Analysis of ductile fractures at the surface of continuous casting steel during hot-core heavy reduction rolling

Abstract

Abstract Hot-core heavy reduction rolling (HHR2) is an innovative thermomechanical technology whereby steel castings are directly rolled and heavily reduced at the solidification endpoint. HHR2 can effectively eliminate shrinkage porosities without the risk of internal cracking, as the centre deformation temperature has avoided the solidification brittleness temperature range. However, the risk of surface cracks is especially concerning because the lower surface temperature is associated with increased brittleness as compared to the centre. In this study, the EH47 was selected as the research material, which was a crack-sensitive steel with microalloy element Nb. Finite element model (FEM) analysis was used to predict surface ductile fracturing during HHR2. Hot compression tests were performed on specially designed specimens to develop the ductile fracture criterion for the FEM simulation. Pilot plant trials of HHR2 were carried out to verify the accuracy of the FEM calculations. The FEM results revealed that the centreline of a steel casting lateral face was the position where a fracture was most likely to take place. Moreover, the cracking risk itself rises with an increase in the reduction ratio, and the critical reduction ratio was about 59 %. The investigation also revealed that the cracking risk reduced with an increase in the work roll diameter.