Derivation of a Kinetics Model for Solute Carbon during Rapid-cooling in Continuous Annealing Process for Low-carbon, Cold-rolled Sheet Steels

Abstract

Continuous annealing process for low-carbon, cold-rolled sheet steels generally consists of annealing, rapid-cooling and over-aging. The rapid-cooling plays a role of increasing the degree of supersaturation of solute carbon to accelerate the carbide precipitation during the following over-aging, which brings anti aging property on the products. Therefore, it is elementally necessary to formulate the behaviour of solute carbon during the rapid-cooling in order to investigate the carbide precipitation kinetics in the whole continuous annealing process.
In this paper, a simple differential equation has been derived for this purpose by an assumption that ferrite grain boundary is an unique site for carbide precipitation.
Numerically calculated results are compared with experiments in which solute carbon of variously heat-treated materials is measured by the internal friction method. In the region of slower cooling rate and smaller grain, the calculated results well explain the experimental results involving the effect of grain size. In the opposite region, however, the experimental data on solute carbon are much less than the calculated. This can be understood the generation of carbon complex during the measurement of internal friction from the additional experiments.
So, it is concluded that the kinetics model is effective to evaluate solute carbon just after the rapid-cooling.