Types of Stainless Steel

2017-05-20 dewei 阅读301

In addition to chromium, nickel, molybdenum, titanium and niobium, other elements may also be added to stainless steels in varying quantities to produce a range of stainless steel grades, each with different properties.

There are a number of grades to choose from, but all stainless steels can be divided into five basic categories:





•Precipitation hardening

These are named according to the microstructure inherent in each steel group (a function of the primary alloying elements). Austenitic and ferritic grades account for approximately 95% of stainless steel 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

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