High Carbon Co-28Cr-6Mo Alloy (ASTM F1537 Alloy 2, ISO 5832-12 Alloy 2, R31538)
R31538 cobalt is a cobalt alloy. ASTM F1537 Alloy 2 is the ASTM designation for this material. R31538 is the UNS number.
The properties of R31538 cobalt include three common variations. This page shows summary ranges across all of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare R31538 cobalt to other cobalt alloys (top) and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.
Mechanical Properties
Elastic (Young's, Tensile) Modulus
220 GPa 32 x 106 psi
Elongation at Break
13 to 23 %
Fatigue Strength
310 to 480 MPa 45 to 69 x 103 psi
Poisson's Ratio
0.29
Reduction in Area
13 to 22 %
Rockwell C Hardness
25 to 35
Shear Modulus
86 GPa 13 x 106 psi
Tensile Strength: Ultimate (UTS)
1020 to 1360 MPa 150 to 200 x 103 psi
Tensile Strength: Yield (Proof)
580 to 930 MPa 84 to 130 x 103 psi
Thermal Properties
Latent Heat of Fusion
320 J/g
Melting Completion (Liquidus)
1360 °C 2480 °F
Melting Onset (Solidus)
1290 °C 2360 °F
Specific Heat Capacity
450 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
13 W/m-K 7.6 BTU/h-ft-°F
Thermal Expansion
13 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
2.0 % IACS
Electrical Conductivity: Equal Weight (Specific)
2.1 % IACS
Otherwise Unclassified Properties
Density
8.4 g/cm3 530 lb/ft3
Embodied Carbon
8.1 kg CO2/kg material
Embodied Energy
110 MJ/kg 46 x 103 BTU/lb
Embodied Water
530 L/kg 63 gal/lb
Common Calculations
Resilience: Ultimate (Unit Rupture Work)
140 to 200 MJ/m3
Resilience: Unit (Modulus of Resilience)
750 to 1920 kJ/m3
Stiffness to Weight: Axial
15 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
34 to 45 points
Strength to Weight: Bending
27 to 32 points
Thermal Diffusivity
3.5 mm2/s
Thermal Shock Resistance
25 to 33 points
Alloy Composition
| Co | 58.7 to 68.9 | |
| Cr | 26 to 30 | |
| Mo | 5.0 to 7.0 | |
| Mn | 0 to 1.0 | |
| Si | 0 to 1.0 | |
| Ni | 0 to 1.0 | |
| Fe | 0 to 0.75 | |
| C | 0.15 to 0.35 | |
| N | 0 to 0.25 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ASTM F799: Standard Specification for Cobalt-28Chromium-6Molybdenum Alloy Forgings for Surgical Implants (UNS R31537, R31538, R31539)
ASTM F1537: Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, UNS R31538, and UNS R31539)