Steel A992 vs. Steel AISI 4340

Compare Steel A992 vs. Steel AISI 4340 strength, stiffness, weight and thermal properties.

Mechanical	Steel A992	Steel AISI 4340
Yield strength	385MPa1	1,035MPa22.69x stronger
Ultimate tensile strength	505MPa1	1,140MPa22.26x stronger
Elongation at break	24.2%134% more ductile	18%2
Young's modulus (stiffness)	design value200GPa3	200GPa4
Density	7,850kg/m³5	7,840kg/m³2
Strength to weight	49kN·m/kg	132kN·m/kg2.69x higher
Stiffness to weight	25.5MN·m/kg	25.5MN·m/kg
Poisson's ratio	design value0.33	0.324
Shear modulus	76.9GPa2% stiffer in shear	75.7GPa
Bulk modulus	167GPa	185GPa11% higher
Speed of sound	5,048m/s	5,049m/s

Stiffness against densityHigher and further left: stiffer for its weight

Strength against densityHigher and further left: stronger for its weight

Thermal	Steel A992	Steel AISI 4340
Thermal conductivity	48W/m·K528% more heat through a fin	37.5W/m·K2
Thermal expansion	12µm/m·K5	mean11.3µm/m·K2
100 mm part over a 50 °C swing	60µm growth	56.5µm growth6% less
Specific heat	base material460–480J/kg·K6	448J/kg·K2
Heats up and cools (diffusivity)	13mm²/s22% faster	10.7mm²/s
Thermal shock resistance	5,390W/m	11,678W/m2.17x more resistant

Thermal conductivity against densityHigher and further left: spreads more heat for its weight

Thermal expansion against thermal conductivityLower and further right: warps less when heated

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Sources6 documents: American Institute of Steel Construction, Carpenter Technology, U.S. Department of Defense, bauforumstahl (ArcelorMittal), Ovako

Steel A992: ASTM A992 W-shapes; Fy/Fu specified minimums from AISC publications (AISC 360-16 Commentary; Modern Steel Construction); elastic constants AISC 360; physical constants from the bauforumstahl structural-steel EPD, which names A992 among covered product standards.
Steel AISI 4340: Carpenter (Latrobe) Lescalloy 4340 VAC-ARC datasheet; mechanical row for 1100 °F temper; physical properties grade-level

1
Updating Standard Shape Material Properties Database for Design and ReliabilityAmerican Institute of Steel Constructionarchived copySteel A992 · Yield strength: typical: mean of 20,295 A992 flange mill-test coupons (1998 SSPC survey), as reported by AISCSteel A992 · Ultimate tensile strength: typical: mean of 20,295 A992 flange mill-test coupons (1998 SSPC survey)Steel A992 · Elongation at break: typical: mean of 24,847 A992 mill-test elongations, web and flange (1998 SSPC mill data), as reported by AISC
2
Lescalloy 4340 VAC-ARC Data SheetCarpenter Technologyarchived copySteel AISI 4340 · Yield strength: typical, transverseSteel AISI 4340 · Ultimate tensile strength: typical, transverseSteel AISI 4340 · Elongation at break: typical, transverseSteel AISI 4340 · Density: typicalSteel AISI 4340 · Thermal conductivity: typicalSteel AISI 4340 · Thermal expansion: mean, -18 to 93 °CSteel AISI 4340 · Specific heat: typical
3
ANSI/AISC 360-16 Specification for Structural Steel Buildings, with CommentaryAmerican Institute of Steel Constructionarchived copySteel A992 · Young's modulus (stiffness): design value (AISC 360-16)Steel A992 · Poisson's ratio: design value (AISC 360-16 Commentary)
4
MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (2003)U.S. Department of DefenseSteel AISI 4340 · Young's modulus (stiffness): MIL-HDBK-5J design value (AISI 4340, quenched and tempered)Steel AISI 4340 · Poisson's ratio: MIL-HDBK-5J design value (AISI 4340, quenched and tempered)
5
Environmental Product Declaration: Structural Steel Sections and Merchant Bars (2023)bauforumstahl (ArcelorMittal)archived copySteel A992 · Density: nominal (constructional data)Steel A992 · Thermal conductivity: nominal at 20 °CSteel A992 · Thermal expansion: nominal (constructional data, no temperature range stated)
6
S275JR Steel GradeOvakoSteel A992 · Specific heat: base material: EN S275JR unalloyed structural steel (the EN counterpart of A36), typical, 50/100 °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 A992 stronger than Steel AISI 4340?

Steel AISI 4340 is stronger: its yield strength is 1,035 MPa against 385 MPa for Steel A992 (2.69x).

Which is lighter, Steel A992 or Steel AISI 4340?

Steel AISI 4340 is lighter: 7,840 kg/m³ against 7,850 kg/m³ for Steel A992.

Which is stiffer, Steel A992 or Steel AISI 4340?

Steel A992 is stiffer: Young's modulus 200 GPa against 200 GPa for Steel AISI 4340, so the same part in Steel A992 deflects less under the same load.

Which is lighter for the same job, Steel A992 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 A992	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	2.69x heavier	lighter
Strong beam	1.94x heavier	lighter
Strong panel or plate	1.64x 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 A992 or Steel AISI 4340?

Steel A992 stretches further before it breaks: 24.2% elongation at break against 18% for Steel AISI 4340.

Thermal

Which conducts heat better, Steel A992 or Steel AISI 4340?

Steel A992 conducts heat better: 48 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 A992.