Steel 4140 · heat-treated state
Steel 4140 Q&T
Properties of the Q&T condition, compared with the other 4140 tempers.
The standard pre-hardened stock condition: good strength/toughness balance and still machinable without further heat treatment.
What is 4140 Q&T?
4140 Q&T is 4140 heat treated to Q&T — the standard pre-hardened stock condition: good strength/toughness balance and still machinable without further heat treatment. 4140 Q&T has a yield strength of 860 MPa (125 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 89% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi). 4140 Q&T has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). HR is the default condition FabDigit quotes; Q&T is available on request or by drawing note.
Advantages
- High strength — 860 MPa (125 ksi), better than 89% of steel grades
- High service temperature — 480°C (896 °F), better than 88% of steel grades
Limitations
- Limited formability — 20/100, worse than 80% of steel grades
4140 Q&T properties
Typical room-temperature values for 4140 Q&T — 17 properties are specific to this condition; the rest are grade-level values shared by every 4140 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4140 Q&T has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical16
4140 Q&T has a yield strength of 860 MPa (125 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 89% of steel grades. Elongation at break is 17% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4140 Q&T is rated for continuous service to 480°C (896 °F). It conducts heat at 42.6 W/m·K (24.6 BTU/hr·ft·°F), better than 50% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4140 Q&T conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4140 Q&T takes about 32 MJ of energy and emits 2.2 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
4140 Q&T's machinability is good (55/100, better than 62% of steel grades); weldability poor (30/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4140 tempers and conditions
4140 is also supplied in 13 other conditions. The full side-by-side table is on the 4140 overview.
- HRDefaultCheapest general stock for parts that will be machined and then heat treated by the user.480 MPa yield · 210 HB
- Q&T 48-52 HRCNear-maximum hardness for wear parts and punches; very low toughness and high hydrogen-embrittlement risk.1,570 MPa yield · 50 HRC
- Q&T 40-45 HRCChoose for high-stress fasteners, torsion bars and dies; machining now needs carbide tooling.1,280 MPa yield · 43 HRC
- Q&T 34-38 HRCFor higher-loaded shafts, gears and holders where wear resistance matters more than impact toughness.1,080 MPa yield · 36 HRC
- As PrintedAs-built AM condition: as-quenched martensite, high strength but low ductility and residual stress — normally tempered or HIP'd afterwards.950 MPa yield · 48 HRC
- HIPFull-density powder or post-AM HIP route giving isotropic, near-wrought properties with closed internal porosity.860 MPa yield · 31 HRC
- Q&TThe standard pre-hardened stock condition: good strength/toughness balance and still machinable without further heat treatment.860 MPa yield · 30 HRC
- NitridedPick when a tough core plus a hard, low-distortion wear/fatigue-resistant surface is required (spindles, screws, cylinders).860 MPa yield · 58 HRC
- Q&T 22-26 HRCHigh-temper condition for H₂S / sour oilfield service where hardness must stay ≤22 HRC per NACE MR0175 in the critical section.690 MPa yield · 24 HRC
- CRThin flat product with tight thickness tolerance and smooth surface; choose for stamped blanks to be hardened later.660 MPa yield · 240 HB
- CDStraight, size-accurate bright bar with higher yield than hot rolled; best for machined shafts not requiring later hardening.660 MPa yield · 22 HRC
- NormalizedUniform fine-grain structure with mid strength; used for forgings before machining or as a delivery condition for weldments.655 MPa yield · 31 HRC
- Stress RelievedApplied after rough machining, cold work or welding to stabilise dimensions with minimal hardness loss.590 MPa yield · 225 HB
- AnnealedSoftest condition — pick for heavy machining, deep cold forming or before final hardening.415 MPa yield · 197 HB
Working with 4140 Q&T
Is 4140 easy to machine?
Machines best at 187–235 HB (annealed/HR) or up to 32 HRC pre-hardened; use rigid setups, carbide inserts, ~120–180 m/min in annealed stock and flood coolant — above 40 HRC treat as tool steel or grind.
Can 4140 be welded?
Weldable with low-hydrogen consumables but requires 200–320 °C preheat, controlled interpass and immediate PWHT/temper at 590–675 °C to avoid HAZ martensite cracking; best welded in the annealed/normalized state and re-heat-treated after.
Can 4140 be formed, bent or molded?
Hot forge 1100–1200 °C then normalize; cold forming only in the annealed condition and with generous bend radii — hardened conditions are essentially non-formable.
What surface finishes work on 4140?
No natural corrosion resistance: use black oxide, manganese phosphate, zinc or hard-chrome plating, nitriding/QPQ or paint; bake after plating to relieve hydrogen embrittlement when above ~30 HRC. Takes a good mechanical polish.
4140 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 |
|---|---|---|
| C42CrMo4 EN: 0.38–0.45 | 0.38 – 0.43 | 0.4 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | 0.75 – 1 | 0.87 |
| P | ≤ 0.04 | — |
| Smax; 4140 resulfurized variants (4140H/41L40) differ | ≤ 0.04 | — |
| Cr | 0.8 – 1.1 | 0.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| Fe | balance | — |
4140 Q&T — frequently asked
What is 4140 Q&T used for?
4140 Q&T is typically used for CNC machined gears, transmission and drive shafts, machine tool spindles, tool holders and arbors, hydraulic cylinder bodies and manifolds and oilfield drill collars and subs. In short: versatile alloy; tough.
What is the yield strength of 4140 Q&T?
4140 Q&T has a typical yield strength of 860 MPa (125 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 89% of steel grades. Strength varies by condition: see the 14 listed tempers.
Is 4140 Q&T easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines best at 187–235 HB (annealed/HR) or up to 32 HRC pre-hardened; use rigid setups, carbide inserts, ~120–180 m/min in annealed stock and flood coolant — above 40 HRC treat as tool steel or grind.
Can 4140 Q&T be welded?
Not readily — weldability is rated poor (30/100). Weldable with low-hydrogen consumables but requires 200–320 °C preheat, controlled interpass and immediate PWHT/temper at 590–675 °C to avoid HAZ martensite cracking; best welded in the annealed/normalized state and re-heat-treated after.
What surface finishes work on 4140 Q&T?
No natural corrosion resistance: use black oxide, manganese phosphate, zinc or hard-chrome plating, nitriding/QPQ or paint; bake after plating to relieve hydrogen embrittlement when above ~30 HRC. Takes a good mechanical polish.
Can 4140 Q&T be formed, bent or molded?
Hot forge 1100–1200 °C then normalize; cold forming only in the annealed condition and with generous bend radii — hardened conditions are essentially non-formable.
What is the maximum service temperature of 4140 Q&T?
4140 Q&T is rated for continuous use to about 480°C (896 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4140-HR and 4140-HIP?
HR is the default condition — cheapest general stock for parts that will be machined and then heat treated by the user. HIP: full-density powder or post-AM HIP route giving isotropic, near-wrought properties with closed internal porosity. Yield strength is 480 MPa in HR versus 860 MPa in HIP.
Can FabDigit make parts in 4140 Q&T?
Yes — 4140 Q&T is available for CNC machining, sheet metal and casting & forging with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM International (2020)
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- EN 10083-3 — Heat treatable steels: 42CrMo4 (1.7225) — CEN (2006)
- GB/T 3077 — (42CrMo) — SAC (2015)
- JIS G4053 — Low-alloyed structural steels (SCM440) — JSA (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- NACE MR0175 / ISO 15156 — Materials for H2S-containing environments — NACE/ISO (2015)
- Low-alloy Cr-Mo steel bar datasheets — Böhler / Ovako / Nucor supplier data (2023)
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.