ASTM A372 Grade K Steel vs. ASTM A387 Grade 21 Steel
Both ASTM A372 grade K steel and ASTM A387 grade 21 steel are iron alloys. They have a very high 97% of their average alloy composition in common.
For each property being compared, the top bar is ASTM A372 grade K steel and the bottom bar is ASTM A387 grade 21 steel.
Metric UnitsUS Customary Units
Mechanical Properties
| Brinell Hardness | 230 | |
| 150 to 180 |
| Elastic (Young's, Tensile) Modulus, GPa | 190 | |
| 190 |
| Elongation at Break, % | 23 | |
| 21 |
| Fatigue Strength, MPa | 440 | |
| 160 to 250 |
| Poisson's Ratio | 0.29 | |
| 0.29 |
| Shear Modulus, GPa | 73 | |
| 74 |
| Shear Strength, MPa | 490 | |
| 310 to 370 |
| Tensile Strength: Ultimate (UTS), MPa | 780 | |
| 500 to 590 |
| Tensile Strength: Yield (Proof), MPa | 620 | |
| 230 to 350 |
Thermal Properties
| Latent Heat of Fusion, J/g | 250 | |
| 260 |
| Maximum Temperature: Mechanical, °C | 440 | |
| 480 |
| Melting Completion (Liquidus), °C | 1460 | |
| 1470 |
| Melting Onset (Solidus), °C | 1420 | |
| 1430 |
| Specific Heat Capacity, J/kg-K | 470 | |
| 470 |
| Thermal Conductivity, W/m-K | 48 | |
| 41 |
| Thermal Expansion, µm/m-K | 13 | |
| 13 |
Electrical Properties
| Electrical Conductivity: Equal Volume, % IACS | 7.8 | |
| 7.6 |
| Electrical Conductivity: Equal Weight (Specific), % IACS | 8.9 | |
| 8.8 |
Otherwise Unclassified Properties
| Base Metal Price, % relative | 4.4 | |
| 4.1 |
| Density, g/cm3 | 7.9 | |
| 7.9 |
| Embodied Carbon, kg CO2/kg material | 1.8 | |
| 1.8 |
| Embodied Energy, MJ/kg | 24 | |
| 23 |
| Embodied Water, L/kg | 57 | |
| 62 |
Common Calculations
| PREN (Pitting Resistance) | 2.7 | |
| 6.4 |
| Resilience: Ultimate (Unit Rupture Work), MJ/m3 | 160 | |
| 84 to 110 |
| Resilience: Unit (Modulus of Resilience), kJ/m3 | 1010 | |
| 140 to 320 |
| Stiffness to Weight: Axial, points | 13 | |
| 13 |
| Stiffness to Weight: Bending, points | 24 | |
| 24 |
| Strength to Weight: Axial, points | 27 | |
| 18 to 21 |
| Strength to Weight: Bending, points | 24 | |
| 18 to 20 |
| Thermal Diffusivity, mm2/s | 13 | |
| 11 |
| Thermal Shock Resistance, points | 23 | |
| 14 to 17 |
Alloy Composition
| Carbon (C), % | 0 to 0.18 | |
| 0.050 to 0.15 |
| Chromium (Cr), % | 1.0 to 1.8 | |
| 2.8 to 3.3 |
| Iron (Fe), % | 93.4 to 96.6 | |
| 94.4 to 96 |
| Manganese (Mn), % | 0.1 to 0.4 | |
| 0.3 to 0.6 |
| Molybdenum (Mo), % | 0.2 to 0.6 | |
| 0.9 to 1.1 |
| Nickel (Ni), % | 2.0 to 3.3 | |
| 0 |
| Phosphorus (P), % | 0 to 0.015 | |
| 0 to 0.025 |
| Silicon (Si), % | 0.15 to 0.35 | |
| 0 to 0.5 |
| Sulfur (S), % | 0 to 0.010 | |
| 0 to 0.025 |