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UNS R30556 (Alloy 556) Fe-Cr-Ni-Co Alloy

R30556 alloy is a superaustenitic (highly alloyed) stainless steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed condition. R30556 is the UNS number for this material. Alloy 556 is the common industry name.

It has a very high base cost among wrought superaustenitic stainless steels. In addition, it has a fairly low thermal conductivity and a very high embodied energy.

The graph bars on the material properties cards below compare R30556 alloy 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

Elastic (Young's, Tensile) Modulus

210 GPa 30 x 106 psi

Elongation at Break

45 %

Fatigue Strength

320 MPa 47 x 103 psi

Poisson's Ratio

0.28

Shear Modulus

81 GPa 12 x 106 psi

Shear Strength

550 MPa 79 x 103 psi

Tensile Strength: Ultimate (UTS)

780 MPa 110 x 103 psi

Tensile Strength: Yield (Proof)

350 MPa 51 x 103 psi

Thermal Properties

Latent Heat of Fusion

300 J/g

Maximum Temperature: Corrosion

450 °C 850 °F

Maximum Temperature: Mechanical

1100 °C 2010 °F

Melting Completion (Liquidus)

1420 °C 2580 °F

Melting Onset (Solidus)

1330 °C 2430 °F

Specific Heat Capacity

450 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

11 W/m-K 6.4 BTU/h-ft-°F

Thermal Expansion

15 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

1.8 % IACS

Electrical Conductivity: Equal Weight (Specific)

1.9 % IACS

Otherwise Unclassified Properties

Base Metal Price

70 % relative

Density

8.4 g/cm3 530 lb/ft3

Embodied Carbon

8.7 kg CO2/kg material

Embodied Energy

130 MJ/kg 55 x 103 BTU/lb

Embodied Water

300 L/kg 36 gal/lb

Common Calculations

PREN (Pitting Resistance)

40

Resilience: Ultimate (Unit Rupture Work)

290 MJ/m3

Resilience: Unit (Modulus of Resilience)

290 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

23 points

Strength to Weight: Axial

26 points

Strength to Weight: Bending

22 points

Thermal Diffusivity

2.9 mm2/s

Thermal Shock Resistance

18 points

Alloy Composition

Among wrought stainless steels, the composition of R30556 alloy is notable for including zinc (Zn) and tantalum (Ta). The literature is unclear on the metallurgical role of zinc in stainless steel. Tantalum is used to improve pitting corrosion resistance.

Iron (Fe) 20.4 to 38.2
Chromium (Cr) 21 to 23
Nickel (Ni) 19 to 22.5
Cobalt (Co) 16 to 21
Molybdenum (Mo) 2.5 to 4.0
Tungsten (W) 2.0 to 3.5
Manganese (Mn) 0.5 to 2.0
Tantalum (Ta) 0.3 to 1.3
Silicon (Si) 0.2 to 0.8
Aluminum (Al) 0.1 to 0.5
Nitrogen (N) 0.1 to 0.3
Niobium (Nb) 0 to 0.3
Carbon (C) 0.050 to 0.15
Lanthanum (La) 0.0050 to 0.1
Zinc (Zn) 0.0010 to 0.1
Phosphorus (P) 0 to 0.040
Boron (B) 0 to 0.020
Sulfur (S) 0 to 0.015

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

Followup Questions

Similar Alloys

Further Reading

ASTM B435: Standard Specification for UNS N06002, UNS N06230, UNS N12160, and UNS R30556 Plate, Sheet, and Strip

ASTM B572: Standard Specification for UNS N06002, UNS N06230, UNS N12160, and UNS R30556 Rod

ASTM B619: Standard Specification for Welded Nickel and Nickel-Cobalt Alloy Pipe

ASTM B626: Standard Specification for Welded Nickel and Nickel-Cobalt Alloy Tube

ASTM B622: Standard Specification for Seamless Nickel and Nickel-Cobalt Alloy Pipe and Tube

Welding Metallurgy and Weldability of Stainless Steels, John C. Lippold and Damian J. Kotecki, 2005

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

Properties and Selection: Irons, Steels and High Performance Alloys, ASM Handbook vol. 1, ASM International, 1993

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