Printed from Kezuriba (kezuriba.net/en/materials/300m/)
300M
ISO P (steel)Nickel-chromium-molybdenum steel with added silicon and vanadium (modified 4340, low-alloy ultra-high-strength steel). Number: UNS K44220. Standard: AMS 6417 (C 0.38-0.43), AMS 6419 (C 0.40-0.45), AMS 6257 (C 0.40-0.44, normalized and tempered).
🌐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 |
|---|---|---|---|---|
| Industry name (also called 4340M or SAE 4340M; composition is specified by AMS 6417, 6419 and 6257) | 300M | UNS K44220 | — | |
| JIS | — | — | Not confirmed | |
| EN | — | — | Not confirmed | |
| GB | — | — | Not confirmed |
Differences between the equivalents (from the sources)
- JIS : There is no 300M row in the Kyocera or Mitsubishi Materials cross-reference tables, and no primary source showing a JIS equivalent was found
- EN : No primary source showing an EN equivalent was found. Liberty's pocketbook lists airline and airframe-manufacturer specifications such as LAT 1.9042, IGQ 41-11 and ZFNL 9207 as related specifications, but these are not EN numbers
- GB : Not confirmed in 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 6417 | Steel, Bars, Forgings, and Tubing, 1.6Si - 0.82Cr - 1.8Ni - 0.40Mo - 0.08V (0.38 - 0.43C), Consumable Electrode Vacuum RemeltedBar, forgings and tubing. Vacuum arc remelted (VAR). C 0.38-0.43 (the page viewed was AMS6417J; AMS6417L is shown as work in progress (WIP)) | Agrees in 2+ sources[7][8] |
| AMS 6419 | Steel, Bars, Forgings, and Tubing, 1.6Si - 0.82Cr - 1.8Ni - 0.40Mo - 0.08V (0.40 - 0.45C), Consumable Electrode Vacuum RemeltedBar, forgings and tubing. VAR. C 0.40-0.45 (the page viewed was AMS6419K) | Agrees in 2+ sources[3] |
| AMS 6257 | Steel Bars, Forgings, and Tubing 1.6Si - 0.82Cr - 1.8Ni - 0.40Mo - 0.08V (0.40 - 0.44C) Consumable Electrode Vacuum Remelted Normalized and TemperedBar, forgings and tubing. VAR, normalized and tempered condition. C 0.40-0.44 (the page viewed was AMS6257A). Latrobe notes it as the "successor to MIL-S-8844 Class 3" | Agrees in 2+ sources[10][12] |
| MIL-S-8844D | Steel Bar, Reforging Stock, and Mechanical Tubing, Low Alloy, Premium Quality1987 edition. Multiple vacuum melted low-alloy steel; bar, forging stock and tubing for use at 260 ksi (1795 MPa) and above. Class 1 is 4340 and Class 2 is 300M. Cancelled and replaced by AMS 6414 and AMS 6257 (per EverySpec) | One source / reference[2] |
All ASTM standards on Kezuriba: ASTM standards quick reference.
✈Main aerospace uses (as stated in the sources)
- Tensile strength class of 270/300 ksi (1862/2068 MPa); used for aircraft landing gear, flap tracks and other structural parts (Latrobe / now Carpenter)[12][13]
- MIL-HDBK-5J: 300M, together with 4340, is used at Ftu of 260 ksi and above, and consumable-electrode melted (vacuum remelted) material is available[11]
⚗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 | Spec ③ | Spec ④ |
|---|---|---|---|---|
| C | 0.38 – 0.43[7][8] | 0.40 – 0.45[3][2] | 0.40 – 0.44[9][10] | — |
| Mn | — | — | — | 0.65 – 0.90[2] |
| P | — | — | — | ≤ 0.01[2] |
| S | — | — | — | ≤ 0.01[2] |
| Si | — | — | — | 1.45 – 1.80[2] |
| Ni | — | — | — | 1.65 – 2.00[2] |
| Cr | — | — | — | 0.70 – 0.95[2] |
| Mo | — | — | — | 0.35 – 0.50[2] |
| V | — | — | — | 0.05 – 0.10[2] |
| Cu | — | — | — | ≤ 0.35[2] |
- Spec ① AMS 6417 (carbon range in the standard title; titles of AMS6417J and 6417L)
- Spec ② AMS 6419 (title of AMS6419K). MIL-S-8844D Class 2 (300M) also has the same 0.40-0.45
- Spec ③ AMS 6257 (carbon range in the standard title)
- Spec ④ MIL-S-8844D Class 2 (300M; cancelled, superseded by AMS 6257)
⚖Density
7.84 g/cm³
Latrobe (now Carpenter) gives 0.283 lb/in³ (7.84 g/cm³). The MIL-HDBK-5J low-alloy steel table (including 300M) also gives 0.283 lb/in³ (converted 7.83)
Calculate weight in 300M →💪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, tubing, C 0.42 type (AMS 6419, AMS 6257). Maximum diameter that can be fully hardened by oil quenching is 5.00 in | ≥ 1931 (280ksi) | ≥ 1586 (230ksi) | ≥ 7 (L direction) | — | Design value (MIL-HDBK-5J, S-basis) One source / reference[11] |
| Quenched and tempered. Bar, forgings, tubing, C 0.40 type (AMS 6417) | ≥ 1862 (270ksi) | ≥ 1517 (220ksi) | ≥ 8 (L direction) | — | Design value (MIL-HDBK-5J, S-basis) One source / reference[11] |
| Normalized at 927°C, oil quenched from 871°C, tempered at 302°C (575°F). Large sections of 12-28 in, transverse direction (specimens 0.252 in and 0.505 in) | 1972–1986 (286–288ksi) | 1655–1689 (240–245ksi) | 8.5–11 | — | Typical value (manufacturer: Latrobe / now Carpenter VAR material datasheet). The same document gives the plane-strain fracture toughness KIc per ASTM E399 as typically 60-70 ksi√in (66-77 MPa√m) One source / reference[12] |
| Normalized and tempered (tempered at about 1200°F/649°C). Condition for machinability | — | — | — | HBW 241-285 (typical) | Typical value (manufacturer: Latrobe / now Carpenter) One source / reference[12] |
1 MPa ≈ 145 psi (0.145 ksi). Hardness conversion · unit converter
🔧Machinability notes (as stated in the sources)
- Latrobe (now Carpenter): for optimum machinability, use the normalized and tempered condition (tempered at about 1200°F). Typical hardness is HBW 241-285. Can be gas welded and arc welded[12]
- Carpenter: the increased silicon allows tempering at a higher temperature than 4340, giving a stress-relieved structure[13]
- Sandvik Coromant: hardened steel above about 45 HRC is ISO H. Machining after quenching and tempering up to the 280 ksi class is treated as ISO H (the normalized and tempered condition is P)[4]
📚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/300m
- everyspec.com https://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-8844D_39737/
- sae.org https://www.sae.org/standards/content/ams6419k/
- 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
- sae.org https://www.sae.org/standards/content/ams6417j/
- sae.org https://www.sae.org/standards/content/ams6417l/
- saemobilus.sae.org https://saemobilus.sae.org/standards/ams6257-steel-bars-forgings-tubing-16si-082cr-18ni-04…
- sae.org https://www.sae.org/standards/content/ams6257a/
- 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/300M.p…
- carpentertechnology.com https://www.carpentertechnology.com/hubfs/Alloy%20Cards/300M_snapshot.pdf
Other materials
Aerospace steel