4130 steel (G41300): properties, composition, equivalents
4130 steel (AISI/SAE 4130, UNS G41300): 0.30 % C, 1 % Cr, 0.2 % Mo weldable chromoly. Normalized 435 MPa yield / 670 MPa tensile; Q&T to 1000+ MPa. Composition, heat treatment, welding, 4130 vs 4140, 25CrMo4/SCM430 equivalents.
What is 4130?
AISI 4130 is the weldable chromoly: the same 1 % Cr / 0.2 % Mo alloying as 4140 but with carbon held to 0.28–0.33 %, so that a welded joint's heat-affected zone does not harden past the point of cracking. That single change made 4130 the aircraft-tube steel of the 1930s (MIL-T-6736) and it is still the material of race-car roll cages, aircraft fuselage frames and engine mounts, bicycle and motorcycle frames, go-kart chassis, sprint-car components and pressure-containing wellhead forgings. UNS G41300.
In the normalized condition — the usual state of 4130 tube — it offers about 435 MPa yield and 670 MPa tensile with 25 % elongation, roughly double mild steel at the same wall thickness, and it keeps good toughness. Quenched and tempered it reaches 860–1000 MPa (aerospace 125–145 ksi level) and, with care, 1240 MPa; deeper hardenability than plain carbon but less than 4140, so through-hardened sections are limited to about 25–35 mm.
EN 25CrMo4 (1.7218) is the usual European substitute (slightly lower carbon); JIS SCM430, GB 30CrMo and GOST 30KhMA are identical. Choose 4130 for welded, impact-loaded structures; 4140 for machined, heat-treated parts needing more strength.
4130 chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | 0.28 – 0.33 | |
| Mn | 0.4 – 0.6 | |
| P | ≤ 0.035 | |
| S | ≤ 0.04 | |
| Si | 0.15 – 0.35 | |
| Cr | 0.8 – 1.1 | |
| Mo | 0.15 – 0.25 |
SAE J404 / ASTM A29 (G41300). Aerospace 4130 (AMS 6345 etc.) uses the same window with tighter P/S and vacuum degassing. Compare EN 25CrMo4 (1.7218): C 0.22–0.29, Cr 0.90–1.20, Mo 0.15–0.30 — slightly lower carbon; 30CrMo4 was the old DIN match.
4130 mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Annealed (865 °C, furnace cool) — typical | ≈ 360 (≈ 52.2) | ≈ 560 (≈ 81.2) | 28 | ≈ 156 HB |
| Normalized (870 °C, air) — typical, the usual tube condition ('N') | ≈ 435 (≈ 63.1) | ≈ 670 (≈ 97.2) | 25 | ≈ 197 HB |
| Condition N tube per A519 (minimum) | ≥ 415 (≥ 60.2) | ≥ 620 (≥ 89.9) | 15 | — |
| Q&T, tempered 540 °C (1000 °F), 25 mm — typical | ≈ 760 (≈ 110.2) | ≈ 860 (≈ 124.7) | 18 | ≈ 255 HB |
| Q&T, tempered 425 °C (800 °F) — typical | ≈ 895 (≈ 129.8) | ≈ 1000 (≈ 145.0) | 16 | ≈ 300 HB |
| Q&T, tempered 315 °C (600 °F) — typical | ≈ 1035 (≈ 150.1) | ≈ 1140 (≈ 165.3) | 13 | ≈ 340 HB |
| Q&T, tempered 205 °C (400 °F) — typical | ≈ 1240 (≈ 179.8) | ≈ 1380 (≈ 200.2) | 10 | ≈ 400 HB |
| As-quenched (oil, 860 °C) | — | — | — | 48–52 HRC |
Typical values for 25 mm rounds (ASM); only A519 condition N carries minimums. Aerospace heat-treat levels per AMS 2759: 125–145 ksi (860–1000 MPa), 150–170 ksi, 180–200 ksi tensile.
Impact toughness
4130 requires a minimum Charpy V-notch energy of 60 J at 20 °C (typical, normalized). Good toughness through the useful strength range; 4130 is preferred over 4140 where impact loading and welded joints coexist (roll cages, aircraft).
4130 equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| 30CrMo4 | EN (European) | Identical | Former DIN 17200 / SEW grade (C 0.26–0.34) — an exact match but no longer in EN 10083-3; still produced by some mills. |
| 30CrMo | GB/T (China) | Identical | GB/T 3077 30CrMo: C 0.26–0.34, Cr 0.80–1.10, Mo 0.15–0.25. |
| 30KhMA | GOST (Russia/CIS) | Identical | GOST 4543 30KhMA: C 0.26–0.33, Cr 0.80–1.10, Mo 0.15–0.25 — used for Russian aircraft tube. |
| SCM430 | JIS (Japan) | Identical | JIS G4053 SCM430: C 0.28–0.33, Cr 0.90–1.20, Mo 0.15–0.30. |
| 4140 | AISI / SAE | Near | 0.40 % C: higher strength and hardenability, much poorer weldability. |
| 4135 | AISI / SAE | Near | Intermediate 0.35 % C grade (API 6A wellhead forgings). |
| 708A30 (EN18) | BS (superseded British) | Near | BS 970 708A30: C 0.28–0.33, Cr 0.85–1.15, Mo 0.15–0.25. |
| 25CrMo4 | EN (European) | Near | 1.7218: C 0.22–0.29, Cr 0.90–1.20, Mo 0.15–0.30 — carbon just below 4130's 0.28–0.33; the standard European substitute for tube and bar. |
| 1026 / E4130 | AISI / SAE | Functional | Plain-carbon DOM tube (1026) is the budget substitute for non-critical tube structures. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for 4130 →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| G41300 | UNS | 4130H = H41300. |
| 25CrMo4 / 1.7218 | EN 10083-3 | Nearest European grade (C slightly lower); 30CrMo4 (DIN 17200) was closer. |
| 708A30 / EN18 | BS 970 | |
| SCM430 | JIS G4053 | |
| MIL-T-6736 / AMS 6360 | US military / SAE Aerospace | Aircraft tubing specifications. |
Product forms and tolerance standards
Product forms: seamless tube (ASTM A519, AMS 6360/6371 — the signature form: roll cages, aircraft frames, bicycle tube), bar (A29, A322, A108), plate and sheet (A829, AMS 6345/6350), forgings (A29, AMS 6370), wire, pressure tube (A423, A213 T11-type Cr-Mo is different), wellhead forgings (API 6A 75K).
Dimensional tolerances: tube: ASTM A519 / AMS 2253; bar: ASTM A29 / A108; sheet: AMS 6345 / 6350.
Key property values
4130 steel yield strength
Typical: annealed ≈ 360 MPa (52 ksi); normalized ≈ 435 MPa (63 ksi) — A519 condition N minimum 415 MPa; Q&T at 540 °C ≈ 760 MPa; at 425 °C ≈ 895 MPa; at 315 °C ≈ 1035 MPa; at 205 °C ≈ 1240 MPa (180 ksi).
4130 tensile strength
Typical: annealed ≈ 560 MPa (81 ksi); normalized ≈ 670 MPa (97 ksi) — A519 N minimum 620 MPa; Q&T 860–1000 MPa (aerospace 125–145 ksi), up to ≈ 1380 MPa (200 ksi) at low temper.
4130 hardness
Annealed ≈ 156 HB; normalized ≈ 197 HB; Q&T 255–400 HB depending on temper; as-quenched 48–52 HRC. Nitrided surface ≈ 55 HRC.
Heat treatment
Anneal 840–870 °C, furnace cool. Normalize 870–900 °C (1600–1650 °F), air cool — the standard tube condition. Harden 855–885 °C, oil quench (water for thin tube with care); temper 205–650 °C. Stress relieve welded assemblies 565–650 °C (600 °C / 1100 °F typical for roll cages). Ac1 ≈ 760 °C, Ac3 ≈ 810 °C, Ms ≈ 380 °C. Ideal critical diameter ≈ 35–50 mm.
Weldability
Good for an alloy steel (CE ≈ 0.55–0.65). Thin-wall tube (< 3 mm) is TIG-welded without preheat using ER70S-2/ER80S-D2; thicker sections need 150–250 °C preheat. Post-weld normalizing or stress relief is recommended for critical structures.
Physical properties
Density 7.85 g/cm³, E = 205 GPa, expansion 12.2 × 10⁻⁶/K, conductivity 42.7 W/m·K.
Weldability
The most weldable of the chromoly family. TIG (GTAW) with ER70S-2 or ER80S-D2 filler for tube < 3 mm wall: no preheat, controlled heat input, no rapid quench (let cool in still air). For > 3–5 mm or heavily restrained joints, preheat 150–250 °C and use low-hydrogen consumables (E8018-B2 for matching Cr-Mo). Post-weld: normalize (870–900 °C) for aircraft-quality structures or stress-relieve at 565–650 °C. Do not weld in the Q&T condition and expect full strength — the HAZ softens; re-heat-treat after welding when strength must be uniform.
Machining, forming and heat treatment
Machinability ≈ 70 % of B1112 annealed/normalized — better than 4140 (index ≈ 65 %). Cold forming: good in the annealed state (tube bending with mandrel at ≥ 2.5 D radius in normalized condition); hot forming 1200–950 °C then normalize. Surface treatments: nitriding (≈ 55 HRC case), induction hardening (limited by 0.30 % C to ≈ 48 HRC), chrome plating with hydrogen bake, cadmium/zinc plating for aerospace.
Typical applications
- Aircraft fuselage trusses, engine mounts, landing-gear components (AMS 6360/6371 tube)
- Racing roll cages, chassis and suspension tubes (SFI/FIA-specified 4130 N tube)
- Bicycle, motorcycle and go-kart frames; sprint-car and midget chassis
- Wellhead and Christmas-tree forgings (API 6A 60K/75K, as 4130/4135)
- Pressure vessels and gas cylinders (with Q&T), hydraulic tubing
- Gears, shafts and fasteners at moderate strength; aircraft bolts (AN/NAS)
- Firearm receivers, sporting goods, tool handles
Frequently asked questions
What is the difference between 4130 and 4140?
Carbon: 4130 has 0.30 %, 4140 has 0.40 %. 4130 welds with little or no preheat and is used for tube structures; 4140 reaches higher hardness and strength (to 52+ HRC) but needs 250–350 °C preheat and post-weld tempering. Same Cr and Mo.
Is 4130 chromoly stronger than mild steel?
Normalized 4130 has about 435 MPa yield versus ~250 MPa for A36/1018, so a 4130 tube can be roughly 40 % thinner (lighter) at the same strength — the reason it is used in roll cages and aircraft. Stiffness (E ≈ 205 GPa) is the same for all steels.
Do 4130 welds need heat treatment?
For thin tube (< 3 mm) TIG-welded with ER70S-2, no — allow slow cooling and the joint retains ~80–90 % of tube strength. For aircraft-critical or thick sections, normalize or stress-relieve (565–650 °C) after welding. Never quench a fresh weld.
What is 4130 equivalent to in EN and JIS?
EN 25CrMo4 (1.7218) is the near match (C 0.22–0.29); the old DIN 30CrMo4 was exact. JIS SCM430, GB 30CrMo and GOST 30KhMA are identical.
Can 4130 be hardened?
Yes — quench from 855–885 °C in oil and temper: 48–52 HRC as-quenched, 25–40 HRC typical in service (860–1240 MPa tensile). Hardenability limits through-hardening to about 25–35 mm sections.
What does 'condition N' mean for 4130 tube?
Normalized: heated to 870–900 °C and air-cooled, giving ≥ 415 MPa yield / ≥ 620 MPa tensile per ASTM A519. It is the standard supply condition for chassis and aircraft tube; 'condition A' is annealed (softer, for bending).
Related grades
Verified against ASTM A29/A29M-20 (SAE J404 chemistry); ASTM A29/A29M-20 Table 2 (G41300); ASTM A519/A519M-17; AMS 2759 (heat treatment); ASM Handbook Vol. 1. Last checked: September 2026.