# SAE-AISI 8642 (G86420) Ni-Cr-Mo Steel

SAE-AISI 8642 steel is an alloy steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed condition. 8642 is the designation in both the SAE and AISI systems for this material. G86420 is the UNS number.

The graph bars on the material properties cards below compare SAE-AISI 8642 steel to: SAE-AISI wrought steels (top), all iron alloys (middle), 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

Brinell Hardness

170

Elastic (Young's, Tensile) Modulus

190 *GPa* 27 *x 10 ^{6} psi*

Elongation at Break

23 *%*

Fatigue Strength

270 *MPa* 40 *x 10 ^{3} psi*

Poisson's Ratio

0.29

Shear Modulus

73 *GPa* 11 *x 10 ^{6} psi*

Shear Strength

370 *MPa* 53 *x 10 ^{3} psi*

Tensile Strength: Ultimate (UTS)

580 *MPa* 84 *x 10 ^{3} psi*

Tensile Strength: Yield (Proof)

380 *MPa* 55 *x 10 ^{3} psi*

## Thermal Properties

Latent Heat of Fusion

250 *J/g*

Maximum Temperature: Mechanical

410 *°C* 780 *°F*

Melting Completion (Liquidus)

1460 *°C* 2660 *°F*

Melting Onset (Solidus)

1420 *°C* 2580 *°F*

Specific Heat Capacity

470 *J/kg-K* 0.11 *BTU/lb-°F*

Thermal Conductivity

39 *W/m-K* 22 *BTU/h-ft-°F*

Thermal Expansion

13 *µm/m-K*

## Electrical Properties

Electrical Conductivity: Equal Volume

7.3 *% IACS*

Electrical Conductivity: Equal Weight (Specific)

8.4 *% IACS*

## Otherwise Unclassified Properties

Base Metal Price

2.6 *% relative*

Density

7.8 *g/cm ^{3}* 490

*lb/ft*

^{3}Embodied Carbon

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

Embodied Energy

20 *MJ/kg* 8.7 *x 10 ^{3} BTU/lb*

Embodied Water

50 *L/kg* 6.0 *gal/lb*

## Common Calculations

Resilience: Ultimate (Unit Rupture Work)

120 *MJ/m ^{3}*

Resilience: Unit (Modulus of Resilience)

390 *kJ/m ^{3}*

Stiffness to Weight: Axial

13 *points*

Stiffness to Weight: Bending

24 *points*

Strength to Weight: Axial

20 *points*

Strength to Weight: Bending

20 *points*

Thermal Diffusivity

10 *mm ^{2}/s*

Thermal Shock Resistance

17 *points*

## Alloy Composition

Among alloy steels, the composition of SAE-AISI 8642 steel is notable for including nickel (Ni). Nickel is used to improve mechanical properties, and to make the alloy easier to heat treat.

Fe | 96.6 to 97.8 | |

Mn | 0.75 to 1.0 | |

Ni | 0.4 to 0.7 | |

Cr | 0.4 to 0.6 | |

C | 0.4 to 0.45 | |

Si | 0.15 to 0.35 | |

Mo | 0.15 to 0.25 | |

S | 0 to 0.040 | |

P | 0 to 0.035 |

All values are % weight. Ranges represent what is permitted under applicable standards.

## Followup Questions

## Similar Alloys

## Further Reading

ASTM A752: Standard Specification for General Requirements for Wire Rods and Coarse Round Wire, Alloy Steel

ASTM A322: Standard Specification for Steel Bars, Alloy, Standard Grades

ASM Specialty Handbook: Carbon and Alloy Steels, J. R. Davis (editor), 1996

Manufacture and Uses of Alloy Steels, Henry D. Hibbard, 2005

Steels: Processing, Structure, and Performance, 2nd ed., George Krauss, 2015