Hainan Steel Wholesale


1. Overheating


Features:The surface of the steel plate presents a large area of continuous or discontinuous blue gray rough pits or scaly raised skin. Usually, a certain depth of decarburization layer appears on the surface, and the internal grain structure is coarse, accompanied by the appearance of Weinstein structure.



Cause:The steel billet stays in the high temperature section of the heating furnace for a long time or the heating temperature is too high, or the oxidation in the home heating furnace is too high, causing excessive oxidation on the surface of the steel billet.



Impact:Overheating of the steel billet causes a certain depth of decarburization layer on the surface of the steel plate, which not only causes severe roughness on the surface of the steel plate and excessive growth of internal grains, but also seriously reduces the mechanical and processing properties of the steel plate, making it easy to form irregular and shallow cracks on the surface of the steel plate during the process, which has a fatal impact on the quality of the steel plate.



Prevention:(1) Develop a reasonable heating system, control heating temperature, heating speed, and heating time to prevent overheating (burning) of steel billets; (2) Control the atmosphere inside the furnace, while ensuring complete combustion of fuel, minimize the amount of excess air, adopt micro positive pressure control, reduce the opening time of the furnace door, and prevent cold air from being sucked in.



2. Pockmarks



Features:Local or continuous rough surfaces are formed on the surface of the steel plate, distributed with iron oxides of different sizes and shapes. After peeling off, small pits or dents of different depths and shapes are presented.



Cause:Due to the formation of excessively thick oxide scale on the surface of the steel billet after heating (some areas of the billet are overheated during heating), the steel is not cleaned or not thoroughly cleaned before rolling, and the oxide scale is pressed into the steel plate body in the form of flakes or blocks before rolling; After rolling, the oxide scale shrinks and falls off when subjected to vibration., Leave small pits or indentations of varying sizes, shapes, and depths on the surface of the steel plate. In addition, the corrosion of gas sprayed or burned by non believers can also form tar pits or gas corrosion pits.



Impact:The degree of impact on the surface quality of the steel plate depends on the depth of the pits or indentations formed by the pitting on the surface of the steel plate and the degree of strictness required for the surface quality of the steel plate. Normally, after grinding and cleaning, if the depth does not exceed the corresponding standard specifications, it will not affect its use.



Prevention:(1) Reasonably control the heating temperature of each section of the heating furnace according to the different specifications and steel grades of the billet, reasonably control the ratio of gas (fuel) and air, and improve the sufficiency of combustion; (2) When the heating furnace is waiting for temperature, the intensity of the burner flame should be effectively controlled to avoid direct erosion of the steel billet by the flame for a long time; (3) Ensure high-pressure water pressure and phosphorus removal efficiency.





3. Iron oxide sheet pressed in



Features:The oxide scale pressed into the surface of the steel plate can be divided into primary oxide scale and secondary oxide scale. The primary oxide scale is mostly a brownish Fe3O4 scale layer; The secondary oxide scale is mostly composed of reddish brown FeO and Fe2O3 scales. Depending on the type of pressed iron oxide, the depth of pressing varies from deep to shallow, and the distribution area varies from large to small, mostly in the form of blocks or strips.



Cause:(1) The addition time is too long, making the oxide scale formed on the surface of the steel billet too thick and difficult to remove; (2) Before rolling, due to insufficient high-pressure water pressure or other reasons, the surface oxide scale of the steel billet cannot be obtained