Steel 31CrMoB2-1 +A vs 31CrMoB2-1 +U
Steel · 31CrMoB2-1 temper comparison
31CrMoB2-1 +A and 31CrMoB2-1 +U are two conditions of the same steel grade, 31CrMoB2-1: +A (annealed) versus +U (hot rolled). The chemistry is identical, so every difference below comes from the condition. 31CrMoB2-1 +U is the stronger of the two: yield strength 430 MPa (62.4 ksi) against 390 MPa (56.6 ksi) for 31CrMoB2-1 +A, about 10% more; tensile strength follows at 680 MPa (98.6 ksi) vs 600 MPa (87 ksi). In exchange, 31CrMoB2-1 +A is the more ductile: elongation 22% versus 18% for 31CrMoB2-1 +U, and 31CrMoB2-1 +U is harder (210 HB vs 185 HB). On the shop floor, 31CrMoB2-1 +A welds better (good vs fair).
31CrMoB2-1 +AChoose it when the part is bent, formed or impact-loaded, or when it will be welded.
31CrMoB2-1 +UChoose it when strength drives the design.
31CrMoB2-1 +A vs 31CrMoB2-1 +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 C
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) 1,420°C2,588 °F · Liquidus Temperature 1,495°C2,723 °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) 12 µm/m·K6.7 µin/in·°F · Latent Heat of Fusion 250 J/g107 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) -0.62 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 65 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 25 MJ/kg10,748 BTU/lb · Embodied Carbon (primary production) 1.9 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.
31CrMoB2-1 +A vs 31CrMoB2-1 +U — frequently asked
Is 31CrMoB2-1 +U stronger than 31CrMoB2-1 +A?
Yes. 31CrMoB2-1 +U has a typical yield strength of 430 MPa (62.4 ksi) against 390 MPa (56.6 ksi) for 31CrMoB2-1 +A — about 10% more. Tensile strength is 680 MPa (98.6 ksi) vs 600 MPa (87 ksi).
Which condition does FabDigit quote by default, +A or +U?
+QT is the default 31CrMoB2-1 condition in the FabDigit quote flow (neither +A 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, 31CrMoB2-1 +A or 31CrMoB2-1 +U?
31CrMoB2-1 +A, by a small margin. Both rate good for machinability — 60/100 against 55/100 for 31CrMoB2-1 +U; for welding the order is 31CrMoB2-1 +A first (good, 55/100) then 31CrMoB2-1 +U (fair, 45/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in 31CrMoB2-1 +A and 31CrMoB2-1 +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.