Effects of Continuous Annealing Conditions on Mechanical Properties of Drawing Quality High Strength Steel Sheet

Abstract

Effects of continuous annealing conditions on mechanical properties of drawing quality high strength steel sheet were studied using the continuous annealing heat cycle simulator which had been developed by the authors.
Continuous annealing conditions which were studied are as follows:
(1) Cooling rate before over aging. (2) Starting temperature of cooling in the cases of AcC (accelerated cooling) method and W. Q (water quenching) method. (3) End temperature of cooling in the case of AcC method. At the same time, changes of the amount of carbon in solution and carbide precipitation during heat treatments were studied.
As a result of this study, it was made clear that the most desirable heat cycle for drawing quality and non aging high strength steel sheet consisted of slow cooling of about 7°C/s from soaking temperature to 675°C, accelerated cooling of about 100°C/s from 675°C to 400°C and over aging at 400°C. In this annealing condition, most of the fine carbides precipitated on grain boundaries and the amount of carbon in solution decreased in short over aging time.