Abstract
A continuous annealing heat cycle is established for the drawing quality cold rolled low-carbon capped steel strip. The heat cycle is composed of the recrystallization treatment, rapid cooling incorporating water quenching, and subsequent over-aging treatment. Sufficient over-aging can be realized in less than lmin by virtue of the rapid cooling, in contrast to the past results in which over-aging times of 30 min-1 hr were employed. The main feature of the heat cycle is as follows: recrystallization treatment at 700°to 720°or 40 see; water quenching from around 600°C; over-aging treatment at 350°-450°C for 60 sec.
The recrystallization in the above temperature range results in the reasonably large ferrite grains without the presence of the pearlite colonies.
The water quenching from around 600°C is essential to balance the beneficial effect of the decrease in solute carbon against the adverse effect of the increase in the fine carbide precipitates.
The over-aging treatment in the above temperature range is beneficial to achieve the efficient over-aging under a reasonably low solubility of the interstitial carbon.
Prolongation of the recrystallization or over-aging treatments does not show any substantial effect.
