Steel 8740 · heat-treated state
Steel 8740 Q&T-125ksi
Properties of the Q&T-125ksi condition, compared with the other 8740 tempers.
Aerospace bolt/stud condition where maximum ductility and hydrogen-embrittlement margin are wanted.
What is 8740 Q&T-125ksi?
8740 Q&T-125ksi is 8740 heat treated to Q&T-125ksi — aerospace bolt/stud condition where maximum ductility and hydrogen-embrittlement margin are wanted. 8740 Q&T-125ksi has a yield strength of 795 MPa (115 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 86% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi). 8740 Q&T-125ksi has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; Q&T-125ksi is available on request or by drawing note.
Advantages
- High strength — 795 MPa (115 ksi), better than 86% of steel grades
8740 Q&T-125ksi properties
Typical room-temperature values for 8740 Q&T-125ksi — 10 properties are specific to this condition; the rest are grade-level values shared by every 8740 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
8740 Q&T-125ksi has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical15
8740 Q&T-125ksi has a yield strength of 795 MPa (115 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 86% of steel grades. Elongation at break is 18% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8740 Q&T-125ksi 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 12.6 µm/m·K (7 µin/in·°F).
Electrical3
8740 Q&T-125ksi conducts electricity at 7.8 % IACS, worse than 58% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 8740 Q&T-125ksi takes about 29 MJ of energy and emits 2 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 30%.
Manufacturability7
8740 Q&T-125ksi's machinability is good (55/100, better than 62% of steel grades); weldability fair (42/100); formability fair (40/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 8740 tempers and conditions
8740 is also supplied in 10 other conditions. The full side-by-side table is on the 8740 overview.
- HRDefaultMost stocked mill condition for bar and forging stock destined for later heat treatment.440 MPa yield · 210 HB
- Q&T-220ksiMaximum practical strength for 8740; only for smooth, well-designed parts with strict hydrogen and stress-raiser control.1,420 MPa yield · 47 HRC
- Q&T-180ksiHigh-strength condition for landing-gear pins, race-car and driveline parts; watch notch sensitivity and hydrogen embrittlement.1,180 MPa yield · 40 HRC
- Q&T-150ksiStandard aircraft bolt / high-strength stud condition — best strength-to-toughness compromise for 8740.965 MPa yield · 34 HRC
- Q&TGeneral engineering condition for shafts, gears and fasteners needing ~1000 MPa with good toughness.900 MPa yield · 30 HRC
- Q&T-125ksiAerospace bolt/stud condition where maximum ductility and hydrogen-embrittlement margin are wanted.795 MPa yield · 28 HRC
- CDPick for close-tolerance straight bar with better surface and higher as-supplied yield strength than hot rolled.635 MPa yield · 18 HRC
- NormalizedUniform fine-grain structure for forgings and weldments before final heat treatment; higher strength than annealed.605 MPa yield · 27 HRC
- AnnealedSoftest condition — choose for deep machining, cold forming or before final quench and temper.415 MPa yield · 201 HB
Working with 8740 Q&T-125ksi
Is 8740 easy to machine?
Machines well at 180–250 HB (≈65% of 1212) with carbide at 120–180 m/min; above 35 HRC drop to rigid setups, low speed and positive coolant, or machine before final temper.
Can 8740 be welded?
Weldable by TIG/MIG/SMAW with matched or ER80S-D2 filler but needs 200–300 °C preheat, low hydrogen practice and a post-weld temper; never leave a high-strength Q&T part as-welded.
Can 8740 be formed, bent or molded?
Cold form only in the annealed condition with generous radii; hot forge 1050–1200 °C then normalize — quench in oil from 830–845 °C and temper to the target strength.
What surface finishes work on 8740?
No natural corrosion resistance: use cadmium, zinc or zinc-nickel plating, phosphate + oil, or black oxide, and bake 190–220 °C after plating for parts above ~1000 MPa to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
8740 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 | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.4 – 0.7 | 0.55 |
| Cr | 0.4 – 0.6 | 0.5 |
| Mohigher Mo than 8640 | 0.2 – 0.3 | 0.25 |
| Pmax; 0.025 max for aerospace AMS grades | ≤ 0.04 | — |
| Smax; 0.025 max for aerospace AMS grades | ≤ 0.04 | — |
| Fe | balance | — |
8740 Q&T-125ksi — frequently asked
What is 8740 Q&T-125ksi used for?
8740 Q&T-125ksi is typically used for aircraft-quality bolts and studs, high-strength shafts and spindles, forged industrial components, threaded rod and tie bars, clevis pins and linkage parts and machined couplings and flanges. In short: standard Ni-Cr-Mo bar.
What is the yield strength of 8740 Q&T-125ksi?
8740 Q&T-125ksi has a typical yield strength of 795 MPa (115 ksi) and a tensile strength of 900 MPa (131 ksi) — stronger than 86% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 8740 Q&T-125ksi easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines well at 180–250 HB (≈65% of 1212) with carbide at 120–180 m/min; above 35 HRC drop to rigid setups, low speed and positive coolant, or machine before final temper.
Can 8740 Q&T-125ksi be welded?
With care — weldability is rated fair (42/100). Weldable by TIG/MIG/SMAW with matched or ER80S-D2 filler but needs 200–300 °C preheat, low hydrogen practice and a post-weld temper; never leave a high-strength Q&T part as-welded.
What surface finishes work on 8740 Q&T-125ksi?
No natural corrosion resistance: use cadmium, zinc or zinc-nickel plating, phosphate + oil, or black oxide, and bake 190–220 °C after plating for parts above ~1000 MPa to avoid hydrogen embrittlement; nitriding gives a hard wear surface.
Can 8740 Q&T-125ksi be formed, bent or molded?
Cold form only in the annealed condition with generous radii; hot forge 1050–1200 °C then normalize — quench in oil from 830–845 °C and temper to the target strength.
What is the maximum service temperature of 8740 Q&T-125ksi?
8740 Q&T-125ksi 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 8740-HR and 8740-CD?
HR is the default condition — most stocked mill condition for bar and forging stock destined for later heat treatment. CD: pick for close-tolerance straight bar with better surface and higher as-supplied yield strength than hot rolled. Yield strength is 440 MPa in HR versus 635 MPa in CD.
Can FabDigit make parts in 8740 Q&T-125ksi?
Yes — 8740 Q&T-125ksi 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)
- SAE J1268 — Hardenability Bands for Alloy H Steels — SAE International (2019)
- AMS 6322 / AMS 6327 — Steel Bars, Forgings and Tubing 0.40C Ni-Cr-Mo (8740) — SAE International (2020)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- 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 Metallic Materials Properties Development and Standardization — Battelle/FAA (2022)
- Machinery's Handbook, 31st ed. — Industrial Press (2020)
- Mysteel / SMM (2025)
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.