Thermodynamic model for carbonitride precipitation in low carbon steels

Carbonitride precipitates have significant effects on the mechanical properties of steels via grain refinement and precipitation hardening. Based on the two-sublattice model (metal atom sublattice and interstitial atom sublattice) of regular solution, a thermodynamic model for the precipitates of titanium carbonitride, aluminium nitride and manganese sulfide was established to study the starting-temperature of precipitates and the austenite composition at a given temperature in a low carbon steel and applied to compact strip production (CSP for short) process. The calculation results show that starting-temperature of the precipitation of Ti(C_xN_1-x), MnS and AIN are 1200℃, 1 440℃ and 1 010℃, their mole fraction are 2.315×10^-5, 4.18×10^-4 and 3.1×10^-4, respectively. By comparison the simulation results of the model are in agreement with the calculated ones by the Thermo-Calc software and the available experimental data from some publications. The thermodynamic model can be a useful tool in studying the precipitates of low carbon steels and in analyzing the CSP process.