18/8 Stainless Steel, Grade 18-8 SS Properties & Meaning
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.
Comments are closed.