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UNS S32550 (Alloy 255) Stainless Steel

S32550 stainless steel is a duplex stainless steel formulated for primary forming into wrought products. Cited properties are appropriate for the annealed condition. S32550 is the UNS number for this material. Alloy 255 is the common industry name.

It has a moderately high thermal conductivity among wrought duplex stainless steels. In addition, it has a moderately high tensile strength and a moderately low ductility.

The graph bars on the material properties cards below compare S32550 stainless steel to: wrought duplex 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

260

Elastic (Young's, Tensile) Modulus

200 GPa 30 x 106 psi

Elongation at Break

21 %

Fatigue Strength

400 MPa 58 x 103 psi

Poisson's Ratio

0.27

Reduction in Area

57 %

Rockwell C Hardness

28

Shear Modulus

80 GPa 12 x 106 psi

Shear Strength

540 MPa 78 x 103 psi

Tensile Strength: Ultimate (UTS)

860 MPa 120 x 103 psi

Tensile Strength: Yield (Proof)

620 MPa 90 x 103 psi

Thermal Properties

Latent Heat of Fusion

300 J/g

Maximum Temperature: Corrosion

450 °C 840 °F

Maximum Temperature: Mechanical

1100 °C 2010 °F

Melting Completion (Liquidus)

1440 °C 2620 °F

Melting Onset (Solidus)

1390 °C 2540 °F

Specific Heat Capacity

480 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

16 W/m-K 9.4 BTU/h-ft-°F

Thermal Expansion

13 µm/m-K

Electrical Properties

Electrical Conductivity: Equal Volume

2.2 % IACS

Electrical Conductivity: Equal Weight (Specific)

2.5 % IACS

Otherwise Unclassified Properties

Base Metal Price

20 % relative

Density

7.8 g/cm3 490 lb/ft3

Embodied Carbon

3.8 kg CO2/kg material

Embodied Energy

53 MJ/kg 23 x 103 BTU/lb

Embodied Water

180 L/kg 22 gal/lb

Common Calculations

PREN (Pitting Resistance)

40

Resilience: Ultimate (Unit Rupture Work)

160 MJ/m3

Resilience: Unit (Modulus of Resilience)

940 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

25 points

Strength to Weight: Axial

31 points

Strength to Weight: Bending

26 points

Thermal Diffusivity

4.4 mm2/s

Thermal Shock Resistance

23 points

Alloy Composition

Among wrought stainless steels, the composition of S32550 stainless steel is notable for containing a comparatively high amount of chromium (Cr). Chromium is the defining alloying element of stainless steel. Higher chromium content imparts additional corrosion resistance.

Iron (Fe) 57.2 to 67
Chromium (Cr) 24 to 27
Nickel (Ni) 4.5 to 6.5
Molybdenum (Mo) 2.9 to 3.9
Copper (Cu) 1.5 to 2.5
Manganese (Mn) 0 to 1.5
Silicon (Si) 0 to 1.0
Nitrogen (N) 0.1 to 0.25
Carbon (C) 0 to 0.040
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 A473: Standard Specification for Stainless Steel Forgings

Duplex Stainless Steels, Iris Alvarez-Armas and Suzanne Degallaix-Moreuil (editors), 2009

Duplex Stainless Steels: Microstructure, Properties and Applications, Robert N. Gunn (editor), 1997

ASTM A479: Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels

ASTM A182: Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service

ASTM A240: Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels and for General Applications

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

ASTM A959: Standard Guide for Specifying Harmonized Standard Grade Compositions for Wrought Stainless Steels

Pressure Vessels: External Pressure Technology, 2nd ed., Carl T. F. Ross, 2011

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