When nickel is added to stainless steel in sufficient amounts the crystal structure changes to "austenite". The basic composition of austenitic stainless steels is 18% chromium and 8% nickel. Austenitic grades are the most commonly used stainless steels accounting for more than 70% of production (type 304 is the most commonly specified grade by far).

Basic properties

• Excellent corrosion resistance

• Excellent weldability (all processes)

• Excellent formability, fabricability and ductility

• Excellent cleanability, and hygiene characteristics

• Eood high and excellent low temperature properties

• Non magnetic (if annealed)

• Hardenable by cold work only

Common uses

• Computer keyboard key springs (301)

• Kitchen sinks (304D)

• Food processing equipment

• Architectural applications

• Chemical plant and equipment

These are plain chromium stainless steels with varying chromium content between 12 and 18%, but with low carbon content.

Basic properties

• Moderate to good corrosion resistance increasing with chromium content

• Not hardenable by heat treatment and always used in the annealed condition magnetic

• Weldability is poor

• Formability not as good as the austenitics

Common uses

• Automotive trim (430)

• Automotive exhausts (409)

• Colliery equipment (3CR12)

• Hot water tanks (444)

  
  

These are stainless steels containing relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). The nickel content is insufficient to generate a fully austenitic structure and the resulting combination of ferritic and austenitic structures is called duplex. Most duplex steels contain molybdenum in a range of 2.5 - 4%.

Basic properties

• High resistance to stress corrosion cracking

• Increased resistance to chloride ion attack

• Higher tensile and yield strength than austenitic or ferritic steels

• Good weldability and formability

Common uses

• Marine applications, particularly at slightly elevated temperatures

• Desalination plant

• Heat exchangers

• Petrochemical plant

  
  

Martensitic stainless steels were the first stainless steels commercially developed (as cutlery) and have relatively high carbon content (0.1 - 1.2%) compared to other stainless steels. They are plain chromium steels containing between 12 and 18% chromium.

Basic properties

• moderate corrosion resistance

• can be hardened by heat treatment and therefore high strength and hardness levels can be achieved

• poor weldability

• magnetic

Common uses

• knife blades

• surgical instruments

• shafts

• spindles

• pins

  
  

Precipitation hardening stainless steels have been formulated so that they can be supplied in a solution treated condition, (in which they are machineable) and can be hardened, after fabrication, in a single low temperature "ageing" process.

Basic properties

• Moderate to good corrosion resistance

• Very high strength

• Good weldability

• Magnetic

Common uses

• Shafts for pumps and valves