Experimental and Numerical Investigation on Surface Damage of Cold Rolled Sheet Caused by Inclusion Movement

In present work, samples were cut from ultra-low carbon steel slab to investigate the formation of surface damage induced by inclusions during cold rolling. Surface damage such as dent, peeling, and pockmark was reproduced by rolling experiment. The inclusions such as Al2O3, SiO2, and MgO·xCaO were found in surface damages. FE method was employed to reveal the relationship between surface damage and Al2O3 inclusion movement. The initial position and size of inclusions are significant to the formation process of surface damage. 50 μm Al2O3 inclusion located at the 1/8 of sheet thickness is easily rolled to the surface and causes the surface damage. Morphology of Al2O3 inclusion is difficult to change due to the higher hardness and larger elastic modulus. However, the Al2O3 inclusion can be crushed into pieces, which increase the damage of steel matrices. Surface damage was formed through the coalescence behavior of microscopic damages.