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.
| Fe | 57.2 to 67 | |
| Cr | 24 to 27 | |
| Ni | 4.5 to 6.5 | |
| Mo | 2.9 to 3.9 | |
| Cu | 1.5 to 2.5 | |
| Mn | 0 to 1.5 | |
| Si | 0 to 1.0 | |
| N | 0.1 to 0.25 | |
| C | 0 to 0.040 | |
| 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 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