Steel C55E +QT vs C55E +SR
Steel · C55E temper comparison
C55E +QT and C55E +SR are two conditions of the same steel grade, C55E: +QT (quenched and tempered) versus +SR (stress relieved). The chemistry is identical, so every difference below comes from the condition. C55E +SR is the stronger of the two: yield strength 600 MPa (87 ksi) against 550 MPa (79.8 ksi) for C55E +QT, about 9% more. In exchange, C55E +QT is the more ductile: elongation 14% versus 10% for C55E +SR, and C55E +QT is harder (250 HB vs 230 HB). C55E +QT runs hotter in service (300°C vs 250°C continuous). On the shop floor, C55E +SR machines more easily (good vs fair).
C55E +QTChoose it when the part is bent, formed or impact-loaded, or when the part sees heat.
C55E +SRChoose it when strength drives the design, or when the part is machined in volume.
C55E +QT vs C55E +SR: 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 7.84 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.
Thermal Conductivity
Max Service Temperature (continuous)
Same in both: Specific Heat Capacity 470 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 11.5 µm/m·K6.4 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -20°C-4 °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) -0.61 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 %)
Weldability
Formability (cold)
Same in both: Brazeability / Solderability 55 / 100 · Polishability 55 / 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 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.
C55E +QT vs C55E +SR — frequently asked
Is C55E +SR stronger than C55E +QT?
Yes. C55E +SR has a typical yield strength of 600 MPa (87 ksi) against 550 MPa (79.8 ksi) for C55E +QT — about 9% more. Tensile strength is 780 MPa (113 ksi) vs 850 MPa (123 ksi).
Which condition does FabDigit quote by default, +QT or +SR?
+QT is the default C55E 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.
Which is easier to machine, C55E +QT or C55E +SR?
C55E +SR. Its machinability rates good (56/100) against fair (45/100) for C55E +QT; for welding the order is C55E +QT first (poor, 25/100) then C55E +SR (poor, 20/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in C55E +QT and C55E +SR 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.