Prediction model for crack sensitive temperature region and phase fractions of slab under continuous casting cooling rates based on finite number of experiments

Abstract

Accurate prediction of the crack sensitive temperature region and phase fractions variation of slabs during continuous cooling is an important guide to avoid cracks and effectively control the quality. Based on finite number of measurements, at different cooling rates of the continuous casting process, a prediction model for characteristic temperatures of austenite decomposition, the variation of phase fractions with temperature, the crack sensitive temperature regions, and the final microstructural compositions of casting slabs at different cooling rates has been established and evaluated the accuracy. The results show that austenite decomposition temperature range moves toward the low temperature region as cooling rate increases, and the independent peak of ferrite transition become weaker. The characteristic temperatures of austenite decomposition can be quantitatively calculated by TC(CR) = A−exp(B + C/CR) at different cooling rates, which the maximum relative error for experimental steels is −2.2%. The ferrite and pearlite phase fractions increases with decreasing temperature during continuous casting cooling, which means that the ability of the billet to resist deformation and external force changes. Meanwhile, the final ferrite content of slabs for Steel B and Steel C at different cooling rates are 83.24620−exp(2.59364–13.72283/CR) and 85.07143−exp(1.71320–15.82244/CR), respectively. The crack sensitive temperature region Ae3 ∼ Tα40%(CR) calculated by the prediction model is in good agreement with the low ductility zone measured by experiment. Moreover, the critical temperatures Tα40%(CR) of the crack sensitive temperature regions are 890.35731−exp(2.99719–20.67781/CR), 745.87462−exp(4.83056–44.18511/CR) and 729.46168−exp(2.96621–12.21949/CR) for three experimental steels under different cooling rates.

Keywords

• Austenite decomposition
• Crack sensitive temperature region
• Phase fraction
• Cooling rate
• Characteristic temperature
• Prediction model