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ASTM A387 Grade 91 Class 2 vs. ASTM A372 Grade K Steel

Both ASTM A387 grade 91 class 2 and ASTM A372 grade K steel are iron alloys. They have a moderately high 91% 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 A372 grade K steel.

Metric UnitsUS Customary Units

Mechanical Properties

Brinell Hardness 200
230
Elastic (Young's, Tensile) Modulus, GPa 190
190
Elongation at Break, % 20
23
Fatigue Strength, MPa 330
440
Poisson's Ratio 0.28
0.29
Shear Modulus, GPa 75
73
Shear Strength, MPa 420
490
Tensile Strength: Ultimate (UTS), MPa 670
780
Tensile Strength: Yield (Proof), MPa 470
620

Thermal Properties

Latent Heat of Fusion, J/g 270
250
Maximum Temperature: Mechanical, °C 600
440
Melting Completion (Liquidus), °C 1460
1460
Melting Onset (Solidus), °C 1420
1420
Specific Heat Capacity, J/kg-K 470
470
Thermal Conductivity, W/m-K 26
48
Thermal Expansion, µm/m-K 13
13

Electrical Properties

Electrical Conductivity: Equal Volume, % IACS 8.9
7.8
Electrical Conductivity: Equal Weight (Specific), % IACS 10
8.9

Otherwise Unclassified Properties

Base Metal Price, % relative 7.0
4.4
Density, g/cm3 7.8
7.9
Embodied Carbon, kg CO2/kg material 2.6
1.8
Embodied Energy, MJ/kg 37
24
Embodied Water, L/kg 88
57

Common Calculations

PREN (Pitting Resistance) 13
2.7
Resilience: Ultimate (Unit Rupture Work), MJ/m3 120
160
Resilience: Unit (Modulus of Resilience), kJ/m3 580
1010
Stiffness to Weight: Axial, points 14
13
Stiffness to Weight: Bending, points 25
24
Strength to Weight: Axial, points 24
27
Strength to Weight: Bending, points 22
24
Thermal Diffusivity, mm2/s 6.9
13
Thermal Shock Resistance, points 19
23

Alloy Composition

Aluminum (Al), % 0 to 0.020
0
Carbon (C), % 0.080 to 0.12
0 to 0.18
Chromium (Cr), % 8.0 to 9.5
1.0 to 1.8
Iron (Fe), % 87.3 to 90.3
93.4 to 96.6
Manganese (Mn), % 0.3 to 0.6
0.1 to 0.4
Molybdenum (Mo), % 0.85 to 1.1
0.2 to 0.6
Nickel (Ni), % 0 to 0.4
2.0 to 3.3
Niobium (Nb), % 0.060 to 0.1
0
Nitrogen (N), % 0.030 to 0.070
0
Phosphorus (P), % 0 to 0.020
0 to 0.015
Silicon (Si), % 0.2 to 0.5
0.15 to 0.35
Sulfur (S), % 0 to 0.010
0 to 0.010
Titanium (Ti), % 0 to 0.010
0
Vanadium (V), % 0.18 to 0.25
0
Zirconium (Zr), % 0 to 0.010
0