Steel 8MoB5-4 Q+T vs 8MoB5-4 +U
Steel · 8MoB5-4 temper comparison
8MoB5-4 Q+T and 8MoB5-4 +U are two conditions of the same steel grade, 8MoB5-4: Q+T (quenched and tempered) versus +U (hot rolled). The chemistry is identical, so every difference below comes from the condition. 8MoB5-4 Q+T is the stronger of the two: yield strength 620 MPa (89.9 ksi) against 300 MPa (43.5 ksi) for 8MoB5-4 +U, about 107% more; tensile strength follows at 780 MPa (113 ksi) vs 470 MPa (68.2 ksi). In exchange, 8MoB5-4 +U is the more ductile: elongation 25% versus 14% for 8MoB5-4 Q+T, and 8MoB5-4 Q+T is harder (245 HB vs 150 HB). On the shop floor, 8MoB5-4 +U machines more easily (good vs fair) and 8MoB5-4 +U welds better (very good vs good).
8MoB5-4 Q+TChoose it when strength drives the design.
8MoB5-4 +UChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
8MoB5-4 Q+T vs 8MoB5-4 +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
Compressive Strength
Shear Strength
Fatigue Strength (Endurance Limit)
Fracture Toughness (K_IC)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 210 GPa30.5 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29
Physical
Density and transition temperatures.
Same in both: Density 7.85 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,450°C2,642 °F · Liquidus Temperature 1,520°C2,768 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Same in both: Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.8 µm/m·K6.6 µin/in·°F · Latent Heat of Fusion 270 J/g116 BTU/lb · Max Service Temperature (continuous) 400°C752 °F · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
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 70 / 100 · Polishability 55 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 30 MJ/kg12,898 BTU/lb · Embodied Carbon (primary production) 2.3 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.
8MoB5-4 Q+T vs 8MoB5-4 +U — frequently asked
Is 8MoB5-4 Q+T stronger than 8MoB5-4 +U?
Yes. 8MoB5-4 Q+T has a typical yield strength of 620 MPa (89.9 ksi) against 300 MPa (43.5 ksi) for 8MoB5-4 +U — about 107% more. Tensile strength is 780 MPa (113 ksi) vs 470 MPa (68.2 ksi).
Which condition does FabDigit quote by default, Q+T or +U?
+A is the default 8MoB5-4 condition in the FabDigit quote flow (neither Q+T 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, 8MoB5-4 Q+T or 8MoB5-4 +U?
8MoB5-4 +U. Its machinability rates good (57/100) against fair (42/100) for 8MoB5-4 Q+T; for welding the order is 8MoB5-4 +U first (very good, 72/100) then 8MoB5-4 Q+T (good, 60/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 8MoB5-4 Q+T and 8MoB5-4 +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.