Steel C55 +A vs C55 +QT
Steel · C55 temper comparison
C55 +A and C55 +QT are two conditions of the same steel grade, C55: +A (annealed) versus +QT (quenched and tempered). The chemistry is identical, so every difference below comes from the condition. C55 +QT is the stronger of the two: yield strength 550 MPa (79.8 ksi) against 350 MPa (50.8 ksi) for C55 +A, about 57% more; tensile strength follows at 870 MPa (126 ksi) vs 640 MPa (92.8 ksi). In exchange, C55 +A is the more ductile: elongation 21% versus 15% for C55 +QT, and C55 +QT is harder (265 HB vs 195 HB). On the shop floor, C55 +A machines more easily (50 vs 40 out of 100).
C55 +AChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
C55 +QTChoose it when strength drives the design.
C55 +A vs C55 +QT: 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 210 GPa30.5 Msi · Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29 · Compressive Strength 420 MPa60.9 ksi · Hardness, Vickers 230 HV
Physical
Density and transition temperatures.
Same in both: Density 7.84 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,420°C2,588 °F · Liquidus Temperature 1,480°C2,696 °F
Thermal
How each material carries heat and how hot it can run.
Same in both: Thermal Conductivity 47 W/m·K27.2 BTU/hr·ft·°F · Specific Heat Capacity 480 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.4 µm/m·K6.3 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Max Service Temperature (continuous) 400°C752 °F · Min Service Temperature -20°C-4 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 8.6 % IACS · Electrical Resistivity 2×10⁻⁷ Ω·m7.87 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.61 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 30 / 100 · 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 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.
C55 +A vs C55 +QT — frequently asked
Is C55 +QT stronger than C55 +A?
Yes. C55 +QT has a typical yield strength of 550 MPa (79.8 ksi) against 350 MPa (50.8 ksi) for C55 +A — about 57% more. Tensile strength is 870 MPa (126 ksi) vs 640 MPa (92.8 ksi).
Which condition does FabDigit quote by default, +A or +QT?
+N is the default C55 condition in the FabDigit quote flow (neither +A nor +QT). 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, C55 +A or C55 +QT?
C55 +A, by a small margin. Both rate fair for machinability — 50/100 against 40/100 for C55 +QT.
Ready to make it?
Upload a CAD file and FabDigit prices the part in C55 +A and C55 +QT 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.