What is the role of alloying elements in weather resistant steel plate?

Compared with ordinary carbon steel, weather resistant steel plate has good resistance to atmospheric corrosion. This is because the alloying elements play a role in reducing the conductivity of the rust layer and hindering the rapid growth of corrosion products.

1. Carbon: Carbon is unfavorable to the atmospheric corrosion resistance of steel. At the same time, carbon has an effect on the welding performance, cold brittleness and stamping performance of steel. Generally, the mass fraction of carbon in weather resistant steel plate is controlled below 0.12%.

2. Copper and sulfur: When w(Cu)=0.2%～0.4% is added to steel, it will have better corrosion resistance than ordinary carbon steel no matter in rural atmosphere, industrial atmosphere or marine atmosphere.

3. Phosphorus: Phosphorus is one of the most effective alloying elements to improve the atmospheric corrosion resistance of steel. Phosphorus can be uniformly dissolved in steel, which helps to form a dense protective film on the surface of the steel, so that the inside is not corroded by the atmosphere.

4. Chromium: Chromium can form a dense oxide film on the surface of steel, improve the passivation ability of steel, and slow down the growth of the rust layer. When chromium and copper are added at the same time, the effect is particularly obvious.

5. Nickel: Nickel is a relatively stable element. The addition of nickel can change the self-corrosion potential of steel in the positive direction and increase the stability of steel. Atmospheric exposure test results show that when w(Ni)≈4%, the atmospheric corrosion resistance of seaside weather resistant steel plate can be significantly improved.

6. Calcium: The research results show that adding a small amount of calcium to weather resistant steel plate can not only significantly improve the overall atmospheric corrosion resistance of the steel, but also can effectively avoid the rusty liquid sagging phenomenon that occurs when the weather resistant steel plate is used.

7. Manganese: At present, the understanding of the influence of manganese on corrosion resistance is not uniform. Most scholars believe that manganese can improve the corrosion resistance of steel to the marine atmosphere, but has almost no effect on the corrosion resistance in the industrial atmosphere.

8. Rare earth element: Rare earth element (RE) is one of the added elements of chromium-free and nickel-free weather resistant steel plate. Generally, the addition amount of rare earth elements is less than or equal to 0.2% (mass fraction). Rare earth elements can refine grains, change the state of inclusions in steel, reduce the number of harmful inclusions, and reduce corrosion sources, thereby improving the steel's atmospheric corrosion resistance.