Secondary Cooling Pattern for the Prevention of Surface Cracks of Continuous Casting Slab

Abstract

In order to prevent surface defects of a continuous casting slab, the most suitable secondary cooling pattern was developed by means of a theoretical calculation and a laboratory scale experiment on the thermal hysteresis similar to those of continuous casting slabs. Moreover, it was considered that thetrans verse corner cracks could be related to the presence of the precipitates which appeared in crystal grain boundaries.
1) Transverse corner cracks are caused by the precipitates of MN which can form on the grain boundary in the austenite region at the temperatures in the range of 700 to 950°C. Especially, the A1N formation is accelerated by reheating below 700°C
2) From the experimental results of roles of secondary cooling patterns and of temperatures at the unbending roll in slabs continuously cast, it is ascertained that the prevention of transverse corner crack is mainly related to the secondary cooling pattern, that is, a good cooling rate is less than 83°C/m in the upper part of continuous casting machine.
3) The newly-developed spray cooling pattern can also give a reduction in the longitudinal surface cracks.