The grain refinement of hot rolled extralow carbon steel steels has been required because it improves the deep drawability of the cold rolled sheets. For refining the ferrite grain, the following processing actions of hot rolling are taken 1 ; ① the increase in reduction, especially in the reduction at final rolling, ② the increase in the cooling rate, ③ the reduction of the interval between the final rolling and the onset of rapid cooling and ④ the proper selection of the finishing temperature. To analyze the grain refinement behavior observed through these actions, a mathematical model for predicting the microstructure of extralow carbon steels has been developed. In this paper, the model is introduced and the experimental results are discussed comparing with the results of the model calculation.2. Results
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