Steel 8645-QT205 vs 8645-QT425
Steel · 8645 temper comparison
8645-QT205 and 8645-QT425 are two conditions of the same steel grade, 8645: QT205 (Q&T 205 °C) versus QT425 (Q&T 425 °C). The chemistry is identical, so every difference below comes from the condition. 8645-QT205 is the stronger of the two: yield strength 1,720 MPa (249 ksi) against 1,380 MPa (200 ksi) for 8645-QT425, about 25% more; tensile strength follows at 2,000 MPa (290 ksi) vs 1,550 MPa (225 ksi). In exchange, 8645-QT425 is the more ductile: elongation 13% versus 10% for 8645-QT205, and 8645-QT205 is harder (560 HB vs 425 HB). 8645-QT425 runs hotter in service (330°C vs 150°C continuous). On the shop floor, 8645-QT425 machines more easily (30 vs 20 out of 100).
8645-QT205Choose it when strength drives the design.
8645-QT425Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
8645-QT205 vs 8645-QT425: 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.
Tensile Strength (Ultimate)
Yield Strength (0.2% offset)
Elongation at Break
Reduction in Area
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 205 GPa29.7 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29 · Compressive Strength 425 MPa61.6 ksi · Shear Strength 460 MPa66.7 ksi · Hardness, Rockwell B 92 HRB
Physical
Density and transition temperatures.
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,420°C2,588 °F · Liquidus Temperature 1,490°C2,714 °F
Thermal
How each material carries heat and how hot it can run.
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 45 W/m·K26 BTU/hr·ft·°F · Specific Heat Capacity 475 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.3 µm/m·K6.8 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 7.8 % IACS · Electrical Resistivity 2.2×10⁻⁷ Ω·m8.66 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V · Corrosion Resistance 12 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Machinability Rating (AISI 1212 = 100 %)
Same in both: Weldability 30 / 100 · Formability (cold) 35 / 100 · Brazeability / Solderability 55 / 100 · Polishability 60 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 34 MJ/kg14,617 BTU/lb · Embodied Carbon (primary production) 2.4 kg CO₂/kg · Embodied Water 65 L/kg7.8 gal/lb · Typical Recycled Content 30%
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.
8645-QT205 vs 8645-QT425 — frequently asked
Is 8645-QT205 stronger than 8645-QT425?
Yes. 8645-QT205 has a typical yield strength of 1,720 MPa (249 ksi) against 1,380 MPa (200 ksi) for 8645-QT425 — about 25% more. Tensile strength is 2,000 MPa (290 ksi) vs 1,550 MPa (225 ksi).
Which condition does FabDigit quote by default, QT205 or QT425?
Annealed is the default 8645 condition in the FabDigit quote flow (neither QT205 nor QT425). 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, 8645-QT205 or 8645-QT425?
8645-QT425, by a small margin. Both rate poor for machinability — 30/100 against 20/100 for 8645-QT205.
Ready to make it?
Upload a CAD file and FabDigit prices the part in 8645-QT205 and 8645-QT425 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.