Recovery of hot ductility by improving thermal pattern of continuously cast low carbon and ultra low carbon steel slabs for hot direct rolling

Continuously cast low carbon and ultra low carbon steel slabs with low Mn/S ratio processed via hot direct rolling route tend to form more surface defects than those via hot charge rolling route. The slab low in Mn/S ratio exhibit poor ductility during hot direct rolling at elevated rolling temperatures and high strain rates. Various thermal patterns have been investigated with hot tensile test to find a suitable one to recover the hot ductility of these slabs in hot direct rolling. When they are once cooled to α-ferrite temperature range and subsequently reheated to austenitic temperature range, remarkable recovery of the hot ductility has been found to occur. This recovery is attributed to the recrystallization of prior austenitic grains which transform first into α-ferrites then to new austenitic grams, leaving manganese sulfides which existed at the prior austenite boundaries not to precipitate at the recrystallized new austenite boundaries.