Steel SKH51 QT 64-66 HRC
Hardness band
JIS SKH51 · AISI/SAE M2
QT 64-66 HRC = hardened & tempered to 64–66 HRC
High austenitising temperature for maximum wear resistance on form tools and gear cutters; toughness is minimal.
Values for the QT 64-66 HRC condition
Other SKH51 tempers and conditions
SKH51 is listed in 6 conditions; see the grade overview at SKH51.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
AnnealedDefault soft (spheroidize) annealed, ≤255 HB | Standard stock condition for bar/plate — machine to shape, then harden and temper. | 550 | 850 | 20 | 22 HRC | 2.9 % IACS |
Hardened, tempered and surface nitrided / steam-tempered | Post-hardening surface treatment adding ~1000–1200 HV case for taps and drills on abrasive work. | 1,950 | 2,100 | 0.5 | 63 HRC | 2.6 % IACS |
QT 64-66 HRCThis page Hardened & tempered to 64–66 HRC | High austenitising temperature for maximum wear resistance on form tools and gear cutters; toughness is minimal. | 2,000 | 2,200 | 0.5 | 65 HRC | 2.6 % IACS |
Hardened & tempered to 58–60 HRC | Lower austenitising / higher tempering temperature for shock-loaded punches and cold-forming tools. | — | 2,100 | 1 | 59 HRC | — |
Hardened & tempered to 60–62 HRC | Balanced hardness/toughness for taps, broaches, cold-work punches and dies. | — | 2,300 | 0.5 | 61 HRC | — |
Hardened & triple tempered to 62–64 HRC | Normal delivery hardness for drills, end mills and hobs — best wear/red-hardness compromise. | — | 2,500 | 0.3 | 63 HRC | — |
What is SKH51 QT 64-66 HRC?
SKH51 QT 64-66 HRC is SKH51 heat treated to QT 64-66 HRC — high austenitising temperature for maximum wear resistance on form tools and gear cutters; toughness is minimal. SKH51 QT 64-66 HRC has a yield strength of 2,000 MPa (290 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 232 GPa (33.6 Msi). SKH51 QT 64-66 HRC has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,370°C (2,498 °F). Annealed is the default condition FabDigit quotes; QT 64-66 HRC is available on request or by drawing note.
Advantages
- High strength — 2,000 MPa (290 ksi), better than 100% of steel grades
- Stiff — 232 GPa (33.6 Msi), better than 100% of steel grades
- High service temperature — 580°C (1,076 °F), better than 97% of steel grades
- Polishes to a fine finish — 70/100, better than 87% of steel grades
Limitations
- Limited ductility — 0.5%, worse than 100% of steel grades
- Low fracture toughness — 14 MPa·√m (12.7 ksi·√in), worse than 100% of steel grades
- Difficult to machine — 3/100, worse than 100% of steel grades
- Limited formability — 2/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
SKH51 QT 64-66 HRC properties
Typical room-temperature values for SKH51 QT 64-66 HRC; 21 are specific to this condition. Other listed values are SKH51 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
SKH51 QT 64-66 HRC has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,370°C (2,498 °F).
Mechanical17
SKH51 QT 64-66 HRC has a yield strength of 2,000 MPa (290 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 100% of steel grades. Elongation at break is 0.5% and the elastic modulus is 232 GPa (33.6 Msi).
Thermal6
SKH51 QT 64-66 HRC 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 11 µm/m·K (6.11 µin/in·°F).
Electrical3
SKH51 QT 64-66 HRC conducts electricity at 2.6 % IACS, worse than 97% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (16/100), better than 79% of steel grades.
Sustainability4
Producing a kilogram of SKH51 QT 64-66 HRC takes about 45 MJ of energy and emits 3.2 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 45%.
Manufacturability7
SKH51 QT 64-66 HRC's machinability is not recommended (3/100, worse than 100% of steel grades); weldability not recommended (8/100); formability not recommended (2/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with SKH51 QT 64-66 HRC
Is SKH51 easy to machine?
Machine only in the annealed condition with rigid setups, cobalt-HSS or coated carbide, low speed and heavy feed; once hardened above ~55 HRC, use grinding, EDM or CBN.
Can SKH51 be welded?
Not a structural weld metal — repair weld only with matched HSS filler, 500–550 °C preheat, immediate post-weld temper; otherwise cracking is certain.
Can SKH51 be formed, bent or molded?
Hot forge 1100→900 °C with slow furnace cooling to soft-anneal (≈860 °C, slow cool); cold forming is impractical.
What surface finishes work on SKH51?
Harden at 1180–1230 °C, oil/vacuum/salt quench, then triple temper 540–560 °C; finish by grinding and protect with black oxide, steam oxide, phosphate or PVD TiN/TiAlN coating.
SKH51 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 SKH51 | 0.8 – 0.88 | 0.85 |
| Si | ≤ 0.45 | 0.3 |
| Mn | ≤ 0.4 | 0.3 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Cr | 3.8 – 4.5 | 4.1 |
| Mo | 4.7 – 5.2 | 5 |
| W | 5.9 – 6.7 | 6.3 |
| V | 1.7 – 2.1 | 1.9 |
| Curesidual | ≤ 0.25 | — |
| Niresidual | ≤ 0.25 | — |
| Fe | balance | — |
SKH51 QT 64-66 HRC — frequently asked
What is SKH51 QT 64-66 HRC used for?
SKH51 QT 64-66 HRC is typically used for drills, end mills, taps and reamers. In short: default general-purpose HSS; AISI M2 equivalent; best HSS cost-toughness balance.
What is the yield strength of SKH51 QT 64-66 HRC?
SKH51 QT 64-66 HRC has a typical yield strength of 2,000 MPa (290 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 100% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is SKH51 QT 64-66 HRC easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 100% of steel grades). Machine only in the annealed condition with rigid setups, cobalt-HSS or coated carbide, low speed and heavy feed; once hardened above ~55 HRC, use grinding, EDM or CBN.
Can SKH51 QT 64-66 HRC be welded?
Not readily — weldability is rated not recommended (8/100). Not a structural weld metal — repair weld only with matched HSS filler, 500–550 °C preheat, immediate post-weld temper; otherwise cracking is certain.
What surface finishes work on SKH51 QT 64-66 HRC?
Harden at 1180–1230 °C, oil/vacuum/salt quench, then triple temper 540–560 °C; finish by grinding and protect with black oxide, steam oxide, phosphate or PVD TiN/TiAlN coating.
Can SKH51 QT 64-66 HRC be formed, bent or molded?
Hot forge 1100→900 °C with slow furnace cooling to soft-anneal (≈860 °C, slow cool); cold forming is impractical.
What is the maximum service temperature of SKH51 QT 64-66 HRC?
SKH51 QT 64-66 HRC 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.
Sources
- JIS G4403 High Speed Tool Steel Steels — JSA (2015)
- ASTM A600 Tool Steel High Speed — ASTM (2021)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Böhler S600 (M2) / Erasteel ASP-M2 datasheet — voestalpine Böhler / Erasteel (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.