The Effect Mechanism of Si on the Cementite Growth Behavior in Fe–Cr–C Steel: First-Principles Calculations and Experiments

In the present study, the Si content (0–1.50 wt%) in Fe–1.5Cr–1.0C steel was systematically varied to shed light on the effect of Si on the microstructure characteristic and precipitation of cementite in steel. Results showed that the Si content in the range of 0–0.42 wt% had a positive effect on the cementite growth, while a negative effect in the range of 0.42–0.71 wt%. Besides, there was an insignificant effect on the cementite growth when the Si content was in the range of 0.71–1.50 wt%. Thus, the adjustment of Si content had a great impact on the cementite growth at the 0.29–0.71 wt% range, the regulation of cementite growth time needed special attention. In addition, the positive effect of Si on the cementite growth might be attributed to the increase in the precipitation temperature of cementite based on thermodynamic analysis. However, a stronger Si barrier around cementite was formed when Si content was higher than 0.42 wt%, which hindered the diffusion of C atoms and the cementite growth. However, the above assistance and resistance to cementite growth might be the near-equilibrium state with the increase in Si content at the 0.71–1.50 wt% range, and thus the effect of Si content was slight on cementite growth in this range. Furthermore, another interesting phenomenon was observed that the nucleation ability of cementite decreased monotonically with the increase in Si content (0–1.50 wt%). The reason for the inhibition effect of Si on the cementite nucleation was further studied by the first-principles calculations that the doping of Si reduced the interface stability at the austenite–cementite interface.