AISI 4130 Chromoly Steel: Properties, Equivalents & Aerospace/Motorsport Applications
AISI/SAE 4130 · Published: 2026-07-15 · Updated: July 2026
AISI 4130 is a low-alloy steel containing 0.30% carbon, 0.95% chromium, and 0.20% molybdenum — the 'chromoly' designation reflects the Cr-Mo alloying. The chromium provides hardenability and mild corrosion resistance; the molybdenum prevents...
AISI 4130 is a low-alloy steel containing 0.30% carbon, 0.95% chromium, and 0.20% molybdenum — the 'chromoly' designation reflects the Cr-Mo alloying. The chromium provides hardenability and mild corrosion resistance; the molybdenum prevents temper embrittlement and enhances high-temperature strength. 4130 is the standard material for aircraft tubular structures (landing gear, engine mounts, fuselage frames), motorsport roll cages and chassis (SCCA, NHRA, FIA regulations specifically permit 4130), hydraulic fittings, and high-strength welded pressure vessels. In the normalized condition, 4130 provides 435 MPa yield strength — 74% stronger than A36 while maintaining good weldability with preheat. When quenched and tempered, 4130 achieves 700-900 MPa yield strength depending on tempering temperature, making it suitable for high-stress machine components. The alloy's excellent weldability (with proper preheat) distinguishes it from higher-carbon alloy steels like 4140 — 4130 is the strongest common alloy steel that can be reliably TIG welded for critical structural joints. This is why 4130 DOM tubing (Drawn Over Mandrel) is the default material for aerospace and motorsport welded structures.
Quick Facts
| Category | Alloy Steel |
| Standard | AISI/SAE 4130 |
| Density | 7.85 g/cm³ |
| Yield Strength | 435 MPa (63 ksi) normalized |
| Tensile Strength | 670 MPa (97 ksi) normalized |
Detailed Mechanical Properties
| Elongation | 17% (normalized), 15% (Q&T) |
| Hardness | 190-220 HB (normalized), 28-36 HRC (Q&T) |
| Charpy V Notch | 54J at 20°C (normalized) |
| Shear Modulus | 79.0 GPa |
Physical Properties
| Melting Point | 1420-1460 °C |
| Thermal Conductivity | 42.7 W/m·K at 20°C |
| Electrical Resistivity | 0.0000205 Ω·cm |
| Specific Heat | 486 J/kg·K |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| 25CrMo4 (EN/DIN) | Compare |
| SCM430 (JIS) | Compare |
| 708M25 (BS) | Compare |
| G41300 (UNS) | Compare |
Heat Treatment & Processing
| Normalizing | 860-890°C, air cool |
| Annealing | 840-870°C, furnace cool |
| Quenching | 840-870°C, oil quench |
| Tempering | 480-650°C based on desired properties, air cool |
| Note | Avoid temper range 250-370°C (tempered martensite embrittlement). Oil quench preferred; water quench only for simple shapes <12mm section. |
Welding & Fabrication
| Preheat | 150-200°C for thicknesses 3-12mm; 200-260°C for >12mm |
| Filler Metal | ER80S-D2 (GTAW/GMAW), E8018-B2 (SMAW) |
| Interpass Temp | Max 315°C |
| Pwht | Stress relieve at 595-650°C for 1h per 25mm; mandatory for pressure vessel service |
| Weldability Rating | Good with preheat — excellent TIG weldability for thin-wall tubing |
Related Materials
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Frequently Asked Questions
Why is 4130 preferred over 4140 for welded tubular structures?
4130 has 0.30% carbon versus 4140's 0.40% carbon. This 0.10% difference significantly affects weldability: 4130 requires 150-200°C preheat and can be TIG welded with ER80S-D2 filler, while 4140 requires 250-350°C preheat and is prone to HAZ cracking in restrained joints. For aircraft structures and roll cages where extensive welding is required, 4130's lower carbon provides a wider safety margin against weld defects. 4140 is preferred for non-welded or minimally-welded components like shafts and gears where higher as-quenched hardness is beneficial.
What tempering temperature gives the best strength-toughness balance for 4130?
For structural applications (aircraft frames, roll cages), tempering at 480-540°C (900-1000°F) after quenching produces yield strength of 700-800 MPa with good toughness and ductility (15-18% elongation). For maximum toughness (impact applications), temper at 650°C (1200°F) for yield strength of 500-600 MPa with 20%+ elongation. Never temper 4130 between 250-370°C (500-700°F) — this range produces tempered martensite embrittlement with significantly reduced impact toughness.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu
Specialty Metals — Engineering Reference
Non-ferrous metals — aluminum, copper, titanium, zinc, magnesium — serve applications where steel cannot: electrical conductivity, thermal management, weight reduction, corrosion resistance in specific chemical environments. Each metal family has its own classification system and selection logic.
ASTM B209/B221 (Al), ASTM B152/B187 (Cu), ASTM B265/B348 (Ti), ASTM B86 (Zn), ASTM B90/B91 (Mg)
Electrical wiring and busbars (Cu), aircraft structures and automotive bodies (Al), medical implants and aerospace fasteners (Ti), die-cast consumer products (Zn), lightweight electronic enclosures (Mg)
Galvanic corrosion is the #1 failure mode in multi-metal assemblies. When joining dissimilar metals, consult the galvanic series: the more anodic metal will corrode preferentially. Use isolating washers, protective coatings, or select metals close together on the galvanic series.