Grades and Series of Stainless Steels - Compositions and Uses

4-Aug-2020

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 2^nd and last Part of this article):

• Types of Stainless Steels
• Series of Stainless Steel
• Stainless steel compositions
• Uses of different Series of Stainless Steels, etc.

Martensitic Stainless Steel (Compositions, Properties)

This category is identified by their Martensitic microstructure in hardened condition.   

Martensitic Stainless Steel contain –

• Chromium: 11 – 18%
• Nickel: 4 – 22%
• Carbon: around 1%
• Manganese: 1 – 1.5%
• Silicon: 1 – 2%

Due to higher carbon to chromium content ratio, Martensitic Stainless Steel has 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 Steel.

Martensitic Stainless Steel can be cold worked and machined without much difficulty, especially with low carbon content. Martensitic Stainless Steel possesses good toughness and can be hot-worked easily.

Duplex Stainless Steel (Compositions, Properties)

Duplex Stainless Steel has chemical composition and balanced (Duplex) microstructure of approximately equivalent fractions of ferrite and austenitite phases in annealed condition. Duplex Stainless Steel can be characterized by high chromium (i.e. 19 – 32%) and molybdenum (up to 5%) and lower nickel contents than Austenitic Stainless Steel. Addition of nitrogen causes formation of interstitial solid solution which promotes structural hardening and eventually, an increase in yield strength. Duplex Stainless Steel has about twice the yield and tensile strength compared to those of Austenitic Stainless Steel. The toughness of Duplex Stainless Steel grade is superior to that of Ferritic Stainless Steel grade but inferior to Austenitic Stainless Steel. The two-phased-microstructure of Duplex Stainless Steel promotes high resistance to pitting and also stress corrosion cracking.       

Precipitation Hardening Stainless Steel (Compositions, Properties)

Precipitation Hardening Stainless Steel contains 15 – 18% chromium and is a kind of chromium-nickel alloys.

In annealed condition, they may be either austenitic or Martensitic. They develop high strength with heat treatment. Precipitation hardening Martensitic stainless steel has corrosion resistance comparable to austenitic stainless steel but can be precipitation hardened to even higher strengths than other martensitic grade stainless steels.        

STAINLESS STEELS SERIES (Stainless Steel Grades)       

Stainless Steels are classified into three series:

1. 200 series Stainless Steels
2. 300 series Stainless Steels
3. 400 series Stainless Steels

The following table shows the chemical compositions of the above three Series of Stainless Steels:

Chemical Compositions of 200, 300 and 400 Series of Stainless Steel

Chemical Composition (in percentage)	200 series Stainless Steel	300 series Stainless Steel	400 series Stainless Steel
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 Minerals	Balance	Balance	Balance

USES OF DIFFERENT SERIES OF STAINLESS STEELS        

The major uses or applications of 200, 300 and 400 Series Stainless Steels

200 Series Stainless Steels

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.

300 Series Stainless Steels

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.

400 Series Stainless Steels

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.      

Also Read

Difference between Stainless Steel, Carbon Steel, and Alloy Steel