, respectively, achieving a balance between strength and ductility in LDED G115 steel. In addition, the established yield strength model has been verified to effectively predict experimental data, with solid solution strengthening and dislocation strengthening identified as the primary strengthening mechanisms in LDED G115 steel.
Xu et al. (Fri,) studied this question.