The role of alloying elements in stainless steel composition
Under normal circumstances, pure metal has relatively high plasticity, when adding other alloying elements, the formation of single-phase solid solution also has good plasticity, such as iron-nickel alloy can form a continuous solid solution, so iron and nickel in any proportion of the case, the plasticity of the alloy is very high.
However, under the condition of containing other elements, the formation of intermetallic compounds that are insoluble in the solid solution or partially soluble in the solid solution reduces the plasticity of the metal, so the plasticity of the alloy is worse than that of the pure metal or single-phase solid solution.
· Iron (Fe) : the basic metal element of stainless steel;
Chromium (Cr) : is the main ferritic forming element, chromium and oxygen can generate corrosion resistant Cr2O3 passivation film, is one of the basic elements of stainless steel to maintain corrosion resistance, chromium content increase can improve the passivation film repair ability of steel, general stainless steel chromium content must be more than 12%;
Carbon (C) : is a strong austenitic forming element that can significantly improve the strength of steel, and carbon also has an adverse effect on corrosion resistance;
Nickel (Ni) : it is the main austenitic forming element, which can slow down the corrosion of steel and the growth of grain during heating;
Molybdenum (Mo) : is a carbide forming element, the formed carbide is extremely stable, can prevent austenite heating grain growth, reduce the overheating sensitivity of steel, in addition, molybdenum element can make the passivation film more dense and solid, so as to effectively improve the Cl corrosion resistance of stainless steel;
· Niobium, titanium (Nb, Ti) : it is a strong carbide forming element, which can improve the resistance of steel to intergranular corrosion. However, titanium carbide has an adverse effect on the surface quality of stainless steel, so the performance of stainless steel with higher surface requirements is generally improved by adding niobium.
Nitrogen (N) : is a strong austenitic forming element that can significantly improve the strength of steel. However, it has a greater impact on the aging cracking of stainless steel, so the nitrogen content should be strictly controlled in the stainless steel for stamping purposes.
Phosphorus, sulfur (P, S) : are harmful elements in stainless steel, will adversely affect the corrosion resistance and stamping ability of stainless steel.