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Dispersion Strengthened Co-28Cr-6Mo Alloy (ASTM F1537 Alloy 3, R31539)

R31539 cobalt is a cobalt alloy. ASTM F1537 Alloy 3 is the ASTM designation for this material. R31539 is the UNS number.

The properties of R31539 cobalt include three common variations. The property values on this page show 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 R31539 cobalt to other cobalt alloys (top) and the entire database (bottom). The length of each bar shows the given value as a % of the largest value in the relevant set.

Mechanical Properties

Elastic (Young's, Tensile) Modulus

220 GPa 32 x 106 psi

Elongation at Break

13 to 22 %

Fatigue Strength

310 to 480 MPa 45 to 70 x 103 psi

Poisson's Ratio


Reduction in Area

13 to 23 %

Rockwell C Hardness

25 to 35

Shear Modulus

86 GPa 13 x 106 psi

Tensile Strength: Ultimate (UTS)

1000 to 1340 MPa 150 to 190 x 103 psi

Tensile Strength: Yield (Proof)

590 to 940 MPa 85 to 140 x 103 psi

Thermal Properties

Latent Heat of Fusion

320 J/g

Melting Completion (Liquidus)

1360 °C 2470 °F

Melting Onset (Solidus)

1290 °C 2350 °F

Specific Heat Capacity

450 J/kg-K 0.11 BTU/lb-°F

Thermal Expansion

13 µm/m-K

Otherwise Unclassified Properties


8.4 g/cm3 520 lb/ft3

Embodied Carbon

8.2 kg CO2/kg material

Embodied Energy

110 MJ/kg 46 x 103 BTU/lb

Embodied Water

530 L/kg 64 gal/lb

Common Calculations

Resilience: Ultimate (Unit Rupture Work)

140 to 190 MJ/m3

Resilience: Unit (Modulus of Resilience)

780 to 2000 kJ/m3

Stiffness to Weight: Axial

15 points

Stiffness to Weight: Bending

24 points

Strength to Weight: Axial

33 to 44 points

Strength to Weight: Bending

27 to 32 points

Thermal Shock Resistance

24 to 32 points

Alloy Composition

Cobalt (Co) 57.7 to 68.7
Chromium (Cr) 26 to 30
Molybdenum (Mo) 5.0 to 7.0
Aluminum (Al) 0.3 to 1.0
Manganese (Mn) 0 to 1.0
Silicon (Si) 0 to 1.0
Nickel (Ni) 0 to 1.0
Iron (Fe) 0 to 0.75
Nitrogen (N) 0 to 0.25
Lanthanum (La) 0.030 to 0.2
Carbon (C) 0 to 0.14

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)

CRC Materials Science and Engineering Handbook, 4th ed., James F. Shackelford et al. (editors), 2015