Cause analysis and optimization practice for the upwarping defect in hot rolling of 780DH steel
There are two kinds of upwarping defects on the surface of the 780DH dual phase steel with high form-ability hot-rolled coil produced by a steel plant,one is upwarping defect within 50 mm from the edge,and the other is upwarping defect distributed in the large rib of the bottom surface of the hot rolled coil.It is found that the trans-verse cracks in the corner of the slab is the direct cause of the upwarping defect at the hot rolling edge.As for the upwarping defect in the large rib,no surface crack defect was found in the corresponding position of the slab by vis-ual inspection,but the metallography and electron microscope analysis of the hot-rolled coil defect sample deter-mined that the cause was still caused by the original crack existing in the slab.After grinding the slab for about 3 mm,it was found that there were dense transverse crack defects under the slab.It is determined that the two kinds of upwarping defects on the surface of 780DH steel hot rolled coil are caused by slab cracks.On this basis,the use performance of 780DH steel special mold protection slag is optimized:the casting speed increased from 0.9 m/min to 1.05 m/min or more,the secondary cooling intensity increased from 0.46 L/kg to 0.5～0.6 L/kg,and replace the secondary cooling regulating valve with poor adjustment accuracy to avoid the fluctuation of secondary cold wa-ter.After taking the above optimization methods,the defect rate of 780DH steel hot rolled coil can be controlled be-low 1％.
dual phase steel with high formabilityhigh alumina steelhot-rolled coilupwarpingslabtransverse cracks
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维普
