Steel 8640
AISI/SAE 8640 · UNS G86400
8640 (G86400, SNCM240) is a medium-carbon Ni-Cr-Mo through-hardening alloy steel from the SAE-AISI 86xx series, with nickel, chromium and molybdenum providing good hardenability in moderate sections.
Values for the HR condition
8640 tempers and conditions
8640 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 |
|---|---|---|---|---|---|---|
Temper | Softest condition (full/spheroidize anneal ~840 °C, furnace cool) — best for deep machining, cold forming or thread rolling before hardening. | 380 | 695 | 22.5 | 184 HB | — |
HRDefault Hot rolled | Standard as-rolled bar for parts that will be heat treated after machining; cheapest stock form. | 570 | 860 | 19 | 20 HRC | — |
Cold rolled | Cold-reduced strip/sheet with tight thickness and a smooth surface, usually supplied soft-annealed for later forming and hardening. | 620 | 760 | 13 | 17 HRC | 7.8 % IACS |
Heat Treat State | Normalized ~900 °C and air cooled: uniform fine grain and moderate strength; typical pre-treatment before machining and final Q&T of forgings. | 690 | 930 | 22 | 27 HRC | — |
Cold drawn | Cold-drawn bar with better size tolerance, straightness and surface than HR; higher yield strength but residual stress can cause distortion on machining. | 760 | 895 | 14 | 25 HRC | 7.8 % IACS |
Q&T to 28–32 HRC | Tough mid-hardness condition (temper ≈600 °C) for drill-pipe tool joints, sour-service and welded-then-tempered assemblies. | 860 | 965 | 19 | 30 HRC | 7.8 % IACS |
Quenched and tempered | General commercial condition: oil quench from ~830 °C and temper ~540 °C for a balanced strength/toughness shaft or gear blank. | 1,000 | 1,100 | 17 | 35 HRC | — |
Q&T to 32–36 HRC | Common shaft/gear-blank hardness giving high fatigue strength while still machinable with carbide tooling. | 1,000 | 1,105 | 16 | 34 HRC | 7.6 % IACS |
Q&T to 38–42 HRC | High-strength condition (temper ≈425 °C) for heavily loaded pins, sprockets and fasteners where wear resistance outweighs toughness. | 1,275 | 1,380 | 14 | 40 HRC | — |
Q&T to 48–52 HRC | Low-temper (≈205–260 °C) condition for maximum hardness/wear in small sections; notch-sensitive and difficult to machine — grind to size. | 1,620 | 1,795 | 11 | 50 HRC | — |
What is 8640?
8640 (G86400, SNCM240) is a medium-carbon Ni-Cr-Mo through-hardening alloy steel from the SAE-AISI 86xx series, with nickel, chromium and molybdenum providing good hardenability in moderate sections. In the default quenched-and-tempered condition it gives 570 MPa yield, 860 MPa tensile, 19 % elongation and 229 HB (20 HRC); bar is also held hot-rolled, cold-rolled, cold-drawn, annealed, normalized and Q&T to 28-32, 32-36, 38-42 or 48-52 HRC. Machinability is 55, welding needs 200-300 °C preheat, and the steel has no corrosion resistance. For heavier sections or higher tempered strength, 4340 is the usual alternative. 8640 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). 8640 has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 74% of steel grades. Elongation at break is 19% and the elastic modulus is 205 GPa (29.7 Msi).
What is 8640 used for?
- Gears
- Shafts
- Bolts
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
8640 properties
Typical room-temperature values for 8640-HR; bars are the position among steel grades.
Physical3
8640 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).
Mechanical16
8640 has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 74% of steel grades. Elongation at break is 19% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8640 is rated for continuous service to 400°C (752 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
8640 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of 8640 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
8640's machinability is good (55/100, better than 62% of steel grades); weldability fair (40/100); formability fair (35/100).
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. 8640 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8640
Is 8640 easy to machine?
Machine in the annealed or ≤32 HRC Q&T condition with carbide tooling and rigid setups; rough before hardening and leave grind stock for finish sizes.
Can 8640 be welded?
Weldable with low-hydrogen consumables but requires ~200–300 °C preheat, interpass control and post-weld temper below the original tempering temperature to avoid martensitic cracking.
Can 8640 be formed, bent or molded?
Cold forming only in the annealed state and with generous bend radii; hot forge at 1050–1200 °C then normalize before final heat treatment.
Manufacturability
The process limits FabDigit applies to 8640. Every 8640 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 | Fair35 / 100 |
|---|---|
| Weldability | Better40 / 100 |
8640 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 |
| Mo | 0.15 – 0.25 | 0.2 |
| Pmax, SAE J404 wrought bar | ≤ 0.04 | |
| Smax; 8640H/resulfurized variants differ | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 8640?
No natural corrosion protection — apply black oxide, phosphate + oil, zinc or hard-chrome plating; bake plated parts above ~38 HRC to relieve hydrogen embrittlement.
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 8640 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G86400
- Similar grades
- SNCM240
How much does 8640 cost?
8640 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.
8640 — frequently asked
What is 8640 used for?
8640 is typically used for gears, shafts and bolts. In short: workhorse Ni-Cr-Mo bar.
What is the yield strength of 8640?
8640 has a typical yield strength of 570 MPa (82.7 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 74% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 8640 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed or ≤32 HRC Q&T condition with carbide tooling and rigid setups; rough before hardening and leave grind stock for finish sizes.
Can 8640 be welded?
With care — weldability is rated fair (40/100). Weldable with low-hydrogen consumables but requires ~200–300 °C preheat, interpass control and post-weld temper below the original tempering temperature to avoid martensitic cracking.
What surface finishes work on 8640?
No natural corrosion protection — apply black oxide, phosphate + oil, zinc or hard-chrome plating; bake plated parts above ~38 HRC to relieve hydrogen embrittlement.
Can 8640 be formed, bent or molded?
Cold forming only in the annealed state and with generous bend radii; hot forge at 1050–1200 °C then normalize before final heat treatment.
What is the maximum service temperature of 8640?
8640 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 8640-HR and 8640-CD?
HR is the default condition — standard as-rolled bar for parts that will be heat treated after machining; cheapest stock form. CD: cold-drawn bar with better size tolerance, straightness and surface than HR; higher yield strength but residual stress can cause distortion on machining. Yield strength is 570 MPa in HR versus 760 MPa in CD.
How much does 8640 cost?
8640 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 8640?
Yes — 8640 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 — General Requirements for 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.4 — Heat Treating (tempering curves for 86xx steels) — ASM International (1991)
- SAE J1268 hardenability / typical mechanical property tables for 8640 — SAE International (2019)
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.