Steel M1 HT64-66
Hardness band
AISI/SAE M1 · UNS T11301 · GB W2Mo9Cr4V2
HT64-66 = hardened & triple tempered
Highest wear resistance and red hardness for finishing cuts and abrasive work; least tough.
Values for the HT64-66 condition
Other M1 tempers and conditions
M1 is listed in 5 conditions; see the grade overview at M1.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | Standard as-supplied bar/coil condition: machine or form to shape, then harden. | 550 | 830 | 18 | 22 HRC | 22 W/m·K |
Cold drawn / ground annealed bar | Annealed bar drawn or centerless-ground to close tolerance for direct tool-blank machining. | 620 | 880 | 14 | 23 HRC | 3.1 % IACS |
Hardened & triple tempered | Pick when shock loading or interrupted cuts dominate — punches, form tools, heavy-feed taps. | — | 2,100 | 1.5 | 59 HRC | 24 W/m·K |
Hardened & triple tempered | Balanced hardness/toughness for drills, end mills and taps in general steel machining. | — | 2,300 | 0.8 | 62 HRC | 24 W/m·K |
HT64-66This page Hardened & triple tempered | Highest wear resistance and red hardness for finishing cuts and abrasive work; least tough. | — | 2,450 | 0.3 | 65 HRC | 24 W/m·K |
What is M1 HT64-66?
M1 HT64-66 is M1 heat treated to HT64-66 — highest wear resistance and red hardness for finishing cuts and abrasive work; least tough. M1 HT64-66 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 71% of steel grades. Elongation at break is 0.3% and the elastic modulus is 226 GPa (32.8 Msi). M1 HT64-66 has a density of 7.89 g/cm³ (0.285 lb/in³), heavier than 93% of steel grades. It melts at 1,290°C (2,354 °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 — 78/100, better than 95% of steel grades
Limitations
- Limited ductility — 0.3%, worse than 100% of steel grades
- Difficult to machine — 3/100, worse than 100% of steel grades
- Limited formability — 1/100, worse than 100% of steel grades
- Difficult to weld — 8/100, worse than 99% of steel grades
- High embodied carbon — 3.6 kg CO₂/kg, worse than 94% of steel grades
M1 HT64-66 properties
Typical room-temperature values for M1 HT64-66; 19 are specific to this condition. Other listed values are M1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M1 HT64-66 has a density of 7.89 g/cm³ (0.285 lb/in³), heavier than 93% of steel grades. It melts at 1,290°C (2,354 °F).
Mechanical16
M1 HT64-66 has a yield strength of 550 MPa (79.8 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 71% of steel grades. Elongation at break is 0.3% and the elastic modulus is 226 GPa (32.8 Msi).
Thermal6
M1 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 10.5 µm/m·K (5.83 µin/in·°F).
Electrical3
M1 HT64-66 conducts electricity at 3.1 % IACS, worse than 89% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of M1 HT64-66 takes about 55 MJ of energy and emits 3.6 kg of CO₂ — more than 94% of steel grades. Typical recycled content is 40%.
Manufacturability8
M1 HT64-66's machinability is not recommended (3/100, worse than 100% of steel grades); weldability not recommended (8/100); formability not recommended (1/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M1 HT64-66
Is M1 easy to machine?
Machine only in the annealed condition (≤248 HB) with rigid setups and cobalt/carbide tooling; after hardening it is a grinding-only material — use soft wheels and coolant to avoid grinding burn.
Can M1 be welded?
Not a structural weld metal: repair only, preheat 480–540 °C, matching HSS or Co-base filler, cool slowly and re-temper twice at 540–560 °C.
Can M1 be formed, bent or molded?
Hot work 1100–900 °C then slow-cool anneal at 870–900 °C; cold forming limited to light straightening — harden from 1175–1220 °C (salt bath/vacuum, protect against decarburization) and triple temper at 540–560 °C.
What surface finishes work on M1?
Bare surfaces rust readily — apply steam-oxide/black oxide, phosphate, nitriding or PVD TiN/TiAlN coatings; polish before coating for edge quality.
M1 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 | 0.78 – 0.88 | 0.83 |
| Mn | 0.15 – 0.4 | 0.3 |
| Si | 0.2 – 0.5 | 0.35 |
| Cr | 3.5 – 4 | 3.75 |
| Moprimary red-hardness carbide former | 8.2 – 9.2 | 8.7 |
| W | 1.4 – 2.1 | 1.75 |
| V | 1 – 1.35 | 1.15 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
M1 HT64-66 — frequently asked
What is M1 HT64-66 used for?
M1 HT64-66 is typically used for drills, taps, reamers, milling cutters and general machine tool bits. In short: economical general-purpose HSS; mo-based alternative to T-grades; grinding-only after hardening.
What is the yield strength of M1 HT64-66?
M1 HT64-66 has a typical yield strength of 550 MPa (79.8 ksi) and a tensile strength of 2,450 MPa (355 ksi) — stronger than 71% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is M1 HT64-66 easy to machine?
Not especially — machinability is rated not recommended (3/100, worse than 100% of steel grades). Machine only in the annealed condition (≤248 HB) with rigid setups and cobalt/carbide tooling; after hardening it is a grinding-only material — use soft wheels and coolant to avoid grinding burn.
Can M1 HT64-66 be welded?
Not readily — weldability is rated not recommended (8/100). Not a structural weld metal: repair only, preheat 480–540 °C, matching HSS or Co-base filler, cool slowly and re-temper twice at 540–560 °C.
What surface finishes work on M1 HT64-66?
Bare surfaces rust readily — apply steam-oxide/black oxide, phosphate, nitriding or PVD TiN/TiAlN coatings; polish before coating for edge quality.
Can M1 HT64-66 be formed, bent or molded?
Hot work 1100–900 °C then slow-cool anneal at 870–900 °C; cold forming limited to light straightening — harden from 1175–1220 °C (salt bath/vacuum, protect against decarburization) and triple temper at 540–560 °C.
What is the maximum service temperature of M1 HT64-66?
M1 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 M1-ANN and M1 CD-ANN?
ANN is the default condition — standard as-supplied bar/coil condition: machine or form to shape, then harden. CD-ANN: annealed bar drawn or centerless-ground to close tolerance for direct tool-blank machining. Yield strength is 550 MPa in ANN versus 620 MPa in CD-ANN.
Sources
- ASTM A600 — Tool Steel High Speed Tool Steels — ASTM International (2021)
- 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)
- Machinery's Handbook (machinability and heat-treat data) — Industrial Press (2020)
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.