Steel 15B2 +QT vs 15B2 +U
Steel · 15B2 temper comparison
15B2 +QT and 15B2 +U are two conditions of the same steel grade, 15B2: +QT (quenched and tempered) versus +U (hot rolled). The chemistry is identical, so every difference below comes from the condition. 15B2 +QT is the stronger of the two: yield strength 700 MPa (102 ksi) against 300 MPa (43.5 ksi) for 15B2 +U, about 133% more; tensile strength follows at 850 MPa (123 ksi) vs 460 MPa (66.7 ksi). In exchange, 15B2 +U is the more ductile: elongation 24% versus 14% for 15B2 +QT, and 15B2 +QT is harder (265 HB vs 135 HB). 15B2 +QT runs hotter in service (350°C vs 300°C continuous). On the shop floor, 15B2 +U welds better (very good vs good).
15B2 +QTChoose it when strength drives the design, or when the part sees heat.
15B2 +UChoose it when the part is bent, formed or impact-loaded, or when it will be welded.
15B2 +QT vs 15B2 +U: 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, Rockwell B
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 420 MPa60.9 ksi
Physical
Density and transition temperatures.
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,465°C2,669 °F · Liquidus Temperature 1,520°C2,768 °F
Thermal
How each material carries heat and how hot it can run.
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 48 W/m·K27.7 BTU/hr·ft·°F · Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12 µm/m·K6.7 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -30°C-22 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 10 % IACS · Electrical Resistivity 1.7×10⁻⁷ Ω·m6.69 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.62 V · Corrosion Resistance 10 / 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 70 / 100 · Polishability 50 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 27 MJ/kg11,608 BTU/lb · Embodied Carbon (primary production) 2 kg CO₂/kg · Embodied Water 50 L/kg6 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.
15B2 +QT vs 15B2 +U — frequently asked
Is 15B2 +QT stronger than 15B2 +U?
Yes. 15B2 +QT has a typical yield strength of 700 MPa (102 ksi) against 300 MPa (43.5 ksi) for 15B2 +U — about 133% more. Tensile strength is 850 MPa (123 ksi) vs 460 MPa (66.7 ksi).
Which condition does FabDigit quote by default, +QT or +U?
+AC+C is the default 15B2 condition in the FabDigit quote flow (neither +QT nor +U). 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, 15B2 +QT or 15B2 +U?
15B2 +U, by a small margin. Both rate fair for machinability — 50/100 against 45/100 for 15B2 +QT; for welding the order is 15B2 +U first (very good, 82/100) then 15B2 +QT (good, 55/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 15B2 +QT and 15B2 +U 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.