(1) Gas corrosion, which is black dotted pits on the surface of the strip. If the residual emulsion, oil, salt, dirt, etc. on the surface of the strip are not cleaned up, part of the surface of the strip or the entire surface (staying in the furnace for a long time) will be corroded by gas. At high temperatures, the corrosion of the strip surface by the gas is more serious.
(2) Overheating, the surface of the strip will turn dark brown when overheated. Although the iron oxide scale on the surface has fallen off, it is not easy to be cleaned by pickling. The reason for this defect is that the heating temperature of the metal is too high or the residence time in the furnace is too long. Overheating may cause intergranular corrosion.
(3) Under heat, the surface of the strip steel has a light gray metallic luster when it is under heat. During the pickling process, the iron oxide scale is difficult to wash away, and the strip is gray after pickling. Insufficient heating is due to low heating temperature or too fast speed of the strip through the furnace.
(4) Scratch. Scratch refers to the black spot-shaped pits that are easy to see on the lower surface of the strip after pickling. This defect is that there are small protrusions on the working surface of the idler table, which will damage the surface of the strip. Therefore, the rollers in the furnace must be ground and replaced regularly.randompackingfactory.com