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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. 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 R31538 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 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

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 Expansion

13 µm/m-K

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 Shock Resistance

25 to 33 points

Alloy Composition

Cobalt (Co) 58.7 to 68.9
Chromium (Cr) 26 to 30
Molybdenum (Mo) 5.0 to 7.0
Manganese (Mn) 0 to 1.0
Silicon (Si) 0 to 1.0
Nickel (Ni) 0 to 1.0
Iron (Fe) 0 to 0.75
Carbon (C) 0.15 to 0.35
Nitrogen (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)