9th ECCC European Continuous Casting Conference – ECCC 2017

The black and white band defects of type 304 stainless steel on the hot and cold rolled coils are chronic. The black and white band defects are subsurface defects and can be found chrome carbide in the defects on the surface of the hot rolled coils. The cause of chrome carbide is an increase of carbon near the oscillation mark on the subsurface of slab due to carbuizing of mold powder during the ormation of oscillation mark at the meniscus. The causes of color differences between the black and white defects are as follows : Formation of chrome carbide due to carburizing of slab surface ; Overpickling of chrome carbide layer compared to the normal part in the acid pickling ; Depth differences of defects between the black and white defects ; Color differences visually according to the reflection light. In order to minimize the contact time between the carbon concentrated layer and the initial solidified shell, we change the mold slag properties. This mold powder improves the slab surface quality and also increases the steel yield by reducing slab grinding process.