Stainless steel and its classification

Update:19 Jul 2019
Summary:

  Metals stored in the atmosphere react chemically […]

 

Metals stored in the atmosphere react chemically with oxygen to form an oxide film on the surface. The oxide film of ordinary carbon steel will continue to oxidize over time, and stainless steel will form a passivated, dense chromium-rich oxide on the surface to protect the surface and prevent further oxidation of the steel.

Stainless acid-resistant steel refers to steel that is resistant to weak corrosive media such as air, steam, water, and chemically etched media such as acid, alkali, salt, etc., referred to as stainless steel.

Stainless steel includes two types of characteristics ----

Stainless and acid resistant properties. In practical applications, steel that is resistant to corrosion by weakly corrosive media is often referred to as stainless steel, while steel that is resistant to chemical media is referred to as acid-resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to chemical media corrosion, while the latter generally has rust.

The corrosion resistance of stainless steel depends on the alloying elements contained in the steel, especially cadmium. Generally speaking, when the cerium content of the steel is more than 12%, the chromium in the steel will react with the oxygen in the corrosive medium to form a thin chromium-rich oxide film on the surface of the steel. This oxide film can prevent the steel from blocking. The substrate is further corroded. When the chromium-rich oxide film on the surface of the stainless steel is destroyed, a new layer of chromium-rich oxide film can be formed immediately. In addition to chromium, commonly used alloying elements are nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the requirements of stainless steel structure and performance for various purposes.