Steel Böhler S390 HT 66-68HRC
Hardness band
also S390
HT 66-68HRC = hardened & triple tempered
The usual working hardness for hobs, milling cutters, broaches and form tools in difficult materials.
Values for the HT 66-68HRC condition
Other Böhler S390 tempers and conditions
Böhler S390 is listed in 4 conditions; see the grade overview at Böhler S390.
- HT 66-68HRC
- Annealed
- HT 68-70HRC
- HT 64-66HRC
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
HT 66-68HRCThis page Hardened & triple tempered | The usual working hardness for hobs, milling cutters, broaches and form tools in difficult materials. | — | — | — | 67 HRC | — |
AnnealedDefault ≤ 340 HB (as-delivered bar/plate) | Standard mill delivery condition for bar, plate and blanks; machine to shape here, then harden. | 700 | 1,000 | 10 | 31 HRC | 3.4 % IACS |
Hardened & triple tempered | High austenitising temperature (~1180 °C) for maximum wear resistance and hot hardness; accept minimum toughness. | 2,000 | 2,100 | 0 | 69 HRC | 2.8 % IACS |
Hardened & triple tempered | Lower austenitising temperature; choose when edge chipping or interrupted cuts dominate over pure wear. | 2,100 | 2,400 | 0.5 | 65 HRC | 2.9 % IACS |
What is Böhler S390 HT 66-68HRC?
Böhler S390 HT 66-68HRC is Böhler S390 heat treated to HT 66-68HRC — the usual working hardness for hobs, milling cutters, broaches and form tools in difficult materials. Böhler S390 HT 66-68HRC has a yield strength of 700 MPa (102 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 81% of steel grades. Elongation at break is 10% and the elastic modulus is 245 GPa (35.5 Msi). Böhler S390 HT 66-68HRC has a density of 8 g/cm³ (0.289 lb/in³), heavier than 95% of steel grades. It melts at 1,260°C (2,300 °F). Annealed is the default condition FabDigit quotes; HT 66-68HRC is available on request or by drawing note.
Advantages
- Stiff — 245 GPa (35.5 Msi), better than 100% of steel grades
- Polishes to a fine finish — 85/100, better than 99% of steel grades
- High service temperature — 580°C (1,076 °F), better than 97% of steel grades
- High strength — 700 MPa (102 ksi), better than 81% of steel grades
Limitations
- Difficult to machine — 4/100, worse than 100% of steel grades
- Low fracture toughness — 17 MPa·√m (15.5 ksi·√in), worse than 99% of steel grades
- High embodied carbon — 5.5 kg CO₂/kg, worse than 97% of steel grades
- Limited ductility — 10%, worse than 91% of steel grades
- Poor heat conductor — 24 W/m·K (13.9 BTU/hr·ft·°F), worse than 90% of steel grades
Böhler S390 HT 66-68HRC properties
Typical room-temperature values for Böhler S390 HT 66-68HRC; 10 are specific to this condition. Other listed values are Böhler S390 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
Böhler S390 HT 66-68HRC has a density of 8 g/cm³ (0.289 lb/in³), heavier than 95% of steel grades. It melts at 1,260°C (2,300 °F).
Mechanical17
Böhler S390 HT 66-68HRC has a yield strength of 700 MPa (102 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 81% of steel grades. Elongation at break is 10% and the elastic modulus is 245 GPa (35.5 Msi).
Thermal5
Böhler S390 HT 66-68HRC is rated for continuous service to 580°C (1,076 °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
Böhler S390 HT 66-68HRC conducts electricity at 3.4 % IACS, worse than 86% of steel grades.
Chemical & Environmental2
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of Böhler S390 HT 66-68HRC takes about 70 MJ of energy and emits 5.5 kg of CO₂ — more than 97% of steel grades. Typical recycled content is 25%.
Manufacturability6
Böhler S390 HT 66-68HRC's machinability is not recommended (4/100, worse than 100% of steel grades); weldability poor (20/100); formability poor (15/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Böhler S390 HT 66-68HRC
Is Böhler S390 easy to machine?
Machine only in the soft-annealed state with rigid setups, low speeds and carbide or coated-carbide tooling; after hardening the 4.8 % V carbides make CBN/diamond grinding the only practical route.
Can Böhler S390 be welded?
Not intended for structural welding; repair only by TIG/laser with matching PM-HSS filler, 450–500 °C preheat and immediate re-temper.
Can Böhler S390 be formed, bent or molded?
Hot forge 1100–900 °C with slow furnace cooling and soft anneal at 850–900 °C; no cold forming.
What surface finishes work on Böhler S390?
Vacuum harden 1150–1180 °C, triple temper 540–560 °C, then grind, lap and finish with TiAlN/AlCrN PVD, steam oxide or nitriding (thin case only).
Böhler S390 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 | 1.55 – 1.7 | 1.64 |
| Si | 0.3 – 0.8 | 0.6 |
| Mn | 0.2 – 0.5 | 0.3 |
| Cr | 4.6 – 5 | 4.8 |
| Mo | 1.8 – 2.2 | 2 |
| W | 10 – 11 | 10.5 |
| V | 4.6 – 5 | 4.8 |
| Cocobalt raises hot hardness and secondary hardening response | 7.5 – 8.5 | 8 |
| Fe | balance | — |
Böhler S390 HT 66-68HRC — frequently asked
What is Böhler S390 HT 66-68HRC used for?
Böhler S390 HT 66-68HRC is typically used for high-performance drills, milling cutters and broaches. In short: high hot hardness PM-HSS; hardenable to 68–70 HRC; 4.8 % V carbide wear resistance.
What is the yield strength of Böhler S390 HT 66-68HRC?
Böhler S390 HT 66-68HRC has a typical yield strength of 700 MPa (102 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 81% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is Böhler S390 HT 66-68HRC easy to machine?
Not especially — machinability is rated not recommended (4/100, worse than 100% of steel grades). Machine only in the soft-annealed state with rigid setups, low speeds and carbide or coated-carbide tooling; after hardening the 4.8 % V carbides make CBN/diamond grinding the only practical route.
Can Böhler S390 HT 66-68HRC be welded?
Not readily — weldability is rated poor (20/100). Not intended for structural welding; repair only by TIG/laser with matching PM-HSS filler, 450–500 °C preheat and immediate re-temper.
What surface finishes work on Böhler S390 HT 66-68HRC?
Vacuum harden 1150–1180 °C, triple temper 540–560 °C, then grind, lap and finish with TiAlN/AlCrN PVD, steam oxide or nitriding (thin case only).
Can Böhler S390 HT 66-68HRC be formed, bent or molded?
Hot forge 1100–900 °C with slow furnace cooling and soft anneal at 850–900 °C; no cold forming.
What is the maximum service temperature of Böhler S390 HT 66-68HRC?
Böhler S390 HT 66-68HRC 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
- BÖHLER S390 MICROCLEAN PM high speed steel data sheet — voestalpine BÖHLER Edelstahl (2022)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels and High-Performance Alloys (High-Speed Tool Steels) — ASM International (1990)
- ISO 4957 — Tool steels — ISO (2018)
- ASM Specialty Handbook: Tool Materials — ASM International (1995)
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.