4140 at a glance
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Designation
| Item | Value |
|---|---|
| Designation | 4140 |
| Class | Steel and stainless |
| Type | alloy steel |
Composition
| Item | Limit | Source |
|---|---|---|
| Composition | Chromium 0.80–1.10 %, molybdenum 0.15–0.25 %, carbon 0.38–0.43 % | AZoM AISI 4140 composition table; the 41 means Cr-Mo steel and 40 about 0.40 % carbon (AMT Handbook, p. 5-16) |
Properties
| Property | Value | Source |
|---|---|---|
| Against 4130 | Can be heat treated in thicker sections and to higher strength levels than 4130 | MIL-HDBK-5J, par. 2.3.1.0 |
| Typical use | Structural machined and forged parts one-half inch and over in thickness | MIL-HDBK-5J, par. 2.3.1.0 |
| Sheet, strip, plate | AMS 6395 | MIL-HDBK-5J, Table 2.3.1.0(a) |
| Bars and forgings | AMS-S-5626, AMS 6382, AMS 6349, AMS 6529 | MIL-HDBK-5J, Table 2.3.1.0(a) |
| Tubing | AMS 6381 | MIL-HDBK-5J, Table 2.3.1.0(a) |
| Alternate | AISI 8740 is listed as the alternate to 4140 | MIL-HDBK-5J, par. 2.3.1.0 |
| Welding rod | 4140 rod, AMS 6452, AWS A5.28 | AC 43.13-1B CHG 1, Table 4-15 |
The handbook gives no design allowables for 4140: its Table 2.3.1.0(a) marks these specifications as not containing minimum mechanical properties. The strength depends on the heat treatment shown on the part drawing or certificate.
Notes from the guide
- No allowables on this page because the public handbook has none for 4140. Use MMPDS or the drawing.
- Not a welding recommendation. TIG weld only with the procedure the SRM or the drawing gives.
- Not a substitute for 4130 tube. Different carbon, different weld behaviour.
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Sources
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures (31 Jan 2003) — par. 2.3.1.0 (4140 comment) and Table 2.3.1.0(a), specifications. Cancelled; superseded by MMPDS.
- FAA AC 43.13-1B CHG 1 — Table 4-15 (welding rod), par. 4-89c, par. 6-165.
- FAA-H-8083-31B, Aviation Maintenance Technician Handbook, Airframe, Volume 1 — p. 5-16, steel designation.
- MMPDS (formerly MIL-HDBK-5) — the current home of design allowables. A repair substantiation cites MMPDS or the SRM, not a website.
- AZoM, AISI 4140 alloy steel — Chemical composition table.
Educational reference only. not approved data. Always consult the applicable SRM, AMM, or AC 43.13-1B and your certifying authority.