Steel M41 HT66-68
Heat-treated state
AISI/SAE M41 · UNS T11341 · JIS SKH59 · GB W6Mo5Cr4V2Co5
HT66-68 = hardened & triple tempered
Chosen for high cutting speeds and hard/abrasive workpieces where wear resistance outranks toughness.
Values for the HT66-68 condition
Other M41 tempers and conditions
M41 is listed in 5 conditions; see the grade overview at M41.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Stress relieved | Intermediate 600–700 °C stress relief after heavy roughing to limit distortion during subsequent hardening. | 580 | 880 | 13 | 24 HRC | 2.9 % IACS |
ANNDefault Annealed | Standard as-supplied condition for bars, blanks and forging stock; machine to shape before hardening. | 600 | 900 | 12 | 262 HB | 21 W/m·K |
Hardened & triple tempered | Peak-hardness condition for form tools and light-cut precision tooling; very low toughness, avoid interrupted cuts. | 2,000 | 2,100 | 0.5 | 69 HRC | 2.6 % IACS |
HT66-68This page Hardened & triple tempered | Chosen for high cutting speeds and hard/abrasive workpieces where wear resistance outranks toughness. | — | 2,200 | — | 67 HRC | — |
Hardened & triple tempered | Balanced toughness/hardness setting for drills, taps, end mills and broaches in general steel machining. | — | 2,300 | 0.5 | 65 HRC | 20 W/m·K |
What is M41 HT66-68?
M41 HT66-68 is M41 heat treated to HT66-68 — chosen for high cutting speeds and hard/abrasive workpieces where wear resistance outranks toughness. M41 HT66-68 has a yield strength of 600 MPa (87 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 77% of steel grades. Elongation at break is 12% and the elastic modulus is 217 GPa (31.5 Msi). M41 HT66-68 has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,250°C (2,282 °F). ANN is the default condition FabDigit quotes; HT66-68 is available on request or by drawing note.
Advantages
- High service temperature — 580°C (1,076 °F), better than 97% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
- High strength — 600 MPa (87 ksi), better than 77% of steel grades
Limitations
- Difficult to machine — 4/100, worse than 100% of steel grades
- Poor heat conductor — 21 W/m·K (12.1 BTU/hr·ft·°F), worse than 95% of steel grades
- High embodied carbon — 3.8 kg CO₂/kg, worse than 94% of steel grades
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Limited formability — 12/100, worse than 92% of steel grades
M41 HT66-68 properties
Typical room-temperature values for M41 HT66-68; 13 are specific to this condition. Other listed values are M41 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
M41 HT66-68 has a density of 8.16 g/cm³ (0.295 lb/in³), heavier than 98% of steel grades. It melts at 1,250°C (2,282 °F).
Mechanical15
M41 HT66-68 has a yield strength of 600 MPa (87 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 77% of steel grades. Elongation at break is 12% and the elastic modulus is 217 GPa (31.5 Msi).
Thermal6
M41 HT66-68 is rated for continuous service to 580°C (1,076 °F). It conducts heat at 21 W/m·K (12.1 BTU/hr·ft·°F), worse than 95% of steel grades. Thermal expansion is 10.8 µm/m·K (6 µin/in·°F).
Electrical3
M41 HT66-68 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 M41 HT66-68 takes about 55 MJ of energy and emits 3.8 kg of CO₂ — more than 94% of steel grades. Typical recycled content is 40%.
Manufacturability6
M41 HT66-68's machinability is not recommended (4/100, worse than 100% of steel grades); weldability poor (18/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with M41 HT66-68
Is M41 easy to machine?
Machine only in the annealed state with rigid setups, sharp cobalt-HSS or coated carbide and generous coolant; after hardening only grinding, EDM or superabrasive finishing is practical.
Can M41 be welded?
Not a structural weld metal — only tip/shank friction or flash welding and TIG repair with matched HSS filler, using 500–600 °C preheat and immediate re-tempering.
Can M41 be formed, bent or molded?
Hot forge 1050–1150 °C with slow furnace cooling and full spheroidize anneal at 850–900 °C; no meaningful cold formability.
What surface finishes work on M41?
Austenitize ~1190–1220 °C in vacuum/salt, quench and triple temper 540–560 °C; finish with black oxide, steam-oxide or PVD TiN/TiAlN for wear and rust protection.
M41 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 | 1.05 – 1.15 | 1.1 |
| Mn | 0.2 – 0.6 | 0.35 |
| Si | 0.15 – 0.65 | 0.35 |
| Cr | 3.75 – 4.5 | 4.1 |
| W | 6.25 – 7 | 6.6 |
| Mo | 3.25 – 4.25 | 3.75 |
| V | 1.75 – 2.25 | 2 |
| Co | 4.75 – 5.75 | 5.25 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
M41 HT66-68 — frequently asked
What is M41 HT66-68 used for?
M41 HT66-68 is typically used for high-speed turning tools, drills for hard materials, reamers and aerospace tooling. In short: cobalt HSS for hot hardness; hardens to 68–70 HRC; grind or EDM after hardening.
What is the yield strength of M41 HT66-68?
M41 HT66-68 has a typical yield strength of 600 MPa (87 ksi) and a tensile strength of 2,200 MPa (319 ksi) — stronger than 77% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is M41 HT66-68 easy to machine?
Not especially — machinability is rated not recommended (4/100, worse than 100% of steel grades). Machine only in the annealed state with rigid setups, sharp cobalt-HSS or coated carbide and generous coolant; after hardening only grinding, EDM or superabrasive finishing is practical.
Can M41 HT66-68 be welded?
Not readily — weldability is rated poor (18/100). Not a structural weld metal — only tip/shank friction or flash welding and TIG repair with matched HSS filler, using 500–600 °C preheat and immediate re-tempering.
What surface finishes work on M41 HT66-68?
Austenitize ~1190–1220 °C in vacuum/salt, quench and triple temper 540–560 °C; finish with black oxide, steam-oxide or PVD TiN/TiAlN for wear and rust protection.
Can M41 HT66-68 be formed, bent or molded?
Hot forge 1050–1150 °C with slow furnace cooling and full spheroidize anneal at 850–900 °C; no meaningful cold formability.
What is the maximum service temperature of M41 HT66-68?
M41 HT66-68 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 M41-ANN and M41 HT68-70?
ANN is the default condition — standard as-supplied condition for bars, blanks and forging stock; machine to shape before hardening. HT68-70: peak-hardness condition for form tools and light-cut precision tooling; very low toughness, avoid interrupted cuts. Yield strength is 600 MPa in ANN versus 2,000 MPa in HT68-70.
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)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- Cobalt high-speed steel bar datasheets (HSS M-series) — 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.