ASTM A387 Grade 91 Class 2 vs. ASTM A387 Grade 21 Steel
Both ASTM A387 grade 91 class 2 and ASTM A387 grade 21 steel are iron alloys. They have a moderately high 94% of their average alloy composition in common.
For each property being compared, the top bar is ASTM A387 grade 91 class 2 and the bottom bar is ASTM A387 grade 21 steel.
Metric UnitsUS Customary Units
Mechanical Properties
| Brinell Hardness | 200 | |
| 150 to 180 |
| Elastic (Young's, Tensile) Modulus, GPa | 190 | |
| 190 |
| Elongation at Break, % | 20 | |
| 21 |
| Fatigue Strength, MPa | 330 | |
| 160 to 250 |
| Poisson's Ratio | 0.28 | |
| 0.29 |
| Shear Modulus, GPa | 75 | |
| 74 |
| Shear Strength, MPa | 420 | |
| 310 to 370 |
| Tensile Strength: Ultimate (UTS), MPa | 670 | |
| 500 to 590 |
| Tensile Strength: Yield (Proof), MPa | 470 | |
| 230 to 350 |
Thermal Properties
| Latent Heat of Fusion, J/g | 270 | |
| 260 |
| Maximum Temperature: Mechanical, °C | 600 | |
| 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 | 26 | |
| 41 |
| Thermal Expansion, µm/m-K | 13 | |
| 13 |
Electrical Properties
| Electrical Conductivity: Equal Volume, % IACS | 8.9 | |
| 7.6 |
| Electrical Conductivity: Equal Weight (Specific), % IACS | 10 | |
| 8.8 |
Otherwise Unclassified Properties
| Base Metal Price, % relative | 7.0 | |
| 4.1 |
| Density, g/cm3 | 7.8 | |
| 7.9 |
| Embodied Carbon, kg CO2/kg material | 2.6 | |
| 1.8 |
| Embodied Energy, MJ/kg | 37 | |
| 23 |
| Embodied Water, L/kg | 88 | |
| 62 |
Common Calculations
| PREN (Pitting Resistance) | 13 | |
| 6.4 |
| Resilience: Ultimate (Unit Rupture Work), MJ/m3 | 120 | |
| 84 to 110 |
| Resilience: Unit (Modulus of Resilience), kJ/m3 | 580 | |
| 140 to 320 |
| Stiffness to Weight: Axial, points | 14 | |
| 13 |
| Stiffness to Weight: Bending, points | 25 | |
| 24 |
| Strength to Weight: Axial, points | 24 | |
| 18 to 21 |
| Strength to Weight: Bending, points | 22 | |
| 18 to 20 |
| Thermal Diffusivity, mm2/s | 6.9 | |
| 11 |
| Thermal Shock Resistance, points | 19 | |
| 14 to 17 |
Alloy Composition
| Aluminum (Al), % | 0 to 0.020 | |
| 0 |
| Carbon (C), % | 0.080 to 0.12 | |
| 0.050 to 0.15 |
| Chromium (Cr), % | 8.0 to 9.5 | |
| 2.8 to 3.3 |
| Iron (Fe), % | 87.3 to 90.3 | |
| 94.4 to 96 |
| Manganese (Mn), % | 0.3 to 0.6 | |
| 0.3 to 0.6 |
| Molybdenum (Mo), % | 0.85 to 1.1 | |
| 0.9 to 1.1 |
| Nickel (Ni), % | 0 to 0.4 | |
| 0 |
| Niobium (Nb), % | 0.060 to 0.1 | |
| 0 |
| Nitrogen (N), % | 0.030 to 0.070 | |
| 0 |
| Phosphorus (P), % | 0 to 0.020 | |
| 0 to 0.025 |
| Silicon (Si), % | 0.2 to 0.5 | |
| 0 to 0.5 |
| Sulfur (S), % | 0 to 0.010 | |
| 0 to 0.025 |
| Titanium (Ti), % | 0 to 0.010 | |
| 0 |
| Vanadium (V), % | 0.18 to 0.25 | |
| 0 |
| Zirconium (Zr), % | 0 to 0.010 | |
| 0 |