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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