Annealed High Carbon Co-28Cr-6Mo Alloy
Annealed R31538 cobalt is R31538 cobalt in the annealed condition. It has the lowest strength and highest ductility compared to the other variants of R31538 cobalt. The graph bars on the material properties cards below compare annealed 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
23 %
Fatigue Strength
310 MPa 45 x 103 psi
Poisson's Ratio
0.29
Reduction in Area
22 %
Rockwell C Hardness
25
Shear Modulus
86 GPa 13 x 106 psi
Tensile Strength: Ultimate (UTS)
1020 MPa 150 x 103 psi
Tensile Strength: Yield (Proof)
580 MPa 84 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)
200 MJ/m3
Resilience: Unit (Modulus of Resilience)
750 kJ/m3
Stiffness to Weight: Axial
15 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
34 points
Strength to Weight: Bending
27 points
Thermal Diffusivity
3.5 mm2/s
Thermal Shock Resistance
25 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
Further Reading
ASTM F1537: Standard Specification for Wrought Cobalt-28Chromium-6Molybdenum Alloys for Surgical Implants (UNS R31537, UNS R31538, and UNS R31539)
ASTM F799: Standard Specification for Cobalt-28Chromium-6Molybdenum Alloy Forgings for Surgical Implants (UNS R31537, R31538, R31539)