Printed from Kezuriba (kezuriba.net/en/materials/aisi4340/)
4340
ISO P (steel)Nickel-chromium-molybdenum steel (low alloy steel). Number: UNS G43400 (UNS G43406 for aircraft VAR material). Standard: SAE J404 (composition standard; table is paywalled and not confirmed) / for aircraft, AMS 6414 (VAR), AMS 6415 (air melted), etc..
🌐JIS and international equivalents
“Close” means composition or properties are not exactly the same. Before substituting, check the values in each standard.
| System | Designation | Number | Relation | Confidence |
|---|---|---|---|---|
| AISI/SAE | 4340 | UNS G43400 (UNS G43406 for aircraft VAR material) | — | |
| JIS | SNCM439 | JIS G 4053 | close | One source / reference[11] |
| EN | 34CrNiMo6 | 1.6582 | close | Agrees in 2+ sources[12][13][14][15] |
| GB | 40CrNiMoA | close | Agrees in 2+ sources[11][15] |
Differences between the equivalents (from the sources)
- JIS SNCM439: Kyocera's cross-reference table lists AISI 4340, GB 40CrNiMoA and DIN 40NiCrMo6 on the SNCM439 row. On the other hand, DEW gives SNCM447 in the JIS column for 34CrNiMo6 (equivalent to 4337/4340), and Mitsubishi Materials leaves the JIS column blank on the 34CrNiMo6 row. Only one primary source directly matches SNCM439 to 4340
- EN 34CrNiMo6: DEW, Saarstahl and SIJ list SAE 4337/4340 alongside it, and Mitsubishi Materials also lists 4340 on the same row. EN 10083-3 34CrNiMo6 is C 0.30–0.38, Cr 1.30–1.70, Ni 1.30–1.70 (DEW), which differs from 4340 (Cr 0.70–0.90, Ni 1.65–2.00) in the Cr and Ni balance
- GB 40CrNiMoA: GB column of Kyocera (SNCM439 / 4340 row) and Mitsubishi Materials (34CrNiMo6 / 4340 row). The composition on the GB side could not be obtained from primary sources
📄Related specifications (AMS, ASTM etc.)
Specifications called up on purchase orders and drawings. AMS are SAE aerospace material specifications, split by product form (bar, plate, forging), melting practice and heat treatment. Standard texts are paid, so only titles and scopes checked on the publishers’ public pages are shown.
| Spec | Scope | Confidence |
|---|---|---|
| AMS 6414 | Steel, Bars, Forgings, Mechanical Tubing, and Forging Stock 0.80Cr - 1.8Ni - 0.25Mo (0.38 - 0.43C) (SAE 4340) Vacuum Consumable Electrode RemeltedBar, forgings, mechanical tubing and stock for forging. Premium aircraft quality by vacuum arc remelting (VAR). AMS6414N (revised 2023-03, shown as current on SAE Mobilus) | Agrees in 2+ sources[3] |
| AMS 6415 | Steel, Bars, Forgings, and Tubing 0.80Cr - 1.8Ni - 0.25Mo (0.38 - 0.43C) (SAE 4340)Bar, forgings and tube. Air melted aircraft quality (Carpenter and Liberty note Air Melt). What was seen on the page was the AMS6415T title | Agrees in 2+ sources[16] |
| AMS 6454 | Steel, Sheet, Strip, and Plate 1.8Ni - 0.80Cr - 0.25Mo (0.38 - 0.43C) (SAE 4340) Vacuum Consumable Electrode RemeltedSheet, strip and plate. VAR (what was seen on the page was AMS6454F) | One source / reference[17] |
| AMS 6484 | Steel, Bars, Forgings, and Tubing 0.80Cr - 1.8Ni - 0.25Mo (0.38 - 0.43C) (SAE 4340) Normalized and TemperedBar, forgings and tube. Normalized and tempered condition (what was seen on the page was AMS6484E) | One source / reference[18] |
| ASTM A29/A29M | Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-WroughtGeneral requirements for hot-rolled carbon and alloy steel bars (including composition tables by grade). What was seen on the page was A29/A29M-20 | One source / reference[19] |
| SAE J404 | Chemical Compositions of SAE Alloy SteelsSAE standard for the chemical composition of alloy steels. What was seen on the page was J404_200901 | Agrees in 2+ sources[20] |
All ASTM standards on Kezuriba: ASTM standards quick reference.
✈Main aerospace uses (as stated in the sources)
- Landing gear parts, aircraft structural parts, gears, shafts, connecting rods, bearing parts (Liberty Speciality Steels AMS 6415/6414 material)[7]
- MIL-HDBK-5J: 4340 can be heat treated to higher strength through thicker sections than 4140. It is used at Ftu 260ksi and above (the 220ksi class is not used because tempering at 500–700°F causes embrittlement)[9]
- SIJ (Ravne) lists aircraft landing gear and power transmission gears and shafts as applications of the equivalent 34CrNiMo6 (description of an EN steel)[14]
⚗Chemical composition (mass %)
Ranges differ between specifications, so each one has its own column (dark figures agree in several sources, light figures come from one source).
| Element | Spec ① | Spec ② |
|---|---|---|
| C | 0.38 – 0.43[3][7][2] | 0.38 – 0.43[8] |
| Si | 0.15 – 0.35[7][2] | 0.15 – 0.35[8] |
| Mn | 0.65 – 0.90[7][2] | 0.65 – 0.85[8] |
| P | ≤ 0.01[7][2] | ≤ 0.025[8] |
| S | ≤ 0.01[7][2] | ≤ 0.025[8] |
| Ni | 1.65 – 2.00[7][2] | 1.65 – 2.00[8] |
| Cr | 0.7 – 0.9[7][2] | 0.7 – 0.9[8] |
| Mo | 0.2 – 0.3[7][2] | 0.2 – 0.3[8] |
| Cu | ≤ 0.35[7][2] | — |
- Spec ① Aircraft VAR 4340: AMS 6414 (title and Liberty's AMS 6415/6414 table) and MIL-S-8844D Class 1 (successor is AMS 6414)
- Spec ② MIL-S-5000E (E4340 air melted, aircraft quality bar. Withdrawn; successor is SAE AMS-S-5000)
⚖Density
7.84 g/cm³
Latrobe (now Carpenter) gives 0.283 lb/in³ (7.84 g/cm³). MIL-HDBK-5J also gives 0.283 lb/in³ (converted 7.83). SIJ's 34CrNiMo6 is 7.84
Calculate weight in 4340 →💪Mechanical properties
“Reference” values are not specified minimums from the standard but figures published by makers and others.
| Condition | Tensile MPa | Yield MPa | Elong. % | Hardness | Type of value |
|---|---|---|---|---|---|
| Quenched and tempered. Bar, forgings and tube (AMS 6414, VAR). Maximum diameter that can be fully hardened: 1.70in with molten salt quench, 2.50in with oil quench, 3.50in with water quench | ≥ 1793 (260ksi) | ≥ 1496 (217ksi) | ≥ 10 (L direction) | — | Design value (MIL-HDBK-5J, S basis). Liberty's AMS 6415/6414 limits table also agrees with tensile 1793MPa and elongation 10% in the L direction (yield could not be checked because the table layout is hard to read) One source / reference[9][7] |
| Normalized 899/927℃ → oil quenched from 816/829℃ → tempered 204℃ (400°F). 3.5in round bar, transverse direction | 1905 (276ksi) | 1530 (222ksi) | 11.0 | — | Typical value (manufacturer: Latrobe / now Carpenter VAR material datasheet). The correspondence of the R.A. column was read from the table layout One source / reference[10] |
| Same pretreatment → tempered 260℃ (500°F). 7.5in square, transverse direction | 1830 (265ksi) | 1530 (222ksi) | 8.0 | — | Typical value (manufacturer: Latrobe / now Carpenter) One source / reference[10] |
| Same pretreatment → tempered 593℃ (1100°F). 10.5in square, transverse direction | 1140 (165ksi) | 1035 (150ksi) | 18.0 | — | Typical value (manufacturer: Latrobe / now Carpenter) One source / reference[10] |
1 MPa ≈ 145 psi (0.145 ksi). Hardness conversion · unit converter
🔧Machinability notes (as stated in the sources)
- Latrobe (now Carpenter): for the best machinability, temper at about 1200°F (written as 629℃ in the datasheet) after normalizing. Because it is air hardening, preheating and furnace cooling after forging, or cooling in ash or lime, is recommended[10]
- Sandvik Coromant: low alloy steels are ISO P, with machinability determined by alloy content and hardness. Hardened steels above about 45HRC are ISO H. Machining after quenching and tempering up to the 260ksi class for aircraft (MIL-HDBK-5J design value) is treated as H[4][9]
- MIL-HDBK-5J (alloy steels in general): a two-stage approach is common, with rough machining in the annealed or hot-finished condition and finishing after the final heat treatment. Free-machining (sulfur- or lead-added) steels are not recommended for high-stress aircraft parts[9]
📚Sources
Primary sources (public documents from makers, industry associations and standards bodies), numbered where each value is cited. Many are in Japanese.
- carpentertechnology.com https://carpentertechnology.com/alloy-finder/4340
- everyspec.com https://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-8844D_39737/
- saemobilus.sae.org https://saemobilus.sae.org/standards/ams6414n-steel-bars-forgings-mechanical-tubing-forgin…
- sandvik.coromant.com https://www.sandvik.coromant.com/en-us/knowledge/materials/workpiece-materials
- kyocera.co.jp https://www.kyocera.co.jp/prdct/tool/wp-content/uploads/2014/07/2024-2026_A.pdf
- sumitool.com https://www.sumitool.com/downloads/cutting-tools/general-catalog/assets/pdf/a.pdf
- libertysteelgroup.com https://libertysteelgroup.com/uk/wp-content/uploads/sites/2/2021/01/Aerospace-AMS-6415-641…
- everyspec.com https://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-5000E_22375/
- everyspec.com https://everyspec.com/MIL-HDBK/MIL-HDBK-0001-0099/MIL_HDBK_5J_139/
- carpentertechnology.com https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/4340.p…
- kyocera.co.jp https://www.kyocera.co.jp/prdct/tool/wp-content/uploads/2016/06/R_2016.pdf
- swisssteel-group.com https://swisssteel-group.com/content-media/documents/Data-Sheets/Engineering-Steel/1.6582_…
- saarstahl.com https://www.saarstahl.com/app/uploads/2024/03/20160318115938-34CrNiMo6.pdf
- cms.sij.si https://cms.sij.si/storage/51/SIQUAL-6582-datasheet.pdf
- mitsubishicarbide.net https://www.mitsubishicarbide.net/contents/mhg/ru/manual/material_cross_reference.pdf
- saemobilus.sae.org https://saemobilus.sae.org/standards/ams6415t-steel-bars-forgings-tubing-080cr-18ni-025mo-…
- sae.org https://www.sae.org/standards/content/ams6454f/
- sae.org https://www.sae.org/standards/content/ams6484e/
- store.astm.org https://store.astm.org/a0029_a0029m-20.html
- saemobilus.sae.org https://saemobilus.sae.org/standards/j404_200901-chemical-compositions-sae-alloy-steels
Other materials
Aerospace steel