Surface inclusions/steel surface presents point-like, block-like or line-shaped non-metallic inclusions, intermittent or continuous distribution along the rolling direction, its color is reddish brown, dark gray or white, and the steel plate will have holes, cracks and breaks in severe cases band. 1) Poor slag formation during steelmaking, high viscosity of molten steel, poor fluidity, slag cannot float, and there are many non-metallic inclusions in steel. 2) The casting temperature is low, the boiling is bad, and the inclusions are not floating. 3) During continuous casting, the slag band is mixed into the steel. 4) The non-metallic materials in the molten steel tank, steel ingot mold or injection pipe are not cleaned. There are irregular tongue-shaped and fish-scale black spots on the surface of the scars/steel strips. The distribution area is different in size and the depth of the pressure is uneven. This kind of iron skin is difficult to wash out in the pickling process. When the iron skin falls off, it forms a pit. The inner wall of the ingot mold is not cleaned in steelmaking, the mold wall loses meat, and when it is injected, the steel decay and stick to the mold wall, oxidation occurs The casting temperature is low, and sometimes the injection flow is interrupted. When the steel injection is continued, the ingot is formed under the skin, and the molten slag is added by improper addition of eight. 2) The residual scars on the surface of the slab are not cleared after rolling, and are left on the steel plate after rolling. The scales/defects are black spots with dots, strips or fish scales. The distribution area is different in size and the depth of the pressure. This type of iron sheet is difficult to wash out in the pickling process, and forms a pit when the iron sheet falls off. 1) The heating temperature of the slab is too high, the time is too long, the furnace is in a strong oxidizing atmosphere, and the raw scale is pressed into the furnace during rolling. 2) The high-pressure water pressure is insufficient, and the scale is not removed before continuous rolling. 3) The high-pressure water nozzle is blocked, and the local scale is not removed. 4) Insufficient number of sets of scale collection pipes are opened, and descaling is not clean. Under pickling/when the upper and lower surfaces of the strip are severe, the entire surface of the plate is strip-shaped, dark gray stripes, and matt. 1) The temperature and cooling rate of the hot-rolled strip are different, that is, the head and the middle of the strip along the length of the strip , The tail, and the width and the sides and middle of the temperature and cooling rate are different, so that the structure and thickness of the steel strip of each part of the same strip are different. Generally speaking, the head and middle of the hot-rolled strip are 30-50 higher than the tail ℃, therefore, the head metal is thicker and the tail metal is thinner. Therefore, when the pickling speed is the same, local unwashing is easy to occur. 2) The pickling process is not suitable, such as the concentration and temperature of pickling are low , The pickling speed is too fast, the pickling time is insufficient, or the concentration of ferrous iron is high, and the acid solution is not added in time. 3) The tensile coefficient of the descaling machine is not enough, so that the iron sheet is not fully broken and peeled, which affects the pickling effect. 4) Poor appearance of strip steel, such as sickle bend, wave shape, etc. makes the mechanical descaling effect poor, and it is easy to cause local under pickling.