Steel SKH57 QT64-66
Hardness band
JIS SKH57
QT64-66 = hardened & tempered to 64–66 HRC
Usual cutting-tool condition: 1180–1200 °C quench + 3 × 550 °C temper, best balance of wear resistance and toughness.
Values for the QT64-66 condition
Other SKH57 tempers and conditions
SKH57 is listed in 6 conditions; see the grade overview at SKH57.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Hardened & tempered to 62–64 HRC | Higher tempering temperature / slightly lower austenitizing for interrupted cuts, broaches and larger cross-sections needing toughness. | — | — | — | 63 HRC | — |
QT64-66This page Hardened & tempered to 64–66 HRC | Usual cutting-tool condition: 1180–1200 °C quench + 3 × 550 °C temper, best balance of wear resistance and toughness. | — | — | — | 65 HRC | — |
Hardened & tempered to 66–68 HRC | Peak secondary-hardening condition for taps, drills and form tools on hardened or abrasive workpieces where wear, not shock, governs. | — | — | — | 67 HRC | — |
ANNDefault Annealed | Standard mill-supplied soft condition for machining tool blanks before hardening. | 540 | 880 | 10 | 26 HRC | — |
Hardened & tempered + steam oxide (blue/black finish) | Choose for taps and drills where the Fe3O4 layer holds lubricant and reduces galling on gummy materials. | 2,150 | 2,600 | 1 | 65 HRC | 2.7 % IACS |
Hardened & tempered + PVD coating | Standard for production cutting tools: coating raises surface hardness and hot-oxidation resistance while the substrate stays at 65–67 HRC. | 2,200 | 2,650 | 1 | 66 HRC | 2.7 % IACS |
What is SKH57 QT64-66?
SKH57 QT64-66 is SKH57 heat treated to QT64-66 — usual cutting-tool condition: 1180–1200 °C quench + 3 × 550 °C temper, best balance of wear resistance and toughness. SKH57 QT64-66 has a yield strength of 540 MPa (78.3 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 70% of steel grades. Elongation at break is 10% and the elastic modulus is 230 GPa (33.4 Msi). SKH57 QT64-66 has a density of 8.3 g/cm³ (0.3 lb/in³), heavier than 99% of steel grades. It melts at 1,260°C (2,300 °F). ANN is the default condition FabDigit quotes; QT64-66 is available on request or by drawing note.
Advantages
- High service temperature — 580°C (1,076 °F), better than 97% of steel grades
Limitations
- Low fracture toughness — 15 MPa·√m (13.7 ksi·√in), worse than 100% of steel grades
- Difficult to machine — 5/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- Poor heat conductor — 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades
- Limited formability — 8/100, worse than 97% of steel grades
SKH57 QT64-66 properties
Typical room-temperature values for SKH57 QT64-66; 12 are specific to this condition. Other listed values are SKH57 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SKH57 QT64-66 has a density of 8.3 g/cm³ (0.3 lb/in³), heavier than 99% of steel grades. It melts at 1,260°C (2,300 °F).
Mechanical12
SKH57 QT64-66 has a yield strength of 540 MPa (78.3 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 70% of steel grades. Elongation at break is 10% and the elastic modulus is 230 GPa (33.4 Msi).
Thermal6
SKH57 QT64-66 is rated for continuous service to 580°C (1,076 °F). It conducts heat at 19 W/m·K (11 BTU/hr·ft·°F), worse than 97% of steel grades. Thermal expansion is 10.2 µm/m·K (5.67 µin/in·°F).
Electrical3
SKH57 QT64-66 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of SKH57 QT64-66 takes about 60 MJ of energy and emits 4.5 kg of CO₂ — more than 96% of steel grades. Typical recycled content is 35%.
Manufacturability8
SKH57 QT64-66's machinability is not recommended (5/100, worse than 100% of steel grades); weldability not recommended (8/100); formability not recommended (8/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SKH57 QT64-66
Is SKH57 easy to machine?
Machine only in the annealed state with sharp cobalt-HSS or coated carbide, low speed and rigid setup; after hardening use grinding (CBN or friable SG wheels), EDM or hard turning with CBN — MC vanadium carbides make grindability poor.
Can SKH57 be welded?
Not a structural weld grade; repair only by TIG/micro-plasma with matching HSS filler, 500–550 °C preheat and immediate re-temper to avoid quench cracks.
Can SKH57 be formed, bent or molded?
Hot work only: forge 1100–1150 °C, stop above 950 °C, cool slowly then spheroidize anneal at 850–900 °C; no cold forming. Harden 1180–1210 °C in vacuum/salt, quench in gas or oil, then temper 3 × 1 h at 540–560 °C.
What surface finishes work on SKH57?
Cannot be anodized; use steam oxide, black oxide, nitrocarburizing (thin case only) or PVD TiN/TiAlN/AlCrN — keep PVD deposition below the tempering temperature to preserve 65+ HRC.
SKH57 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 |
|---|---|---|
| CJIS G4403 | 1.2 – 1.45 | 1.3 |
| Si | ≤ 0.45 | 0.3 |
| Mn | ≤ 0.4 | 0.3 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cr | 3.5 – 4.5 | 4 |
| Mo | 3 – 4 | 3.5 |
| W | 9 – 11 | 10 |
| V | 3 – 3.5 | 3.3 |
| Cogives red hardness | 9 – 11 | 10 |
| Niresidual | ≤ 0.25 | — |
| Curesidual | ≤ 0.25 | — |
| Fe | balance | — |
SKH57 QT64-66 — frequently asked
What is SKH57 QT64-66 used for?
SKH57 QT64-66 is typically used for hobs, broaches and high-speed cutting tools. In short: highest red hardness HSS; high-cobalt M42 type; grinds slower than M2.
What is the yield strength of SKH57 QT64-66?
SKH57 QT64-66 has a typical yield strength of 540 MPa (78.3 ksi) and a tensile strength of 880 MPa (128 ksi) — stronger than 70% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SKH57 QT64-66 easy to machine?
Not especially — machinability is rated not recommended (5/100, worse than 100% of steel grades). Machine only in the annealed state with sharp cobalt-HSS or coated carbide, low speed and rigid setup; after hardening use grinding (CBN or friable SG wheels), EDM or hard turning with CBN — MC vanadium carbides make grindability poor.
Can SKH57 QT64-66 be welded?
Not readily — weldability is rated not recommended (8/100). Not a structural weld grade; repair only by TIG/micro-plasma with matching HSS filler, 500–550 °C preheat and immediate re-temper to avoid quench cracks.
What surface finishes work on SKH57 QT64-66?
Cannot be anodized; use steam oxide, black oxide, nitrocarburizing (thin case only) or PVD TiN/TiAlN/AlCrN — keep PVD deposition below the tempering temperature to preserve 65+ HRC.
Can SKH57 QT64-66 be formed, bent or molded?
Hot work only: forge 1100–1150 °C, stop above 950 °C, cool slowly then spheroidize anneal at 850–900 °C; no cold forming. Harden 1180–1210 °C in vacuum/salt, quench in gas or oil, then temper 3 × 1 h at 540–560 °C.
What is the maximum service temperature of SKH57 QT64-66?
SKH57 QT64-66 is rated for continuous use to about 580°C (1,076 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SKH57-ANN and SKH57 QT-PVD?
ANN is the default condition — standard mill-supplied soft condition for machining tool blanks before hardening. QT-PVD: standard for production cutting tools: coating raises surface hardness and hot-oxidation resistance while the substrate stays at 65–67 HRC. Yield strength is 540 MPa in ANN versus 2,200 MPa in QT-PVD.
Sources
- JIS G4403 High-speed tool steel materials — JSA (2015)
- ASTM A600 Standard Specification for Tool Steel High Speed — ASTM (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys (Tool Steels) — ASM International (1990)
- ASM Specialty Handbook: Tool Materials — ASM International (1995)
- Cobalt high-speed steel (SKH57/M42-class) bar datasheets — Hitachi Metals / Proterial, Nachi-Fujikoshi, Böhler (2022)
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.