Scarring
Scarring can occur when cracks in the slab are not thoroughly cleaned before rolling. Overheating of the slab—especially in chromium stainless steel—can also lead to scarring. Additionally, a high concentration of non-metallic inclusions on the billet surface is another common cause of scarring.
Edge Cracks
Edge cracks typically result from existing defects on the sides of the slab, which propagate during rolling and cause cracking along the edges of the strip.
Overheating
When a slab remains at high temperatures for extended periods, severe cracks and surface spalling can occur during rolling. Overheating can also lead to the formation of fine cracks around the affected area, which may later develop into scarring during further rolling. To prevent overheating, it is essential to strictly follow the prescribed heating schedule, particularly the soaking time at high temperatures.
Mechanical Damage
Surface defects such as debris, indentations, and scratches are common in hot-rolled stainless steel. Rolled-in debris and indentations result from scar fragments or foreign matter on the strip surface. Scratches often form on the lower surface due to contact with rough guides, uneven rolls, or driven rolls. Upper surface scratches are typically caused by friction between the layers of the coil, as well as between the strip and forming or feed rolls, resulting in numerous short scratches.
Uneven Strip Thickness
Variation in strip thickness is mainly due to inconsistent heating along the length of the slab and improper tension control between stands. The front and rear ends of the strip are usually thicker than the middle section, primarily because of insufficient tension at the strip ends during continuous finishing mill operations.
