Steel M7 HT64-66
Hardness band
AISI/SAE M7 · UNS T11307 · JIS SKH58
HT64-66 = hardened & tempered, 64–66 HRC
Peak-hardness condition for small drills, saw segments and punches cutting abrasive materials; lowest toughness.
Values for the HT64-66 condition
Other M7 tempers and conditions
M7 is listed in 5 conditions; see the grade overview at M7.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard supply condition for machining tool blanks before hardening; max 255 HB. | 520 | 830 | 18 | 235 HB | — |
Cold drawn / centreless ground, annealed | Precision-ground annealed rod for drills and taps where a size-to-tolerance blank is needed. | 600 | 880 | 14 | 23 HRC | 3.1 % IACS |
Hardened & tempered, 62–64 HRC | Toughness-biased working hardness for taps, reamers and larger drills; austenitize ~1190 °C, triple temper 540–560 °C. | 1,950 | 2,200 | 1 | 63 HRC | 23 W/m·K |
Hardened + steam/nitride/PVD surface treated | Hardened tool with a surface layer (steam oxide, nitride or TiN/TiAlN) for higher tool life on abrasive or gummy work. | 2,100 | 2,400 | 1 | 64 HRC | 2.8 % IACS |
HT64-66This page Hardened & tempered, 64–66 HRC | Peak-hardness condition for small drills, saw segments and punches cutting abrasive materials; lowest toughness. | — | 2,400 | 0.5 | 65 HRC | — |
What is M7 HT64-66?
M7 HT64-66 is M7 heat treated to HT64-66 — peak-hardness condition for small drills, saw segments and punches cutting abrasive materials; lowest toughness. M7 HT64-66 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 2,400 MPa (348 ksi) — stronger than 67% of steel grades. Elongation at break is 0.5% and the elastic modulus is 217 GPa (31.5 Msi). M7 HT64-66 has a density of 7.95 g/cm³ (0.287 lb/in³), heavier than 94% of steel grades. It melts at 1,250°C (2,282 °F). ANN is the default condition FabDigit quotes; HT64-66 is available on request or by drawing note.
Advantages
- High service temperature — 560°C (1,040 °F), better than 96% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited ductility — 0.5%, worse than 100% of steel grades
- 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 — 12/100, worse than 96% of steel grades
- High embodied carbon — 3.3 kg CO₂/kg, worse than 92% of steel grades
M7 HT64-66 properties
Typical room-temperature values for M7 HT64-66; 13 are specific to this condition. Other listed values are M7 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M7 HT64-66 has a density of 7.95 g/cm³ (0.287 lb/in³), heavier than 94% of steel grades. It melts at 1,250°C (2,282 °F).
Mechanical16
M7 HT64-66 has a yield strength of 520 MPa (75.4 ksi) and a tensile strength of 2,400 MPa (348 ksi) — stronger than 67% of steel grades. Elongation at break is 0.5% and the elastic modulus is 217 GPa (31.5 Msi).
Thermal6
M7 HT64-66 is rated for continuous service to 560°C (1,040 °F). It conducts heat at 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades. Thermal expansion is 10.9 µm/m·K (6.06 µin/in·°F).
Electrical3
M7 HT64-66 conducts electricity at 3.1 % IACS, worse than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of M7 HT64-66 takes about 44 MJ of energy and emits 3.3 kg of CO₂ — more than 92% of steel grades. Typical recycled content is 40%.
Manufacturability8
M7 HT64-66's machinability is not recommended (5/100, worse than 100% of steel grades); weldability not recommended (12/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M7 HT64-66
Is M7 easy to machine?
Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or coated-carbide tools and generous coolant; hardened M7 needs grinding or EDM.
Can M7 be welded?
Essentially non-weldable structurally — repair welding only with matched HSS filler, 500–550 °C preheat and immediate re-temper.
Can M7 be formed, bent or molded?
Hot forge 1050–1150 °C (stop above 900 °C) and cool slowly to a full spheroidize anneal at 850–900 °C; no meaningful cold forming.
What surface finishes work on M7?
Protect from decarburization in vacuum, salt bath or controlled atmosphere during hardening; finish with grinding plus steam oxide, black oxide, nitriding or TiN/TiAlN PVD — no anodizing.
M7 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 | 0.97 – 1.05 | 1 |
| Mn | 0.15 – 0.4 | 0.3 |
| Si | 0.2 – 0.55 | 0.4 |
| Cr | 3.5 – 4 | 3.75 |
| Mo | 8.2 – 9.2 | 8.7 |
| W | 1.4 – 2.1 | 1.75 |
| V | 1.75 – 2.25 | 2 |
| Niresidual | ≤ 0.3 | — |
| Curesidual | ≤ 0.25 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
M7 HT64-66 — frequently asked
What is M7 HT64-66 used for?
M7 HT64-66 is typically used for twist drills, taps and reamers, general machine-shop cutting tools and punches. In short: deep-hardening molybdenum HSS; 62–66 HRC tool grade; drill and tap standard.
What is the yield strength of M7 HT64-66?
M7 HT64-66 has a typical yield strength of 520 MPa (75.4 ksi) and a tensile strength of 2,400 MPa (348 ksi) — stronger than 67% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is M7 HT64-66 easy to machine?
Not especially — machinability is rated not recommended (5/100, worse than 100% of steel grades). Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or coated-carbide tools and generous coolant; hardened M7 needs grinding or EDM.
Can M7 HT64-66 be welded?
Not readily — weldability is rated not recommended (12/100). Essentially non-weldable structurally — repair welding only with matched HSS filler, 500–550 °C preheat and immediate re-temper.
What surface finishes work on M7 HT64-66?
Protect from decarburization in vacuum, salt bath or controlled atmosphere during hardening; finish with grinding plus steam oxide, black oxide, nitriding or TiN/TiAlN PVD — no anodizing.
Can M7 HT64-66 be formed, bent or molded?
Hot forge 1050–1150 °C (stop above 900 °C) and cool slowly to a full spheroidize anneal at 850–900 °C; no meaningful cold forming.
What is the maximum service temperature of M7 HT64-66?
M7 HT64-66 is rated for continuous use to about 560°C (1,040 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between M7-ANN and M7 HT-N?
ANN is the default condition — standard supply condition for machining tool blanks before hardening; max 255 HB. HT-N: hardened tool with a surface layer (steam oxide, nitride or TiN/TiAlN) for higher tool life on abrasive or gummy work. Yield strength is 520 MPa in ANN versus 2,100 MPa in HT-N.
Sources
- ASTM A600 — Tool Steel, High Speed — ASTM International (2021)
- JIS G 4403 (SKH58) — JSA (2015)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys (Tool Steels) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- High-speed steel grade datasheets (M2/M7 class) — Erasteel / Böhler / Crucible (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.