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UNS R30155 (formerly Grade 661) Iron-Cobalt Alloy

R30155 cobalt is a superaustenitic (highly alloyed) stainless steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed and aged condition. R30155 is the UNS number for this material. Older literature may refer to this material as ASTM Grade 661, but this is now discouraged.

It has the highest base cost among wrought superaustenitic stainless steels. In addition, it has the highest embodied energy and a moderately low ductility.

The graph bars on the material properties cards below compare R30155 cobalt to: wrought superaustenitic stainless 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

220

Elastic (Young's, Tensile) Modulus

210 GPa 30 x 106 psi

Elongation at Break

34 %

Fatigue Strength

310 MPa 45 x 103 psi

Poisson's Ratio

0.29

Reduction in Area

34 %

Shear Modulus

81 GPa 12 x 106 psi

Shear Strength

570 MPa 82 x 103 psi

Tensile Strength: Ultimate (UTS)

850 MPa 120 x 103 psi

Tensile Strength: Yield (Proof)

390 MPa 57 x 103 psi

Thermal Properties

Latent Heat of Fusion

300 J/g

Maximum Temperature: Corrosion

570 °C 1050 °F

Maximum Temperature: Mechanical

1100 °C 2000 °F

Melting Completion (Liquidus)

1470 °C 2680 °F

Melting Onset (Solidus)

1420 °C 2590 °F

Specific Heat Capacity

450 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

12 W/m-K 7.1 BTU/h-ft-°F

Thermal Expansion

14 µm/m-K

Otherwise Unclassified Properties

Base Metal Price

80 % relative

Density

8.5 g/cm3 530 lb/ft3

Embodied Carbon

9.7 kg CO2/kg material

Embodied Energy

150 MJ/kg 63 x 103 BTU/lb

Embodied Water

300 L/kg 36 gal/lb

Common Calculations

PREN (Pitting Resistance)

37

Resilience: Ultimate (Unit Rupture Work)

230 MJ/m3

Resilience: Unit (Modulus of Resilience)

370 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

23 points

Strength to Weight: Axial

28 points

Strength to Weight: Bending

24 points

Thermal Diffusivity

3.2 mm2/s

Thermal Shock Resistance

21 points

Alloy Composition

Among wrought stainless steels, the composition of R30155 cobalt is notable for including tantalum (Ta) and cobalt (Co). Tantalum is used to improve pitting corrosion resistance. Cobalt is used to improve mechanical strength at elevated temperatures.

Iron (Fe) 24.3 to 36.2
Chromium (Cr) 20 to 22.5
Nickel (Ni) 19 to 21
Cobalt (Co) 18.5 to 21
Molybdenum (Mo) 2.5 to 3.5
Tungsten (W) 2.0 to 3.0
Manganese (Mn) 1.0 to 2.0
Niobium (Nb) 0.75 to 1.3
Tantalum (Ta) 0.75 to 1.3
Silicon (Si) 0 to 1.0
Carbon (C) 0.080 to 0.16
Nitrogen (N) 0 to 0.2
Phosphorus (P) 0 to 0.040
Sulfur (S) 0 to 0.030

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

Followup Questions

Similar Alloys

Further Reading

ASTM B639: Standard Specification for Precipitation Hardening Cobalt-Containing Alloys (UNS R30155 and UNS R30816) Rod, Bar, Forgings, and Forging Stock for High-Temperature Service

Machining of Stainless Steels and Super Alloys: Traditional and Nontraditional Techniques, Helmi A. Youssef, 2016

Corrosion of Austenitic Stainless Steels: Mechanism, Mitigation and Monitoring, H. S. Khatak and B. Raj (editors), 2002

Austenitic Stainless Steels: Microstructure and Mechanical Properties, P. Marshall, 1984

ASM Specialty Handbook: Stainless Steels, J. R. Davis (editor), 1994

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