Determination of Austenite Grain Coarsening Temperature of a Nb-Microalloyed Steel Sheet

Thermomechnical processing and controlled rolling of microalloyed steel sheets are affected by several factors according to the final properties of product. To create the high mechanical properties, a uniform and fine-grain structure is necessary in hot rolled final products. To produce such microstructures, every stage of the thermomechanical processing of the steel rolling has to be carefully controlled. Hence, first step is grain coarsening control that it usually occurs during reheating for slab. For this purpose, seven different reheating temperatures between 1000 to 1300 °C with 50 °C increments were chosen in this investigation for soaking treatment. By soaking the specimens in furnace, the grain coarsening temperature (Tgc) is obtained about 1250 °C. Moreover, it is observed that increasing the reheating temperatures causes more decreasing of the precipitates percentage. Hence, for these kinds of steels, the reheating temperature 1200 to 1250 °C is recommended.