Cr is the main element to decide the resistance of corrosion in stainless steel. Metal corrosion divide into chemical corrosion and non-chemical corrosion. Under high temperature, metal produce rust through oxygen, it named chemical corrosion. Otherwise, under normal temperature, this phenonmenon named non-chemical corrosion.
The higher content of chromium, the better the corrosion resistance of steel is, the chromium content reaches 25% and 37.5%, it makes the steel have higher corrosion resistance. Eleven percent is the minimum limit for chromium, which is less than 11% chromium, and is generally not named stainless steel.
It is a good corrosion resistant material, which is the main element of austenite in steel. After adding nickel to stainless steel, the organization changed significantly. As the content of nickel increases in stainless steel, the austenitic body will increase, and the corrosion resistance, high temperature resistance and processing resistance of stainless steel will be enhanced, thus improving the cold processing performance of steel. Therefore, the stainless steel with higher nickel is suitable for drawing filaments and microfilaments.
In stainless steel, carbon content and its distribution form, to a great extent, influences the performance of stainless steel and organization: on the one hand, carbon austenitic elements are stable, and effect of the degree is very big, about 30 times that of the nickel, high carbon content of martensite stainless steel, perfectly acceptable to quenching strengthening, which can greatly improve its performance in the mechanical strength; On the other hand, due to the high affinity of carbon and chromium, the chromium of 17 times of carbon in stainless steel is combined with chromium carbide. With the increase of carbon content in steel, the more chromium is formed with carbon, thus significantly reducing the corrosion resistance of steel. The increase of carbon content will reduce the corrosion resistance of stainless steel, but can improve the hardness of stainless steel.
It can improve the corrosion resistance of stainless steel. Adding molybdenum in stainless steel can further blunt the surface of the stainless steel and further improve the corrosion resistance of the stainless steel. Molybdenum can not form precipitated molybdenum in stainless steel, which improves the tensile strength of stainless steel. Molybdenum can also significantly improve the corrosion resistance of chloride ions (such as) and organic acids. However, stainless steel with molybdenum is not suitable for use in nitric acid. The corrosion rate of stainless steel with molybdenum is twice as fast as that without molybdenum.
Copper can improve the corrosion resistance of stainless steel and acetic acid. Copper is added to chromium manganese nitrogen stainless steel, which will accelerate the corrosion of stainless steel. Molybdenum has an adverse effect on the single austenitic structure of steel, so in the molybdenum steel, in order to make the steel have a single austenitic structure after heat treatment. The content of nickel in manganese and other elements should be increased correspondingly.
It is a strong carbide forming element which can improve the corrosion resistance of steel. However, titanium carbide has an adverse effect on the surface quality of stainless steel, so it is generally improved by adding niobium to the stainless steel with higher surface requirements.
Silicon has a significant effect on the antioxidant capacity of chromium steel, with 5% chromium and 1% silicon steel, and the antioxidant capacity is equal to 12% chromium steel. Such as make steel at 1000 ℃ can resist oxidation, need 22% of chromium containing 0.5% silicon, such as join after 2.5 ~ 3% of silicon, only need 12% of chromium. It is also recommended to add 2.5% silicon to Cr15Ni20 chromium nickel steel, and the antioxidant properties can be equivalent to Cr15Ni60 chromium nickel alloy.
Manganese (Mn) and Nitrogen (N)
Manganese and nitrogen have the same effect as nickel in stainless steel. The stable austenite of manganese is one half of nickel, and nitrogen is much larger than nickel, about 40 times as much as nickel. Thus, manganese and nitrogen can obtain a single austenite structure. However, the addition of manganese will reduce the corrosion resistance of stainless steel with low chromium. Meanwhile, high manganese austenitic steel is not easy to be processed. As a result, manganese is not used in stainless steel alone and only partially substituted for nickel.
Phosphorus (P) and Sulfur (S)
It is a harmful element in stainless steel, which has adverse effects on corrosion resistance and ramming of stainless steel.