300M Alloy Steel (UNS K44220)
Ultra-high-strength low-alloy steel — ~1930–2070 MPa with the toughness demanded of landing-gear-class parts.
- UNS
- K44220
- W.Nr / EN
- Modified 4340 (Si–V)
- Density
- 7.83 g/cm³
- Service range
- Ambient structural service
About 300M Alloy Steel
300M is 4340 rebuilt for the 1900–2100 MPa class: raised silicon delays temper embrittlement so the steel can be tempered low for maximum strength, while vanadium refines grain and a slightly higher carbon secures hardenability in heavy sections. It is normally produced by vacuum-arc remelting for fatigue-critical cleanliness.
The grade is the historic and current benchmark for landing-gear structures and other ultra-high-strength airframe parts. DMK Alloys supplies 300M as remelted bars and forged blanks with heat treatment and testing per order.
300M Alloy Steel chemical composition (weight %)
| Element | Limit / range |
|---|---|
| Fe | Balance |
| C | 0.40 – 0.45 |
| Si | 1.45 – 1.80 |
| Mn | 0.65 – 0.90 |
| Cr | 0.70 – 0.95 |
| Ni | 1.65 – 2.00 |
| Mo | 0.30 – 0.45 |
| V | ≥ 0.05 |
Composition limits per the commonly referenced standards listed below. Order-specific limits may differ — confirm against the governing specification.
300M Alloy Steel mechanical properties (typical)
| Condition / form | Tensile, MPa | 0.2% Yield, MPa | Elongation, % |
|---|---|---|---|
| Bar, quenched + tempered (280 ksi class) | 1930 – 2070 | ≥ 1590 | ≥ 8 |
Values are typical or specification-minimum levels for guidance only — not a guarantee of properties. Certified values are established by testing against the ordered specification.
300M Alloy Steel specifications & international equivalents
| System | Designation | Covers |
|---|---|---|
| UNS | K44220 | All product forms |
| AMS | AMS 6257 | Bars, forgings (VAR premium) |
| AMS | AMS 6417 | Bars, forgings |
| AMS | AMS 6419 | Bars, forgings (CEVM) |
Cross-references are for guidance; the governing document is always the specification cited on your purchase order or drawing.
300M Alloy Steel physical properties
| Property | Typical value |
|---|---|
| Density | 7.83 g/cm³ |
| Melting range | ≈ 1425 °C |
| Modulus of elasticity (family-typical) | ≈ 190 – 210 GPa |
| Indicative service range | Ambient structural service |
Forms we manufacture
- Remelted bars
- Forged blanks
- Machined components to drawing
Dimensional ranges and delivery conditions are confirmed per enquiry.
Where 300M Alloy Steel earns its keep
Typically specified for:
- Landing-gear components
- Flap tracks
- Axles
- Other ultra-high-strength structural parts
Also consider
15-5PH Stainless
UNS S15500 · W.Nr 1.4545AMS 5659 · ASTM A564 XM-12
The ferrite-free refinement of 17-4PH: better transverse toughness for critical forged and premium-melted parts.
4340 Alloy Steel
UNS G43400AMS 6414 · AMS 6415
The reference nickel–chromium–molybdenum steel: deep hardenability with dependable toughness across strength levels.
440C Stainless
UNS S44004 · W.Nr 1.4125AMS 5630 · AMS 5618
The hardest standard stainless steel: bearing-grade wear resistance at up to ~60 HRC with corrosion protection.
Request 300M Alloy Steel to your specification
State the governing standard, form, dimensions, quantity and testing requirements — the export team responds with a manufacturer's quotation.