Steel E4340 · hardness band
Steel E4340 Q&T 36-40 HRC
Properties of the Q&T 36-40 HRC condition, compared with the other E4340 tempers.
Higher-strength band for gears, torsion bars and highly loaded shafting.
What is E4340 Q&T 36-40 HRC?
E4340 Q&T 36-40 HRC is E4340 heat treated to Q&T 36-40 HRC — higher-strength band for gears, torsion bars and highly loaded shafting. E4340 Q&T 36-40 HRC has a yield strength of 1,160 MPa (168 ksi) and a tensile strength of 1,270 MPa (184 ksi) — stronger than 94% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi). E4340 Q&T 36-40 HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,427°C (2,601 °F). HR is the default condition FabDigit quotes; Q&T 36-40 HRC is available on request or by drawing note.
Advantages
- High strength — 1,160 MPa (168 ksi), better than 94% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Difficult to machine — 36/100, worse than 81% of steel grades
E4340 Q&T 36-40 HRC properties
Typical room-temperature values for E4340 Q&T 36-40 HRC — 12 properties are specific to this condition; the rest are grade-level values shared by every E4340 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
E4340 Q&T 36-40 HRC has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,427°C (2,601 °F).
Mechanical16
E4340 Q&T 36-40 HRC has a yield strength of 1,160 MPa (168 ksi) and a tensile strength of 1,270 MPa (184 ksi) — stronger than 94% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
E4340 Q&T 36-40 HRC is rated for continuous service to 400°C (752 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
E4340 Q&T 36-40 HRC conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of E4340 Q&T 36-40 HRC takes about 30 MJ of energy and emits 2.3 kg of CO₂ — more than 55% of steel grades. Typical recycled content is 40%.
Manufacturability8
E4340 Q&T 36-40 HRC's machinability is fair (36/100, worse than 81% of steel grades); weldability poor (30/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other E4340 tempers and conditions
E4340 is also supplied in 13 other conditions. The full side-by-side table is on the E4340 overview.
- HRDefaultStandard mill stock for re-heat-treating; not for final load-bearing use in as-rolled state.620 MPa yield · 30 HRC
- Q&T 50-53 HRCMaximum-strength aerospace condition (VAR stock only); use where mass is critical and fracture control is engineered.1,720 MPa yield · 52 HRC
- Q&T 44-48 HRCVery high strength for landing-gear-class parts; notch sensitivity and hydrogen embrittlement risk rise sharply.1,400 MPa yield · 46 HRC
- Q&T 40-44 HRCUsed for high-strength fasteners, tooling and aircraft fittings needing wear plus strength.1,270 MPa yield · 42 HRC
- Q&T 36-40 HRCHigher-strength band for gears, torsion bars and highly loaded shafting.1,160 MPa yield · 38 HRC
- Q&TGeneral service condition for shafts, gears and structural parts needing balanced strength and toughness.1,035 MPa yield · 34 HRC
- Q&T 32-36 HRCMost common commercial hardness band for shafts, couplings and machinery components.1,035 MPa yield · 34 HRC
- Q&T 28-32 HRCToughest Q&T level; for weld-repaired or impact-loaded parts and thick sections.880 MPa yield · 30 HRC
- NormalizedGrain-refining condition used before machining/hardening; high strength but low ductility for a deep-hardening steel.862 MPa yield · 39 HRC
- CDClose-tolerance bright bar for shafts and parts machined without further heat treatment.720 MPa yield · 25 HRC
- N&TMachining-friendly pre-treatment for large aerospace bar/forgings that will be finish heat treated later.700 MPa yield · 29 HRC
- AnnealedSoftest supply condition for machining, deep hole drilling and cold forming before final Q&T.470 MPa yield · 217 HB
Working with E4340 Q&T 36-40 HRC
Is E4340 easy to machine?
Machine in annealed or ≤32 HRC condition with rigid setups, carbide tooling and flood coolant; above 45 HRC use CBN/ceramic or grinding.
Can E4340 be welded?
Weldable only with preheat 200–320 °C, low-hydrogen or matching filler, and immediate post-weld temper below the part's tempering temperature; avoid welding at high-strength tempers.
Can E4340 be formed, bent or molded?
Cold form only in the annealed state with generous radii; hot forge 1050–1200 °C, finish above 900 °C, then normalize before hardening.
What surface finishes work on E4340?
No anodizing (ferrous): use Cd or Zn-Ni plating, hard chrome, black oxide, phosphate or shot peening; bake 190 °C ≥23 h after plating to relieve hydrogen at strengths above ~1240 MPa.
E4340 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 |
|---|---|---|
| C | 0.38 – 0.43 | 0.4 |
| Mn | 0.65 – 0.85 | 0.75 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 1.65 – 2 | 1.8 |
| Cr | 0.7 – 0.9 | 0.8 |
| Mo | 0.2 – 0.3 | 0.25 |
| PE-prefix electric-furnace limit; AMS 6414 VAR restricts to 0.010 max | ≤ 0.03 | 0.01 |
| SAMS 6414 VAR restricts to 0.010 max | ≤ 0.03 | 0.01 |
| Curesidual | ≤ 0.35 | 0.1 |
| Fe | balance | — |
E4340 Q&T 36-40 HRC — frequently asked
What is E4340 Q&T 36-40 HRC used for?
E4340 Q&T 36-40 HRC is typically used for aircraft landing gear components, power-transmission shafts, gears and pinions, high-strength bolts and studs, torsion bars and forging die holders. In short: aerospace high-strength bar.
What is the yield strength of E4340 Q&T 36-40 HRC?
E4340 Q&T 36-40 HRC has a typical yield strength of 1,160 MPa (168 ksi) and a tensile strength of 1,270 MPa (184 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 14 listed tempers.
Is E4340 Q&T 36-40 HRC easy to machine?
Not especially — machinability is rated fair (36/100, worse than 81% of steel grades). Machine in annealed or ≤32 HRC condition with rigid setups, carbide tooling and flood coolant; above 45 HRC use CBN/ceramic or grinding.
Can E4340 Q&T 36-40 HRC be welded?
Not readily — weldability is rated poor (30/100). Weldable only with preheat 200–320 °C, low-hydrogen or matching filler, and immediate post-weld temper below the part's tempering temperature; avoid welding at high-strength tempers.
What surface finishes work on E4340 Q&T 36-40 HRC?
No anodizing (ferrous): use Cd or Zn-Ni plating, hard chrome, black oxide, phosphate or shot peening; bake 190 °C ≥23 h after plating to relieve hydrogen at strengths above ~1240 MPa.
Can E4340 Q&T 36-40 HRC be formed, bent or molded?
Cold form only in the annealed state with generous radii; hot forge 1050–1200 °C, finish above 900 °C, then normalize before hardening.
What is the maximum service temperature of E4340 Q&T 36-40 HRC?
E4340 Q&T 36-40 HRC 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 E4340-HR and E4340-CD?
HR is the default condition — standard mill stock for re-heat-treating; not for final load-bearing use in as-rolled state. CD: close-tolerance bright bar for shafts and parts machined without further heat treatment. Yield strength is 620 MPa in HR versus 720 MPa in CD.
Can FabDigit make parts in E4340 Q&T 36-40 HRC?
Yes — E4340 Q&T 36-40 HRC 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
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- AMS 6414 — Steel Bars, Forgings, Tubing 0.80Cr-1.8Ni-0.25Mo, Consumable Electrode Vacuum Melted — SAE International (2019)
- AMS 6415 — Steel Bars, Forgings and Tubing 4340 — SAE International (2019)
- GB/T 3077 (40CrNiMoA) — SAC (2015)
- 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)
- MMPDS-17 (4340 and 4340 VAR allowables) — Battelle/FAA (2022)
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.