METHOD FOR REGULATING QUALITY OF HOT-ROLLED STEEL MATERIAL

PURPOSE:To manufacture efficiently a steel material of necessary quality in good yield by setting the hot-rolling conditions, cooling velocity, and the temp. to stop cooling satisfying the ferrite grain size estimating equations, and forming the desired quality. CONSTITUTION:The hot-rolling conditions, cooling velocity, and temp. to stop cooling are set by the ferrite grain estimating equations I and IV to regulate the desired quality. In the equations I and IV, Nalpha is the ferrite grain size number, Ceq is the carbon equivalent (=C+Mn/6, unit %), CR is the cooling velocity ( deg.C/s), CT is the winding temp. or the temp. to stop cooling ( deg.C), Z is the Zener- Hollomor parameter at the final pass, Z is equation II, epsilon is the strain velocity at the final pass (sec), T is the rolling temp. at the final pass (K), Q is equation III, R is the gas constant (k) is equation V, (r) is equation VI, epsilon' total is equation VII, epsiloni is strain added at the i-th pass, epsiloni is strain velocity at the i-th pass, ti is the time from the i-th pass to the completion of the pass, and A1- A6 are constants (coefficients determined by a statistical technique).