MODELING OF MICROSTRUCTURAL EVOLUTION DURING ACCELERATED COOLING OF HOT STRIP ON THE RUNOUT TABLE

Microstructural evolution in the hot strip after finishing and subsequ ent accelerated cooling on the runout table has been modelled in order to assess their suitability for further processing. Transient heat tr ansfer and kinetics of phase change comprising austenite to ferrite pl us pearlite have been coupled to ascertain temperature profile, taking into accout the heat generated during phase change. Johnson-Mehl-Avra mi relation together with Scheil's rule of additivity have been invoke d. Several process parameters such as, coefficient of heat transfer, t emperature at the exit of finishing stand, thickness and the speed of strip have been varied to determine their influence on the extent of p hases engendered on the runout table. It has been demonstrated that gr eater spreadout in cooling arrangement with relatively lower heat tran sfer coefficient ensures homogeneity in microstructure. Cooling from c omparatively higher finishing temperatures may result in greater micro structural uniformity. Two grades of steel - namely 0.05C-0.23Mn-0.015 Si and 0.08C-0.37Mn-0.06Si - were chosen to carry out plant trials to validate the model. Special features of the microstructure have been b rought out and the mechanical properties have been correlated.