300M Ultra-High-Strength Alloy Steel
4340 with about 1.6 percent silicon and vanadium for 280 ksi and above — one of the highest-strength low-alloy steels, and the standard landing-gear alloy.
What 300M is.
300M is 4340 modified with about 1.6 percent silicon, slightly more carbon and molybdenum, and a vanadium addition. Silicon moves the temper-embrittlement range to higher temperatures, so the steel can be tempered around 575 °F and reach about 280 ksi and above. It is supplied vacuum-arc remelted to AMS 6257, 6419 or 6417, and is the standard landing-gear steel; it also appears in motorsport and other high-performance hardware.
We machine 300M components, studs and pins from certified aerospace-quality bar, heat treat to the AMS strength range and finish grind where the drawing requires, with magnetic particle inspection after heat treatment.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | 0.40 | 0.44 |
| Manganese | Mn | 0.65 | 0.90 |
| Phosphorus | P | — | 0.010 |
| Sulfur | S | — | 0.008 |
| Silicon | Si | 1.45 | 1.80 |
| Nickel | Ni | 1.65 | 2.00 |
| Chromium | Cr | 0.70 | 0.95 |
| Molybdenum | Mo | 0.30 | 0.50 |
| Vanadium | V | 0.05 | 0.10 |
| Copper | Cu | — | 0.35 |
Limits per AMS 6257, confirmed by titanium.com, Service Steel Aerospace and Gautier Specialty Metals. AMS 6419 allows carbon 0.40–0.45 %; AMS 6417 is lower, about 0.38–0.43 %, and some sources give sulfur 0.010 % max for it.
Mechanical properties.
| Condition | Tensile strength (ksi) | Yield strength 0.2% offset (ksi) | Elongation (%) | Reduction of area (%) | Hardness |
|---|---|---|---|---|---|
| AMS 6417 minimum, quenched and double tempered | 270 | 220 | 8 | 30 | — |
| Typical, double tempered at 575 °F | 286–288 | 240–245 | 8.5–11 | 31–39 | about 53 HRC |
AMS 6417 minimums confirmed by Service Steel Aerospace and Aircraft Materials. AMS 6419 and 6257 set their own minimums; confirm the requirement on your order with our estimating team. Typical values are from the Latrobe (Carpenter) Lescalloy 300M VAC-ARC datasheet, transverse, 12 to 28 in. sections.
Specifications that apply.
How 300M ships from Houston.
- Machined components from certified bar
- Studs, threaded rod and U-bolts
- Hex bolts and cap screws
- Nuts, washers and spacers
- Pins, shafts and bushings
300M fasteners we make.
Every item is manufactured to your drawing or standard in 300M, imperial or metric, with an EN 10204 3.1 certificate.
What is 300M steel?
300M is one of the strongest low-alloy steels in regular use. Its extra silicon shifts the tempering behaviour so the steel can be tempered around 575 °F, above the embrittlement range that limits 4340, and the result is about 280 ksi tensile and above. That strength comes with rules: the steel is sensitive to hydrogen, so plated parts must be baked, and it is not a corrosion-resistant material, so it needs a protective finish.
Testing, certification and marking
- Tensile and hardness per heat-treat lot; Charpy on request
- Magnetic particle inspection after heat treatment
- Hydrogen embrittlement bake logged after plating
- EN 10204 3.1 material test report; 3.2 witness available
AISI 4340 Alloy Steel (UNS G43400)
The deep-hardening high-strength steel — 4340 reaches 155 ksi and beyond in large sections — for crankshafts, drilling tools, aircraft parts and A320 L43 bolting.
AMS 6427 (aircraft quality) · AMS 6411 (vacuum-arc remelted)4330V Modified Alloy Steel
A 4340-class steel with lower carbon and a vanadium addition for toughness: 220 to 240 ksi with good impact resistance — the aerospace and oil-tool grade for highly stressed components.
ASTM A322 bar · ASTM A434 Q&T barAISI 4140 Alloy Steel (UNS G41400)
The workhorse Cr-Mo steel behind B7, L7 and Grade 7 — the bar stock for studs, shafts, couplings and any part that needs 100 to 150 ksi and good toughness.