Steel 300M
300M is a silicon- and vanadium-modified 4340 low-alloy ultrahigh-strength steel, normally vacuum melted (VIM/VAR) and used quenched and tempered to about 1930 MPa (280 ksi) with better toughness and hardenability than plain 4340.
Values for the HR condition
300M tempers and conditions
300M is supplied in 9 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/spheroidize anneal (~650–680 °C soak, slow cool) for machining and inspection | Softest supply condition — pick for rough machining of forgings and billets before final quench and temper. | 700 | 1,030 | 14 | 31 HRC | — |
HRDefault Hot rolled | Pick for stock removal blanks and forging stock where the customer performs all final heat treatment. | 760 | 1,100 | 12 | 34 HRC | 8 % IACS |
Cold drawn | Pick for close-tolerance small-diameter bar to be finish heat treated; cold work is limited by the alloy's high work-hardening rate. | 950 | 1,150 | 9 | 36 HRC | 7.5 % IACS |
Cold rolled | Pick only for thin sheet/strip feedstock; heavy cold reduction of 300M is impractical and parts are heat treated after forming. | 1,000 | 1,200 | 7 | 38 HRC | 7.5 % IACS |
~900 °C air cool plus high temper for machinable, uniform structure | Pick for grain refinement of forgings/bar and a machinable intermediate state before final heat treatment. | 1,000 | 1,300 | 11 | 41 HRC | — |
Hot isostatic pressed | Pick for additively manufactured or powder 300M parts needing full density and isotropic properties before final quench and temper. | 1,150 | 1,450 | 10 | 44 HRC | 7 % IACS |
laser powder-bed fusion / DED, as-built (untempered martensite, residual stress) | Pick only for geometry trials — as-built 300M is hard, highly stressed and low in ductility, and normally must be HIP'd and Q&T'd. | 1,200 | 1,650 | 4 | 51 HRC | — |
sub-critical stress relief (typically at or just below the tempering temperature) | Pick after rough machining, straightening or grinding of hardened parts to cut residual stress without losing strength. | 1,600 | 1,900 | 9 | 52 HRC | 7 % IACS |
Quenched and tempered | Standard aerospace 280 ksi condition — pick for landing gear, shafts and fittings needing maximum strength with usable toughness. | 1,620 | 1,930 | 9 | 53 HRC | — |
What is 300M?
300M is a silicon- and vanadium-modified 4340 low-alloy ultrahigh-strength steel, normally vacuum melted (VIM/VAR) and used quenched and tempered to about 1930 MPa (280 ksi) with better toughness and hardenability than plain 4340. It is the classic material for landing gear, actuator rods, arresting-gear and highly loaded shafts where strength-to-weight and section hardenability matter more than cost. Limits are almost no corrosion resistance (requires cadmium/IVD-Al or chrome plating with hydrogen-embrittlement relief bake), high notch/hydrogen sensitivity, difficult machining at full hardness and a service ceiling near the ~300 °C tempering temperature. 300M has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F). 300M has a yield strength of 760 MPa (110 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 85% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi).
What is 300M used for?
- Landing gear components
- Aircraft actuator rods and pistons
- Arresting-gear components
- Highly loaded drive shafts
- Torsion bars
- High-strength structural fasteners
- Airframe structural forgings
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- High strength — 760 MPa (110 ksi), better than 85% of steel grades
Limitations
- High embodied carbon — 2.8 kg CO₂/kg, worse than 90% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Limited formability — 18/100, worse than 84% of steel grades
- Difficult to machine — 38/100, worse than 80% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
300M properties
Typical room-temperature values for 300M-HR; bars are the position among steel grades.
Physical3
300M has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
300M has a yield strength of 760 MPa (110 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 85% of steel grades. Elongation at break is 12% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
300M is rated for continuous service to 400°C (752 °F). It conducts heat at 40 W/m·K (23.1 BTU/hr·ft·°F), worse than 64% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
300M conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 300M takes about 40 MJ of energy and emits 2.8 kg of CO₂ — more than 91% of steel grades. Typical recycled content is 20%.
Manufacturability8
300M's machinability is fair (38/100, worse than 80% of steel grades); weldability poor (25/100); formability poor (18/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 300M is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 300M
Is 300M easy to machine?
Rough machine annealed (≈300 HB) with rigid setups and carbide; at 51–55 HRC use CBN/ceramic hard turning or grinding, low stock removal and no sharp corners to avoid grinding burn and residual tensile stress.
Can 300M be welded?
Not recommended for primary structure — high hardenability and Si content make it crack-sensitive; if welded, use matching or low-hydrogen filler with 260–320 °C preheat, immediate post-weld temper and full re-heat-treatment.
Can 300M be formed, bent or molded?
Hot forge 1050–1180 °C with slow cooling and immediate anneal; cold forming is impractical, so form or bend in the annealed state only and heat treat afterwards.
Manufacturability
The process limits FabDigit applies to 300M. Every 300M part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair38 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair18 / 100 |
|---|---|
| Weldability | Fair25 / 100 |
300M chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CAMS 6417/6419 | 0.38 – 0.43 | 0.4 |
| Siraises tempering resistance vs 4340 | 1.45 – 1.8 | 1.6 |
| Mn | 0.6 – 0.9 | 0.75 |
| Cr | 0.7 – 0.95 | 0.82 |
| Ni | 1.65 – 2 | 1.82 |
| Mo | 0.3 – 0.45 | 0.38 |
| V0.05 % min; grain refinement | 0.05 – 0.1 | 0.07 |
| Cu | ≤ 0.35 | |
| P | ≤ 0.01 | |
| Spremium (VIM/VAR) melting typically ≤0.005 | ≤ 0.01 | |
| Fe | balance |
What surface finishes work on 300M?
Always protect: cadmium, IVD aluminium, nickel-chrome or shot-peen-plus-primer; grind before plating, keep temper below the tempering temperature and bake 190 °C ≥8–23 h after plating to relieve hydrogen.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
How much does 300M cost?
300M is a specialty-cost steel ($$$$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
300M — frequently asked
What is 300M used for?
300M is typically used for landing gear components, aircraft actuator rods and pistons, arresting-gear components, highly loaded drive shafts, torsion bars and high-strength structural fasteners. In short: extreme tensile strength.
What is the yield strength of 300M?
300M has a typical yield strength of 760 MPa (110 ksi) and a tensile strength of 1,100 MPa (160 ksi) — stronger than 85% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 300M easy to machine?
Not especially — machinability is rated fair (38/100, worse than 80% of steel grades). Rough machine annealed (≈300 HB) with rigid setups and carbide; at 51–55 HRC use CBN/ceramic hard turning or grinding, low stock removal and no sharp corners to avoid grinding burn and residual tensile stress.
Can 300M be welded?
Not readily — weldability is rated poor (25/100). Not recommended for primary structure — high hardenability and Si content make it crack-sensitive; if welded, use matching or low-hydrogen filler with 260–320 °C preheat, immediate post-weld temper and full re-heat-treatment.
What surface finishes work on 300M?
Always protect: cadmium, IVD aluminium, nickel-chrome or shot-peen-plus-primer; grind before plating, keep temper below the tempering temperature and bake 190 °C ≥8–23 h after plating to relieve hydrogen.
Can 300M be formed, bent or molded?
Hot forge 1050–1180 °C with slow cooling and immediate anneal; cold forming is impractical, so form or bend in the annealed state only and heat treat afterwards.
What is the maximum service temperature of 300M?
300M is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 300M-HR and 300M-HIP?
HR is the default condition — pick for stock removal blanks and forging stock where the customer performs all final heat treatment. HIP: pick for additively manufactured or powder 300M parts needing full density and isotropic properties before final quench and temper. Yield strength is 760 MPa in HR versus 1,150 MPa in HIP.
How much does 300M cost?
300M is a specialty-cost steel ($$$$$), pricier than about 58% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 300M?
Yes — 300M is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- AMS 6417 — Steel Bars, Forgings and Tubing 0.95Cr-1.8Ni-0.35Mo-0.09V (300M), Consumable Electrode Vacuum Melted — SAE International (2020)
- AMS 6419 — Steel Bars and Forgings, Premium Quality, 300M, Heat Treated to 1930 MPa — SAE International (2019)
- MMPDS-17, Metallic Materials Properties Development and Standardization (300M section) — Battelle/FAA (2022)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
- Ultra-high-strength steel 300M bar and forging datasheet — Carpenter/Latrobe & Aubert&Duval typical data (2021)
- GB/T 6478 / 40CrNi2Si2MoVA (2015)
- 40CrNi2Si2MoVA/300M — Mysteel / 1688 (2026)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.