Influence of cooling rate on austenite transformation and contraction of continuously cast steels

Abstract

Based on thermodynamic calculations and dilatometry experiments performed over a wide range of cooling rates with on two continuously cast steels, an empirical model was developed to describe the relationship between the critical temperatures of austenite transformation, the cooling rates, and the equilibrium temperatures of phase transformation, written as Ar(°C) = Ae−exp(B+C/C_r). The model was verified to be applicable to the calculation of Ar₃ and Ar₁ temperatures at various cooling rates for different steel blanks during continuous casting process. Results indicated that, the Ar₃ and Ar₁ temperatures decreased with increasing cooling rate; and the temperature window for ferrite formation enlarged while the cooling rate was increasing. The influence of cooling rate on the linear and bulk thermal expansion coefficients was discussed. Results showed that the peaks of thermal expansion coefficients during new phase formation apparently moved toward low temperatures as the cooling rate increased; The linear and bulk thermal expansion coefficients of single austenite phase were steady at 2.1×10⁻⁵ and 6.8×10⁻⁵°C ⁻¹ respectively. The relative contraction of steels would be larger at lower cooling rate during continuous casting.

Keywords:

• Cooling rate
• Austenite transformation
• Cooling contraction
• Ar₃ and Ar₁ temperatures
• Steel continuous casting