The 400 series stainless steels have some special uses such as in coinage, auto-exhausts, razor blades, power packing in petrochemicals etc. Besides, these are also used in consumer durable and transport industries.
The 300 series stainless steels have got all uses mentioned under 200 series besides, in refineries, petrochemicals, diary farm industries. They are also used in high temperature instruments such as in electric furnaces, pharmaceutical appliances, nuclear appliances, power plants, railway coaches, automobiles etc.
The 200 series stainless steel is mainly used in making utensils, households including kitchen appliances, architecture and decorative items, furniture, tubes, pipes, automobiles, railways and transport industries.
The major uses or applications of 200, 300 and 400 Series of Stainless Steels:
|Manganese||5.5 - 10.0||2.0 (max)||1.5 (max)|
|Nickel||1.0 - 6.0||6.0 - 22.0||1.5 (max)|
|Chromium||15.5 - 19.0||16.0 - 26.0||10.5 - 19.0|
|Iron & other materials||Balance||Balance||Balance|
Stainless Steels are classified into three series:
The following table shows the chemical compositions of the above three Series of Stainless Steels:
Precipitation Hardening Stainless Steels contains 15 – 18% chromium and are basically chromium-nickel alloys.
In annealed condition, they may be either austenitic or Martensitic. They develop high strength with heat treatment. Precipitation hardening martensitic stainless steels has corrosion resistance comparable to austenitic stainless steels but can be precipitation hardened to even higher strengths than other martensitic grade stainless steels.
Duplex Stainless Steels have chemical composition and balanced (Duplex) microstructure of approximately equivalent fractions of ferrite and austenitite phases in annealed condition. Duplex Stainless Steels are characterized by high chromium (i.e. 19 – 32%) and molybdenum (up to 5%) and lower nickel contents than Austenitic Stainless Steels. Addition of nitrogen causes formation of interstitial solid solution which promotes structural hardening and eventually, an increase in yield strength. Duplex Stainless Steels have about twice the yield and tensile strength compared to those of Austenitic Stainless Steels. The toughness of Duplex Stainless Steel grades is superior to that of Ferritic Stainless Steel grades but inferior to Austenitic Stainless Steel grades. The two-phased-microstructure of Duplex Stainless Steels promotes high resistance to pitting and also stress corrosion cracking.
These categories of stainless steels are identified by their Martensitic microstructure in hardened condition.
Martensitic Stainless Steels contain –
Due to higher carbon to chromium content ratio, Martensitic Stainless Steels have an exclusive property that it can be hardened by heat treatment. They are usually less resistant to corrosion than other categories of stainless steels. Hardness, ductility and ability to hold an edge are some important characteristics of Martensitic Stainless Steels.
Martensitic Stainless Steels can be cold worked and machined without much difficulty, especially with low carbon content. Martensitic Stainless Steels possess good toughness and are easily hot-worked.
In continuation of our previous article on stainless steel (Categories and Types of Stainless Steels: Compositions and Properties), the key points that will be discussed in short here are (this is the 2nd and last Part of this article):