SAE-AISI 4042 (G40420) Molybdenum Steel
SAE-AISI 4042 steel is an alloy steel formulated for primary forming into wrought products. Cited properties are appropriate for the cold worked (strain hardened) condition. 4042 is the designation in both the SAE and AISI systems for this material. G40420 is the UNS number.
It has a moderately high tensile strength and a moderately low ductility among SAE-AISI wrought steels.
The graph bars on the material properties cards below compare SAE-AISI 4042 steel to: SAE-AISI wrought steels (top), all iron alloys (middle), and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.
Mechanical Properties
Brinell Hardness
200
Elastic (Young's, Tensile) Modulus
190 GPa 27 x 106 psi
Elongation at Break
13 %
Fatigue Strength
360 MPa 52 x 103 psi
Poisson's Ratio
0.29
Shear Modulus
73 GPa 11 x 106 psi
Shear Strength
410 MPa 59 x 103 psi
Tensile Strength: Ultimate (UTS)
680 MPa 98 x 103 psi
Tensile Strength: Yield (Proof)
570 MPa 82 x 103 psi
Thermal Properties
Latent Heat of Fusion
250 J/g
Maximum Temperature: Mechanical
400 °C 760 °F
Melting Completion (Liquidus)
1460 °C 2660 °F
Melting Onset (Solidus)
1420 °C 2580 °F
Specific Heat Capacity
470 J/kg-K 0.11 BTU/lb-°F
Thermal Conductivity
49 W/m-K 28 BTU/h-ft-°F
Thermal Expansion
12 µm/m-K
Electrical Properties
Electrical Conductivity: Equal Volume
7.1 % IACS
Electrical Conductivity: Equal Weight (Specific)
8.2 % IACS
Otherwise Unclassified Properties
Base Metal Price
2.1 % relative
Density
7.8 g/cm3 490 lb/ft3
Embodied Carbon
1.5 kg CO2/kg material
Embodied Energy
19 MJ/kg 8.3 x 103 BTU/lb
Embodied Water
47 L/kg 5.6 gal/lb
Common Calculations
Resilience: Ultimate (Unit Rupture Work)
81 MJ/m3
Resilience: Unit (Modulus of Resilience)
860 kJ/m3
Stiffness to Weight: Axial
13 points
Stiffness to Weight: Bending
24 points
Strength to Weight: Axial
24 points
Strength to Weight: Bending
22 points
Thermal Diffusivity
13 mm2/s
Thermal Shock Resistance
22 points
Alloy Composition
Among alloy steels, the composition of SAE-AISI 4042 steel is notable for containing comparatively high amounts of manganese (Mn) and carbon (C). Manganese is used to improve hardenability, hot workability, and surface quality. There is some loss of ductility and weldability, however. Carbon is used to increase strength at the cost of a decrease in formability.
| Fe | 97.9 to 98.6 | |
| Mn | 0.7 to 0.9 | |
| C | 0.4 to 0.45 | |
| Si | 0.15 to 0.35 | |
| Mo | 0.2 to 0.3 | |
| S | 0 to 0.040 | |
| P | 0 to 0.035 |
All values are % weight. Ranges represent what is permitted under applicable standards.
Followup Questions
Similar Alloys
Further Reading
ASM Specialty Handbook: Carbon and Alloy Steels, J. R. Davis (editor), 1996
Manufacture and Uses of Alloy Steels, Henry D. Hibbard, 2005
Steels: Processing, Structure, and Performance, 2nd ed., George Krauss, 2015