Steel 8740
AISI/SAE 8740 · UNS G87400
8740 is a medium-carbon Ni-Cr-Mo alloy steel (UNS G87400) from the SAE-AISI 87xx family, with molybdenum raised for deeper hardenability and better toughness.
Values for the HR condition
8740 tempers and conditions
8740 is supplied in 11 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full anneal ~815 °C, slow cool | Softest condition — choose for deep machining, cold forming or before final quench and temper. | 415 | 696 | 22 | 201 HB | — |
HRDefault Hot rolled | Most stocked mill condition for bar and forging stock destined for later heat treatment. | 440 | 725 | 20 | 15 HRC | 7.8 % IACS |
~870 °C, air cool | Uniform fine-grain structure for forgings and weldments before final heat treatment; higher strength than annealed. | 605 | 930 | 16 | 27 HRC | — |
Cold rolled | Thin strip/sheet form for stamped parts that will be heat treated after forming. | 620 | 780 | 13 | 20 HRC | 7.8 % IACS |
Stress relieved / tempered after normalizing | Use for welded 4130/8740 tube and bracket assemblies where the weld HAZ must be softened and stresses removed. | 620 | 860 | 18 | 25 HRC | 43 W/m·K |
Cold drawn | Pick for close-tolerance straight bar with better surface and higher as-supplied yield strength than hot rolled. | 635 | 745 | 15 | 18 HRC | 44 W/m·K |
quenched and tempered to 862 MPa min UTS (AMS 6322 / NAS fastener class) | Aerospace bolt/stud condition where maximum ductility and hydrogen-embrittlement margin are wanted. | 795 | 900 | 18 | 28 HRC | — |
Quenched and tempered | General engineering condition for shafts, gears and fasteners needing ~1000 MPa with good toughness. | 900 | 1,000 | 16 | 30 HRC | — |
quenched and tempered to 1034 MPa min UTS | Standard aircraft bolt / high-strength stud condition — best strength-to-toughness compromise for 8740. | 965 | 1,080 | 15 | 34 HRC | — |
quenched and tempered to 1241 MPa min UTS | High-strength condition for landing-gear pins, race-car and driveline parts; watch notch sensitivity and hydrogen embrittlement. | 1,180 | 1,290 | 12 | 40 HRC | — |
quenched and tempered to ~1517 MPa UTS (low temper) | Maximum practical strength for 8740; only for smooth, well-designed parts with strict hydrogen and stress-raiser control. | 1,420 | 1,550 | 10 | 47 HRC | — |
What is 8740?
8740 is a medium-carbon Ni-Cr-Mo alloy steel (UNS G87400) from the SAE-AISI 87xx family, with molybdenum raised for deeper hardenability and better toughness. It is used as bar and forging stock for aircraft-quality fasteners, shafts and heavy-duty structural parts; Q&T tempers on file cover 125–220 ksi, and the default condition gives 440 MPa yield, 725 MPa tensile, 20 % elongation and about 210 HB. The alloy has no corrosion resistance of its own and needs plating or phosphating, and welding demands preheat plus a post-weld temper. 4140 is the cheaper, more widely stocked alternative when the extra nickel toughness is not required. 8740 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). 8740 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 50% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
What is 8740 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
- Machined couplings and flanges
8740 properties
Typical room-temperature values for 8740-HR; bars are the position among steel grades.
Physical3
8740 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).
Mechanical17
8740 has a yield strength of 440 MPa (63.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 50% of steel grades. Elongation at break is 20% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8740 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 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (13/100), better than 66% of steel grades.
Sustainability4
Producing a kilogram of 8740 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's machinability is good (55/100, better than 62% of steel grades); weldability fair (42/100); formability fair (40/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 8740 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8740
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.
Manufacturability
The process limits FabDigit applies to 8740. Every 8740 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better55 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair40 / 100 |
|---|---|
| Weldability | Better42 / 100 |
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 8740 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G87400
How much does 8740 cost?
8740 is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
8740 — frequently asked
What is 8740 used for?
8740 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?
8740 has a typical yield strength of 440 MPa (63.8 ksi) and a tensile strength of 725 MPa (105 ksi) — stronger than 50% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 8740 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 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?
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 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?
8740 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.
How much does 8740 cost?
8740 is a standard-cost steel ($$), cheaper than about 61% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 8740?
Yes — 8740 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.