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ASTM Grade HP (26Cr-35Ni, N08705) Cast Stainless Steel

ASTM grade HP steel is an austenitic stainless steel formulated for casting. Cited properties are appropriate for the as-fabricated (no temper or treatment) condition. HP is the ASTM designation for this material. N08705 is the UNS number. And 26Cr-35Ni is the common industry name.

It has a moderately low thermal conductivity among cast austenitic stainless steels. In addition, it has a fairly low ductility and a fairly high base cost.

The graph bars on the material properties cards below compare ASTM grade HP steel to: cast austenitic 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

140

Elastic (Young's, Tensile) Modulus

200 GPa 29 x 106 psi

Elongation at Break

5.1 %

Fatigue Strength

130 MPa 18 x 103 psi

Poisson's Ratio

0.28

Shear Modulus

78 GPa 11 x 106 psi

Tensile Strength: Ultimate (UTS)

490 MPa 71 x 103 psi

Tensile Strength: Yield (Proof)

260 MPa 38 x 103 psi

Thermal Properties

Latent Heat of Fusion

320 J/g

Maximum Temperature: Corrosion

440 °C 820 °F

Maximum Temperature: Mechanical

1100 °C 2010 °F

Melting Completion (Liquidus)

1370 °C 2510 °F

Melting Onset (Solidus)

1330 °C 2420 °F

Specific Heat Capacity

480 J/kg-K 0.11 BTU/lb-°F

Thermal Conductivity

12 W/m-K 7.1 BTU/h-ft-°F

Thermal Expansion

16 µm/m-K

Otherwise Unclassified Properties

Base Metal Price

34 % relative

Density

7.9 g/cm3 500 lb/ft3

Embodied Carbon

5.8 kg CO2/kg material

Embodied Energy

82 MJ/kg 35 x 103 BTU/lb

Embodied Water

220 L/kg 27 gal/lb

Common Calculations

PREN (Pitting Resistance)

27

Resilience: Ultimate (Unit Rupture Work)

21 MJ/m3

Resilience: Unit (Modulus of Resilience)

170 kJ/m3

Stiffness to Weight: Axial

14 points

Stiffness to Weight: Bending

25 points

Strength to Weight: Axial

17 points

Strength to Weight: Bending

17 points

Thermal Diffusivity

3.2 mm2/s

Thermal Shock Resistance

11 points

Alloy Composition

Among cast stainless steels, the composition of ASTM grade HP steel is notable for containing comparatively high amounts of nickel (Ni) and silicon (Si). Nickel is primarily used to achieve a specific microstructure. In addition, it has a beneficial effect on mechanical properties and certain types of corrosion. Silicon content is typically governed by metallurgical processing concerns, but it can also be added for the purpose of improving oxidation resistance.

Iron (Fe) 29.2 to 42.7
Nickel (Ni) 33 to 37
Chromium (Cr) 24 to 28
Silicon (Si) 0 to 2.5
Manganese (Mn) 0 to 2.0
Carbon (C) 0.35 to 0.75
Molybdenum (Mo) 0 to 0.5
Phosphorus (P) 0 to 0.040
Sulfur (S) 0 to 0.040

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

Followup Questions

Similar Alloys

Further Reading

ASTM A297: Standard Specification for Steel Castings, Iron-Chromium and Iron-Chromium-Nickel, Heat Resistant, for General Application

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