The main defects caused by rolling strip steel on a tropical mill are as follows:

 

(1) Scar. The cracks and cracks were not completely removed when the slab was cleaned, resulting in scarring during rolling. Slabs overheat when heated, especially chromium stainless steel, and form scars on the strip when rolled. The accumulation of non-metallic inclusions on the billet surface is also the cause of scarring.

 

(2) Split edge. The side defects of the slab are not completely removed, which is the cause of the split edge of the strip.

 

(3) Overheating. The slab will overheat if it stays at too high a temperature for a long time. Large cracks and spalling occur when the slab is rolled. A fine crack appears near the overheated part, and the fine crack becomes a scar when further rolled. In order to prevent the slab from overheating, the prescribed heating system must be strictly observed, especially the soaking time at high temperatures. When heating ferritic steel, it must be heated quickly after the temperature exceeds 850℃.

 

(4) Mechanical damage. Chip, indentation and scratch are the most characteristic defects on the surface of hot rolled stainless steel strip. Chip and indentation defects are caused by scarring on the blank, splinters falling on the strip surface when the edge is rubbed against the guide, and other things being crushed by the roll or straightener roller.

 

Scratches are mostly formed when the lower surface of the strip is in contact with the uneven guide, roller and passive roller during the movement of the strip. The scratches on the upper surface are usually caused by the friction between the coil layers when the coil is not tightly rolled. During coiling, when friction occurs between the strip and the coiler's forming and feeding rolls, many short strip scratches occur on the surface of the strip.

 

(5) Uneven thickness of strip steel. The uneven thickness along the length of the strip is related to the uniformity of heating along the length of the slab and the tension value of the strip between the frames. The front and back ends of the strip are generally thicker than the middle because there is no tension at the end of the strip in the continuous finishing mill. The back end of the strip is generally thicker than the front end, which is due to the difference in temperature.