Stainless Steel

The main justification for selecting Stainless Steel for a given application is its outstanding corrosion and oxidation resistance.  They equally possess other exceptional properties, such as the ability to develop very high strength through cold working or heat treatment, excellent formability and the capability to withstand cryogenic temperatures, makes it a very versatile material.

Stainless steels have a wide range of microstructures which are controlled by composition.  However, all Stainless Steels must contain chromium to form the complex oxide surface which gives Stainless Steel its protective corrosion resistance.  Other alloying elements have significant effects to the mechanical properties of the material. As Stainless Steels is such a large group, with many variations in characteristics and composition, it is often more beneficial to categorise them in terms of microstructure.  Commercial forms of Stainless steel fall into the following categories:

Stainless Steels Summary Table

MaterialGrades SuppliedMain featuresAdvantagesDisadvantages
Austenitic Steel with Manganese201
  • Non magnetic*
  • Low Carbon
  • Main alloying element is chromium, typically 16-20%
  • Nickel typically 7-13%
  • Strengthens significantly during cold working
  • Good weldability
  • High strength and ductility
  • Cannot be hardened by heat treatment
  • Low stress corrosion cracking resistance
Austenitics301, 304L, 304, 305, 320, 321, 347,
Austenitic Steel with Molybdenum316, 316L, 316Ti, 904L
Ferritics409, 410S, 430, 430L, 430Ti (439), 441, 444
  • Magnetic
  • Low Carbon
  • Main alloying element is chromium, typically 10.5-17%
  • Good formability
  • Low cost
  • Good stress corrosion cracking resistance
  • Moderate ductility
  • Limited corrosion resistance
  • Cannot be hardened by heat treatment
Martensitics410, 420, 431
  • Can be magnetic or non magnetic
  • Low Carbon
  • Main alloying element is chromium, typically 12 to 15%, molybdenum (0.2-1%)
  • Hardened by quenching and tempered to give improved toughness and ductility
  • Less resistant to corrosion compared to Austenitic and Ferritic grades.
  • Limited formability and welding capabilities
Precipitation hardening17/4PH, 17/7PH
  • Contains Aluminium or Copper
  • High work hardening rates
  • Very high strengths
  • Better Corrosion resistance compared to martensitics
  • Limited availability
  • Lower corrosion resistance, formability and weldability compared to austenitics
Duplex309, 310
  • Magnetic
  • Low Carbon
  • Combined Austenitic-Ferritic structure
  • Chromium typically 21-26%
  • Nickel typically 3.5-6.5%
  • Superior tensile strength in annealed condition
  • Good corrosion and pitting resistance
  • Lighter weight
  • Lower cost due to lower Nickel content
  • Cannot be hardened by heat treatment, but offers higher annealed strength levels than Ferritic or Austenitic grades
  • Restricted application temperature range when compared to Austenitics
* cold working of the less alloyed grades will induce structural changes leading to increased levels of magnetism.

**Super Austenitics, Super Ferritic and Super Duplexes are available by request