Austenitic stainless steel refers to stainless steel with an austenitic structure at room temperature. The most common representative grades are 304 (18-8 type) and 316 (18-12 type). Its mechanical properties are very distinctive, mainly reflected in the following aspects:
- Excellent plasticity and toughnessThis is the most prominent characteristic of austenitic stainless steel.
- Features: It has very high elongation and large reduction of area. This means the material is very “soft” and tough, and can withstand large deformations without fracture.
- Performance: It is extremely easy to form by cold working, such as deep drawing, bending, stretching, etc., making it an ideal material for manufacturing complex-shaped parts. At the same time, it has extremely high impact toughness. Even at very low temperatures (even close to absolute zero), it will not suffer from cold brittle fracture like ordinary carbon steel.
- Non-magnetic (or weakly magnetic)
- Features: In the annealed condition, austenitic stainless steel is usually completely non-magnetic.
- Note: It is worth mentioning that after severe cold working (such as stamping into elbows, cold-drawn steel wires), a small amount of martensitic structure will be formed inside, resulting in weak magnetism. This does not mean the material will rust or is unqualified.
- Significant work hardening effect (cold working hardening)This is the most important property to note during machining of austenitic stainless steel.
- Features: With increasing deformation, its strength and hardness rise rapidly while plasticity decreases.
- Influence: This characteristic is an advantage in cold working (e.g., cold-rolled sheets), as strength can be greatly improved through cold deformation. However, it is a disadvantage in cutting operations (turning, drilling), easily causing accelerated tool wear, increased cutting force, and difficulty in chip breaking.
- Medium yield strength, but can be strengthened by cold working
- Features: Compared with high-strength alloy steel or quenched carbon steel, annealed austenitic stainless steel has relatively low yield strength (usually around 200–300 MPa).
- Strengthening method: Since it cannot be hardened by heat treatment (quenching) like martensitic stainless steel, its strength is normally improved by “cold working”. After cold working, the tensile strength of austenitic stainless steel can easily exceed 1000 MPa.
- Excellent corrosion resistance
- Features: With the combination of chromium (Cr) and nickel (Ni), a dense chromium oxide protective film forms on the surface, providing excellent corrosion resistance in atmosphere, fresh water, steam and many chemical media.
- Improvement: Adding molybdenum (Mo) (as in grade 316) further enhances pitting corrosion and crevice corrosion resistance, making it especially suitable for marine or chloride-containing environments.
- Low thermal conductivity and high linear expansion coefficient
- Thermal conductivity: Very low thermal conductivity, only about 1/3 to 1/4 that of carbon steel. This means heat dissipates slowly during welding or heating, easily causing local overheating.
- Expansion: High linear expansion coefficient, about 1.5 times that of carbon steel. Large thermal stress may occur under rapid temperature changes, leading to deformation or cracking.
SummaryThe mechanical properties of austenitic stainless steel can be summarized as: soft, tough, sticky, non-magnetic.
- Soft / Tough: Good plasticity, impact resistance, rust-free, excellent low-temperature performance.
- Sticky: Severe work hardening, difficult to machine.
- Non-magnetic: Unique physical property.
It is the most widely used type of stainless steel at present, accounting for more than 70% of total stainless steel production.
