In Situ Microstructural Evolution and Mechanical Performance of Nickel Alloying Steels during High‐Temperature Heat Treatment

This study investigates the microstructural evolution and mechanical properties of steel subjected to high‐temperature heat treatment, with a focus on the formation and effects of second‐phase precipitates. High temperature confocal laser scanning microscopy is employed to observe the in situ changes in microstructure as the steel is heated from room temperature to 900 °C. During continuous heating, precipitates are first observed in situ at ≈820 °C. Both the size and number of precipitates reach their maximum at 900 °C. Compositional analysis identifies these precipitates as chromium carbides (Cr 7 C 3 ). Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy confirm that these precipitates significantly enhance the material's hardness, with microhardness values of 330 HV for the precipitates compared to 240 HV for the matrix. Tensile tests show that the tensile strength of the steel increases with soaking time at 900 °C, reaching a maximum after 3 min due to the strengthening effect of the precipitates. Beyond this point, strength decreases due to grain coarsening.