Steel T8 · hardness band
Steel T8 HT 64-66 HRC
Properties of the HT 64-66 HRC condition, compared with the other T8 tempers.
The normal working hardness for T8 cutting tools — best balance of red hardness and wear resistance.
What is T8 HT 64-66 HRC?
T8 HT 64-66 HRC is T8 heat treated to HT 64-66 HRC — the normal working hardness for T8 cutting tools — best balance of red hardness and wear resistance. T8 HT 64-66 HRC has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 2,250 MPa (326 ksi) — stronger than 74% of steel grades. Elongation at break is 0.3% and the elastic modulus is 225 GPa (32.6 Msi). T8 HT 64-66 HRC has a density of 8.6 g/cm³ (0.311 lb/in³), heavier than 99% of steel grades. It melts at 1,400°C (2,552 °F). Annealed is the default condition FabDigit quotes; HT 64-66 HRC is available on request or by drawing note.
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- Limited ductility — 0.3%, worse than 100% of steel grades
- Difficult to machine — 5/100, worse than 100% of steel grades
- High embodied carbon — 4.2 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
- Difficult to weld — 15/100, worse than 91% of steel grades
T8 HT 64-66 HRC properties
Typical room-temperature values for T8 HT 64-66 HRC — 13 properties are specific to this condition; the rest are grade-level values shared by every T8 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
T8 HT 64-66 HRC has a density of 8.6 g/cm³ (0.311 lb/in³), heavier than 99% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical13
T8 HT 64-66 HRC has a yield strength of 570 MPa (82.7 ksi) and a tensile strength of 2,250 MPa (326 ksi) — stronger than 74% of steel grades. Elongation at break is 0.3% and the elastic modulus is 225 GPa (32.6 Msi).
Thermal6
T8 HT 64-66 HRC is rated for continuous service to 600°C (1,112 °F). It conducts heat at 22 W/m·K (12.7 BTU/hr·ft·°F), worse than 93% of steel grades. Thermal expansion is 11.2 µm/m·K (6.22 µin/in·°F).
Electrical3
T8 HT 64-66 HRC 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 T8 HT 64-66 HRC takes about 60 MJ of energy and emits 4.2 kg of CO₂ — more than 95% of steel grades. Typical recycled content is 35%.
Manufacturability7
T8 HT 64-66 HRC's machinability is not recommended (5/100, worse than 100% of steel grades); weldability poor (15/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other T8 tempers and conditions
T8 is also supplied in 5 other conditions. The full side-by-side table is on the T8 overview.
- AnnealedDefaultStandard stocked condition for machining tool blanks before hardening.570 MPa yield · 240 HB
- HT 64-66 HRCThe normal working hardness for T8 cutting tools — best balance of red hardness and wear resistance.2,250 MPa tensile
- HT 62-64 HRCChoose when interrupted cuts or shock demand extra toughness at some loss of wear resistance.2,100 MPa tensile
- HT 66-67 HRCUse only for rigid, continuous-cut tooling on abrasive work where maximum wear resistance outweighs chipping risk.2,100 MPa tensile
Working with T8 HT 64-66 HRC
Is T8 easy to machine?
Machine only in the annealed condition with rigid setups, sharp carbide or cobalt-HSS tooling, low speed and heavy flood coolant; hardened T8 must be ground or EDM'd, using soft wheels and light dressing to avoid grinding burn.
Can T8 be welded?
Not a structural welding grade — repair only, by GTAW/PTA with matching HSS or high-Co filler, preheat 500–550 °C, immediate re-temper; expect cracking if cooled to room temperature unbuffered.
Can T8 be formed, bent or molded?
Hot work at 1050–1150 °C with slow furnace cooling and mandatory full anneal (~870 °C, slow cool) afterwards; no meaningful cold forming — harden from 1230–1260 °C (salt or vacuum), oil/air/salt quench, double temper 540–595 °C.
What surface finishes work on T8?
Stress-relieve rough-machined blanks before hardening; finish by precision grinding and lapping, then steam-oxide, black-oxide, nitriding or TiN/TiAlN PVD (below temper temperature) for wear and rust protection — never anodise.
T8 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 | 0.75 – 0.85 | 0.8 |
| W | 13.25 – 14.75 | 14 |
| Co | 4.25 – 5.75 | 5 |
| Cr | 3.75 – 4.5 | 4.1 |
| V | 1.8 – 2.4 | 2 |
| Mo | 0.4 – 1 | 0.7 |
| Mn | 0.15 – 0.4 | 0.28 |
| Si | 0.15 – 0.4 | 0.28 |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
T8 HT 64-66 HRC — frequently asked
What is T8 HT 64-66 HRC used for?
T8 HT 64-66 HRC is typically used for cold cutting knives and blades, hand tools, lathe tool bits and form tools, milling cutters, twist drills and taps and punches and trim dies. In short: tough water-hardening tool.
What is the yield strength of T8 HT 64-66 HRC?
T8 HT 64-66 HRC has a typical yield strength of 570 MPa (82.7 ksi) and a tensile strength of 2,250 MPa (326 ksi) — stronger than 74% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is T8 HT 64-66 HRC 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 carbide or cobalt-HSS tooling, low speed and heavy flood coolant; hardened T8 must be ground or EDM'd, using soft wheels and light dressing to avoid grinding burn.
Can T8 HT 64-66 HRC be welded?
Not readily — weldability is rated poor (15/100). Not a structural welding grade — repair only, by GTAW/PTA with matching HSS or high-Co filler, preheat 500–550 °C, immediate re-temper; expect cracking if cooled to room temperature unbuffered.
What surface finishes work on T8 HT 64-66 HRC?
Stress-relieve rough-machined blanks before hardening; finish by precision grinding and lapping, then steam-oxide, black-oxide, nitriding or TiN/TiAlN PVD (below temper temperature) for wear and rust protection — never anodise.
Can T8 HT 64-66 HRC be formed, bent or molded?
Hot work at 1050–1150 °C with slow furnace cooling and mandatory full anneal (~870 °C, slow cool) afterwards; no meaningful cold forming — harden from 1230–1260 °C (salt or vacuum), oil/air/salt quench, double temper 540–595 °C.
What is the maximum service temperature of T8 HT 64-66 HRC?
T8 HT 64-66 HRC is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between T8 Annealed and T8-CDA?
Annealed is the default condition — standard stocked condition for machining tool blanks before hardening. CDA: pick for small-diameter precision bar and drill-rod blanks needing close size and straightness before hardening. Yield strength is 570 MPa in Annealed versus 750 MPa in CDA.
Can FabDigit make parts in T8 HT 64-66 HRC?
Yes — T8 HT 64-66 HRC is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A600 — Tool Steel, High Speed, Tool and Die Steels — 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)
- SAE J437/J438 — Tool and Die Steels — SAE International (2015)
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.