Stainless steel is the abbreviation of stainless acid-resistant steel. Stainless steel is resistant to corrosion by weak corrosive media such as air, steam, and water. Stainless steel composed of different elements has specific properties and unique application fields. Therefore, understanding the elemental composition of stainless steel plays a key role in understanding its performance and application fields.
The Role Of Each chemical Element In Stainless Steel:
Standard
GB/T20878-2007
Certification
BV, SGS, CE, TUV
Fe
Fe is the basic component of stainless steel;
Cr:
Chromium is the main ferrite-forming element. Chromium combines with oxygen to form a corrosion-resistant Cr2O3 passivation film, which is one of the basic elements for stainless steel to maintain corrosion resistance.
Increasing the chromium content can improve the passive film repair ability of steel. Generally, the chromium content in stainless steel must be above 12%;
C:
Carbon is a strong austenite-forming element, which can significantly improve the strength of steel. With an increase in carbon content, the tensile strength increases, the plasticity decreases, and the atmospheric corrosion resistance of steel is also reduced.
Carbon can form compounds such as Cr23C6, NbC, TiC, TaC and other carbides with other elements in stainless steel.
In terms of corrosion resistance, when the carbon in the solid solution austenite forms Cr23C6 with chromium, the sensitivity of the steel to intergranular corrosion and pitting corrosion increases sharply. Therefore, for equipment with high corrosion resistance requirements, stainless steel with low carbon content (below 0.03%) should be used.
Ni:
Nickel is the main austenite forming element. The main role of nickel in stainless steel is that it changes the crystal structure of steel. One of the main reasons for adding nickel to stainless steel is to form an austenite crystal structure, thereby improving the properties of stainless steel such as plasticity, weldability and toughness, so nickel is called an austenite forming element.
With the increase of nickel content, the hardness and tensile strength of austenitic steel decrease, the toughness increases, and the stress corrosion resistance increases. Austenitic stainless steel with low nickel content is unstable. After cold working, the austenite hardens significantly and the toughness decreases.
Nickel has significant corrosion resistance to non-oxidizing acids and neutral chloride solutions, but is not resistant to high-temperature sulfur-containing gases.
Mo:
Molybdenum is a carbide-forming element. The carbide formed is extremely stable, which can prevent the grain growth when austenite is heated and reduce the overheating sensitivity of steel.
The addition of molybdenum stabilizes the passivation film of stainless steel and improves corrosion resistance. Especially in chloride solution, molybdenum can improve the performance of pitting corrosion resistance and effectively inhibit crevice corrosion. In addition, molybdenum can make the passivation film denser and firmer, thereby effectively improving the CI-corrosion resistance of stainless steel;
Mo-containing stainless steel is generally not used for nitric acid corrosion resistance. Stainless steel without Mo cannot be used for sulfuric acid corrosion resistance.
Nb and Ti:
Niobium and titanium are strong carbide-forming elements, which can improve the intergranular corrosion resistance of steel.
However, titanium carbide has an adverse effect on the surface quality of stainless steel. Therefore, in stainless steel with high surface requirements, niobium is generally added to improve the performance;
N:
Nitrogen is a strong austenite-forming element, which can significantly improve the strength of steel. However, it has a greater impact on the aging cracking of stainless steel. Therefore, in stainless steel for stamping purposes, the ammonia content must be strictly controlled;
P and S:
They are harmful elements in stainless steel, which will have an adverse effect on the corrosion resistance and stamping properties of stainless steel.
Si:
Silicon can improve the acid resistance in austenitic stainless steel. Silicon can significantly improve the elastic limit, yield point and tensile strength of steel, and is widely used in spring steel.
In addition, silicon is also used as a reducing agent and deoxidizer in the steelmaking process.
Mn:
Manganese can improve the hardenability of steel and improve the hot working properties of steel.
Steel with a manganese content of 11-14% has higher wear resistance and can be used for ball mill liners, etc. Higher manganese will reduce corrosion and oxidation resistance.
