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ASTM A387 Grade 21 Steel vs. R30021 Cobalt

ASTM A387 grade 21 steel belongs to the iron alloys classification, while R30021 cobalt belongs to the cobalt alloys. There are 27 material properties with values for both materials. Properties with values for just one material (7, in this case) are not shown.

For each property being compared, the top bar is ASTM A387 grade 21 steel and the bottom bar is R30021 cobalt.

Metric UnitsUS Customary Units

Mechanical Properties

Elastic (Young's, Tensile) Modulus, GPa 190
220
Elongation at Break, % 21
9.0
Fatigue Strength, MPa 160 to 250
250
Poisson's Ratio 0.29
0.29
Shear Modulus, GPa 74
86
Tensile Strength: Ultimate (UTS), MPa 500 to 590
700
Tensile Strength: Yield (Proof), MPa 230 to 350
500

Thermal Properties

Latent Heat of Fusion, J/g 260
330
Melting Completion (Liquidus), °C 1470
1350
Melting Onset (Solidus), °C 1430
1190
Specific Heat Capacity, J/kg-K 470
450
Thermal Conductivity, W/m-K 41
15
Thermal Expansion, µm/m-K 13
11

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 7.6
1.9
Electrical Conductivity: Equal Weight (Specific), % IACS 8.8
2.1

Otherwise Unclassified Properties

Density, g/cm3 7.9
8.4
Embodied Carbon, kg CO2/kg material 1.8
8.0
Embodied Energy, MJ/kg 23
110
Embodied Water, L/kg 62
520

Common Calculations

Resilience: Ultimate (Unit Rupture Work), MJ/m3 84 to 110
57
Resilience: Unit (Modulus of Resilience), kJ/m3 140 to 320
570
Stiffness to Weight: Axial, points 13
15
Stiffness to Weight: Bending, points 24
24
Strength to Weight: Axial, points 18 to 21
23
Strength to Weight: Bending, points 18 to 20
21
Thermal Diffusivity, mm2/s 11
3.8
Thermal Shock Resistance, points 14 to 17
21

Alloy Composition

Carbon (C), % 0.050 to 0.15
0.2 to 0.35
Chromium (Cr), % 2.8 to 3.3
26 to 29
Cobalt (Co), % 0
61.7 to 67.3
Iron (Fe), % 94.4 to 96
0 to 3.0
Manganese (Mn), % 0.3 to 0.6
0
Molybdenum (Mo), % 0.9 to 1.1
4.5 to 6.0
Nickel (Ni), % 0
2.0 to 3.0
Phosphorus (P), % 0 to 0.025
0
Silicon (Si), % 0 to 0.5
0 to 1.5
Sulfur (S), % 0 to 0.025
0