Steel 8660 · hardness band
Steel 8660 Q&T 40-45 HRC
Properties of the Q&T 40-45 HRC condition, compared with the other 8660 tempers.
High-strength wear-resistant level for cams, sprockets and tool bodies; ductility drops noticeably.
What is 8660 Q&T 40-45 HRC?
8660 Q&T 40-45 HRC is 8660 heat treated to Q&T 40-45 HRC — high-strength wear-resistant level for cams, sprockets and tool bodies; ductility drops noticeably. 8660 Q&T 40-45 HRC has a yield strength of 1,280 MPa (186 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 95% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi). 8660 Q&T 40-45 HRC 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). HR is the default condition FabDigit quotes; Q&T 40-45 HRC is available on request or by drawing note.
Advantages
- High strength — 1,280 MPa (186 ksi), better than 95% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to machine — 22/100, worse than 96% of steel grades
- Limited ductility — 11%, worse than 89% of steel grades
- Difficult to weld — 20/100, worse than 84% of steel grades
8660 Q&T 40-45 HRC properties
Typical room-temperature values for 8660 Q&T 40-45 HRC — 11 properties are specific to this condition; the rest are grade-level values shared by every 8660 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
8660 Q&T 40-45 HRC 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).
Mechanical13
8660 Q&T 40-45 HRC has a yield strength of 1,280 MPa (186 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 95% of steel grades. Elongation at break is 11% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8660 Q&T 40-45 HRC 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 Q&T 40-45 HRC 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 Q&T 40-45 HRC takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 55% of steel grades. Typical recycled content is 30%.
Manufacturability6
8660 Q&T 40-45 HRC's machinability is poor (22/100, worse than 96% of steel grades); weldability poor (20/100); formability poor (25/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 8660 tempers and conditions
8660 is also supplied in 9 other conditions. The full side-by-side table is on the 8660 overview.
- HRDefaultStandard stock condition for bar and plate that will be machined and then heat treated by the user.585 MPa yield · 29 HRC
- Q&T 48-52 HRCMaximum practical hardness/wear level for this grade; use only where impact and notch sensitivity are controlled.1,500 MPa yield · 50 HRC
- Q&T 40-45 HRCHigh-strength wear-resistant level for cams, sprockets and tool bodies; ductility drops noticeably.1,280 MPa yield · 42 HRC
- Q&TGeneral-purpose hardened-and-tempered condition for shafts and machine parts needing high strength with usable toughness.1,080 MPa yield · 38 HRC
- Q&T 33-37 HRCBalanced strength/toughness level widely specified for gears and highly loaded shafting.1,000 MPa yield · 35 HRC
- Q&T 28-32 HRCTough, machinable strength level for larger shafts and torsion members where impact matters.855 MPa yield · 30 HRC
- CDChoose for close size tolerance and straight bright bar where no further heat treatment is planned.790 MPa yield · 28 HRC
- NormalizedUse to homogenize forgings and refine grain before hardening; gives high strength but low ductility for this carbon level.690 MPa yield · 34 HRC
- AnnealedPick when maximum machinability or cold-forming ability is needed before hardening.460 MPa yield · 230 HB
Working with 8660 Q&T 40-45 HRC
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.
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.
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 | — |
8660 Q&T 40-45 HRC — frequently asked
What is 8660 Q&T 40-45 HRC used for?
8660 Q&T 40-45 HRC 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 Q&T 40-45 HRC?
8660 Q&T 40-45 HRC has a typical yield strength of 1,280 MPa (186 ksi) and a tensile strength of 1,400 MPa (203 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 10 listed tempers.
Is 8660 Q&T 40-45 HRC easy to machine?
Not especially — machinability is rated poor (22/100, worse than 96% 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 Q&T 40-45 HRC 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 Q&T 40-45 HRC?
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 Q&T 40-45 HRC 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 Q&T 40-45 HRC?
8660 Q&T 40-45 HRC 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.
Can FabDigit make parts in 8660 Q&T 40-45 HRC?
Yes — 8660 Q&T 40-45 HRC 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)
- 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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.