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.
| Fe | 29.2 to 42.7 | |
| Ni | 33 to 37 | |
| Cr | 24 to 28 | |
| Si | 0 to 2.5 | |
| Mn | 0 to 2.0 | |
| C | 0.35 to 0.75 | |
| Mo | 0 to 0.5 | |
| P | 0 to 0.040 | |
| 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