Austenitic stainless steel Material Properties

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Carbon:
Silicon:
Manganese:
Chromium:
Nickel:
Molybdenum:
Titanium:
Copper:
Nitrogen:
GS (ASTM):
Niobium:
Md30 - Temperature:
Celcius
CrEq/NiEq:
Ferrite Number (FNA):
Pitting Resistance Equivalence (CPT):

Austenitic stainless steels are one of the most commonly used families of stainless steel due to their excellent combination of mechanical properties, corrosion resistance, and formability. Here are some key material properties of austenitic stainless steel:

1. Composition

  • Primarily made of iron, chromium (16-26%), and nickel (8-22%).
  • May also contain manganese, molybdenum, and other elements in smaller quantities.
  • The high nickel content is what gives it its characteristic face-centered cubic (FCC) crystal structure.

2. Mechanical Properties

  • Tensile Strength: Generally, austenitic stainless steels have high tensile strength, typically ranging from 520 MPa to 860 MPa depending on the specific alloy and heat treatment.
  • Yield Strength: Typically 200 MPa to 500 MPa.
  • Elongation: These steels are highly ductile, often offering elongation values in the range of 40% to 60% in standard conditions.
  • Hardness: It can range from 150 HB (Brinell hardness) for annealed steels up to 300 HB for hardened grades.
  • Impact Toughness: Excellent impact resistance at both low and high temperatures.

3. Corrosion Resistance

  • Excellent resistance to a wide range of corrosive environments, including oxidizing acids (e.g., nitric acid) and chloride environments (e.g., seawater).
  • However, they are susceptible to pitting and crevice corrosion in chloride-rich environments, especially at elevated temperatures.
  • Adding molybdenum (Mo) to the alloy, such as in 316 stainless steel, enhances its resistance to pitting and crevice corrosion.

4. Thermal Properties

  • Melting Point: Approximately 1400-1450°C.
  • Coefficient of Thermal Expansion: Around 16-17 µm/m·°C (typically a little higher than carbon steels).
  • Thermal Conductivity: Lower than carbon steels, at about 15-20 W/m·K.

5. Magnetic Properties

  • Generally non-magnetic in the annealed condition due to the face-centered cubic (FCC) crystal structure, but can become slightly magnetic if cold-worked.

6. Formability

  • Excellent weldability and formability.
  • Can be easily welded, formed, and machined, though some grades (e.g., high-carbon variants) may require special care during welding to avoid sensitization (formation of chromium carbides at grain boundaries).
  • Common forms include plates, sheets, tubes, bars, and wires.

7. Common Grades

  • 304: The most common austenitic grade, used in a wide variety of applications, from kitchen equipment to structural applications.
  • 316: Contains molybdenum, offering improved corrosion resistance, especially in chloride environments.
  • 321: Titanium-stabilized, offering better resistance to high-temperature intergranular corrosion.
  • 347: Colbat-stabilized, also providing better high-temperature performance.

8. Applications

  • Food processing, medical devices, and pharmaceutical equipment: due to its non-reactivity and ease of cleaning.
  • Chemical processing equipment: due to corrosion resistance to a wide variety of chemicals.
  • Heat exchangers, power plants, marine environments: as it maintains strength at high temperatures and resists corrosion in saltwater.
  • Architectural applications: for both aesthetic appeal and durability.