Abstract
A systematic theoretical and experimental study has been conducted to predict the heating rates required to obtain a pre-defined percentage of overlap between the ferrite recrystallization process and the austenite formation process in dual phase steel manufacture. Isothermal recrystallization kinetics for three different cold-reduced low-carbon micro-alloyed steels (50%, 60%, and 75%) with ferrite-pearlite-bainite initial microstructures was evaluated. Using various experimentally determined rate kinetic constants and critical temperatures, a continuous heating rate model which predicts the heating rate required for a predefined amount of overlap was successfully developed. The model predicted the heating rates required for a predefined 1%, 15%, 34%, 67%, 88% and 99% of overlap to be 0.2°C/s, 0.9°C/s, 1.8°C/s, 7°C/s, 50.5°C/s and 511°C/s, respectively. The experimentally determined recrystallization percentage values validated the predicted heating rates.
Highlights
In recent decades, the automotive industry has been able to manufacture vehicles with high crash safety and better fuel efficiency thanks to the rapid development of advanced high-strength steels (AHSS).[1]
It can be clearly seen that the amount of deformation in the ferrite grains and its corresponding aspect ratios increases with increase in cold reduction (CR)
JMAK parameters were determined for three different CR low-carbon steels
Summary
The automotive industry has been able to manufacture vehicles with high crash safety and better fuel efficiency thanks to the rapid development of advanced high-strength steels (AHSS).[1]. Massardier et al, used heating rates ranging from 20°C/s to 1000°C/s for 75% cold-rolled Al-killed low-carbon steels.[24] Kulakov et al.,[25] chose a heating rate of 100°C/s for 50% cold-rolled materials of three different initial microstructures These wide ranges of heating rates produce different percentages of overlap, which makes the comparison between the various studies ineffective. The effect of stored deformation energy on the heating rate required for a given percentage of overlap, the as-received 2-mm HR and pickled material, from the Tata Steel pickling plant, was cold-rolled with a Hille-Muller laboratory cold-rolling mill to three different CRs of 50% (1 mm), 60% (0.8 mm) and 75% (0.5 mm)
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