Steel 8645-HR vs 8645-QT425
Steel · 8645 temper comparison
8645-HR and 8645-QT425 are two conditions of the same steel grade, 8645: HR (hot rolled) versus QT425 (Q&T 425 °C). The chemistry is identical, so every difference below comes from the condition. 8645-QT425 is the stronger of the two: yield strength 1,380 MPa (200 ksi) against 500 MPa (72.5 ksi) for 8645-HR, about 176% more; tensile strength follows at 1,550 MPa (225 ksi) vs 830 MPa (120 ksi). In exchange, 8645-HR is the more ductile: elongation 17% versus 13% for 8645-QT425, and 8645-QT425 is harder (425 HB vs 235 HB). 8645-HR runs hotter in service (400°C vs 330°C continuous). On the shop floor, 8645-HR machines more easily (fair vs poor).
8645-HRChoose it when the part is bent, formed or impact-loaded, or when the part sees heat.
8645-QT425Choose it when strength drives the design.
8645-HR 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
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Hardness, Brinell
Hardness, Rockwell B
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 · Fracture Toughness (K_IC) 70 MPa·√m63.7 ksi·√in · Charpy V-Notch Impact (RT) 20 J14.8 ft·lbf
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 %)
Weldability
Formability (cold)
Same in both: 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-HR vs 8645-QT425 — frequently asked
Is 8645-QT425 stronger than 8645-HR?
Yes. 8645-QT425 has a typical yield strength of 1,380 MPa (200 ksi) against 500 MPa (72.5 ksi) for 8645-HR — about 176% more. Tensile strength is 1,550 MPa (225 ksi) vs 830 MPa (120 ksi).
Which condition does FabDigit quote by default, HR or QT425?
Annealed is the default 8645 condition in the FabDigit quote flow (neither HR 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-HR or 8645-QT425?
8645-HR. Its machinability rates fair (50/100) against poor (30/100) for 8645-QT425; for welding the order is 8645-QT425 first (poor, 30/100) then 8645-HR (poor, 25/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 8645-HR 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.