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.
- Moderate to good corrosion resistance
- Very high strength
- Good weldability
- Shafts for pumps and valves
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.
- moderate corrosion resistance
- can be hardened by heat treatment and therefore high strength and hardness levels can be achieved
- poor weldability
- knife blades
- surgical instruments
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%.
- 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
- Marine applications, particularly at slightly elevated temperatures
- Desalination plant
- Heat exchangers
- Petrochemical plant
These are plain chromium stainless steels with varying chromium content between 12 and 18%, but with low carbon content.
- 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
- Automotive trim (430)
- Automotive exhausts (409)
- Colliery equipment (3CR12)
- Hot water tanks (444)
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).
- 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
- Computer keyboard key springs (301)
- Kitchen sinks (304D)
- Food processing equipment
- Architectural applications
- Chemical plant and equipment
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