Study On High Temperature Properties And Secondary Cooling System Of Continuous Casting Slab

Continuous casting played an important role in improving productivity and product quality, which was the component part of contemporary steel production. The efficient steel production of continuous casting made tremendous contribution to the international steel production increasing gradually. However, there was always some product quality problem in continuous casting production, and the main problem was crack of slab. The main reason of casting cracks closely related with the law of high temperature properties. Therefore, study on the high temperature properties of slab has been needed for decreasing the crack of slab and improving the quality of the products. According to the particular case of producing the section of 200mm×1400mm slab on No.4 super-low head slab continuous caster in a certain steel plant, the paper tested the high temperature properties of steel A slab on 100℃/min, 200℃/min, 300℃/min and steel B slab on 100℃/min, 300℃/min, 600℃/min cooling rate in the range between 700℃and 1000℃using Gleeble-1500D system. The strength of slab on high temperature was increasing while the cooling rates were decreasing, but the number of strength was not changed obvious with high cooling rates. And the strength was not decreasing when the cooling rates were increased a certain value. The ductility of the both slab were decreased with the high cooling rates, while the low ductility area of plastic curves were enlarged and extended towards low temperature, and the ductility grooves were deepened. And the temperature of both slab on straightening points need to control over 1000℃to avoid secondary brittleness temperature range. The fractures of hot tensile test specimens were analyzed by using scanning electron microscope. The inner dendrite of both slab growth fast and the big dendrites were observed on fracture surfaces of specimen. While internal structural transformation of slab between austenite and ferrite made the ferrite increasing and contagious distribution, also reducing the slab plastic.Physical properties of steel A and steel B on high temperature were tested using the DIL409 and STA449 machines. Thermal expansion curves, heat capacity and DSC of both steel were measured.Combining the structure and technological feature of No.4 super-low head slab continuous caster, the paper established the slab mathematical model of solidification and heat transfer, which was in agreement with the caster. Systems of secondary cooling process of both steel A and steel B slab were simulated by using the high temperature properties of both steels. With the change rule of high temperature performance, the detailed analyses of casting billet original second cooling process system, puts forward the shortcomings of straightening segment of reduced cooling strength, improve casting billet temperature measures. Through the field application result indicates that the straightening section low cooling rates on improving billet quality have pretty good effect.