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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

Table: Typical physical properties - Annealed condition

Table: Mechanical properties of wrought stainless steel

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

Common martensitic stainless steel grades and their applications

 

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

Common duplex grades and their applications

 

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)

Common ferritic stainless grades and their applications

 

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

Table: Common austenitic stainless steel grades and their applications

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