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Types of Stainless Steel

There are five types of Stainless steel:

  • Ferritic
  • Austenitic
  • Duplex
  • Martensitic
  • Precipitation Hardening

Ferritic Stainless Steels

These are nickel-free stainless steels. They have a varying chromium (Cr) content of 12- 18%, and a small amount of carbon (C), normally less than 0.10%.


  • They are magnetic and have similar microstructure to carbon and low alloy steels.
  • Moderate to good corrosion resistance increasing with chromium content
  • Poor Weldability
  • Non-hardenable and always used in the annealed condition
  • Generally resistant to stress corrosion cracking
  • More difficult to form than the austenitics

Austenitic Stainless Steels

Austenitic is the most widely used type of stainless steel, the basic composition is 18% Cr and 8% Ni (Grade 304). If further corrosion resistance is required 2-3% molybdenum (Mo) is added (Grade 316).


  • Excellent corrosion resistance.
  • Excellent weldability
  • Easy to clean, excellent for sterile environments.
  • Easy to form and fabricated.
  • Hardened by cold work, not by heat treatment.
  • Usually used in the fully annealed condition in which they are essentially non-magnetic.
  • Wide working temperature – from cryogenic -150oC to approximately 600oC. (or higher if scaling resistance is the only consideration)

Martensitic Stainless Steels

Martensitic stainless steels are very hard and strong and contains approximately 12-18% chromium. As they have carbon levels up to 1% they are not as corrosion resistant as Austenitic or Ferritic.


  • Magnetic
  • Difficult to form
  • Very low weldability
  • High Strength and hardness by heat treating

Duplex Stainless Steels

Duplex stainless steel contain relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). Most duplex steels contain molybdenum in a range of 2.5 – 4%. Duplex may be referred to as ferritic-austenitic stainless steel as they a microstructure of approximately 50% ferritic and 50% austenitic 50%.


  • An increased level of passivity due to higher Cr, Mo and N
  • Good weldability
  • Good to form.
  • Higher tensile and yield strengths (compared with austenitic and ferritic stainless steels).
  • High resistance to stress corrosion cracking

Precipitation hardening Stainless Steel

Precipitation hardening Stainless Steel have extra elements such as Copper, Niobium and Aluminium in their composition. These types of steel are designed to be machinable and then develop very high strength after fabrication by a single low temperature aging treatment.


  • Magnetic
  • Very high strength
  • Good weldability
  • Moderate to good corrosion resistance

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