Key facts
| Property | Value | Source |
|---|---|---|
| Composition | Chromium 0.80–1.10 %, molybdenum 0.15–0.25 %, carbon 0.28–0.33 % | AC 43.13-1B CHG 1, Chapter 4, Section 1, designation of “4130”; Table 4-2 |
| Interchangeable tubing | Welded to MIL-T-6731 and seamless to MIL-T-6736 | AC 43.13-1B CHG 1, par. 4-3a |
| Sheet, strip and plate specification | AMS 6345, normalized or otherwise heat treated | SAE AMS6345 (title) |
| Normalizing | Heat to about 150–225 °F above the critical range, cool in still air; soak about ¼ hour per inch of thickness | AC 43.13-1B CHG 1, par. 4-1c |
| TIG welding, wall under 0.120 in | Preheat not necessary; post-weld stress relief still recommended | FAA-H-8083-31, Chapter 5, TIG Welding 4130 Steel Tubing |
Table 4-6 (bend radii) covers aluminum only, so there is no bend radius for 4130 on this page. The drawing or SRM gives it.
Design allowables — AISI 4130 sheet, strip, plate and tubing
0.188 in and under, normalized and tempered, stress relieved. MIL-HDBK-5J Table 2.3.1.0(c1). S basis in ksi unless a unit is shown.
| Property | S basis | Unit |
|---|---|---|
| Ftu | 95 | ksi |
| Fty | 75 | ksi |
| Fcy | 75 | ksi |
| Fsu | 57 | ksi |
| Fbru, e/D = 1.5 | — | ksi |
| Fbru, e/D = 2.0 | 200 | ksi |
| Fbry, e/D = 1.5 | — | ksi |
| Fbry, e/D = 2.0 | 129 | ksi |
| Elongation, sheet, strip and plate, under 0.062 in (minimum) | 8 | % |
| Property | S basis | Unit |
|---|---|---|
| Elongation, sheet, strip and plate, over 0.062 to 0.125 in (minimum) | 10 | % |
| Elongation, sheet, strip and plate, over 0.125 to 0.187 in (minimum) | 12 | % |
| Elongation, tubing (L), full tube, wall up to 0.035 in (minimum) | 10 | % |
| Elongation, tubing (L), full tube, wall over 0.035 to 0.188 in (minimum) | 12 | % |
| E | 29.0 | 10³ ksi |
| Ec | 29.0 | 10³ ksi |
| G | 11.0 | 10³ ksi |
| Density | 0.283 | lb/in³ |
Form: sheet, strip, plate and tubing; condition: normalized and tempered, stress relieved; specification: AMS 6360, AMS 6373, AMS 6374, AMS-T-6736 and AMS-S-18729; thickness or diameter 0.188 in and under. The handbook gives S basis only for 4130, with no A or B values and no L or LT direction, so there is no B column. Design values apply only to parts for which the Ftu has been substantiated by adequate quality control testing (handbook footnote b). Elongation is from Table 2.3.1.0(d), p. 2-21 (condition N). Source: MIL-HDBK-5J (31 Jan 2003), Table 2.3.1.0(c1), p. 2-17. MIL-HDBK-5J (2003) is superseded by MMPDS; check current MMPDS before design use. Density 0.283 lb/in³ is about 7.83 g/cm³ (converted); the sheet weight calculator uses the same figure.
Where it is used
The AMT Handbook calls SAE 4130 an ideal material for fuselages and framework on small aircraft. The tubing has high tensile strength, malleability, and is easy to weld (p. 5-16).
Forms in the sources: welded and seamless tubing (AC par. 4-3), and sheet, strip and plate under AMS 6345.
The 41 in 4130 means a chromium-molybdenum low-alloy steel, and the 30 means about 0.30 percent carbon (AMT Handbook, p. 5-16).
Welding and heat treatment
Clean first. Remove oil, grease and paint, and use a stainless steel wire brush. TIG is highly susceptible to porosity and hydrogen embrittlement from contamination (AMT Handbook, Chapter 5).
Filler. If you use 4130 filler rod, preheat the work and heat-treat afterward to avoid cracking. The handbook says engineering should determine the preheat and post-weld treatment in that case.
Cool slowly. No drafts; the fast cooling of TIG makes untempered martensite beside the weld, which is why stress relief is recommended.
Do not weld heat-treated parts. The AC says not to weld alloy steel parts such as aircraft bolts and turnbuckle ends that have been heat-treated for their mechanical properties (par. 4-89c).
Questions people actually ask
Can I weld 4130 tube with 4130 rod?
You can, but the AMT Handbook says to preheat and heat-treat afterward to avoid cracking, and to have engineering set the cycle.
Is welded 4130 tubing interchangeable with seamless?
AC par. 4-3a says 4130 welded tubing to MIL-T-6731 and 4130 seamless tubing to MIL-T-6736 are interchangeable.
Limits — when NOT to use this
- Not a source of design allowables. The strength depends on heat treatment and form. Use MMPDS with the basis; the SRM governs a repair.
- Not a substitute for an aluminum tube or the reverse. Different weight, stiffness and corrosion behaviour. Material substitution in a structural repair is approved-data territory.
- Weld repair of tube structure is a procedure, not a tip. The AC and the SRM define acceptable repairs (AC 43.13-1B, Chapter 4).
- No corrosion data here. Neither source gives a corrosion rating for 4130; protective finish is set by the SRM.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4 — Section 1, pars. 4-1 to 4-3, Table 4-2; par. 4-89 — composition, steel numbering, tubing interchangeability, normalizing, and parts not to be welded.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 5 (Steel including SAE 4130, p. 5-16; TIG welding 4130 steel tubing) — use, designation and TIG welding practice.
- SAE AMS6345, Steel, Sheet, Strip, and Plate 0.95Cr-0.20Mo (0.28-0.33C) (SAE 4130), Normalized or Otherwise Heat Treated — title of the governing sheet, strip and plate specification.
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures — density (Table 2.3.1.0(c1)), and the home of the 4130 design allowables (Chapter 2, steels). Cancelled; replaced by MMPDS.
- MIL-HDBK-5J (31 Jan 2003), Table 2.3.1.0(c1), p. 2-17 — AISI 4130 sheet, strip, plate and tubing, normalized and tempered, stress relieved, 0.188 in and under: S-basis allowables, E, Ec, G and density.
- MIL-HDBK-5J (31 Jan 2003), Table 2.3.1.0(d), p. 2-21 — minimum elongation values for low-alloy steels in condition N.
- MMPDS (formerly MIL-HDBK-5) — the current home of design allowables with A, B and S basis. Cancelled MIL-HDBK-5J was superseded by it. A repair substantiation cites MMPDS or the SRM, not a website.