Introduction of stainless steel
All metal and atmospheric oxygen are carried out reactions in the surface oxide film. Unfortunately, in the ordinary carbon steel to form oxide of iron oxide to continue to expand rust and eventually the formation of holes. Can make use of paint or oxidation-resistant metal (for example, zinc, nickel and chromium) plating to ensure the carbon steel surface, but, as what people know, this protection is only a thin film. If the protective layer is damaged, the following steel began to rust.
Chromium is to corrosion resistance of stainless steel to obtain the basic elements, when the steel contains up to 12% of chromium, the chromium and oxygen in the corrosion medium role in the steel surface to form a thin oxide film (since the passive film) , can prevent the further corrosion of the steel substrate. In addition to chromium, the commonly used alloying elements are nickel, molybdenum, titanium, niobium, copper, nitrogen, in order to meet a variety of uses and properties of stainless steel requirements.
Stainless steel is usually organized according to the matrix is divided into:
1 Ferritic stainless steel. Chromium 12% ~ 30%. Its corrosion resistance, toughness and weldability with the chromium content increased with increasing resistance to chloride stress corrosion is superior to other types of stainless steel.
2 Austenitic stainless steel. Is greater than 18% chromium, but also contains about 8% nickel and a small amount of molybdenum, titanium, nitrogen and other elements. Comprehensive performance, and can be corrosion-resistant variety of media.
3, austenitic - ferritic duplex stainless steel. Both austenitic and ferritic stainless steel of the advantages, and has superplasticity.
4, martensitic stainless steel. High intensity, but the ductility and weldability is poor.
