TEMPERATURE-CHANGES IN HOT FLAT ROLLING OF STEELS AT LOW STRAIN RATESAND LOW REDUCTION

A finite difference (two-dimensional) model developed to describe the heat flow at low strain rates (0.08-1.5 s(-1)) and low reduction (simi lar to 10 per cent) for a hot flat rolled slab both during air cooling and during roll contact has been used in conjunction with experimenta lly measured temperatures through specimen thickness during roll conta ct after reheating to temperatures in the range 1000-1200 degrees C fo r mild steel, low carbon SS316 and high carbon SS316 (with Nb, V and T i). At high strain rates (similar to 1.5 s(-1)) a steep temperature gr adient was produced in the specimen near the surface whereas for low s train rates (similar to 0.08 s(-1)) this temperature gradient penetrat ed deep into the thickness, leading to a large drop in the mean rollin g temperature. Roll chilling, leading to higher values of the Zener-Ho lloman parameter, Z, resulted from a decrease in the mean rolling temp erature and the large temperature gradient during roll contact. Temper ature changes due to material composition, reheating temperature, cont act time and rolling conditions led to precipitation strengthening and roll chilling effects which have accounted for the excess load and to rque observed experimentally and industrially.