ASTM A387 Grade 9 (K90941) 9Cr-1Mo Steel
ASTM A387 grade 9 steel is an alloy steel formulated for primary forming into wrought products. ASTM A387 Grade 9 is the ASTM designation for this material. K90941 is the UNS number.
It has a fairly low thermal conductivity among wrought alloy steels in the same category. In addition, it has a fairly high electrical conductivity and a fairly high base cost.
The properties of ASTM A387 grade 9 steel include two common variations. This page shows summary ranges across both of them. For more specific values, follow the links immediately below. The graph bars on the material properties cards further below compare ASTM A387 grade 9 steel to: wrought alloy steels in the same category (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
150 to 180
Elastic (Young's, Tensile) Modulus
190 GPa 28 x 106 psi
Elongation at Break
20 to 21 %
Fatigue Strength
160 to 240 MPa 23 to 35 x 103 psi
Poisson's Ratio
0.28
Shear Modulus
75 GPa 11 x 106 psi
Shear Strength
310 to 380 MPa 45 to 55 x 103 psi
Tensile Strength: Ultimate (UTS)
500 to 600 MPa 73 to 87 x 103 psi
Tensile Strength: Yield (Proof)
230 to 350 MPa 34 to 50 x 103 psi
Thermal Properties
Latent Heat of Fusion
270 J/g
Maximum Temperature: Mechanical
600 °C 1110 °F
Melting Completion (Liquidus)
1460 °C 2650 °F
Melting Onset (Solidus)
1410 °C 2580 °F
Specific Heat Capacity
470 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
26 W/m-K 15 BTU/h-ft-°F
Thermal Expansion
13 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
9.0 % IACS
Electrical Conductivity: Equal Weight (Specific)
10 % IACS
Otherwise Unclassified Properties
Base Metal Price
6.5 % relative
Density
7.8 g/cm3 490 lb/ft3
Embodied Carbon
2.1 kg CO2/kg material
Embodied Energy
28 MJ/kg 12 x 103 BTU/lb
Embodied Water
87 L/kg 10 gal/lb
Common Calculations
PREN (Pitting Resistance)
12
Resilience: Ultimate (Unit Rupture Work)
83 to 110 MJ/m3
Resilience: Unit (Modulus of Resilience)
140 to 310 kJ/m3
Stiffness to Weight: Axial
14 points
Stiffness to Weight: Bending
25 points
Strength to Weight: Axial
18 to 21 points
Strength to Weight: Bending
18 to 20 points
Thermal Diffusivity
6.9 mm2/s
Thermal Shock Resistance
14 to 17 points
Alloy Composition
Among alloy steels, the composition of ASTM A387 grade 9 steel is notable for containing a comparatively high amount of chromium (Cr) and including vanadium (V). Chromium is used to improve corrosion resistance and most mechanical properties (particularly at higher temperatures). Vanadium has a strong hardening effect, but this effect is particularly sensitive to the type of tempering.
| Fe | 87.1 to 90.8 | |
| Cr | 8.0 to 10 | |
| Mo | 0.9 to 1.1 | |
| Si | 0 to 1.0 | |
| Mn | 0.3 to 0.6 | |
| C | 0 to 0.15 | |
| V | 0 to 0.040 | |
| P | 0 to 0.025 | |
| S | 0 to 0.025 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ASTM A387: Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum
ASTM A182: Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
Pressure Vessels: External Pressure Technology, 2nd ed., Carl T. F. Ross, 2011
Manufacture and Uses of Alloy Steels, Henry D. Hibbard, 2005
Steels: Processing, Structure, and Performance, 2nd ed., George Krauss, 2015