Influence of rolling temperature and cooling rate on nano-size carbides in a Ti-Mo microalloyed steel

Abstract

Carbide precipitation in Ti-Mo ferrite-containing low carbon steel was investigated by hardness testing and transmission electron microscopy. Both the rolling temperature and cooling rate after holding affect the hardness of ferrite, and prolonged holding caused the small carbides to coarsen and aggregate, so that the hardness of ferrite decreased rapidly. The same hardness, however, was obtained at a slow cooling rate even after the same prolonged holding. Rolling in the recrystallization region created a precipitation-free zone near both the grain boundary and grain interior, and the low hardness of ferrite may be caused by low carbide density in ferrite due to precipitation-free zone near the grain boundary and within grains after short and prolonged holding times, and coarsening of carbides after prolonged holding times.