Steel 4340M · temper
Steel 4340M Annealed
Properties of the Annealed condition, compared with the other 4340M tempers.
Softest supply condition — pick for rough machining, deep drilling and forming before final quench and temper.
What is 4340M Annealed?
4340M Annealed is 4340M in the Annealed temper — softest supply condition — pick for rough machining, deep drilling and forming before final quench and temper. 4340M Annealed has a yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi). 4340M Annealed has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F). HR is the default condition FabDigit quotes; Annealed is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- High strength — 690 MPa (100 ksi), better than 80% of steel grades
Limitations
- Difficult to weld — 15/100, worse than 91% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 86% of steel grades
- Low fracture toughness — 60 MPa·√m (54.6 ksi·√in), worse than 79% of steel grades
4340M Annealed properties
Typical room-temperature values for 4340M Annealed — 13 properties are specific to this condition; the rest are grade-level values shared by every 4340M temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4340M Annealed has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
4340M Annealed has a yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4340M Annealed is rated for continuous service to 400°C (752 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 72% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
4340M Annealed conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of 4340M Annealed takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 88% of steel grades. Typical recycled content is 25%.
Manufacturability8
4340M Annealed's machinability is fair (42/100, worse than 72% of steel grades); weldability poor (15/100); formability poor (30/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4340M tempers and conditions
4340M is also supplied in 8 other conditions. The full side-by-side table is on the 4340M overview.
- HRDefaultMill product as rolled or forged — air-hardened martensite, too hard and brittle to machine; always annealed or normalized before use.1,150 MPa yield · 47 HRC
- Q&T-2070Maximum-strength condition for weight-critical rocket motor cases and springs; accept lower toughness and high notch sensitivity.1,720 MPa yield · 56 HRC
- VARConsumable-electrode vacuum remelted stock — choose for fatigue- and fracture-critical aerospace parts needing best transverse ductility and low inclusion count.1,640 MPa yield · 54 HRC
- Q&TThe standard 300M service condition (AMS 6419): highest strength/toughness balance for landing gear, actuator rods and shafts.1,620 MPa yield · 54 HRC
- Q&T-1790Slightly higher temper for parts where fracture toughness and ductility matter more than peak strength.1,520 MPa yield · 51 HRC
- NormalizedNormalize ~925 °C then temper for uniform grain and moderate hardness — a machining/stock condition and a grain-refining step before final hardening.965 MPa yield · 40 HRC
- CDSmall-diameter annealed bar/wire cold drawn to size for tight tolerance and better surface before heat treatment; rarely stocked in this grade.860 MPa yield · 31 HRC
- AnnealedSoftest supply condition — pick for rough machining, deep drilling and forming before final quench and temper.690 MPa yield · 26 HRC
Working with 4340M Annealed
Is 4340M easy to machine?
Rough machine in the annealed condition (≈40% of B1112) with carbide and rigid setups; at 52–56 HRC only hard turning with CBN, creep-feed or plunge grinding is practical — grind gently to avoid re-tempering burn and grinding cracks.
Can 4340M be welded?
Not weldable in the hardened state; if welding is unavoidable use electron-beam or GTAW with matching filler, 260–320 °C preheat/interpass, and immediately re-austenitize, quench and temper the whole part.
Can 4340M be formed, bent or molded?
Hot forge/upset at 1050–1200 °C with finish above 900 °C, then normalize and anneal; no meaningful cold forming above the annealed condition — bend and straighten only warm and re-stress-relieve.
What surface finishes work on 4340M?
Shot peen highly stressed fillets, then low-hydrogen-embrittlement cadmium or IVD aluminium plating (or HVOF WC-Co on journals) with a 190 °C/23 h bake within 4 h of plating; chrome plating requires strict bake and peening control.
4340M 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 |
|---|---|---|
| C | 0.4 – 0.46 | 0.43 |
| Sikey modification vs 4340 — raises temper resistance | 1.45 – 1.8 | 1.6 |
| Mn | 0.6 – 0.9 | 0.75 |
| Cr | 0.7 – 0.95 | 0.82 |
| Ni | 1.65 – 2 | 1.83 |
| Mo | 0.3 – 0.45 | 0.38 |
| Vgrain refinement | 0.05 – 0.1 | 0.07 |
| P | ≤ 0.01 | 0.01 |
| S | ≤ 0.01 | 0 |
| Cu | ≤ 0.35 | 0.1 |
| Fe | balance | — |
4340M Annealed — frequently asked
What is 4340M Annealed used for?
4340M Annealed is typically used for aircraft landing gear cylinders and axles, arresting hooks, high-strength airframe fittings, rocket motor cases, torsion bars and high-strength drive shafts. In short: high-strength aerospace bar.
What is the yield strength of 4340M Annealed?
4340M Annealed has a typical yield strength of 690 MPa (100 ksi) and a tensile strength of 930 MPa (135 ksi) — stronger than 80% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4340M Annealed easy to machine?
Not especially — machinability is rated fair (42/100, worse than 72% of steel grades). Rough machine in the annealed condition (≈40% of B1112) with carbide and rigid setups; at 52–56 HRC only hard turning with CBN, creep-feed or plunge grinding is practical — grind gently to avoid re-tempering burn and grinding cracks.
Can 4340M Annealed be welded?
Not readily — weldability is rated poor (15/100). Not weldable in the hardened state; if welding is unavoidable use electron-beam or GTAW with matching filler, 260–320 °C preheat/interpass, and immediately re-austenitize, quench and temper the whole part.
What surface finishes work on 4340M Annealed?
Shot peen highly stressed fillets, then low-hydrogen-embrittlement cadmium or IVD aluminium plating (or HVOF WC-Co on journals) with a 190 °C/23 h bake within 4 h of plating; chrome plating requires strict bake and peening control.
Can 4340M Annealed be formed, bent or molded?
Hot forge/upset at 1050–1200 °C with finish above 900 °C, then normalize and anneal; no meaningful cold forming above the annealed condition — bend and straighten only warm and re-stress-relieve.
What is the maximum service temperature of 4340M Annealed?
4340M Annealed is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4340M-HR and 4340M-VAR?
HR is the default condition — mill product as rolled or forged — air-hardened martensite, too hard and brittle to machine; always annealed or normalized before use. VAR: consumable-electrode vacuum remelted stock — choose for fatigue- and fracture-critical aerospace parts needing best transverse ductility and low inclusion count. Yield strength is 1,150 MPa in HR versus 1,640 MPa in VAR.
Can FabDigit make parts in 4340M Annealed?
Yes — 4340M 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
- AMS 6419 — Steel Bars, Forgings, Tubing 1.6Si-0.82Cr-1.8Ni-0.40Mo-0.08V, Consumable Electrode Melted, 1930 MPa — SAE International (2020)
- AMS 6417 — 300M Steel Bars and Forgings, Normalized and Tempered / Annealed — SAE International (2019)
- MMPDS-2023, Chapter 2 (Low-Alloy Ultrahigh-Strength Steels) — Battelle / FAA (2023)
- Aerospace Structural Metals Handbook — 300M — CINDAS (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- 300M (UNS K44220) alloy steel bar data — Carpenter Technology / Aubert & Duval (2022)
- 40CrNi2Si2MoVA (2015)
- 300M/40CrNi2Si2MoVA — 1688 / Mysteel (2026)
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.