Why do high-quality steels require sulfur and phosphorus content below 0.03%?
In the routine determination of carbon, silicon, manganese, phosphorus, and sulfur in steel, sulfur and phosphorus are harmful two elements.
S exists in the form of FeS in steel. FeS and Fe can form a eutectic with a low melting point (985 ° C). When the processing temperature during hot working is higher than this temperature, the eutectic distributed on the grain boundaries melts, leading to processing cracking. This is called hot brittleness and contains S The higher the amount, the more severe the hot brittleness. (Especially in heat-treated parts)
P can be completely dissolved in the ferrite, so that the strength of the ferrite at room temperature is increased, the toughness is reduced, and cold brittleness is generated. Makes the cold workability and welding performance of steel worse. Therefore, desulfurization and dephosphorization is one of the basic tasks of steelmaking. There is a limit. National standards tell you that sulfur and phosphorus should be less than 0.035%, and more than 0.035% will be unqualified. Qualified below 0.035%, high-quality steel has higher requirements for sulfur and phosphorus. Therefore, national standards stipulate that the sulfur and phosphorus content must be reduced to less than 0.03% in order to be called high-quality steel.
Nanjing Kirin Scientific Instrument Group Co., Ltd.