Steel SKH59-ANN vs SKH59 QT66-68
Steel · SKH59 temper comparison
SKH59-ANN and SKH59 QT66-68 are two conditions of the same steel grade, SKH59: ANN (annealed) versus QT66-68 (hardened & tempered, 66–68 HRC). The chemistry is identical, so every difference below comes from the condition. Both yield at about 600 MPa — the mechanical properties are the same, and the difference is in how the stock is processed and what it is certified to (annealed versus hardened & tempered, 66–68 HRC). SKH59-ANN is the more ductile: elongation 12% versus 0% for SKH59 QT66-68, and SKH59 QT66-68 is harder (67 HRC vs 25 HRC). SKH59 QT66-68 runs hotter in service (600°C vs 300°C continuous). On the shop floor, SKH59-ANN machines more easily (poor vs not recommended).
SKH59-ANNChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
SKH59 QT66-68Choose it when the part sees heat.
SKH59-ANN vs SKH59 QT66-68: 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
Elongation at Break
Compressive Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Rockwell C
Hardness, Vickers
Same in both: Shear Modulus 86 GPa12.5 Msi · Bulk Modulus 170 GPa24.7 Msi · Poisson's Ratio 0.28 · Tensile Strength (Ultimate) 900 MPa131 ksi · Yield Strength (0.2% offset) 600 MPa87 ksi · Reduction in Area 25% · Shear Strength 560 MPa81.2 ksi · Hardness, Brinell 255 HB · Hardness, Rockwell B 101 HRB
Physical
Density and transition temperatures.
Same in both: Density 7.98 g/cm³0.29 lb/in³ · Melting Point (Solidus) 1,290°C2,354 °F · Liquidus Temperature 1,430°C2,606 °F
Thermal
How each material carries heat and how hot it can run.
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 19 W/m·K11 BTU/hr·ft·°F · Specific Heat Capacity 420 J/kg·K0.1 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 10.6 µm/m·K5.9 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -50°C-58 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 2.9 % IACS · Electrical Resistivity 6×10⁻⁷ Ω·m23.6 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Same in both: Machinability Rating (AISI 1212 = 100 %) 25% · Weldability 15 / 100 · Formability (cold) 10 / 100 · Castability 25 / 100 · Brazeability / Solderability 60 / 100 · Polishability 80 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 55 MJ/kg23,646 BTU/lb · Embodied Carbon (primary production) 4.2 kg CO₂/kg · Embodied Water 120 L/kg14.4 gal/lb · Typical Recycled Content 25%
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.
SKH59-ANN vs SKH59 QT66-68 — frequently asked
What is the difference between SKH59-ANN and SKH59 QT66-68?
SKH59-ANN and SKH59 QT66-68 are two conditions of the same steel grade, SKH59: ANN (annealed) versus QT66-68 (hardened & tempered, 66–68 HRC). The chemistry is identical, so every difference below comes from the condition. Both yield at about 600 MPa — the mechanical properties are the same, and the difference is in how the stock is processed and what it is certified to (annealed versus hardened & tempered, 66–68 HRC).
Which condition does FabDigit quote by default, ANN or QT66-68?
ANN is the default SKH59 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, SKH59-ANN or SKH59 QT66-68?
SKH59-ANN. Its machinability rates poor (25/100) against not recommended (4/100) for SKH59 QT66-68.
Ready to make it?
Upload a CAD file and FabDigit prices the part in SKH59-ANN and SKH59 QT66-68 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.