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.
| Fe | 24.3 to 36.2 | |
| Cr | 20 to 22.5 | |
| Ni | 19 to 21 | |
| Co | 18.5 to 21 | |
| Mo | 2.5 to 3.5 | |
| W | 2.0 to 3.0 | |
| Mn | 1.0 to 2.0 | |
| Nb | 0.75 to 1.3 | |
| Ta | 0.75 to 1.3 | |
| Si | 0 to 1.0 | |
| C | 0.080 to 0.16 | |
| N | 0 to 0.2 | |
| P | 0 to 0.040 | |
| 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