Two Age-Hardenable Superalloys
nickel alloy UNS N07718 (UNS N07718) and nickel alloy UNS N07750 (UNS N07750) are both precipitation-hardenable nickel-based superalloys, but their strengthening systems, temperature capability and fabrication behavior differ in ways that matter for component design.
nickel alloy UNS N07750 (UNS N07750): Properties
X-750 develops excellent high-temperature strength from gamma prime precipitation and can maintain sufficient mechanical properties and durability at extreme temperatures. It offers good corrosion resistance in different environments, including high-temperature acid corrosion, saltwater environments and oxidizing atmospheres; it resists high-temperature oxidation by forming a protective oxide layer that prevents further oxidation of the metal surface; and its small thermal expansion coefficient helps it maintain thermal stability in high-temperature service.
nickel alloy UNS N07718 (UNS N07718): Properties
nickel alloy UNS N07718 has excellent strength at high temperatures and can be used over a wide temperature range of -253 °C to 704 °C. It has good corrosion resistance to many strong acids and alkalis, resists oxidation in high-temperature atmospheres, and can be formed, forged and welded through hot and cold processing, making it relatively easy to machine into complex shapes. Its tolerance for weld cracking is significantly better than most other age-hardened superalloys, which is why it dominates welded fabrications.
Applications Compared
X-750 is used in the aerospace industry for high-temperature combustion chambers, jet-engine turbine blades and gas turbines; in the nuclear industry for reactor pipelines, storage tanks and other high-temperature, high-pressure components; in the chemical industry for high-temperature corrosion-resistant towers, pipelines and valves; and in the oil and gas industry for corrosion-resistant components of oil-field equipment and offshore platforms. nickel alloy UNS N07718 is widely used in jet engines, turbine blades, combustion-chamber liners and guide vanes; in oil and gas drilling equipment, well casings, valves and wellbore hardware; and in chemical reactors, catalyst carriers and distillation equipment. When an application combines the highest strength with extensive welding, 718 is usually preferred; when oxidation resistance, low thermal expansion and high-temperature strength in blades and springs matter most, X-750 is the classic choice.
Selection Guidance
Choose nickel alloy UNS N07718 when the operating window spans cryogenic to about 650-700 °C and the component must be welded and formed into complex shapes, as in casings, ducts, fasteners and rotating hardware. Choose X-750 when service is at high temperature with strong oxidation and thermal-cycling demands, and where precipitation hardening by gamma prime provides the required creep and stress-rupture performance. Confirm the grade, heat-treatment condition and governing specification before finalizing the design.
Frequently Asked Questions
What is the difference between nickel alloy UNS N07718 and X-750? nickel alloy UNS N07718 is gamma double-prime strengthened, works from -253 °C to about 704 °C and is highly weldable. X-750 is gamma prime strengthened, with excellent high-temperature oxidation resistance and a small thermal expansion coefficient, but it is more sensitive to welding.
Which is stronger, nickel alloy UNS N07718 or X-750? t room and moderate temperatures, age-hardened nickel alloy UNS N07718 typically reaches higher tensile and yield strength. X-750 maintains good strength to higher temperatures with better oxidation resistance.
Can nickel alloy UNS N07750 be welded? Yes, but X-750 is prone to strain-age cracking, so it requires careful procedure qualification, low-restraint joint design and controlled preheat or post-weld treatment; nickel alloy UNS N07718 is far easier to weld.
What temperature range can nickel alloy UNS N07718 serve? nickel alloy UNS N07718 can be used from -253 °C to 704 °C, with good oxidation resistance up to about 980 °C; above 704 °C its creep and rupture strength fall rapidly.
Is nickel alloy UNS N07750 used in nuclear reactors? Yes. X-750 is used for nuclear-reactor internals such as bolts, springs and fuel-element hardware because of its high-temperature strength, oxidation resistance and stability, subject to strict qualification.
Which grade is better for oil and gas service? nickel alloy UNS N07718 is more common for oil-field drilling equipment, casing hangers, valves and wellbore components because of its strength, corrosion resistance and fabricability; X-750 suits high-temperature, corrosion-resistant hardware where oxidation dominates.
