Steel 81B45 QT28-32 vs 81B45 QT34-38
Steel · 81B45 temper comparison
81B45 QT28-32 and 81B45 QT34-38 are two conditions of the same steel grade, 81B45: QT28-32 (Q&T 28–32 HRC) versus QT34-38 (Q&T 34–38 HRC). The chemistry is identical, so every difference below comes from the condition. 81B45 QT34-38 is the stronger of the two: yield strength 1,060 MPa (154 ksi) against 860 MPa (125 ksi) for 81B45 QT28-32, about 23% more; tensile strength follows at 1,170 MPa (170 ksi) vs 1,000 MPa (145 ksi). In exchange, 81B45 QT28-32 is the more ductile: elongation 18% versus 15% for 81B45 QT34-38, and 81B45 QT34-38 is harder (341 HB vs 293 HB). 81B45 QT28-32 runs hotter in service (480°C vs 420°C continuous).
81B45 QT28-32Choose it when the part is bent, formed or impact-loaded, or when the part sees heat.
81B45 QT34-38Choose it when strength drives the design.
81B45 QT28-32 vs 81B45 QT34-38: 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
Shear Strength
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 400 MPa58 ksi · Hardness, Rockwell B 90 HRB
Physical
Density and transition temperatures.
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,416°C2,581 °F · Liquidus Temperature 1,470°C2,678 °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 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.2 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) -0.61 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 45 / 100 · Formability (cold) 50 / 100 · Brazeability / Solderability 60 / 100 · Polishability 60 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 30 MJ/kg12,898 BTU/lb · Embodied Carbon (primary production) 2.1 kg CO₂/kg · Embodied Water 60 L/kg7.2 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.
81B45 QT28-32 vs 81B45 QT34-38 — frequently asked
Is 81B45 QT34-38 stronger than 81B45 QT28-32?
Yes. 81B45 QT34-38 has a typical yield strength of 1,060 MPa (154 ksi) against 860 MPa (125 ksi) for 81B45 QT28-32 — about 23% more. Tensile strength is 1,170 MPa (170 ksi) vs 1,000 MPa (145 ksi).
Which condition does FabDigit quote by default, QT28-32 or QT34-38?
A is the default 81B45 condition in the FabDigit quote flow (neither QT28-32 nor QT34-38). 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, 81B45 QT28-32 or 81B45 QT34-38?
81B45 QT28-32, by a small margin. Both rate fair for machinability — 46/100 against 38/100 for 81B45 QT34-38.
Ready to make it?
Upload a CAD file and FabDigit prices the part in 81B45 QT28-32 and 81B45 QT34-38 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.