Thermal conductivity against densityHigher and further left: spreads more heat for its weightThermal expansion against thermal conductivityLower and further right: warps less when heated
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MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseSteel AISI 1018 · Young's modulus (stiffness): base material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018)Steel AISI 4340 · Young's modulus (stiffness): MIL-HDBK-5J design value (AISI 4340, quenched and tempered)Steel AISI 1018 · Density: base material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018)Steel AISI 1018 · Poisson's ratio: base material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018)Steel AISI 4340 · Poisson's ratio: MIL-HDBK-5J design value (AISI 4340, quenched and tempered)Steel AISI 1018 · Thermal conductivity: base material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018)Steel AISI 1018 · Specific heat: base material: AISI 1025 plain carbon steel (MIL-HDBK-5J design value; ASTM A108 bar is the cold-finished carbon-steel bar spec that also covers 1018)
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S275JR Steel GradeOvakoSteel AISI 1018 · Thermal expansion: base material: unalloyed carbon steel, Ovako family table (S275JR, 'none alloyed structural steels', C <= 0.21%); mean 20-300 °C
Each number points to the document that states it, with the exact basis. Values without a number are computed from the sourced ones. "Not sourced" means no citable source states it (or only a specification minimum); figures computed from it are left out too.
Questions
Mechanical
Is Steel AISI 1018 stronger than Steel AISI 4340?
Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 372 MPa for Steel AISI 1018 (2.78x).
Which is lighter, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 4340 is lighter: 7,840 kg/m³ against 7,861 kg/m³ for Steel AISI 1018.
Which is stiffer, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 1018 is stiffer: Young's modulus 200 GPa against 200 GPa for Steel AISI 4340, so the same part in Steel AISI 1018 deflects less under the same load.
Which is lighter for the same job, Steel AISI 1018 or Steel AISI 4340?
For the same stiffness or strength: Steel AISI 4340 is lighter for a strong rod or tie, strong beam, strong panel or plate.
Part that must be
Steel AISI 1018
Steel AISI 4340
Stiff rod or tie (tension)
about equal
about equal
Stiff beam (bending)
about equal
about equal
Stiff panel or plate
about equal
about equal
Strong rod or tie
2.79x heavier
lighter
Strong beam
1.98x heavier
lighter
Strong panel or plate
1.67x heavier
lighter
For the same stiffness or strength, mass scales with density over stiffness (or strength) raised to a power set by how the part is loaded: 1 for a rod in tension, 1/2 for a beam in bending, 1/3 for a panel (the standard material-selection indices).
Which is more ductile, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 4340 stretches further before it breaks: 18% elongation at break against 15% for Steel AISI 1018.
Thermal
Which conducts heat better, Steel AISI 1018 or Steel AISI 4340?
Steel AISI 1018 conducts heat better: 51.9 W/m·K against 37.5 W/m·K for Steel AISI 4340.
Which expands less with temperature?
Steel AISI 4340 expands less: 11.3 µm/m·K against 12 µm/m·K for Steel AISI 1018.