What affects the corrosion resistance of stainless steel?
1. Chromium
Chromium is the main element to determine the corrosion resistance of stainless steel, when the chromium content (atomic ratio) reaches 1 / 8, 2 / 8...... The electrode potential of iron increases by leaps and bounds, and the corrosion resistance also increases. The chromium oxide is compact and can form a relatively corrosion-resistant protective film.
2. Carbon
Carbon can strongly stabilize austenite, the ability of stabilizing austenite is about 30 times of Ni; at the same time, it is the main element of stainless steel strengthening; carbon and chromium can form a series of carbides, which seriously affect the corrosion resistance of stainless steel; at the same time, carbon can make the processing performance and welding performance of stainless steel worse, and make ferritic stainless steel brittle. Therefore, in the production and development of stainless steel, carbon is the most important element It is an important work to apply and control the system.
When the carbon content is low and the chromium content is high, the ferrite structure will be obtained; when the carbon content is high and the chromium content is low, the martensite structure will be obtained.
3. Nickel
Nickel is one of the three important elements in stainless steel, which can improve the corrosion resistance of stainless steel; nickel is also a stabilizing element of γ phase, which is the main element to obtain single-phase austenite and promote the formation of austenite in stainless steel. The increase of Ni content will decrease the solubility of C and N in austenitic steel, and increase the tendency of carbon and nitrogen compounds precipitation. In addition, nickel can also improve the high temperature oxidation resistance of austenitic stainless steel, which is mainly related to the improvement of the composition, structure and properties of chromium oxide film by nickel, but the existence of nickel will reduce the high temperature vulcanization resistance of steel.
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