A Kinetics Model for Carbide Precipitation during Over-aging in Continuous Annealing of Low-carbon, Cold-rolled Sheet Steels

Abstract

Rapid-cooling and over-aging treatment just after recrystallization annealing is necessary to continuous annealing for low-carbon, cold-rolled sheet steels to prevent carbon aging of the products. In this paper, a theoretical model for carbide precipitation kinetics during this stage has been derived. The model involves two rate processes, the one being precipitation to ferrite grain boundaries, and the other within grains. As the latter one, the model expresses nucleation and growth, and besides, heterogeneous nucleation on manganese sulfides.
This model has only one adjusting parameter which was decided experimentally. Nevertheless, one can calculate decay of solute carbon in various cases including such cases that temperature varies.
In order to prove this theory available, an experiment of quench aging using commercially produced. low-carbon steel was conducted. Results of theoretical calculation have good agreement with the experimental results, although the theoretical precipitation rate is slightly slower at early stage, and slightly faster at late stage than the experimental value. Arrhenius plotting of the experimental data showing no simple linearity against the inverse of temperature, represents the phenomenon complicated.
Differences between the present theory and the previous ones were discussed.