Research Of Surface Defect In Cold-rolled Sheet Induced By Inclusions

The main quality problem of cold-rolled sheet is surface defect, which is believed to be the common and difficult to be eliminated. Therefore, the research and analysis of formation reason and evolution rule of surface defect in cold-rolled sheet has great importance of improving the surface quality of cold-rolled sheet. Linear defects, cavity and scar/pit are three main defects which induced by inclusions. There is still not a unanimous view about the formation mechanism of these three defects.Based on the analysis of data on spot about surface defects, we can conclude that: the probability of the top surface defect is more than the bottom surface of cold-rolled sheet; Every first furnace in a cast plan are more easy to generate surface defect than others; According to the macro-feature there are six types of surface defect in the cold-rolled sheet which we have researched.We analysed the formation reason and evolution of surface defect through the simulated rolling. The following conclusions can be derived from the result of simulated rolling.(1) The press-in defect of Iron Oxidation sheet on Cold-rolled sheet is directly inherited from the remaining oxidation iron on hot-rolled sheet. The defect has just a little change on size but the place will keep the same.(2) Peeling defects are mainly caused by subcutaneous inclusions.(3) With the increase of strain hardening and machining stress, in the cold rolling process, the additional stress around inclusions and the partition effect of inclusion firstly make steel surface rupture, which caused the cavity in cold-rolled sheet finally.(4) The formation of "black slivers" is directly related to inclusions which are MnO, Al2O3 and TiO₂.(5) "White slivers" were caused by the interaction of bubbles and inclusions.(6) The formation of the scar/pit is not directly related with the inclusions, but it is evolved from similar defect on hot -rolled sheet and just only has change in size.