Steel 4335V (Modified 4340)-QT280
Heat-treated state
also 4335V Mod
QT280 = q&T 1930 MPa
Only for strength-critical, low-fracture-risk parts; very hydrogen- and notch-sensitive, tight process control required.
Values for the QT280 condition
Other 4335V (Modified 4340) tempers and conditions
4335V (Modified 4340) is listed in 8 conditions; see the grade overview at 4335V (Modified 4340).
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full anneal, soft condition for deep machining/forming | Pick for maximum machinability or cold straightening before final quench and temper. | 620 | 800 | 20 | 210 HB | — |
Normalized and tempered | The as-supplied mill condition: rough-machine here, then quench and temper to the required strength level. | 900 | 1,080 | 15 | 33 HRC | — |
Q&T 1240 MPa | Choose when fracture toughness and impact energy dominate over peak static strength. | 1,140 | 1,240 | 15 | 40 HRC | — |
Q&T 1380 MPa | Balanced strength/toughness level for actuators, shafts and structural fittings. | 1,240 | 1,380 | 13 | 43 HRC | — |
QT220Default Q&T 1520 MPa | The standard landing-gear / high-load fitting condition where 4335V's vanadium-refined grain buys extra toughness over 4340. | 1,380 | 1,520 | 12 | 46 HRC | — |
VAR / CEVM | Specify for fatigue- and fracture-critical landing-gear forgings: lower gas/inclusion content raises transverse ductility and K_IC at the same strength. | 1,380 | 1,520 | 13 | 46 HRC | 8 % IACS |
Q&T 1655 MPa | Use where section size or weight forces 240 ksi; toughness and HE tolerance drop noticeably. | 1,450 | 1,655 | 10 | 49 HRC | — |
QT280This page Q&T 1930 MPa | Only for strength-critical, low-fracture-risk parts; very hydrogen- and notch-sensitive, tight process control required. | 1,620 | 1,930 | 8 | 53 HRC | — |
What is 4335V (Modified 4340)-QT280?
4335V (Modified 4340)-QT280 is 4335V (Modified 4340) heat treated to QT280 — only for strength-critical, low-fracture-risk parts; very hydrogen- and notch-sensitive, tight process control required. 4335V (Modified 4340)-QT280 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 8% and the elastic modulus is 200 GPa (29 Msi). 4335V (Modified 4340)-QT280 has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,416°C (2,581 °F). QT220 is the default condition FabDigit quotes; QT280 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 — 78/100, better than 95% of steel grades
Limitations
- Difficult to machine — 12/100, worse than 99% of steel grades
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited ductility — 8%, worse than 95% of steel grades
- Limited formability — 10/100, worse than 95% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
4335V (Modified 4340)-QT280 properties
Typical room-temperature values for 4335V (Modified 4340)-QT280; 15 are specific to this condition. Other listed values are 4335V (Modified 4340) reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4335V (Modified 4340)-QT280 has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
4335V (Modified 4340)-QT280 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 8% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
4335V (Modified 4340)-QT280 is rated for continuous service to 200°C (392 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4335V (Modified 4340)-QT280 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 4335V (Modified 4340)-QT280 takes about 34 MJ of energy and emits 2.6 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 25%.
Manufacturability7
4335V (Modified 4340)-QT280's machinability is not recommended (12/100, worse than 99% of steel grades); weldability not recommended (12/100); formability not recommended (10/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4335V (Modified 4340)-QT280
Is 4335V (Modified 4340) easy to machine?
Rough machine in the normalized-and-tempered or annealed state; at 45+ HRC use rigid setups, negative-rake carbide or CBN, low speed and heavy coolant, and grind/EDM only with stress-relief to avoid untempered martensite.
Can 4335V (Modified 4340) be welded?
Weldable only with matching low-alloy filler, 250–320 °C preheat, tight interpass control and immediate post-weld temper/re-heat-treat; hydrogen-free consumables mandatory and welding is normally avoided on flight-critical Q&T parts.
Can 4335V (Modified 4340) be formed, bent or molded?
Hot forge 1150–1200 °C, finish above 950 °C, then normalize before hardening; cold forming is essentially limited to the annealed state — no cold bending after quench and temper.
What surface finishes work on 4335V (Modified 4340)?
Requires protective coating: low-embrittlement Cd, Ni-Cr, IVD aluminium or WC-Co HVOF for gear bores, always with 190 °C/23 h hydrogen bake after plating; shot peening is standard for fatigue-critical surfaces.
4335V (Modified 4340) 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 |
|---|---|---|
| Cslightly lower than 4340 for toughness | 0.33 – 0.38 | 0.35 |
| Mn | 0.6 – 0.9 | 0.75 |
| Sielevated Si — raises tempering resistance and toughness | 0.65 – 0.9 | 0.75 |
| Cr | 0.75 – 0.95 | 0.85 |
| Ni | 1.65 – 2 | 1.82 |
| Mo | 0.3 – 0.4 | 0.35 |
| Vgrain refiner; 0.05 % min per AMS 6429 | 0.05 – 0.1 | 0.06 |
| P | ≤ 0.01 | — |
| S | ≤ 0.01 | — |
| Cumax, residual | ≤ 0.35 | — |
| Fe | balance | — |
4335V (Modified 4340)-QT280 — frequently asked
What is 4335V (Modified 4340)-QT280 used for?
4335V (Modified 4340)-QT280 is typically used for landing gear cylinders and forgings, landing gear axles, high-strength structural shafts, wing and fuselage attachment fittings, hinge and lug pins and hydraulic actuator rods. In short: tougher than standard 4340; landing gear forging steel; VAR fine-grain quality.
What is the yield strength of 4335V (Modified 4340)-QT280?
4335V (Modified 4340)-QT280 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 8 listed tempers.
Is 4335V (Modified 4340)-QT280 easy to machine?
Not especially — machinability is rated not recommended (12/100, worse than 99% of steel grades). Rough machine in the normalized-and-tempered or annealed state; at 45+ HRC use rigid setups, negative-rake carbide or CBN, low speed and heavy coolant, and grind/EDM only with stress-relief to avoid untempered martensite.
Can 4335V (Modified 4340)-QT280 be welded?
Not readily — weldability is rated not recommended (12/100). Weldable only with matching low-alloy filler, 250–320 °C preheat, tight interpass control and immediate post-weld temper/re-heat-treat; hydrogen-free consumables mandatory and welding is normally avoided on flight-critical Q&T parts.
What surface finishes work on 4335V (Modified 4340)-QT280?
Requires protective coating: low-embrittlement Cd, Ni-Cr, IVD aluminium or WC-Co HVOF for gear bores, always with 190 °C/23 h hydrogen bake after plating; shot peening is standard for fatigue-critical surfaces.
Can 4335V (Modified 4340)-QT280 be formed, bent or molded?
Hot forge 1150–1200 °C, finish above 950 °C, then normalize before hardening; cold forming is essentially limited to the annealed state — no cold bending after quench and temper.
What is the maximum service temperature of 4335V (Modified 4340)-QT280?
4335V (Modified 4340)-QT280 is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4335V (Modified 4340)-QT220 and 4335V (Modified 4340)-QT180?
QT220 is the default condition — the standard landing-gear / high-load fitting condition where 4335V's vanadium-refined grain buys extra toughness over 4340. QT180: choose when fracture toughness and impact energy dominate over peak static strength. Yield strength is 1,380 MPa in QT220 versus 1,140 MPa in QT180.
Sources
- AMS 6429 — Steel Bars, Forgings and Tubing 1.8Ni-0.80Cr-0.35Mo-0.05V (0.33-0.38C), Consumable Electrode Vacuum Remelted — SAE International (2020)
- AMS 6435 / AMS 2759 heat-treatment practice for low-alloy steels — SAE International (2019)
- 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)
- 4335V Mod aircraft-quality alloy steel bar datasheet — Carpenter Technology / Latrobe Specialty Metals (2019)
- Aerospace Structural Metals Handbook — Ni-Cr-Mo ultra-high-strength steels — CINDAS (2010)
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.