Steel C4C +AC vs C4C +U
Steel · C4C temper comparison
C4C +AC and C4C +U are two conditions of the same steel grade, C4C: +AC (spheroidize annealed) versus +U (hot rolled). The chemistry is identical, so every difference below comes from the condition. C4C +U is the stronger of the two: yield strength 210 MPa (30.5 ksi) against 175 MPa (25.4 ksi) for C4C +AC, about 20% more; tensile strength follows at 330 MPa (47.9 ksi) vs 300 MPa (43.5 ksi). In exchange, C4C +AC is the more ductile: elongation 43% versus 38% for C4C +U, and C4C +U is harder (95 HB vs 85 HB).
C4C +ACChoose it when the part is bent, formed or impact-loaded.
C4C +UChoose it when strength drives the design.
C4C +AC vs C4C +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, 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 · Compressive Strength 210 MPa30.5 ksi · Fracture Toughness (K_IC) 120 MPa·√m109 ksi·√in · Hardness, Rockwell B 55 HRB
Physical
Density and transition temperatures.
Same in both: Density 7.87 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,500°C2,732 °F · Liquidus Temperature 1,533°C2,791 °F
Thermal
How each material carries heat and how hot it can run.
Same in both: Thermal Conductivity 58 W/m·K33.5 BTU/hr·ft·°F · Specific Heat Capacity 480 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.9 µm/m·K6.6 µin/in·°F · Latent Heat of Fusion 247 J/g106 BTU/lb · Max Service Temperature (continuous) 400°C752 °F · Min Service Temperature -40°C-40 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 11.5 % IACS · Electrical Resistivity 1.5×10⁻⁷ Ω·m5.91 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.65 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 %)
Formability (cold)
Same in both: Weldability 95 / 100 · Brazeability / Solderability 80 / 100 · Polishability 45 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 25 MJ/kg10,748 BTU/lb · Embodied Carbon (primary production) 2 kg CO₂/kg · Embodied Water 40 L/kg4.8 gal/lb · Typical Recycled Content 25%
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.
C4C +AC vs C4C +U — frequently asked
Is C4C +U stronger than C4C +AC?
Yes. C4C +U has a typical yield strength of 210 MPa (30.5 ksi) against 175 MPa (25.4 ksi) for C4C +AC — about 20% more. Tensile strength is 330 MPa (47.9 ksi) vs 300 MPa (43.5 ksi).
Which condition does FabDigit quote by default, +AC or +U?
+U is the default C4C condition in the FabDigit quote flow. 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.
When should I choose C4C +AC over C4C +U?
Pick C4C +AC when the part is bent, formed or impact-loaded. Pick C4C +U when strength drives the design.
Ready to make it?
Upload a CAD file and FabDigit prices the part in C4C +AC and C4C +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.