# 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 10 ^{6} psi*

Elongation at Break

23 *%*

Fatigue Strength

310 *MPa* 45 *x 10 ^{3} psi*

Poisson's Ratio

0.29

Reduction in Area

22 *%*

Rockwell C Hardness

25

Shear Modulus

86 *GPa* 13 *x 10 ^{6} psi*

Tensile Strength: Ultimate (UTS)

1020 *MPa* 150 *x 10 ^{3} psi*

Tensile Strength: Yield (Proof)

580 *MPa* 84 *x 10 ^{3} 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/cm ^{3}* 530

*lb/ft*

^{3}Embodied Carbon

8.1 *kg CO _{2}/kg material*

Embodied Energy

110 *MJ/kg* 46 *x 10 ^{3} BTU/lb*

Embodied Water

530 *L/kg* 63 *gal/lb*

## Common Calculations

Resilience: Ultimate (Unit Rupture Work)

200 *MJ/m ^{3}*

Resilience: Unit (Modulus of Resilience)

750 *kJ/m ^{3}*

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 *mm ^{2}/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)