Stainless steel the great invention in the history of metallurgy in the 20th century
Stainless steel is a major invention in the history of metallurgy in the 20th century.
The reason why stainless steel has stainless steel is that the steel contains chromium. The minimum chromium content required in the United States and European standards is not less than 10.5% (mass fraction, the same), and the Japanese industry standard is generally not less than about 11%. China generally considers not less than 12%.
Due to the influence of chromium, a strong and dense oxide film is formed on the surface of the steel under the action of corrosive medium, which is called "passivation film". This film separates the metal from the external medium and prevents the metal from being further corroded. The stainless steel also has the ability to repair itself. If it is destroyed, the chromium in the steel will re-generate the passivation film with the oxygen in the medium and continue to protect.
Stainless steel is divided into five categories: austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, austenitic-ferritic duplex stainless steel and precipitation hardened stainless steel. Among them, only austenitic stainless steel and a part of precipitation hardening stainless steel (austenitic precipitation hardening stainless steel) are non-magnetic and cannot be attracted by magnetite; while other types of stainless steel are magnetic. Steel that does not rust in weak corrosive media such as air, water, steam, etc. is stainless steel. Corrosion-resistant steel in strong corrosive media such as acid, alkali, and salt solution is corrosion-resistant steel. Stainless steel may not resist corrosion, and corrosion-resistant steel must not rust.
According to the main chemical composition, stainless steel can be divided into chromium stainless steel, chromium nickel stainless steel, chromium manganese nitrogen stainless steel, chromium nickel molybdenum stainless steel and ultra low carbon stainless steel, high molybdenum stainless steel, high purity stainless steel, etc.; according to the performance characteristics and use classification of steel, such as resistance Nitric acid (nitric acid grade) stainless steel, sulfuric acid resistant stainless steel, pitting resistant stainless steel, stress resistant stainless steel, high strength stainless steel, etc.
Classified according to the functional characteristics of steel, such as low temperature stainless steel, non-magnetic stainless steel, free-cutting stainless steel, superplastic stainless steel, etc.
It is usually classified by metallographic organization. Classified by metallographic structure:
|ferrite (F) type stainless steel||martensite (M) type stainless steel||austenitic (A) type stainless steel||austenitic-ferritic (AF) type duplex stainless steel||Austria Austenitic-martensitic (AM) type duplex stainless steel||precipitation hardened (PH) type stainless steel|
For a long time, due to the large proportion of non-magnetic austenitic stainless steel (also known as 300 series stainless steel) used in China, people have created the illusion that all stainless steel is non-magnetic. This is also one of the reasons for the fact that some chrome-manganese austenitic stainless steels (also known as 200 series stainless steels), which are not in line with international and domestic standards, have poor rust resistance and corrosion resistance, are shoddy and distracted. The quality of this part of stainless steel is very poor. If it is used in the industrial sector, it will cause significant losses.
In recent years, with the rapid development of China's stainless steel production and consumption, China's stainless steel industry organizations are vigorously promoting the production and use of magnetic ferritic stainless steel (also known as 400 series stainless steel) according to China's resource conditions. This stainless steel does not contain precious metal nickel, low cost, excellent performance, in electronics, building roof and decoration (main: stainless steel seamless pipe, duplex pipe), car exhaust system, household appliances (washing machine inner cylinder , microwave ovens, water heaters, range hoods, etc.), containers, outdoor water tanks, etc. have a very wide range of applications.