Steel M44 HT64-66
Hardness band
AISI/SAE M44 · UNS T11344
HT64-66 = hardened & triple tempered
Standard working hardness for hobs, form tools and drills cutting high-strength and heat-resistant alloys.
Values for the HT64-66 condition
Other M44 tempers and conditions
M44 is listed in 4 conditions; see the grade overview at M44.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ANNDefault Annealed | As-supplied soft condition for machining tool blanks before hardening. | 620 | 930 | 12 | 27 HRC | — |
Hardened & triple tempered | Pick when interrupted cuts or larger tools demand more edge toughness than peak hardness. | — | 2,100 | 1 | 63 HRC | 22 W/m·K |
HT64-66This page Hardened & triple tempered | Standard working hardness for hobs, form tools and drills cutting high-strength and heat-resistant alloys. | — | 2,200 | 0.7 | 65 HRC | 22 W/m·K |
Hardened & tempered | Peak red-hardness setting for light finishing cuts and abrasive workpieces where toughness is secondary. | — | 2,250 | 0.4 | 67 HRC | — |
What is M44 HT64-66?
M44 HT64-66 is M44 heat treated to HT64-66 — standard working hardness for hobs, form tools and drills cutting high-strength and heat-resistant alloys. M44 HT64-66 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 78% of steel grades. Elongation at break is 0.7% and the elastic modulus is 224 GPa (32.5 Msi). M44 HT64-66 has a density of 8 g/cm³ (0.289 lb/in³), heavier than 95% of steel grades. It melts at 1,240°C (2,264 °F). ANN is the default condition FabDigit quotes; HT64-66 is available on request or by drawing note.
Advantages
- High service temperature — 620°C (1,148 °F), better than 99% of steel grades
- High strength — 620 MPa (89.9 ksi), better than 78% of steel grades
Limitations
- Difficult to machine — 4/100, worse than 100% of steel grades
- Limited ductility — 0.7%, worse than 99% of steel grades
- High embodied carbon — 4 kg CO₂/kg, worse than 94% of steel grades
- Poor heat conductor — 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
M44 HT64-66 properties
Typical room-temperature values for M44 HT64-66; 16 are specific to this condition. Other listed values are M44 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M44 HT64-66 has a density of 8 g/cm³ (0.289 lb/in³), heavier than 95% of steel grades. It melts at 1,240°C (2,264 °F).
Mechanical14
M44 HT64-66 has a yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 78% of steel grades. Elongation at break is 0.7% and the elastic modulus is 224 GPa (32.5 Msi).
Thermal6
M44 HT64-66 is rated for continuous service to 620°C (1,148 °F). It conducts heat at 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades. Thermal expansion is 10.5 µm/m·K (5.83 µin/in·°F).
Electrical3
M44 HT64-66 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (18/100), better than 83% of steel grades.
Sustainability4
Producing a kilogram of M44 HT64-66 takes about 48 MJ of energy and emits 4 kg of CO₂ — more than 93% of steel grades. Typical recycled content is 30%.
Manufacturability8
M44 HT64-66's machinability is not recommended (4/100, worse than 100% of steel grades); weldability poor (15/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M44 HT64-66
Is M44 easy to machine?
Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or carbide tooling and low speeds; hardened parts require CBN/diamond or vitrified alumina grinding with generous coolant to avoid burn cracks.
Can M44 be welded?
Not a structural weld grade; tool repair only with matched HSS or Co filler using 500–600 °C preheat, small beads and immediate re-temper.
Can M44 be formed, bent or molded?
Hot form 1050–900 °C followed by slow cooling and spheroidize anneal at 870–900 °C; no cold forming — austenitize about 1190–1225 °C (salt/vacuum), quench, then triple temper 540–560 °C for 2 h each.
What surface finishes work on M44?
Steam or black oxide, sulfinuz/nitride or PVD TiN/TiAlN to raise surface hardness and reduce galling; keep post-hardening grinding light and always temper after grinding to relieve stress.
M44 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 | 1.1 – 1.2 | 1.15 |
| Mn | 0.2 – 0.4 | 0.3 |
| Si | 0.3 – 0.55 | 0.4 |
| Cr | 4 – 4.75 | 4.35 |
| W | 5 – 5.75 | 5.4 |
| Mo | 6 – 7 | 6.5 |
| V | 1.85 – 2.2 | 2 |
| Cored-hardness contributor | 11 – 12.25 | 11.75 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
M44 HT64-66 — frequently asked
What is M44 HT64-66 used for?
M44 HT64-66 is typically used for heavy interrupted-cut tooling, milling cutters, lathe tool bits and aerospace alloy machining. In short: high-cobalt HSS; red hardness to 500 °C; abrasion-resistant tool grade.
What is the yield strength of M44 HT64-66?
M44 HT64-66 has a typical yield strength of 620 MPa (89.9 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 78% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is M44 HT64-66 easy to machine?
Not especially — machinability is rated not recommended (4/100, worse than 100% of steel grades). Machine only in the annealed condition with rigid setups, sharp cobalt-HSS or carbide tooling and low speeds; hardened parts require CBN/diamond or vitrified alumina grinding with generous coolant to avoid burn cracks.
Can M44 HT64-66 be welded?
Not readily — weldability is rated poor (15/100). Not a structural weld grade; tool repair only with matched HSS or Co filler using 500–600 °C preheat, small beads and immediate re-temper.
What surface finishes work on M44 HT64-66?
Steam or black oxide, sulfinuz/nitride or PVD TiN/TiAlN to raise surface hardness and reduce galling; keep post-hardening grinding light and always temper after grinding to relieve stress.
Can M44 HT64-66 be formed, bent or molded?
Hot form 1050–900 °C followed by slow cooling and spheroidize anneal at 870–900 °C; no cold forming — austenitize about 1190–1225 °C (salt/vacuum), quench, then triple temper 540–560 °C for 2 h each.
What is the maximum service temperature of M44 HT64-66?
M44 HT64-66 is rated for continuous use to about 620°C (1,148 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM A600 — Standard Specification for Tool Steel High Speed — ASTM International (2016)
- ASM Handbook Vol. 1: Properties and Selection — Irons, Steels, and High-Performance Alloys (High-Speed Tool Steels) — ASM International (1990)
- ASM Specialty Handbook: Tool Materials — ASM International (1995)
- 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.