Steel HP9-4-30-QT540 vs HP9-4-30-QT590
Steel · HP9-4-30 temper comparison
HP9-4-30-QT540 and HP9-4-30-QT590 are two conditions of the same steel grade, HP9-4-30: QT540 (Q&T, austenitize 830–860 °C, oil quench, −73 °C refrigerate, double…) versus QT590 (Q&T, double temper 565–595 °C). The chemistry is identical, so every difference below comes from the condition. HP9-4-30-QT540 is the stronger of the two: yield strength 1,400 MPa (203 ksi) against 1,310 MPa (190 ksi) for HP9-4-30-QT590, about 7% more; tensile strength follows at 1,655 MPa (240 ksi) vs 1,520 MPa (220 ksi). In exchange, HP9-4-30-QT590 is the more ductile: elongation 15% versus 13% for HP9-4-30-QT540, and HP9-4-30-QT540 is harder (48 HRC vs 45 HRC).
HP9-4-30-QT540Choose it when strength drives the design.
HP9-4-30-QT590Choose it when the part is bent, formed or impact-loaded.
HP9-4-30-QT540 vs HP9-4-30-QT590: 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, Rockwell C
Hardness, Vickers
Same in both: Elastic (Young's) Modulus 200 GPa29 Msi · Shear Modulus 78 GPa11.3 Msi · Bulk Modulus 160 GPa23.2 Msi · Poisson's Ratio 0.3 · Compressive Strength 1,450 MPa210 ksi · Hardness, Brinell 461 HB
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 1,490°C2,714 °F
Thermal
How each material carries heat and how hot it can run.
Max Service Temperature (continuous)
Same in both: Thermal Conductivity 24 W/m·K13.9 BTU/hr·ft·°F · Specific Heat Capacity 460 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 260 J/g112 BTU/lb · Min Service Temperature -73°C-99 °F
Electrical
Conductivity and insulation.
Same in both: Electrical Conductivity 3.8 % IACS · Electrical Resistivity 4.5×10⁻⁷ Ω·m17.7 µΩ·in
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Same in both: Galvanic Potential (seawater, vs SCE) -0.6 V · Corrosion Resistance 20 / 100
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Same in both: Machinability Rating (AISI 1212 = 100 %) 15% · Weldability 45 / 100 · Formability (cold) 15 / 100 · Castability 30 / 100 · Brazeability / Solderability 35 / 100 · Polishability 70 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 45 MJ/kg19,347 BTU/lb · Embodied Carbon (primary production) 3.4 kg CO₂/kg · Embodied Water 85 L/kg10.2 gal/lb · Typical Recycled Content 15%
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.
HP9-4-30-QT540 vs HP9-4-30-QT590 — frequently asked
Is HP9-4-30-QT540 stronger than HP9-4-30-QT590?
Yes. HP9-4-30-QT540 has a typical yield strength of 1,400 MPa (203 ksi) against 1,310 MPa (190 ksi) for HP9-4-30-QT590 — about 7% more. Tensile strength is 1,655 MPa (240 ksi) vs 1,520 MPa (220 ksi).
Which condition does FabDigit quote by default, QT540 or QT590?
QT540 is the default HP9-4-30 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.
When should I choose HP9-4-30-QT540 over HP9-4-30-QT590?
Pick HP9-4-30-QT540 when strength drives the design. Pick HP9-4-30-QT590 when the part is bent, formed or impact-loaded.
Ready to make it?
Upload a CAD file and FabDigit prices the part in HP9-4-30-QT540 and HP9-4-30-QT590 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.