ASTM A372 Grade K Alloy Steel
ASTM A372 grade K steel is an alloy steel formulated for primary forming into wrought products. Cited properties are appropriate for the quenched and tempered condition. ASTM A372 Grade K is the ASTM designation for this material. Older literature may refer to this material as Type VI, but this is now discouraged.
It has a moderately high ductility among wrought alloy steels in the same category. In addition, it has a very high tensile strength and a moderately high base cost.
The graph bars on the material properties cards below compare ASTM A372 grade K 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
230
Elastic (Young's, Tensile) Modulus
190 GPa 27 x 106 psi
Elongation at Break
23 %
Fatigue Strength
440 MPa 64 x 103 psi
Poisson's Ratio
0.29
Shear Modulus
73 GPa 11 x 106 psi
Shear Strength
490 MPa 71 x 103 psi
Tensile Strength: Ultimate (UTS)
780 MPa 110 x 103 psi
Tensile Strength: Yield (Proof)
620 MPa 89 x 103 psi
Thermal Properties
Latent Heat of Fusion
250 J/g
Maximum Temperature: Mechanical
440 °C 830 °F
Melting Completion (Liquidus)
1460 °C 2670 °F
Melting Onset (Solidus)
1420 °C 2590 °F
Specific Heat Capacity
470 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
48 W/m-K 28 BTU/h-ft-°F
Thermal Expansion
13 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
7.8 % IACS
Electrical Conductivity: Equal Weight (Specific)
8.9 % IACS
Otherwise Unclassified Properties
Base Metal Price
4.4 % relative
Density
7.9 g/cm3 490 lb/ft3
Embodied Carbon
1.8 kg CO2/kg material
Embodied Energy
24 MJ/kg 10 x 103 BTU/lb
Embodied Water
57 L/kg 6.8 gal/lb
Common Calculations
PREN (Pitting Resistance)
2.7
Resilience: Ultimate (Unit Rupture Work)
160 MJ/m3
Resilience: Unit (Modulus of Resilience)
1010 kJ/m3
Stiffness to Weight: Axial
13 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
27 points
Strength to Weight: Bending
24 points
Thermal Diffusivity
13 mm2/s
Thermal Shock Resistance
23 points
Alloy Composition
Among alloy steels, the composition of ASTM A372 grade K steel is notable for including nickel (Ni) and containing a comparatively high amount of chromium (Cr). Nickel is used to improve mechanical properties, and to make the alloy easier to heat treat. Chromium is used to improve corrosion resistance and most mechanical properties (particularly at higher temperatures).
| Fe | 93.4 to 96.6 | |
| Ni | 2.0 to 3.3 | |
| Cr | 1.0 to 1.8 | |
| Mo | 0.2 to 0.6 | |
| Mn | 0.1 to 0.4 | |
| Si | 0.15 to 0.35 | |
| C | 0 to 0.18 | |
| P | 0 to 0.015 | |
| S | 0 to 0.010 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ASTM A372: Standard Specification for Carbon and Alloy Steel Forgings for Thin-Walled Pressure Vessels
Pressure Vessels: External Pressure Technology, 2nd ed., Carl T. F. Ross, 2011
ASM Specialty Handbook: Carbon and Alloy Steels, J. R. Davis (editor), 1996
Manufacture and Uses of Alloy Steels, Henry D. Hibbard, 2005
Steels: Processing, Structure, and Performance, 2nd ed., George Krauss, 2015