Aerospace and Maraging Steel
Aerospace steels are the grades chosen when nothing lighter reaches the required strength in the available space: landing gear, actuator pistons, rocket motor cases, helicopter transmission gears. Maraging steels (Maraging 250, Maraging 300, C300) are 18 % Ni-Co-Mo alloys with almost no carbon that harden to 1,700–2,000 MPa yield by a single 480 °C age with negligible distortion; the quenched-and-tempered ultrahigh-strength group (E4340, 300M, AF1410, AerMet 310, HP9-4-30) reaches 1,500–1,900 MPa with higher fracture toughness; 9310 is the carburizing grade for aerospace gears and 15CDV6 the weldable steel for motor cases.
Popular aerospace steel grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Maraging 300 | 800 | 1,010 | 8 | Fair | Very good | About 2,000 MPa with minimal age distortion |
| Maraging 250 | 810 | 1,010 | 8 | Fair | Very good | Tougher maraging grade for shafts and tooling |
| C300 | 850 | 1,050 | 8 | Fair | Very good | Vacuum-melted Maraging 300 for flight hardware |
| E4340 | 620 | 950 | 7.85 | Fair | Poor | Vacuum-melted 4340 for landing gear |
| 9310 | 600 | 950 | 7.85 | Fair | Fair | Carburized aerospace gears and pinions |
| 15CDV6 | 650 | 900 | 7.85 | Fair | Very good | Weldable motor cases and roll bars |
| AF1410 | 1,520 | 1,660 | 7.89 | Poor | Good | High-toughness structure at 1,700 MPa tensile |
Choose aerospace steel for
Landing gear and arresting hooks, actuator rods and pistons, helicopter and turboprop gears and shafts, rocket motor cases, high-load springs and fasteners, and die-casting dies or mold inserts that must be hardened without distortion — where strength per cubic centimetre and dimensional control justify the material.
Look elsewhere when
The design works at 1,000–1,300 MPa (4340 or 300M in the alloy group are cheaper and more available), the part must resist corrosion bare (17-4 PH or 13-8 PH stainless, or Custom 465 at similar strength), the section is thin and weight matters most (Ti-6Al-4V gives comparable specific strength with no coating), or the part is a plain hardened shaft (4140 quenched and tempered is enough).
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Aerospace steel by application
- Landing gear, hooks and actuators
- E4340 and 300M quenched and tempered to 1,650–1,950 MPa tensile, shot-peened and plated; AF1410, AerMet 310 or Ferrium M54 where fracture toughness at that strength decides; Ferrium S53 when bare corrosion resistance must replace cadmium plating.
- Transmission gears and shafts
- 9310 carburized to 58–62 HRC on the teeth over a tough core; Maraging 250 or Maraging 300 for shafts, splines and housings that need strength through the section with negligible heat-treat distortion.
- Motor cases and welded structure
- 15CDV6 welded, then hardened and tempered to about 1,000 MPa for solid-rocket motor cases and roll cages; HP9-4-20 and HP9-4-30 for thicker welded sections at higher strength.
- Tooling that must not move
- Maraging 300 and C300 for die-casting dies, mold inserts and cold-forging punches machined to size at about 30 HRC and aged to 52–54 HRC with almost no distortion; the same grade is the standard maraging steel for laser powder-bed printing.
Working with aerospace steel
- Machining
- Maraging steels are supplied solution-annealed at about 30–35 HRC and machine like 4140 in that state — finish machine, then age. E4340 and 300M are rough-machined annealed or normalized, heat-treated, then finish-ground; anything above 50 HRC is ground or hard-turned with CBN. 9310 machines easily before carburizing; SUH660 machines like a gummy stainless.
- Heat treatment
- Maraging: solution anneal at about 820 °C, air cool, age at 480 °C for 3–6 hours; shrinkage under 0.1 %, no quench cracking, no decarburized skin to grind off. E4340 / 300M: austenitize at about 870 °C, oil quench, double temper (300M at about 300 °C for 1,950 MPa). Vacuum or protective-atmosphere furnaces and certified procedures (AMS 2759) are the norm for flight parts.
- Welding
- Maraging steel welds well by TIG or electron beam in the annealed state with matching filler and needs only the age afterwards to bring the joint close to base-metal strength; 15CDV6 and the HP9-4 grades are designed to be welded and then heat-treated. E4340 and 300M are welded only for repair, with preheat, immediate post-heat and re-tempering — hydrogen cracking is the risk.
- Finishing
- Bare maraging and low-alloy ultrahigh-strength steels rust and are highly sensitive to hydrogen embrittlement: electroplating (cadmium, hard chrome, nickel) requires a 190 °C hydrogen-relief bake within hours of plating under AMS 2759 / ASTM F519 practice; HVOF tungsten carbide or physical vapour deposition avoids the problem. Shot peening to specification is standard on gear roots and fatigue-critical fillets.
Other steel series
- Low-Carbon and Mild Steel
- Medium and High-Carbon Steel
- Free-Machining Steel
- Alloy Steel
- Case-Hardening Steel
- Tool Steel
- Mold Steel
- Spring and Bearing Steel
- Structural and HSLA Steel
- Wear Plate and Advanced High-Strength Steel
- Pressure Vessel and Chromium-Molybdenum Steel
- Electrical Steel and Soft Magnetic Alloys
- Cast Steel
- Cast Iron
- Steel Welding Consumables
Aerospace and Maraging Steel — frequently asked
What is aerospace steel?
Aerospace steels are the grades chosen when nothing lighter reaches the required strength in the available space: landing gear, actuator pistons, rocket motor cases, helicopter transmission gears. Maraging steels (Maraging 250, Maraging 300, C300) are 18 % Ni-Co-Mo alloys with almost no carbon that harden to 1,700–2,000 MPa yield by a single 480 °C age with negligible distortion; the quenched-and-tempered ultrahigh-strength group (E4340, 300M, AF1410, AerMet 310, HP9-4-30) reaches 1,500–1,900 MPa with higher fracture toughness; 9310 is the carburizing grade for aerospace gears and 15CDV6 the weldable steel for motor cases.
Which grade of aerospace steel should I use?
Maraging 300 (C300 when vacuum-melted for flight hardware) is the default when a part needs about 2,000 MPa tensile and must be machined close to finished size before hardening — the 480 °C age shrinks it by less than 0.1 %. Maraging 250 gives up about 15 % strength for better toughness and is the common tooling and shaft grade. E4340 and 300M are the landing-gear steels; AF1410 and AerMet 310 when fracture toughness and stress-corrosion resistance at 1,700–1,900 MPa are the requirement; HP9-4-20 and HP9-4-30 for weldable thick-section structure. 9310 is carburized for gears and pinions that carry high tooth loads at speed; 15CDV6 (0.15 C, Cr-Mo-V) is welded, then heat-treated to about 1,000 MPa for rocket cases and roll bars. SUH660 (the A-286 class) is the iron-based superalloy for fasteners and rings to about 700 °C.
Which grade of aerospace steel is the strongest?
18Ni(400) has the highest yield strength in the series at 2,680 MPa; 18Ni(350) Maraging Steel follows at 2,320 MPa. Values are for each grade's default condition.
Which grade of aerospace steel is easiest to machine?
15CDV6 (machinability fair, 50/100), then 18NiCrMo14-6 (45/100).
Is aerospace steel heat-treatable?
Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.
Maraging 300 or 4340 / 300M?
At the same 1,900–2,000 MPa, Maraging 300 wins on heat treatment: it is machined to finished size in the soft state and aged at 480 °C with less than 0.1 % shrinkage and no quench, so complex or thin parts stay in tolerance. 300M reaches similar strength through oil quench and temper at lower material cost and with higher surface hardness for wear, but it distorts, decarburizes and must be finish-ground afterwards. Maraging steel has comparable or better toughness at equal strength; 300M has the longer aerospace qualification record for landing gear.
Why is E4340 different from 4340?
E4340 is the same chemistry melted under vacuum (consumable-electrode remelt, AMS 6414) to hold oxygen, sulphur and inclusions far lower than air-melt 4340. The cleaner steel has markedly better transverse fatigue life and fracture toughness in the 1,800–1,950 MPa condition, and flight hardware such as landing gear is specified to it. For a ground shaft heat-treated to 1,000–1,300 MPa, ordinary 4340 (or 34CrNiMo6 / EN24) performs the same at lower cost.