A Comprehensive Guide to Nickel-Based Superalloys: Inconel X-750 (UNS N07750/W.NR 2.4669)
What is Inconel X-750?
Designated as UNS N07750 or W. Nr. 2.4669, Inconel X750, also known as "Alloy X750", is a nickel-chromium alloy similar to Inconel 600, but precipitation hardened by the addition of aluminum and titanium. The alloy has good corrosion and oxidation resistance and high tensile and creep-rupture properties at temperatures up to 1300°F (700°F). Its excellent relaxation resistance is useful for high-temperature springs and bolts. Inconel X-750 is also used in gas turbines, rocket engines, nuclear reactors, pressure vessels, tooling, and aircraft structures.
The Inconel X-750 alloy is primarily a nickel-base superalloy that ages to produce the γ′[Ni3(al,Ti,Nb)] phase. It has good corrosion resistance and oxidation resistance below 980℃, high strength below 800℃, good anti-relaxation performance below 540℃, and good performance formability and weldability. The alloy is mainly used to manufacture high-strength, corrosion-resistant annular parts, structural parts and bolts, as well as medium and low stress, anti-relaxation flat springs and spiral springs working below 540℃. It can also be used to manufacture turbine blades and other parts.
Characteristics of Inconel X-750 (UNS N07750/W.NR 2.4669)
Iron-nickel-chromium-based alloy hardened by elemental aluminum and elemental titanium.
It has good corrosion resistance and oxidation resistance even at high temperatures of 980℃,
Good mechanical strength before 800°C,
Good anti-relaxation performance before 540°C,
Good processing performance and welding performance,
Excellent mechanical properties in low temperature environment.
Heat treatment system Inconel X-750 (UNS N07750/W.NR 2.4669)
The hot steel temperature is 980℃, and the hot steel temperature is 980℃. For the intermediate heat treatment system of materials and parts, the following processes can be selected for heat treatment.
(1) Annealing: 955～1010℃, water cooling.
(2) Pre-welding annealing: 980℃, 1H.
(3) Stress relief annealing: 900℃, 2h.
(4) Stress relief annealing: 885℃±15℃, 24h, air cooling.
Heat treatment process of inconelx-750 parts
Heat treatment The processing of parts should be carried out in a neutral or reducing atmosphere without sulfur to avoid sulfidation. Parts should avoid "hot and cold" treatment between 870℃ and 650℃. For large-section parts, in order to prevent cracks, the parts should be placed in air for cooling after solution treatment. The final heat treatment of finished parts is as follows:
(1) For parts working at above 600℃ and requiring the best creep resistance:
Solution treatment: 1150℃±15℃, keep warm for 2-4h, air cooling;
Aging: 845℃±15℃, keep warm for 24h, air cooling + 705℃±15℃, keep warm for 24h, air cooling.
(2) For parts working below 600℃ and requiring the best room temperature and high temperature tensile properties:
Solution treatment: 980℃±15℃, keep warm for 1h, air cooling;
Aging: 730℃±15℃, keep warm for 8h, furnace cooling at 50℃/h to 620℃±10℃, keep warm for 8h, air cooling.
(3) The following heat treatment system is generally used for ring parts:
Solution treatment: 1095℃±15℃, keep warm for 2-4h, air cooling;
Aging: 845℃±15℃, keep warm for 24h, air cooling or furnace cooling to +705℃±15℃, keep warm for 20h, air cooling.
(4) The following system should be used for heat treatment of bars and forgings below 600℃
Homogenization: 885℃±15℃, keep warm for 24h, air cooling;
Aging: 705℃±15℃, keep warm for 20±1H, air cooling.
(5) Annealed plates, strips and plates, strips and wires for springs can be heat treated using the following system:
Aging:
1) 705℃±15℃, keep warm for 22h, air cooling;
2) 760℃±10℃, keep warm for 1h, air cooling.
Solution: 980℃±15℃, hold for 1h, air cooling;
Aging: 730℃±10℃, hold for 8h, furnace cooling at 50℃/h to +620℃±10℃, hold for 8h, air cooling.
Melting and casting process of Inconel X-750 (UNS N07750/W.NR 2.4669)
The alloy is remelted by arc furnace plus vacuum consumable remelting, vacuum induction plus electroslag, electroslag plus vacuum consumable remelting or vacuum induction plus vacuum consumable remelting.
Process performance and requirements of inconel x-750
1. The forming properties of Inconelx-750 are as follows: The forging temperature range of the alloy is 1220℃ to 950℃. In order to obtain good structure and performance of the final forging or bar, the subsequent forging heating temperature should be carried out at a correspondingly lower temperature. The final forging temperature should not be lower than 950℃. The alloy should be solution treated after intense forming.
2. Inconel X-750 welding performance: The alloy has good weldability and can be welded in a variety of ways, but welding large-section parts is difficult, but welding small-section parts and thin plates is better. Welding must be carried out after annealing or solution treatment, stress relief treatment should be carried out after welding, and humidity should be kept at 980℃ for 0.5h or 900℃ for 2h. After aging treatment, the strength of the welded assembly in a state close to complete heat treatment can be obtained.
