Steel 8660
AISI/SAE 8660 · UNS G86600
8660 is the highest-carbon member of the SAE-AISI 86xx nickel-chromium-molybdenum alloy steel family (UNS G86600), with about 0.60 % C for very high quenched hardness and strength.
Values for the HR condition
8660 tempers and conditions
8660 is supplied in 10 conditions, soft to hard. HR is the default FabDigit quotes; the values on this page are for it.
Compare all 10 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/spheroidize anneal, softest machining condition | Pick when maximum machinability or cold-forming ability is needed before hardening. | 460 | 800 | 20 | 230 HB | — |
HRDefault Hot rolled | Standard stock condition for bar and plate that will be machined and then heat treated by the user. | 585 | 965 | 13 | 29 HRC | 7.2 % IACS |
austenitized ~870 °C, air cooled | Use to homogenize forgings and refine grain before hardening; gives high strength but low ductility for this carbon level. | 690 | 1,105 | 14 | 34 HRC | 7 % IACS |
Cold drawn | Choose for close size tolerance and straight bright bar where no further heat treatment is planned. | 790 | 930 | 10 | 28 HRC | 7.2 % IACS |
Cold rolled | Strip/sheet form for blanking and spring-type parts that are subsequently hardened and tempered. | 800 | 950 | 9 | 29 HRC | 7.2 % IACS |
Quenched and high-temperature tempered | Tough, machinable strength level for larger shafts and torsion members where impact matters. | 855 | 965 | 17 | 30 HRC | — |
Quenched and tempered ~540 °C | Balanced strength/toughness level widely specified for gears and highly loaded shafting. | 1,000 | 1,110 | 15 | 35 HRC | — |
Quenched and tempered | General-purpose hardened-and-tempered condition for shafts and machine parts needing high strength with usable toughness. | 1,080 | 1,200 | 13 | 38 HRC | — |
Quenched and tempered ~430 °C | High-strength wear-resistant level for cams, sprockets and tool bodies; ductility drops noticeably. | 1,280 | 1,400 | 11 | 42 HRC | — |
Quenched and low-temperature tempered | Maximum practical hardness/wear level for this grade; use only where impact and notch sensitivity are controlled. | 1,500 | 1,720 | 8 | 50 HRC | — |
What is 8660?
8660 is the highest-carbon member of the SAE-AISI 86xx nickel-chromium-molybdenum alloy steel family (UNS G86600), with about 0.60 % C for very high quenched hardness and strength. It is specified as bar and forging stock for drive shafts, pinion shafts and wear parts, reaching 585 MPa yield, 965 MPa tensile and 285 HB (29 HRC) in the default quenched-and-tempered condition, with Q&T ranges on file up to 48–52 HRC. Weldability is poor at that carbon level, corrosion resistance is nil, and toughness drops at high hardness; 8650 or 4140 are the usual choices when welding or heavy machining is required. 8660 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,415°C (2,579 °F). 8660 has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 75% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi).
What is 8660 used for?
- Drive shafts
- Pinion shafts
- Gears and gear blanks
- Torsion bars and spring anchors
- Wear plates and liners
- Forged sprockets and couplings
- Heavy-duty axle shafts
Advantages
- Polishes to a fine finish — 65/100, better than 78% of steel grades
- High strength — 585 MPa (84.8 ksi), better than 75% of steel grades
Limitations
- Difficult to weld — 20/100, worse than 84% of steel grades
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
8660 properties
Typical room-temperature values for 8660-HR; bars are the position among steel grades.
Physical3
8660 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,415°C (2,579 °F).
Mechanical16
8660 has a yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 75% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8660 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 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
8660 conducts electricity at 7.2 % IACS, worse than 71% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 8660 takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability6
8660's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (20/100); formability poor (25/100).
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. 8660 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8660
Is 8660 easy to machine?
Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above ~40 HRC switch to grinding or CBN turning.
Can 8660 be welded?
Poor weldability at 0.60 % C — avoid if possible; if required use low-hydrogen consumables, 250–350 °C preheat, interpass control and immediate post-weld temper.
Can 8660 be formed, bent or molded?
Cold forming is limited to mild bends in the spheroidize-annealed state; hot forge at 1100–1200 °C, finish above 900 °C and slow cool or normalize afterwards.
Manufacturability
The process limits FabDigit applies to 8660. Every 8660 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better40 / 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 | Fair25 / 100 |
|---|---|
| Weldability | Better20 / 100 |
8660 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 | 0.56 – 0.64 | 0.6 |
| 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 |
| Mo | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 8660?
Not anodizable; protect with phosphate + oil, black oxide, zinc or hard chrome, and stress-relieve/bake after plating to avoid hydrogen embrittlement at high hardness.
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 8660 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G86600
How much does 8660 cost?
8660 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.
8660 — frequently asked
What is 8660 used for?
8660 is typically used for drive shafts, pinion shafts, gears and gear blanks, torsion bars and spring anchors, wear plates and liners and forged sprockets and couplings. In short: workhorse Ni-Cr-Mo bar.
What is the yield strength of 8660?
8660 has a typical yield strength of 585 MPa (84.8 ksi) and a tensile strength of 965 MPa (140 ksi) — stronger than 75% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 8660 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine in the annealed or ≤32 HRC condition with rigid setups, carbide tooling and generous coolant; above ~40 HRC switch to grinding or CBN turning.
Can 8660 be welded?
Not readily — weldability is rated poor (20/100). Poor weldability at 0.60 % C — avoid if possible; if required use low-hydrogen consumables, 250–350 °C preheat, interpass control and immediate post-weld temper.
What surface finishes work on 8660?
Not anodizable; protect with phosphate + oil, black oxide, zinc or hard chrome, and stress-relieve/bake after plating to avoid hydrogen embrittlement at high hardness.
Can 8660 be formed, bent or molded?
Cold forming is limited to mild bends in the spheroidize-annealed state; hot forge at 1100–1200 °C, finish above 900 °C and slow cool or normalize afterwards.
What is the maximum service temperature of 8660?
8660 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 8660-HR and 8660-CR?
HR is the default condition — standard stock condition for bar and plate that will be machined and then heat treated by the user. CR: strip/sheet form for blanking and spring-type parts that are subsequently hardened and tempered. Yield strength is 585 MPa in HR versus 800 MPa in CR.
How much does 8660 cost?
8660 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 8660?
Yes — 8660 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)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- SAE J1268 — Hardenability Bands for Carbon and Alloy H Steels — SAE International (2019)
- 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)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
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.