Steel SUJ4-A vs SUJ4 QT55-58HRC
Steel · SUJ4 temper comparison
SUJ4-A and SUJ4 QT55-58HRC are two conditions of the same steel grade, SUJ4: A (solution annealed) versus QT55-58HRC. The chemistry is identical, so every difference below comes from the condition. SUJ4 QT55-58HRC is the stronger of the two: yield strength 1,650 MPa (239 ksi) against 420 MPa (60.9 ksi) for SUJ4-A, about 3.9 times as much; tensile strength follows at 1,950 MPa (283 ksi) vs 700 MPa (102 ksi). In exchange, SUJ4-A is the more ductile: elongation 22% versus 1% for SUJ4 QT55-58HRC, and SUJ4 QT55-58HRC is harder (600 HB vs 190 HB). SUJ4 QT55-58HRC runs hotter in service (250°C vs 200°C continuous) and SUJ4-A conducts heat better (45 W/m·K vs 40 W/m·K). On the shop floor, SUJ4-A machines more easily (fair vs not recommended).
SUJ4-AChoose it when the part is bent, formed or impact-loaded, or when the part is machined in volume.
SUJ4 QT55-58HRCChoose it when strength drives the design, or when the part sees heat.
SUJ4-A vs SUJ4 QT55-58HRC: 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)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Vickers
Same in both: Shear Modulus 80 GPa11.6 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.3 · Hardness, Rockwell B 91 HRB
Physical
Density and transition temperatures.
Same in both: Density 7.81 g/cm³0.28 lb/in³ · Melting Point (Solidus) 1,400°C2,552 °F · Liquidus Temperature 1,450°C2,642 °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 465 J/kg·K0.11 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12 µm/m·K6.7 µin/in·°F · Latent Heat of Fusion 250 J/g107 BTU/lb · Min Service Temperature -50°C-58 °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) -0.6 V · Corrosion Resistance 12 / 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 35 / 100 · Polishability 85 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 33 MJ/kg14,187 BTU/lb · Embodied Carbon (primary production) 2.4 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.
SUJ4-A vs SUJ4 QT55-58HRC — frequently asked
Is SUJ4 QT55-58HRC stronger than SUJ4-A?
Yes. SUJ4 QT55-58HRC has a typical yield strength of 1,650 MPa (239 ksi) against 420 MPa (60.9 ksi) for SUJ4-A — about 3.9 times as much. Tensile strength is 1,950 MPa (283 ksi) vs 700 MPa (102 ksi).
Which condition does FabDigit quote by default, A or QT55-58HRC?
A is the default SUJ4 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, SUJ4-A or SUJ4 QT55-58HRC?
SUJ4-A. Its machinability rates fair (40/100) against not recommended (8/100) for SUJ4 QT55-58HRC; for welding the order is SUJ4-A first (not recommended, 10/100) then SUJ4 QT55-58HRC (not recommended, 3/100).
Ready to make it?
Upload a CAD file and FabDigit prices the part in SUJ4-A and SUJ4 QT55-58HRC 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.