Steel 300M · heat-treated state
Steel 300M Q&T
Properties of the Q&T condition, compared with the other 300M tempers.
Standard aerospace 280 ksi condition — pick for landing gear, shafts and fittings needing maximum strength with usable toughness.
What is 300M Q&T?
300M Q&T is 300M heat treated to Q&T — standard aerospace 280 ksi condition — pick for landing gear, shafts and fittings needing maximum strength with usable toughness. 300M Q&T has a yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 98% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi). 300M Q&T 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). HR is the default condition FabDigit quotes; Q&T is available on request or by drawing note.
Advantages
- High strength — 1,620 MPa (235 ksi), better than 98% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited formability — 5/100, worse than 99% of steel grades
- Difficult to machine — 15/100, worse than 98% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- High embodied carbon — 2.8 kg CO₂/kg, worse than 90% of steel grades
300M Q&T properties
Typical room-temperature values for 300M Q&T — 16 properties are specific to this condition; the rest are grade-level values shared by every 300M temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
300M Q&T 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 Q&T has a yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 98% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
300M Q&T is rated for continuous service to 290°C (554 °F). It conducts heat at 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 74% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
300M Q&T conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 300M Q&T 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 Q&T's machinability is poor (15/100, worse than 98% of steel grades); weldability not recommended (10/100); formability not recommended (5/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 300M tempers and conditions
300M is also supplied in 8 other conditions. The full side-by-side table is on the 300M overview.
- HRDefaultPick for stock removal blanks and forging stock where the customer performs all final heat treatment.760 MPa yield · 34 HRC
- Q&TStandard aerospace 280 ksi condition — pick for landing gear, shafts and fittings needing maximum strength with usable toughness.1,620 MPa yield · 53 HRC
- As PrintedPick 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 MPa yield · 51 HRC
- HIPPick for additively manufactured or powder 300M parts needing full density and isotropic properties before final quench and temper.1,150 MPa yield · 44 HRC
- NormalizedPick for grain refinement of forgings/bar and a machinable intermediate state before final heat treatment.1,000 MPa yield · 41 HRC
- AnnealedSoftest supply condition — pick for rough machining of forgings and billets before final quench and temper.700 MPa yield · 31 HRC
Working with 300M Q&T
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.
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.
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 | — |
300M Q&T — frequently asked
What is 300M Q&T used for?
300M Q&T 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 Q&T?
300M Q&T has a typical yield strength of 1,620 MPa (235 ksi) and a tensile strength of 1,930 MPa (280 ksi) — stronger than 98% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 300M Q&T easy to machine?
Not especially — machinability is rated poor (15/100, worse than 98% 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 Q&T be welded?
Not readily — weldability is rated not recommended (10/100). 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 Q&T?
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 Q&T 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 Q&T?
300M Q&T is rated for continuous use to about 290°C (554 °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.
Can FabDigit make parts in 300M Q&T?
Yes — 300M Q&T is available for CNC machining and sheet metal with instant online pricing. 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.