All metals react with oxygen in the atmosphere to form an oxide film on the surface. Unfortunately, the iron oxide formed on the ordinary carbon steel continues to oxidize, so that the corrosion is enlarged, and finally the hole is formed. We can use a paint or oxidation resistant metal (e.g., zinc, nickel, and chromium) to ensure the surface of the carbon steel, but, as is known, this protection is only a thin film. If the protective layer is damaged, the following steel begins to rust.

The corrosion resistance of stainless steel depends on chromium, but chromium is one of the components of steel, so the protection methods are not the same.

The corrosion resistance of the steel increased significantly when the content of Cr gets 10.5%, but if the chromium content is higher, although it could improve the corrosion resistance, but not obvious. The reason is that when the steel is treated with chromium, the type of surface is changed into a surface oxide similar to that of pure chromium metal. This close adhesion chromium oxide protection surface, prevent further oxidation. This very thin oxide plate, through which you can see the natural luster of steel surface, to make the stainless steel a unique surface. Moreover, if the surface plate is damaged, the exposed steel surface will be self - repaired with the atmospheric reaction to form the oxide passivation film and continue to play a protective role.

Therefore, all stainless steel elements have a common characteristic, that is, chromium content of more than 10.5%.

Stainless steel 204Cu compared with 304, has stronger tensile strength and yield strength, lower strain hardening rate and better cold forming performance; corrosion resistance is superior at least equivalent to 304. Plus 200 series’own advantages of wear-resistant, low cost, 204Cu absolutely can replace 304 stainless processing, it is used for railway vehicles.

3, 304 is composed of 18Cr-9Ni, the most widely used stainless steel and heat-resistant steel. It is good for food production equipment, chemical equipment, nuclear power, etc.