Steel T8 Annealed vs T8 HT 64-66 HRC
Steel · T8 temper comparison
T8 Annealed and T8 HT 64-66 HRC are two conditions of the same steel grade, T8: Annealed versus HT 64-66 HRC (hardened (1230–1260 °C) and double tempered ~550 °C). The chemistry is identical, so every difference below comes from the condition. T8 HT 64-66 HRC is the stronger of the two: tensile strength 2,250 MPa (326 ksi) against 900 MPa (131 ksi) for T8 Annealed, about 150% more. In exchange, T8 Annealed is the more ductile: elongation 15% versus 0.3% for T8 HT 64-66 HRC, and T8 HT 64-66 HRC is harder (840 HV vs 250 HV). T8 HT 64-66 HRC runs hotter in service (600°C vs 400°C continuous). On the shop floor, T8 Annealed machines more easily (fair vs not recommended).
T8 AnnealedChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
T8 HT 64-66 HRCChoose it when strength drives the design, or when the part sees heat.
T8 Annealed vs T8 HT 64-66 HRC: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all steel grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Tensile Strength (Ultimate)
Elongation at Break
Compressive Strength
Charpy V-Notch Impact (RT)
Hardness, Vickers
Same in both: Shear Modulus 85 GPa12.3 Msi · Bulk Modulus 170 GPa24.7 Msi · Poisson's Ratio 0.29 · Yield Strength (0.2% offset) 570 MPa82.7 ksi · Reduction in Area 25% · Hardness, Brinell 240 HB · Hardness, Rockwell B 99 HRB
Physical
Density and transition temperatures.
Same in both: Density 8.6 g/cm³0.31 lb/in³ · Melting Point (Solidus) 1,400°C2,552 °F · Liquidus Temperature 1,460°C2,660 °F
Thermal
How each material carries heat and how hot it can run.
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 22 W/m·K12.7 BTU/hr·ft·°F · Specific Heat Capacity 420 J/kg·K0.1 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.2 µm/m·K6.2 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 3.1 % IACS · Electrical Resistivity 5.5×10⁻⁷ Ω·m21.7 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V · Corrosion Resistance 18 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Polishability
Same in both: Weldability 15 / 100 · Formability (cold) 12 / 100 · Brazeability / Solderability 55 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 60 MJ/kg25,795 BTU/lb · Embodied Carbon (primary production) 4.2 kg CO₂/kg · Embodied Water 90 L/kg10.8 gal/lb · Typical Recycled Content 35%
Strength versus weight
Yield strength against density for every steel grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
T8 Annealed vs T8 HT 64-66 HRC — frequently asked
Is T8 HT 64-66 HRC stronger than T8 Annealed?
Yes. T8 HT 64-66 HRC has a typical tensile strength of 2,250 MPa (326 ksi) against 900 MPa (131 ksi) for T8 Annealed — about 150% more.
Which condition does FabDigit quote by default, Annealed or HT 64-66 HRC?
Annealed is the default T8 condition in the FabDigit quote flow. The other condition is available on request or by drawing note — specify it in the material field or the part notes and the quote is priced for it.
Which is easier to machine, T8 Annealed or T8 HT 64-66 HRC?
T8 Annealed. Its machinability rates fair (35/100) against not recommended (5/100) for T8 HT 64-66 HRC.
Ready to make it?
Upload a CAD file and FabDigit prices the part in T8 Annealed and T8 HT 64-66 HRC side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.