300M Steel
A Ni-Cr-Mo-Si-V ultra-high-strength alloy steel
Typical values for the temper in the title
300M is 4340 with added silicon (about 1.6%) and vanadium. Silicon allows tempering at a higher temperature without losing strength, so it reaches about 1930 MPa tensile and more, with better toughness than 4340 at the same strength.
It is the classic material for aircraft landing gear, and is also used for ultra-high-strength shafts and structural parts. It is produced by vacuum remelting.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 1930 MPa | |
| Yield strength Rp0.2 | 1690 MPa | |
| Elongation A | 7% | |
| Hardness | 530-570 HB | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 7.83 g/cm³ | |
| Machinability | 25% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| C carbon | about 0.42 (nominal) | strength |
| Si silicon | about 1.6 (nominal) | allows a higher temper |
| Ni nickel | about 1.8 (nominal) | toughness and hardenability |
| Cr chromium | about 0.8 (nominal) | hardenability |
| Mo molybdenum | about 0.4 (nominal) | hardenability |
| V vanadium | about 0.08 (nominal) | fine grains |
| Fe iron | balance |
Nominal (typical) composition. Exact ranges are defined in the AMS specifications. Equivalents in other standards are close in composition, not identical.
Conditions and heat treatment
In alloy steels, chromium, molybdenum and nickel raise hardenability: thicker parts reach full hardness even at the center. Properties are set mainly by heat treatment.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed / normalized and tempered | for machining | delivery condition |
| Hardened and tempered | tensile strength about 1930 MPa and more | landing gear |
Applications
- Aircraft landing gear
- Ultra-high-strength shafts
- Aerospace structural parts
- Critical bolts
- Racing parts
Fabrication
Hydrogen embrittlement
At this strength the material is very sensitive to hydrogen: electroplating requires immediate baking, and alternative processes are often used.
Surface
Shot peening and controlled grinding are critical for fatigue. Improper grinding can burn the surface.
Welding
Not suited to welding.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 4340 | 1080–1470 / 970–1380 MPa | Difficult — Preheat 200C | the base version, lower strength · material page |
| 4330V | 1170 / 1070 MPa | Medium | high toughness, lower strength · material page |
| 17-4 PH (630) | 930–1310 / 725–1170 MPa | Excellent | a PH stainless, corrosion resistant · material page |
Common mistakes
Plating without baking
Hydrogen from plating causes delayed fracture.
Aggressive grinding
Grinding burn creates cracks and lowers fatigue resistance.
Welding 300M
The material is not suited to welding.
Equivalents, standards and supply
| Standards | AMS 6417 / MIL-S-8844 |
|---|---|
| Forms | rod · forging |
| Producers | Latrobe · Carpenter · TimkenSteel |
Learn more
Values are typical and for comparison only, and depend strongly on condition and diameter. For design, rely on the standard and on the mill certificate. Sources: SAE J403 and J404, ASTM A29, A322 and A519 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026