Austenitic Stainless Steels
The most common austenitic alloys are iron-chromium-nickel steels and are frequently referred to as 300 series stainless.
The best known austenitic Stainless Steel grades are 304/L & 316/L with other well-known grades such as 321 and 310. These grades contain minimum 16% chromium and 6% nickel commonly referred as 18/8 stainless (grade 304). Austenitic grades are generally preferred for their ease of fabrication resulting from a stable metallurgical microstructure at all temperatures combined with good corrosion resistance, mechanical and physical properties.
The addition of molybdenum to a steel containing 18% chromium and 8% nickel improves corrosion resistance and increases significantly the high temperature strength. Grade 316/L is the most common example of this.
Included is the high alloys or “Super Austenitic” with increased chromium and nickel such as 904/L & 310/L containing up to 26% chromium and 22% nickel. Ideal for high temperature use with excellent corrosion resistance to strong acids and chlorides.
Characteristics of Austenitic Stainless Steels:
- Excellent ductility.
- Good strength and scaling resistance at high temperatures(310 to 1100 Degrees Celsius)
- Cold working to increase hardness.
- Low temperature applications, cryogenic applications.
- Cannot be hardened by heat treatment.
- Weldable using all standard procedures and equipment.
Grade and Typical application:
304 – General purpose with good corrosion properties, used for architectural, food processing and domestic industries.
304L – A version of 304 with lower carbon and no requirement for post weld annealing.
310 – A high temperature grade for use in furnace parts.
316 – Used for higher corrosion resistance e.g. marine applications.
316L – A version of 316 with lower carbon and is immune from sensitisation.
321 – Titanium stabilised and suitable for heat resisting applications up to 800°C.
Special chemical balance for welding.
Cold Heading Grades
Copper is added to improve the austenitic structure and make the steel less prone to cold work hardening.
* Free machining grade: only for moderate amount of cold heading.