In Situ Observation on the Structure Transformation Behavior of Rare Earth Ce‐Modified 7CrSiMnMoV Steel

In this paper, the evolution of the solidification and heat treatment microstructure of 7CrSiMnMoV steel modified by rare earth Ce was observed in situ by confocal laser scanning microscopy (CLSM). The results show that the initial solidifying temperature points are 1456°C, 1476°C, and 1490°C, respectively, and the complete solidifying temperature points are 1365°C, 1316°C, and 1315°C with rare earth Ce of 0.000%, 0.009%, and 0.100%, respectively. Consequently, it causes a wider mushy zone range during solidification, which results in a large amount of refined dendrites and the shrinkage becoming larger, and the solidified surface roughness ( Ra max ) is 56.18, 59.23, and 103.84 μm with rare earth Ce content of 0.000%, 0.009%, and 0.100%. This is due to the fact that the rare earth Ce addition formed high‐melting‐point inclusions (e.g., Ce 2 O 3 , Ce 2 O 2 S) that purified the steel liquid and raised its initial solidifying temperature, while Ce segregation at grain boundaries generates low‐melting‐point phases that lower the complete solidifying temperature. Moreover, the strong interactions of Ce with impurities and alloying elements (such as C, V, and Mn) hinder austenite dynamic recrystallization, inhibit cementite precipitation, and also suppress martensite transformation through grain boundary strengthening.