4140 Alloy Steel
Tailwind Aerospace Solutions is a certified 4140 steel supplier for aerospace, defense, energy, automotive, and industrial manufacturers. We stock 4140 alloy steel bar and rod with mill test reports and full traceability, cut to size and ready for machining or heat treatment.
What Is 4140 Alloy Steel (UNS G41400)?
4140 is a chromium-molybdenum low-alloy steel with a nominal carbon content of 0.40%. Chromium adds hardenability and wear resistance. Molybdenum adds strength, gives more uniform hardness through the section, and reduces the risk of temper embrittlement. 4140 carries more carbon than 4130, so it reaches higher hardness after heat treatment. It also keeps its strength at moderately elevated service temperatures.
Typical chemistry per SAE J404 and ASTM A29:
- Carbon: 0.38% to 0.43%
- Manganese: 0.75% to 1.00%
- Chromium: 0.80% to 1.10%
- Molybdenum: 0.15% to 0.25%
- Silicon: 0.15% to 0.35%
4140 Specifications We Supply
- AMS 6382: 4140 bars, forgings, and rings for aerospace use
- AMS 6349: 4140 bars in the normalized condition
- AMS 6395: 4140 sheet, strip, and plate, annealed
- ASTM A29: General requirements for hot-wrought carbon and alloy steel bars
- ASTM A322 / ASTM A331: Hot-rolled and cold-finished alloy steel bars
Heat Treat Conditions and Mechanical Properties
4140 is one of the most heat treat responsive alloys available, and its properties depend almost entirely on condition:
- Annealed: The softest state, at about 197 HB, and the best choice for heavy machining before hardening.
- Normalized: Refines grain structure and raises strength over the annealed condition.
- Quenched and tempered: Oil quenched, then tempered to the target hardness. Lower tempering temperatures give higher strength and hardness. Higher temperatures give more ductility and toughness.
- Pre-hardened: Quenched and tempered at the mill, typically to 28 to 32 HRC, so parts can be machined to finish without a separate heat treatment.
4140 can also be flame hardened, induction hardened, or nitrided for a hard, wear-resistant surface.
| Condition | Tensile Strength (ksi) | Yield Strength (ksi) | Elongation (%) | Hardness |
|---|---|---|---|---|
| Annealed (1500°F) | 95 | 60.5 | 25.7 | 197 HB |
| Normalized (1600°F) | 148 | 95 | 17.7 | 302 HB |
| Quenched, tempered at 1200°F | 110 | 95 | 22 | 230 HB |
| Quenched, tempered at 1000°F | 156 | 143 | 15 | 311 HB |
| Quenched, tempered at 600°F | 250 | 228 | 11.5 | Approx. 50 HRC |
Source: Typical values from ASM International handbook data for small-section round bar. These are typical values, not guaranteed minimums. Properties vary with section size, so confirm against the governing specification and the mill test report.
Available Forms and Sizes
- Round bar and rod
- Square and flat bar
- Hex bar
Our precision cutting services supply 4140 blanks cut to your dimensions.
Your Certified 4140 Steel Supplier
Request a quote today for 4140 alloy steel or call 888-304-7075.
Applications and Industries for 4140
- Aerospace and defense: ground support equipment, tooling, fixtures, shafts, and fasteners
- Oil and gas: drill collars, tool joints, subs, and couplings
- Automotive and heavy equipment: gears, axles, spindles, crankshafts, and hydraulic piston rods
- Industrial manufacturing: die holders, molds, bolts, studs, and machine components
4140 vs. 4130, 4330, and 4340
- 4130 has about 0.30% carbon, which makes it easier to weld. It is the standard for welded airframe tubing and assemblies. Choose 4140 when hardness and wear resistance matter more than weldability.
- 4340 adds nickel to the chromium-molybdenum chemistry. That gives it deeper hardenability and higher toughness in large cross sections, which is why it is specified for landing gear and highly loaded structures.
- 4330 is a nickel-chromium-molybdenum steel with lower carbon than 4340. It delivers high strength with excellent toughness for flight-critical structural parts.
For the most demanding airframe applications, see 300M or browse all alloy steel grades.
Frequently Asked Questions About 4140 Alloy Steel
4140 is used for parts that need high strength, toughness, and wear resistance, including gears, shafts, axles, spindles, couplings, bolts and studs, hydraulic piston rods, tooling, fixtures, and oil and gas drill collars.
Yes. 4140 contains about 1% chromium, far below the roughly 10.5% needed for a stainless steel, so it will rust without protection. Parts are typically oiled, painted, plated, or nitrided for corrosion protection.
Yes, but its 0.40% carbon content makes it prone to cracking without the proper procedure. Preheating, controlled interpass temperature, and post-weld stress relief are recommended. For welded assemblies, 4130 is often the better choice.
Pre-hardened 4140 is quenched and tempered at the mill, typically to about 28 to 32 HRC. It can be machined directly into finished parts without a separate heat treatment step, which avoids distortion and saves lead time.
4340 adds nickel to the chromium-molybdenum chemistry of 4140. The nickel gives 4340 deeper hardenability and higher toughness in large sections, which is why it is specified for landing gear and other highly loaded aerospace parts. 4140 is the more economical choice for gears, shafts, and tooling.
Yes. Every 4140 shipment includes mill test reports with full traceability, and our quality management system is certified to ISO 9001 and AS9100.
Services
Quality System
Management
of specialty metals
Contact Us Today
Give us a call or fill out the form and our team will be in touch as soon as possible.
Company Headquarters
1751 California Ave.
Suite 103, Corona, CA 92881