Nickel Alloy Alloy 684-HF vs Alloy 684-ST
Nickel Alloy · Alloy 684 temper comparison
Alloy 684-HF and Alloy 684-ST are two conditions of the same nickel alloy grade, Alloy 684: HF (as hot forged / hot rolled) versus ST (solution annealed). The chemistry is identical, so every difference below comes from the condition. Alloy 684-HF is the stronger of the two: yield strength 700 MPa (102 ksi) against 585 MPa (84.8 ksi) for Alloy 684-ST, about 20% more; tensile strength follows at 1,100 MPa (160 ksi) vs 965 MPa (140 ksi). In exchange, Alloy 684-ST is the more ductile: elongation 35% versus 22% for Alloy 684-HF, and Alloy 684-HF is harder (300 HB vs 255 HB).
Alloy 684-HFChoose it when strength drives the design.
Alloy 684-STChoose it when the part is bent, formed or impact-loaded.
Alloy 684-HF vs Alloy 684-ST: propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all nickel alloy 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 nickel alloy 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)
Charpy V-Notch Impact (RT)
Hardness, Brinell
Hardness, Rockwell C
Hardness, Vickers
Same in both: Shear Modulus 82 GPa11.9 Msi · Bulk Modulus 178 GPa25.8 Msi · Poisson's Ratio 0.3
Physical
Density and transition temperatures.
Same in both: Density 8.02 g/cm³0.29 lb/in³ · Melting Point (Solidus) 1,300°C2,372 °F · Liquidus Temperature 1,395°C2,543 °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 420 J/kg·K0.1 BTU/lb·°F · Thermal Expansion (CTE, 20–100 °C) 12.1 µm/m·K6.7 µin/in·°F · Latent Heat of Fusion 290 J/g125 BTU/lb · Min Service Temperature -196°C-321 °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) -0.15 V · Corrosion Resistance 72 / 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 55 / 100 · Brazeability / Solderability 40 / 100 · Polishability 70 / 100
Sustainability
Primary-production footprint per kilogram.
Same in both: Embodied Energy (primary production) 165 MJ/kg70,937 BTU/lb · Embodied Carbon (primary production) 14 kg CO₂/kg · Embodied Water 1,500 L/kg180 gal/lb · Typical Recycled Content 35%
Strength versus weight
Yield strength against density for every nickel alloy grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Alloy 684-HF vs Alloy 684-ST — frequently asked
Is Alloy 684-HF stronger than Alloy 684-ST?
Yes. Alloy 684-HF has a typical yield strength of 700 MPa (102 ksi) against 585 MPa (84.8 ksi) for Alloy 684-ST — about 20% more. Tensile strength is 1,100 MPa (160 ksi) vs 965 MPa (140 ksi).
Which condition does FabDigit quote by default, HF or ST?
STA is the default Alloy 684 condition in the FabDigit quote flow (neither HF nor ST). 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 Alloy 684-HF over Alloy 684-ST?
Pick Alloy 684-HF when strength drives the design. Pick Alloy 684-ST when the part is bent, formed or impact-loaded.
Ready to make it?
Upload a CAD file and FabDigit prices the part in Alloy 684-HF and Alloy 684-ST 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.