Inverse segregation of tin-phosphorus bronze horizontal continuous casting billet and its effect on rolling edge crack

During the horizontal continuous casting process， a network of hard and brittle Sn-rich phase is formed at the edges of tin phosphorus bronze casting billet due to inverse segregation， which becomes crack sources during rolling and continuously propagates to induce significant edge cracks in the strip. To solve this problem， the graphite mold structure is improved， and the cooling intensity distribution law of the billet is adjusted to slow down the serious inverse segregation phenomenon caused by excessive cooling of the billet edge. Numerical simulation and experimental verification show that after the optimization of the mold structure， the thickness gradient of the air gap between the side of the billet and the mold is reduced， the solidification shrinkage of the mushy zone is more gentle； the liquid phase surface is more straight， the angle between the liquid phase and the mushy zone is reduced by 18.3°， and the solidification position difference between the middle and the side of the billet is reduced by 18.62 mm. In addition， the billet grain tends to be equiaxial， the Sn-rich phase is transformed from the inter-crystalline stripe to the point distribution， the degree of inverse segregation is reduced. The degree of inverse segregation is reduced， the content of Sn-rich phases in the inverse segregation layer is reduced by 2.3%， and the width of the inverse segregation layer is reduced by 214 μm. The number of cracks at the edge of the rough rolled strip is reduced from 21 before the structural optimization to 4.