Corner Defect Controlling Technology On Continuous Casting Slab Of Micro-alloyed Steels

Micro-Alloyed Steel used for structure has developed rapidly after last 1960 s. In the HSLA sheet and strip producing technology, the surface quality is always a critical technical problem which obsessed all major steel producers all over the world for long time. The main defect in the slab is transverse edge crack, accounting for more than 50% of all kinds of defects. Therefore the micro-alloyed continuous casting slabs must be processed with corner cutting in cold state. This not only caused a huge waste of energy, material and man-sources but also increases storage area, at the same time efficient production rhythm of steelmaking-continuous casting-rolling is disrupted.In order to solve the problem of surface transverse cracks in the HSLA steel slab, this article investigated the second phase particle precipitation behavior in the X65 micro-alloyed slab produced in HANBAO STEEL. The main reason of the reduction of ductility and elongation in high temperature caused by the precipitation of nitride and carbon nitride is analyzed.Then the mathematic model is established for normal and chamfered mould, which consists of steel flow, heat transfer and solidification in the mould. The solidification process as well as the influence of different shape of corners(including chamfer angel and length) to the steel flow, temperature distribution and solidification process is investigated with common and chamfered mould.Finally the designed chamfered mould is tested and applied in the real industry production.The application in the industry shows that the chamfered mould technology has significant effect on the control of transverse corner crack in the slab production, which ensures the slabs can meet the rolling requirement without edge cutting, and provide important guarantee of hot charging and direct rolling.