Stainless steel metallurgical structures are classified according to three groups:
- Austenitic
- Martensitic
- Ferritic
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Stainless steel includes a large number of variants, but always at least 12% chromium (Cr) and most other additive elements such as nickel (Ni) and molybdenum (Mo) are one of the most important.
Austenitic group of stainless steel material: is further divided into three groups according todifferent corrosion resistance and application method.
A1 is particularly good for cutting thanks to the high percentage of phosphorus and sulfur, butcorrosion resistance is thus reduced. (rarely used for the production of connecting members)
A2 is the most common type of steel containing 18% Cr and 8% Ni. In normal atmospheric conditions (humid environment, oxidation, organic acid, most of alkaline and salt solutions) hasexceptional corrosion resistance.
A4 has the highest degree of corrosion resistance (increased by content of nickel andmolybdenum). It is used in particularly aggressive environments (sea water - chloride, sulfur dioxide, oxidizing acids, applications, potentially pitting)
| Inclusion of steel | Steel of group | Chemical composition v % 1) | |||||||
|---|---|---|---|---|---|---|---|---|---|
| C | Si | Mn | P | S | Cr | Mo | Ni | ||
| Austenitic | A12) | 0,12 | 1,0 | 2,0 | 0,2 | 0,15 | 17,0 | 0,6 | 8,0 |
| 0,35 | 19,0 | 10,0 | |||||||
| A23),4) | 0,08 | 1,0 | 2,0 | 0,05 | 0,03 | 17,0 | - | 8,0 | |
| 20,0 | 13,0 | ||||||||
| A4 | 0,08 | 1,0 | 2,0 | 0,05 | 0,03 | 16,0 | 2,0 | 10,0 | |
| 18,5 | 3,0 | 14,0 | |||||||
- includes a maximum value, unless otherwise specified
- sulfur can be replaced by selenite
- can contain up to 4% of copper.
- According to the manufacturer's discretion may be added Molybdenum