Steel SK4-HR vs SK4 QT50-55
Steel · SK4 temper comparison
SK4-HR and SK4 QT50-55 are two conditions of the same steel grade, SK4: HR (hot rolled) versus QT50-55 (Q&T 50–55 HRC). The chemistry is identical, so every difference below comes from the condition. SK4 QT50-55 is the stronger of the two: yield strength 1,500 MPa (218 ksi) against 450 MPa (65.3 ksi) for SK4-HR, about 3.3 times as much; tensile strength follows at 1,750 MPa (254 ksi) vs 780 MPa (113 ksi). In exchange, SK4-HR is the more ductile: elongation 12% versus 3% for SK4 QT50-55, and SK4 QT50-55 is harder (515 HB vs 240 HB). SK4-HR conducts heat better (46 W/m·K vs 37 W/m·K). On the shop floor, SK4-HR machines more easily (fair vs not recommended).
SK4-HRChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
SK4 QT50-55Choose it when strength drives the design.
SK4-HR vs SK4 QT50-55: 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)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell B
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 205 GPa29.7 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 7.83 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,400°C2,552 °F · Liquidus Temperature 1,465°C2,669 °F
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
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 · Max Service Temperature (continuous) 250°C482 °F · Min Service Temperature -40°C-40 °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: Castability 25 / 100 · Brazeability / Solderability 45 / 100 · Polishability 75 / 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 60 L/kg7.2 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.
SK4-HR vs SK4 QT50-55 — frequently asked
Is SK4 QT50-55 stronger than SK4-HR?
Yes. SK4 QT50-55 has a typical yield strength of 1,500 MPa (218 ksi) against 450 MPa (65.3 ksi) for SK4-HR — about 3.3 times as much. Tensile strength is 1,750 MPa (254 ksi) vs 780 MPa (113 ksi).
Which condition does FabDigit quote by default, HR or QT50-55?
A is the default SK4 condition in the FabDigit quote flow (neither HR nor QT50-55). 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, SK4-HR or SK4 QT50-55?
SK4-HR. Its machinability rates fair (35/100) against not recommended (12/100) for SK4 QT50-55; for welding the order is SK4-HR first (not recommended, 12/100) then SK4 QT50-55 (not recommended, 4/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in SK4-HR and SK4 QT50-55 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.