300M is 4340 modified with roughly 1.6 percent silicon plus vanadium and a small molybdenum increase. The silicon raises the tempering temperature at which the steel keeps its strength, which lets 300M be tempered high enough to relieve stress while still delivering 280 to 300 ksi tensile strength.
It is the traditional ultra high strength landing gear steel, always vacuum melted, and is used where the structure has to carry very high loads in a limited envelope. Because strength is so high, surface condition, decarburization control, grinding practice and hydrogen control all become part of the process specification rather than afterthoughts.
We stock 300M as bar and forging billet, typically supplied annealed or normalized and tempered for machining and heat treated to the ordered class afterward.
Sizes and stock
- Round bar: through 11" DIA
- Flat bar: through 12" THK
- Custom shapes and forgings: per request
Processing capabilities
- Vacuum melted (VAR / VIM-VAR) stock with full melt traceability
- Normalize, anneal, quench and temper to the ordered condition
- Saw cutting, trepanning, gun drilling and rough machining
- Magnetic particle and ultrasonic inspection to AMS 2301 / AMS 2154 on request
Specifications
Material is released to the applicable specification with mill test reports and, on request, independent lab verification.
Why engineers specify 300M
- 280 to 300 ksi tensile strength with usable toughness
- Higher tempering temperature than 4340 for better stress relief and reduced hydrogen sensitivity
- Vacuum melted with full melt traceability
- Long service history on landing gear and high load structure
Nominal chemistry
Percent by weight, nominal composition per the governing specification. The mill test report for your heat is the controlling document.
Typical mechanical properties
| Condition | Tensile strength | Yield strength | Elongation | Hardness |
|---|---|---|---|---|
| Annealed | ~120 ksi | ~75 ksi | ~15% | - |
| Q&T, 280 ksi class | 280 ksi min | 230 ksi min | 8% min | 53-55 HRC |
Typical published values for reference only, not for design. Properties vary with section size, product form and processing. Order to the specification and condition your drawing requires.
Heat treatment and conditions
- 01Normalize around 1700F
- 02Austenitize around 1600F, oil quench
- 03Double temper around 575F to 600F for the 280 ksi class
- 04Bake to relieve hydrogen after plating or acid exposure, per the applicable process spec
If our stock is not already in the condition you need, we can quote the material with the heat treatment performed before it ships.
Typical applications
- Main and nose landing gear cylinders and pistons
- Arresting hooks and catapult hardware
- High load airframe fittings
- Heavy press and die tooling
Fabrication notes
Machining
Best machined in the annealed or normalized-and-tempered condition, then heat treated to final strength. Rough machining before hardening, with a finish pass after temper, controls distortion on long or thin sections. We can supply rough turned, trepanned or gun drilled stock so your first operation starts closer to net shape.
Welding
Weldable with low hydrogen practice, preheat appropriate to carbon equivalent and section size, and a post weld stress relief or full re-heat treat. For high strength conditions the weld and heat affected zone should be re-treated to restore properties.
Forming
Hot work in the annealed condition. Cold forming is limited at high hardness, so bend and form before hardening and follow with stress relief where the geometry is tight.
300M compared with similar grades
4340 VAR
Lower strength ceiling but easier processing and lower cost.
Aermet 100
Comparable strength with substantially better fracture toughness and stress corrosion resistance.
Designations and cross reference
- Material family
- Alloy Steels
Working from an obsolete, foreign or superseded designation? Send it over and we will cross reference it to a current grade and specification.
Quality, testing and traceability
Supplied aircraft quality with mill test reports, melt and heat traceability, and, on request, magnetic particle inspection to AMS 2301 or AMS 2300, ultrasonic inspection to AMS 2154, chemical assay, hardness and full mechanical testing.
We are AS9100D and ISO 9001:2015 registered. If our stock does not already carry the inspection your specification requires, we can quote the material with that work performed. More on our quality system
Available forms
Custom sizes converted from billet, plus saw cut, waterjet and near-net blanks. See custom conversions
300M frequently asked questions
What is 300M?
300M is 4340 modified with roughly 1.6 percent silicon plus vanadium and a small molybdenum increase. The silicon raises the tempering temperature at which the steel keeps its strength, which lets 300M be tempered high enough to relieve stress while still delivering 280 to 300 ksi tensile strength.
What forms is 300M available in?
We supply 300M in bar, forging. Custom sizes are converted from billet, and we can provide saw cut, waterjet or near net blanks so material arrives closer to your finished part.
What specifications can 300M be supplied to?
Commonly ordered specifications include AMS 6257, AMS 6419. Material is released to the specification and condition on your purchase order, with mill test reports supplied as standard.
What conditions can 300M be ordered in?
We can supply Annealed, Q&T, 280 ksi class. If our stock is not already in the condition you need, we can quote it with the heat treatment performed before shipment.
Can you cut 300M to size?
Yes. Saw cutting, waterjet, laser and shearing are available, along with trepanning, gun drilling, lathe turning and CNC machining, so you can order blanks or rough machined pieces rather than full lengths.
Do you provide test reports and additional testing on 300M?
Every order ships with mill test reports and heat traceability. If your print calls for ultrasonic inspection, penetrant dye, magnetic particle, chemical assay, micrography, hardness or mechanical testing and our stock does not already carry it, we can quote the material with that work performed.
Can 300M be supplied to DFARS domestic melt requirements?
Tell us at quote stage if the order is DFARS or domestic melt restricted and we will confirm availability against that requirement before you commit.
What do you need to quote 300M?
Grade, form, dimensions, quantity, specification and condition, plus any testing or certification requirements and the date you need it. Send a drawing if you have one. Quotes are typically ready within 24 hours.
How does 300M compare with 4340 VAR?
Lower strength ceiling but easier processing and lower cost.