METHOD FOR REGULATING QUALITY OF HOT ROLLED STEEL MATERIAL

PURPOSE:To improve accuracy in the estimation of the quality of a steel material in hot rolling by setting an austenite grain size and cooling conditions which satisfy a prescribed equation for estimating a ferrite grain size and by regulating the quality of the steel material. CONSTITUTION:A required ferrite grain size is decided, and a cooling rate and an austenite grain size for attaining the ferrite grain size are calculated in accordance with the equation [where dalpha is the ferrite grain size (mum), dgamma is the austenite grain size (mum), C is the concn. (%) of carbon, CR is the cooling rate ( deg.C/sec), Ae3 is the equilibrium transformation temp. ( deg.K), and each of A1-A7 is a constant]. Ordinary carbon steel is rolled at the Ar3 transformation point or above, and it is cooled at once under cooling conditions decided in accordance with said equation to regulate the quality.