Steel 18MnB4 +AC vs 18MnB4 +U
Steel · 18MnB4 temper comparison
18MnB4 +AC and 18MnB4 +U are two conditions of the same steel grade, 18MnB4: +AC (spheroidize annealed) versus +U (hot rolled). The chemistry is identical, so every difference below comes from the condition. 18MnB4 +U is the stronger of the two: yield strength 380 MPa (55.1 ksi) against 310 MPa (45 ksi) for 18MnB4 +AC, about 23% more; tensile strength follows at 570 MPa (82.7 ksi) vs 470 MPa (68.2 ksi). In exchange, 18MnB4 +AC is the more ductile: elongation 26% versus 20% for 18MnB4 +U, and 18MnB4 +U is harder (168 HB vs 140 HB).
18MnB4 +ACChoose it when the part is bent, formed or impact-loaded.
18MnB4 +UChoose it when strength drives the design.
18MnB4 +AC vs 18MnB4 +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)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 207 GPa30 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 1,505°C2,741 °F
Thermal
How each material carries heat and how hot it can run.
Same in both: Thermal Conductivity 46 W/m·K26.6 BTU/hr·ft·°F · Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.1 µm/m·K6.7 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Max Service Temperature (continuous) 350°C662 °F · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 9 % IACS · Electrical Resistivity 1.9×10⁻⁷ Ω·m7.48 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 55 / 100 · Polishability 60 / 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 55 L/kg6.6 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.
18MnB4 +AC vs 18MnB4 +U — frequently asked
Is 18MnB4 +U stronger than 18MnB4 +AC?
Yes. 18MnB4 +U has a typical yield strength of 380 MPa (55.1 ksi) against 310 MPa (45 ksi) for 18MnB4 +AC — about 23% more. Tensile strength is 570 MPa (82.7 ksi) vs 470 MPa (68.2 ksi).
Which condition does FabDigit quote by default, +AC or +U?
+AC+C is the default 18MnB4 condition in the FabDigit quote flow (neither +AC 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, 18MnB4 +AC or 18MnB4 +U?
18MnB4 +U, by a small margin. Both rate good for machinability — 60/100 against 55/100 for 18MnB4 +AC.
Ready to make it?
Upload a CAD file and FabDigit prices the part in 18MnB4 +AC and 18MnB4 +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.