Material Selection8–10 min read
4140 vs 4340 Alloy Steel: Heat Treatment and Shaft Selection
Compare section size, toughness evidence and the final heat-treated condition.
Author: Mat Grades Editorial DeskRead Guide →
SAE 4340 Alloy Steel
Primary Designation:SAE 4340
Mat Grades internal verification confirms source-backed fidelity and data integrity. It does not constitute external certification or guaranteed lot conformity. Read engineering disclaimer →
Data Completeness:8 composition elements and 14 condition-specific property values cataloged.
Omitted fields represent unverified properties. "Missing is better than invented."
Key Engineering Properties
Representative source rows, qualified by their reported conditions. Inspect the tables below for all values, limits, and source notes.
Density
7.85 g/cm³TYPICAL · temperature not stated
Thermal Conductivity
44.5 W/(m·K)TYPICAL · at 100 °C
Composition Excerpt
C 0.38–0.43 wt%Carbon (range)
Standard Elemental Basis: RANGETensile Strength
≥ 745 MPaMINIMUM · Annealed Bar · temperature not stated
Engineering Summary
SAE 4340 Alloy Steel. Source-scoped engineering data is shown with its reported limits and conditions. Unreported properties are not inferred.
Recognized Aliases
Source-backed commercial trade name and short designations cataloged in canonical data.
SAE 4340 Alloy Steel Specifications & Designations
Standard Designations & Applicable Specifications — Semantically classified designations distinguishing primary standard identifiers, commercial trade names, and applicable specification references.
Direct Standard DesignationsDIRECT DESIGNATION
1 Primary IdentifierScroll horizontally for full designation data
| System | Identifier | Standard System Name | Classification Notes & Provenance |
|---|---|---|---|
| SAEPRIMARY | 4340 | SAE | —Ref: Practical Data for Metallurgists, 19th edition |
Applicable Specifications & Product Form ReferencesSPECIFICATION REFERENCE
1 Applicable StandardsScroll horizontally for full standard specifications
| Standards Body | Specification Code | Specification Title / Scope | Relationship Type |
|---|---|---|---|
| SAE | SAE 4340 Alloy Steel Engineering Datasheet | Applicable specification reference. | Specification Reference |
Engineering Notice: Applicable specifications establish manufacturing requirements, dimensional tolerances, and test criteria for specific product forms (e.g. bus bar, wire, plate, pipe). They represent applicable technical standards, not alternative or equivalent alloy grades.
SAE 4340 Alloy Steel Chemical Composition
Chemical Composition (Weight %) — Elemental limits and values from the cited source. Preserves exact semantic limits (minimums, maximums, and ranges).
Scroll horizontally for full elemental limits
| Element | Symbol | Atomic No. | Semantic Basis | Specified Value | Unit | Metallurgical Notes & Qualification | Data Status |
|---|---|---|---|---|---|---|---|
| Carbon | C | 6 | RANGE | 0.38 – 0.43 | wt% | Source cell: .38/.43. Scope: p6, SAE 4340.Ref: Metallus | VERIFIED |
| Manganese | Mn | 25 | RANGE | 0.60 – 0.80 | wt% | Source cell: .60/.80. Scope: p6, SAE 4340.Ref: Metallus | VERIFIED |
| Chromium | Cr | 24 | RANGE | 0.70 – 0.90 | wt% | Source cell: .70/.90. Scope: p6, SAE 4340.Ref: Metallus | VERIFIED |
| Nickel | Ni | 28 | RANGE | 1.65 – 2.00 | wt% | Source cell: 1.65/2.00. Scope: p6, SAE 4340.Ref: Metallus | VERIFIED |
| Molybdenum | Mo | 42 | RANGE | 0.20 – 0.30 | wt% | Source cell: .20/.30. Scope: p6, SAE 4340.Ref: Metallus | VERIFIED |
| Silicon | Si | 14 | RANGE | 0.15 – 0.35 | wt% | Source cell: .15/.35. Scope: p6, SAE 4340; p7 default footnote / row override.Ref: Metallus | VERIFIED |
| Phosphorus | P | 15 | MAXIMUM | ≤ 0.04 | wt% | Source cell: .035max. Scope: p6, SAE 4340; p7 default footnote / row override.Ref: Metallus | VERIFIED |
| Sulfur | S | 16 | MAXIMUM | ≤ 0.04 | wt% | Source cell: .040max. Scope: p6, SAE 4340; p7 default footnote / row override.Ref: Metallus | VERIFIED |
* Elemental percentages are expressed in weight percent (wt%). Values represent applicable specification limits. Unspecified trace elements are not fabricated or assumed.Preserves exact semantic basis
Property Display UnitsSwitch between Canonical SI and Source / US Customary units:
SAE 4340 Alloy Steel Physical Properties
Source-specific physical properties. Test temperatures are shown only where reported.
Scroll horizontally for full property parameters
| Property Parameter | Canonical SI Value | Semantic Basis | Test Temperature / Context Range | Source Raw Reference | Source Reference | Status |
|---|---|---|---|---|---|---|
| Density | 7.85 g/cm³ | TYPICAL | 7.85 g/cm3 | Ovako / Technical Steel Navigator | VERIFIED | |
| Elastic Modulus | 205 GPa | TYPICAL | 205 GPa | Ovako / Technical Steel Navigator | VERIFIED | |
| Poisson's Ratio | 0.29 dimensionless | TYPICAL | 0.29 dimensionless | Ovako / Technical Steel Navigator | VERIFIED |
SAE 4340 Alloy Steel Thermal & Thermodynamic Properties
Phase change temperatures, thermal conductivity, specific heat, mean coefficients of thermal expansion across standardized temperature ranges, and recommended thermal processing windows.
Scroll horizontally for full property parameters
| Property Parameter | Canonical SI Value | Semantic Basis | Test Temperature / Context Range | Source Raw Reference | Source Reference | Status |
|---|---|---|---|---|---|---|
| Coefficient of Thermal Expansion | 12.3 µm/(m·K) | TYPICAL | Test Temp: 100 °C | 12.3 10^-6/K | Ovako / Technical Steel Navigator | VERIFIED |
| Thermal Conductivity | 44.5 W/(m·K) | TYPICAL | Test Temp: 100 °C | 44.5 W/(m·K) | Ovako / Technical Steel Navigator | VERIFIED |
SAE 4340 Alloy Steel Mechanical Properties
Contextual Mechanical Properties & Tempers: Engineering strength, ductility, and hardness values grouped by product form, temper, and section thickness. Mechanical properties are contextual and not isotropic averages.
Showing 8 of 8 conditions
Scroll horizontally for all conditions & tempers
| Product Form | Temper / Condition | Section Size | Tensile (UTS) | Yield Strength | Elongation | Shear Strength | Fatigue Strength | Hardness (Scales Preserved) | Status |
|---|---|---|---|---|---|---|---|---|---|
| Bar | Annealed Bar · Annealed 840°C furnace cooledSource values and qualifiersUltimate Tensile Strength: ≥ 745 MPa (MINIMUM)ASTM A29Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Annealed Properties | — | ≥ 745 MPa | — | — | — | — | — | VERIFIED |
| Bar | Annealed Bar · Annealed 840°C furnace cooledSource values and qualifiersYield Strength: ≥ 470 MPa (MINIMUM)ASTM A29 (0.2% offset)Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Annealed Properties | — | — | ≥ 470 MPa | — | — | — | — | VERIFIED |
| Bar | Annealed Bar · Annealed 840°C furnace cooledSource values and qualifiersElongation at Break: ≥ 22 % (MINIMUM)ASTM A29Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Annealed Properties | — · in 50 mm (2 in) | — | — | ≥ 22 % | — | — | — | VERIFIED |
| Bar | Quenched and Tempered Bar (540°C temper) · Oil quenched 845°C, tempered 540°CSource values and qualifiersUltimate Tensile Strength: ≥ 1110 MPa (MINIMUM)ASTM A29Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Heat Treated Properties Reduction of Area: ≥ 50 % (MINIMUM)ASTM A29Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Heat Treated Properties | — | ≥ 1110 MPa | — | — | — | — | — | VERIFIED |
| Bar | Quenched and Tempered Bar (540°C temper) · Oil quenched 845°C, tempered 540°CSource values and qualifiersYield Strength: ≥ 1015 MPa (MINIMUM)ASTM A29 (0.2% offset)Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Heat Treated Properties | — | — | ≥ 1015 MPa | — | — | — | — | VERIFIED |
| Bar | Quenched and Tempered Bar (540°C temper) · Oil quenched 845°C, tempered 540°CSource values and qualifiersElongation at Break: ≥ 15 % (MINIMUM)ASTM A29Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Heat Treated Properties | — · in 50 mm (2 in) | — | — | ≥ 15 % | — | — | — | VERIFIED |
| Bar | Annealed BarSource values and qualifiersHB Hardness: ≤ 217 HB (MAXIMUM)Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Annealed Properties | — | — | — | — | — | — | ≤ 217 HB | VERIFIED |
| Bar | Quenched and Tempered Bar (540°C temper)Source values and qualifiersHB Hardness: ≥ 330 HB (MINIMUM)Ovako / Technical Steel Navigator — Ovako 4340 Datasheet, Table: Heat Treated Properties | — | — | — | — | — | — | ≥ 330 HB | VERIFIED |
Hardness Integrity Notice: Rockwell B (HRB), Rockwell F (HRF), and Superficial 30T (HR30T) scales are reported on their measured scales without cross-scale mathematical conversion.
Source: See fact-level citations
Practical Engineering & Fabrication Notes
By Mat Grades Editorial Desk · Updated 2026-11-14. Use alongside the specified product standard and supplier certificate.
Machining & shop-floor behavior
For SAE 4340 Alloy Steel, a qualified cutting-speed or tool-life recommendation is not supplied in the available record. A relevant hardness example is HB Hardness: maximum 217 HB (maximum; Annealed Bar, Bar). Use that supplied condition for a trial of the difficult feature. Record tool changes, burr removal, unclamped dimensions and accepted parts per hour. Relative machinability ratings from different reference scales should not be compared as if they were one common test.
Weldability, brazing & joining
No qualified weld procedure, filler selection or preheat/interpass schedule is established by this material record. Obtain a procedure for the actual joint, supplied condition and section rather than copying one from a nearby grade. The first cataloged strength example is Ultimate Tensile Strength: minimum 745 MPa (minimum; Annealed Bar, Bar). Assess the final part after joining or thermal processing. Include distortion, cleanup and inspection in the quotation. A material designation or favorable process rating is a starting point for qualification, not evidence that an untested joint meets the drawing.
Corrosion & service environment
Plan corrosion protection and inspect how the finish affects threads, bearing fits and repaired surfaces. A steel strength value does not establish corrosion life. Where cyclic load or impact matters, retain the surface condition and the required toughness evidence with the material decision. The recorded thermal example is Coefficient of Thermal Expansion: 12.3 µm/(m·K) (typical; ; test temperature 100 °C). State the exposure and inspection access in the design record so that a change of installation or cleaning method triggers a review. The selected composition entries are C 0.38–0.43 wt%, Mn 0.6–0.8 wt%, Cr 0.7–0.9 wt%. Chemistry documents identity; it does not establish fluid compatibility.
Selection trade-offs & applications
For a demanding shaft, compare supplier-supported section ranges and toughness evidence with 4140. Nickel-bearing alloy chemistry does not remove the need to qualify heat treatment, notches, surface condition and any proposed repair. The listed forms include Bar; confirm the actual stock offered by the supplier. Compare the complete route through machining, joining, finish and inspection. Keep the certificate, required test location and acceptance criteria with the first-article record. A later change of grade, condition or source should be assessed against that same requirement.
Technical references: Ovako / Technical Steel Navigator; Metallus
Nickel-Chromium-Molybdenum Alloy Steel Cluster (43xx & 86xx Series)
Triple-alloy Ni-Cr-Mo steels engineered for high core toughness and predictable hardenability in heavy-duty transmission components.
4340Current Grade
SAE 4340 Alloy Steel
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Contextual technical guides explaining degradation mechanisms, testing methodologies, and selection criteria relevant to SAE 4340 Alloy Steel.
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Sources
Sources & Provenance Trail: Authoritative reference publications, standards specifications, and data registers cited across this material record.
MetallusPractical Data for Metallurgists, 19th edition
PRIMARY PRODUCER
Reviewed factual transcription; source document SHA-256 is recorded in the capture metadata. No cross-standard equivalence is asserted.
MetallusPractical Data for Metallurgists, 19th edition
PRIMARY PRODUCER
Reviewed factual transcription; source document SHA-256 is recorded in the capture metadata. No cross-standard equivalence is asserted.
Ovako / Technical Steel NavigatorOvako Steel Navigator & Technical Engineering Specifications
PRIMARY PRODUCER
Reviewed factual transcription from primary producer engineering datasheet.
Issuing Body: Ovako / Technical Steel NavigatorRevision: Steel Navigator Revision 2024View Source Record ↗
Ovako / Technical Steel NavigatorOvako Steel Navigator & Technical Engineering Specifications
PRIMARY PRODUCER
Reviewed factual transcription from primary producer engineering datasheet.
Issuing Body: Ovako / Technical Steel NavigatorRevision: Steel Navigator Revision 2024View Source Record ↗
Ovako / Technical Steel NavigatorOvako Steel Navigator & Technical Engineering Specifications
PRIMARY PRODUCER
Reviewed factual transcription from primary producer engineering datasheet.
Issuing Body: Ovako / Technical Steel NavigatorRevision: Steel Navigator Revision 2024View Source Record ↗
Ovako / Technical Steel NavigatorOvako Steel Navigator & Technical Engineering Specifications
PRIMARY PRODUCER
Reviewed factual transcription from primary producer engineering datasheet.
Issuing Body: Ovako / Technical Steel NavigatorRevision: Steel Navigator Revision 2024View Source Record ↗
Ovako / Technical Steel NavigatorOvako Steel Navigator & Technical Engineering Specifications
PRIMARY PRODUCER
Reviewed factual transcription from primary producer engineering datasheet.
Issuing Body: Ovako / Technical Steel NavigatorRevision: Steel Navigator Revision 2024View Source Record ↗
Intellectual Property & Provenance Notice: Mat Grades cites technical literature from recognized industry associations and standards organizations. Underlying technical standards and publication data remain the intellectual property of their respective issuing organizations.