Abstract
The aim of this paper was to evaluate the dependence of precipitation on casting rate in the surface zone of a TiNb microalloyed steel slab, and to compare the results with those in a TiNb IF steel slab. In the microalloyed steel TEM revealed fine and larger globular particles and larger angular particles of TiN and TiC. For higher casting rates TEM revealed more fine particles of similar shape, but NbC was combined with TiN and TiC. Precipitates in the slab surface zone of the TiNb IF steel were both globular and oval. They were based on Al and Ti in combination with MnS and stick shape particles based on Al. Comparison of precipitates in the surface zone of slabs cast at the same pulling rate 0.8m/min for both TiNb micro-alloyed steel and TiNb IF steel grades, showed fewer particles in the IF steel. This is assumed to be due to the very low carbon content in the IF steel compared to the microalloyed one.