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Stainless steel is not a single alloy. Understanding stainless steel classes and grades will help you understand where each type is best used and what for. Stainless steel grades fall under 4 families: austenitic, ferritic, duplex, and martensitic.

Austenitic

  • Non-magnetic when annealed with a solution
  • Cannot be hardened with heat treatment
  • Excellent resistance to corrosion
  • Great for welding

Popular grades of austenitic stainless steel are 301, 303, 304, 316, and 321.

301- This is very ductile. It hardens quickly during mechanical working and has good weldability and wear resistance.

303- This has additional sulphur and phosphorus, making it an easier machining version of 304.

304- This is the most common grade. It’s a classic 18/8 stainless steel. 18% chromium and 8% nickel.

316- This is the second most common grade. The alloy addition of molybdenum prevents some kinds of corrosion. It’s also referred to as ‘marine grade’ steel because of its extended resistance to chloride corrosion.

321- Like 304 but added titanium gives it a lower risk of weld decay.

Ferritic

  • Lower nickel content
  • Often contain chromium, molybdenum, niobium, and titanium
  • One of the most cost-effective families
  • Mainly magnetic
  • Good corrosion and oxidation resistance
  • Good weldability
  • Common use in indoor or hidden applications
  • Cost and performance outweigh visual appearance

Popular grades of ferritic stainless steels are 409 and 430

409- the cheapest type, commonly used for car exhausts.

430- for decorative use, it has good formability. However, has reduced temperature and corrosion resistance.

Duplex

  • Combination of properties from austenitic and ferritic stainless steels
  • Created with different alloys to address specific concerns
  • Good weldability and formability
  • Some improved corrosion resistance

Some common duplex alloys are 318L, LDX2101, LDX2304, 2507, 4501

Martensitic

  • Can be tempered and hardened as a result of added carbon
  • Popular for blades, knifes, scissors, medical tools
  • Chromium steel without nickel
  • All grades are magnetic

410- High levels of strength and resistant to wear and corrosion and can be heat treated.

420- Known as ‘surgical steel’. It is like 410 but has more strength and hardness. Can be hardened through heat treatment meaning good ductility for metal fabricators.

Here we have highlighted just some of the different stainless steel classes and grades. At ANY Weld we use stainless steel for many projects, for any more information about specific grades get in touch with us at [email protected]