Stainless Steel is highly resistance alloy that contain iron, low carbon, chromium and nickel. To increase the corrosion resistance or manufacturing requirements in specific applications usually the manfuacturer increase chromium content and other element such as manganese, aluminum, titanium and/or molybdenum can be added as required.
It's because of High Chromium content (it's about 10.5%). The Chromium forms a tenacious refractory oxide protective film on any exposed layer. This tiny layer can self-repair. If it's broken, the exposure to oxidizing agent such as air or nitric acid can automatically form the layer to protect itself. Under Specific condition the content of chromium can be added to more than 10.5% along with other elements such as Nickel, Molybdenum and Copper.
Right now we categorize Stainless Steel to 4 group base on metallurgical structure. They are:
Austenitic Stainless Steel is a stainless steel which compose of 18% Chromium and 8% Nickel.
There are several type of Austenitic Stainless Steel such as 301, 304, 304L, 316, 316L, 321, 310.
The most common one is 304.
The Austenitic Stainless Steel have this following features:
1. Can be strengthened by cold working.
2. Easily welded.
3. High ductility.
4. Highly resistance to corrosion.
5. Suitable for low and high temperature.
6. Non-magnetic
Duplex Stainless Steel is a stainless steel that compose of 18%-28% of Chromium content and 4.5%-8% of Nickel. Most type also contain Molybdenum.
The Duplex Stainless Steel have this following features:
1. Highly resistance to stress corrosion.
2. Easily welded.
3. Easily formed.
4. High tensile and yield strength rather than Austenitic and Ferritic Stainless Steel.
Ferritic Stainless Steel is a stainless steel that compose of 12%-18% of Chromium content but not using Nickel element. There are several type of Ferritic Stainless Steel such as 409, 430, 3CR12.
The Ferritic Stainless Steel have this following features:
1. Easily formed.
2. Harder to weld.
3. Low resistance to corrosion.
4. Lower high temperature then Austenitic Stainless Steel.
5. Highly resistance to stress corrosion cracking.
6. Magnetic.
7. Lower price.
Martensitic Stainless Steel is a stainless steel that compose of iron, 12-18% of chromium and up to 1% of cabron. Martensitic Stainless steel can be hardened with heat treatement, have a very high mechanical strength and also corrosion resistance. The application usually made for knife.