Steel SKD1 QT55-58 vs SKD1-SR
Steel · SKD1 temper comparison
SKD1 QT55-58 and SKD1-SR are two conditions of the same steel grade, SKD1: QT55-58 (hardened & tempered 55–58 HRC) versus SR (stress relieved). The chemistry is identical, so every difference below comes from the condition. SKD1 QT55-58 is the stronger of the two: yield strength 1,620 MPa (235 ksi) against 470 MPa (68.2 ksi) for SKD1-SR, about 3.4 times as much; tensile strength follows at 1,850 MPa (268 ksi) vs 790 MPa (115 ksi). In exchange, SKD1-SR is the more ductile: elongation 11% versus 1% for SKD1 QT55-58, and SKD1 QT55-58 is harder (600 HB vs 240 HB). SKD1 QT55-58 runs hotter in service (350°C vs 200°C continuous). On the shop floor, SKD1-SR machines more easily (poor vs not recommended) and SKD1-SR welds better (poor vs not recommended).
SKD1 QT55-58Choose it when strength drives the design, or when the part sees heat.
SKD1-SRChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
SKD1 QT55-58 vs SKD1-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.
Elastic (Young's) Modulus
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)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Same in both: Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.29 · Charpy V-Notch Impact (RT) 11 J8.1 ft·lbf
Physical
Density and transition temperatures.
Same in both: Density 7.7 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,270°C2,318 °F · Liquidus Temperature 1,400°C2,552 °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 460 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 10.8 µm/m·K6 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -30°C-22 °F
Electrical
Conductivity and insulation.
Electrical Conductivity
Electrical Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Same in both: Galvanic Potential (seawater, vs SCE) -0.4 V
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: Castability 25 / 100 · Brazeability / Solderability 35 / 100 · Polishability 60 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 34 MJ/kg14,617 BTU/lb · Embodied Carbon (primary production) 2.6 kg CO₂/kg · Embodied Water 60 L/kg7.2 gal/lb · Typical Recycled Content 40%
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.
SKD1 QT55-58 vs SKD1-SR — frequently asked
Is SKD1 QT55-58 stronger than SKD1-SR?
Yes. SKD1 QT55-58 has a typical yield strength of 1,620 MPa (235 ksi) against 470 MPa (68.2 ksi) for SKD1-SR — about 3.4 times as much. Tensile strength is 1,850 MPa (268 ksi) vs 790 MPa (115 ksi).
Which condition does FabDigit quote by default, QT55-58 or SR?
ANN is the default SKD1 condition in the FabDigit quote flow (neither QT55-58 nor SR). 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, SKD1 QT55-58 or SKD1-SR?
SKD1-SR. Its machinability rates poor (27/100) against not recommended (10/100) for SKD1 QT55-58; for welding the order is SKD1-SR first (poor, 18/100) then SKD1 QT55-58 (not recommended, 5/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in SKD1 QT55-58 and SKD1-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.