Steel 4340 · temper
Steel 4340 Annealed
Properties of the Annealed condition, compared with the other 4340 tempers.
Softest and most machinable condition; used as the supply state for parts that will be finish heat treated.
What is 4340 Annealed?
4340 Annealed is 4340 in the Annealed temper — softest and most machinable condition; used as the supply state for parts that will be finish heat treated. 4340 Annealed has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 58% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). 4340 Annealed has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). HR is the default condition FabDigit quotes; Annealed is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 130 MPa·√m (118.3 ksi·√in), better than 89% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
4340 Annealed properties
Typical room-temperature values for 4340 Annealed — 17 properties are specific to this condition; the rest are grade-level values shared by every 4340 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4340 Annealed has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical17
4340 Annealed has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 58% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4340 Annealed is rated for continuous service to 425°C (797 °F). It conducts heat at 44.5 W/m·K (25.7 BTU/hr·ft·°F), better than 63% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4340 Annealed conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4340 Annealed takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
4340 Annealed's machinability is good (55/100, better than 62% of steel grades); weldability fair (38/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4340 tempers and conditions
4340 is also supplied in 12 other conditions. The full side-by-side table is on the 4340 overview.
- HRDefaultCheapest stock form for parts that will be rough-machined and then heat treated by the customer.620 MPa yield · 29 HRC
- Q&T 50-54 HRCMaximum-strength condition; only for wear/strength-critical parts where low toughness and embrittlement risk are acceptable.1,860 MPa yield · 52 HRC
- Q&T 46-50 HRCVery high strength for landing-gear and heavy-section tooling; toughness and hydrogen tolerance drop sharply.1,620 MPa yield · 48 HRC
- Q&T 40-44 HRCHigh-strength condition for aircraft structural fittings and highly stressed pins; machining requires carbide tooling.1,360 MPa yield · 42 HRC
- Q&T 36-40 HRCHigher strength for torsion bars, tool holders and mid-strength aerospace fittings still needing decent toughness.1,160 MPa yield · 38 HRC
- Q&T 32-36 HRCBalanced strength/toughness for gears, couplings and heavy-duty shafting.1,010 MPa yield · 34 HRC
- Q&T+NitridedPick when a Q&T core (typically 32–36 HRC) needs a hard, wear- and fatigue-resistant 0.2–0.5 mm case without distortion.1,010 MPa yield · 58 HRC
- Q&TStandard commercial heat-treated stock ("4340HT"): high strength with good toughness and still machinable.880 MPa yield · 31 HRC
- NormalizedUniform fine-grained structure with high as-cooled strength; usually a preparatory step before machining and Q&T.860 MPa yield · 39 HRC
- Q&T 28-32 HRCToughest useful Q&T level; for shafts and machine parts needing impact resistance and easy finishing.860 MPa yield · 30 HRC
- CDChoose for close-tolerance, bright-finish shafting used without further heat treatment.830 MPa yield · 29 HRC
- AnnealedSoftest and most machinable condition; used as the supply state for parts that will be finish heat treated.470 MPa yield · 217 HB
Working with 4340 Annealed
Is 4340 easy to machine?
Machine in the annealed or ≤34 HRC condition with rigid setups; above 40 HRC use coated carbide/CBN, low speeds and heavy positive feed, and finish-grind critical surfaces.
Can 4340 be welded?
Weldable only with 250–350 °C preheat, low-hydrogen or matching Ni-Cr-Mo filler and immediate post-weld temper below the part's tempering temperature; avoid welding fully hardened parts.
Can 4340 be formed, bent or molded?
Hot forge/roll at 1050–1200 °C and always normalize afterwards; cold bending is limited to the annealed state with generous radii.
What surface finishes work on 4340?
Requires protection — zinc/cadmium or Cr plating, phosphate + oil, or paint; bake at 190 °C after plating to relieve hydrogen, and shot-peen highly loaded fillets to restore fatigue life.
4340 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CASTM A29 / SAE J404 | 0.38 – 0.43 | 0.4 |
| Mn | 0.6 – 0.8 | 0.7 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 1.65 – 2 | 1.8 |
| Cr | 0.7 – 0.9 | 0.8 |
| Mo | 0.2 – 0.3 | 0.25 |
| Pmax; aircraft quality (AMS 6414) ≤0.010 | ≤ 0.04 | — |
| Smax; aircraft quality ≤0.010 | ≤ 0.04 | — |
| Fe | balance | — |
4340 Annealed — frequently asked
What is 4340 Annealed used for?
4340 Annealed is typically used for landing gear components, drive shafts, heavy-duty gears, crankshafts, machine tool spindles and tool holders and arbors. In short: ultra-high fatigue strength.
What is the yield strength of 4340 Annealed?
4340 Annealed has a typical yield strength of 470 MPa (68.2 ksi) and a tensile strength of 745 MPa (108 ksi) — stronger than 58% of steel grades. Strength varies by condition: see the 13 listed tempers.
Is 4340 Annealed easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed or ≤34 HRC condition with rigid setups; above 40 HRC use coated carbide/CBN, low speeds and heavy positive feed, and finish-grind critical surfaces.
Can 4340 Annealed be welded?
With care — weldability is rated fair (38/100). Weldable only with 250–350 °C preheat, low-hydrogen or matching Ni-Cr-Mo filler and immediate post-weld temper below the part's tempering temperature; avoid welding fully hardened parts.
What surface finishes work on 4340 Annealed?
Requires protection — zinc/cadmium or Cr plating, phosphate + oil, or paint; bake at 190 °C after plating to relieve hydrogen, and shot-peen highly loaded fillets to restore fatigue life.
Can 4340 Annealed be formed, bent or molded?
Hot forge/roll at 1050–1200 °C and always normalize afterwards; cold bending is limited to the annealed state with generous radii.
What is the maximum service temperature of 4340 Annealed?
4340 Annealed is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4340-HR and 4340-CD?
HR is the default condition — cheapest stock form for parts that will be rough-machined and then heat treated by the customer. CD: choose for close-tolerance, bright-finish shafting used without further heat treatment. Yield strength is 620 MPa in HR versus 830 MPa in CD.
Can FabDigit make parts in 4340 Annealed?
Yes — 4340 Annealed is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- AMS 6414 — Steel Bars, Forgings, Tubing 4340 (Vacuum Consumable Electrode Remelted) — SAE Aerospace (2019)
- GB/T 3077 — (40CrNiMoA) — SAC (2015)
- EN 10083-3 — 34CrNiMo6 (1.6582) — CEN (2006)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- MMPDS-2023 typical low-alloy steel data — Battelle/FAA (2023)
- Machinery's Handbook, 31st ed. (machinability ratings) — Industrial Press (2020)
- Mysteel / SMM (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.