18/8 Stainless Steel, Grade 18-8 SS Properties & Meaning

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What is 18/8 Stainless Steel

18/8 stainless steel means the composition of stainless steel containing 18% chromium and 8% nickel. Its precursor is 20-7 stainless steel, invented by German metallurgists Benno Strauss and Eduard Maurer. It was first introduced in America during a symposium held by ASTM in 1924. The first production of this alloy in the United States was not until 1927. Before stainless steel was standardized, grade 18/8 was used as the trade name of many steel companies. In 1930s, AISI decided on a three-digit numbering system for stainless steels, 18-8 was named type 304 stainless steel.

18-8 Stainless Steel Properties

Grade 18-8 stainless steel density is 7.93 g/cm3 (0.286 lb/in3), yield strength at 0.2% is minimum 30 ksi (205 MPa), tensile strength is minimum 75 ksi (515 MPa), maximum Brinell hardness is 201 HB, maximum Rockwell hardness is 92 HRB. Grade 18-8 SS material is non-magnetic in the annealed condition, but may be slightly magnetic after cold working.

Chemical Composition

Grade 18-8 Stainless Steel Composition, %
AISI C, ≤ Si, ≤ Mn, ≤ P, ≤ S, ≤ Cr Ni N, ≤
304 0.08 1.00 2.00 0.045 0.03 18.0-20.0 8.0-11.0
304L 0.03 1.00 2.00 0.045 0.03 18.0-20.0 8.0-12.0
304N 0.08 1.00 2.00 0.045 0.03 18.0-20.0 8.0-11.0 0.10-0.16

Physical Properties

Grade 18-8 SS Physical Properties Metric Imperial
Density 7.93 g/cm3 0.286 lb/in3
Melting point 1400-1450 °C 2550-2650 °F
Specific heat capacity 500 J/kg·K at 20 °C 0.12 Btu/lb ·°F at 68 °F
Electrical resistivity 0.72 μΩ·m at 20 °C 28.35 μΩ·in. at 68 °F
Conductivity, %, IACS 2.5
Magnetic permeability 1.02 (Approximate)
Elastic modulus (Modulus of Elasticity) 193 GPa 28 x 106 psi
Thermal diffusivity 3.84 mm2/s 0.006 in2/s
Thermal conductivity 16.2 W/m·K at 100 °C 9.4 Btu/ft·h·°F at 212 °F
21.5 W/m·K at 500 °C 12.4 Btu/ft·h·°F at 932 °F
Coefficient of thermal expansion (CTE) 17.2 10-6/K at 0-100 °C 9.6 μin./in.·°F at 32-212 °F
17.8 10-6/K at 0-315 °C 9.9 μin./in.·°F at 32-600 °F
18.4 10-6/K at 0-538 °C 10.2 μin./in.·°F at 32-1000 °F

Notes:

  • 10-6·K-1 = 10-6/K
  • 1 Ω·mm²/m = 1 μΩ·m
  • 1 g/cm3 = 1 kg/dm3 = 1000 kg/m3
  • 1 GPa = 1 kN/mm2
  • 1 MPa = 1 N/mm2

Mechanical Properties

ASTM A276 Grade 18/8 SS Mechanical Properties
Stainless Steel 0.2% Yield Strength, MPa (ksi), ≥ Tensile Strength, MPa (ksi), ≥ Elongation in 2 in. (50 mm), %, ≥ Reduction of Area, %, ≥ Conditions
18/8 205 (30) 515 (75) 40 50 Annealed, Hot finished
310 (45) 620 (90) 30 40 Annealed, Cold finished, Dia ≤ 1/2 in (12.7mm)
205 (30) 515 (75) 30 40 Annealed, Cold finished, Dia > 1/2 in (12.7mm)
ASTM A240 18-8 SS Mechanical Properties
Stainless Steel 0.2% Yield Strength, MPa (ksi), ≥ Tensile Strength, MPa (ksi), ≥ Elongation in 2 in. (50 mm), %, ≥ Brinell Hardness, HB, ≤ Rockwell Hardness, HRB,  ≤
18-8 205 (30) 515 (75) 40 201 92

For more data sheet of grade 18-8 material, you can view 304 Stainless Steel Properties.

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