High temperature alloys
| UNS Number | UNS N07750 |
| Industry Name | Alloy X-750, Inconel X-750, W.Nr.2.4669, NiCr73Fe15Nb2.5Ti2.5 |
Product Forms | Billets, Rods, Bars, Wires |
General Characteristics
Alloy X-750 is a precipitation-hardened nickel-chromium superalloy.
Alloy X-750 was developed based on Inconel 600. Inconel 600 is a solid-solution strengthened nickel-chromium alloy with good corrosion and oxidation resistance, but its high-temperature strength, creep resistance and stress relaxation performance were poor under sustained load. By adding aluminium and titanium to form gamma prime precipitates, X-750 retains Inconel 600’s excellent corrosion and oxidation resistance while gaining age-hardening capability. It achieves much higher tensile strength, creep resistance and stress relaxation resistance at elevated temperatures, suitable for springs and fasteners under long-term high-temperature preload.
Typical service scenarios include gas turbine springs, nuclear hold-down springs, high-temperature fasteners and petrochemical thermal hardware.
C | Cr | Ni | Co | Al | Ti | Fe | Nb | Si | Mn | P | S | Cu |
≤0.08 | 14-17 | ≥70 | ≤1.00 | 0.4-1.00 | 2.25-2.75 | 5.0-9.0 | 0.7-1.2 | ≤0.5 | ≤1.00 | ≤0.015 | ≤0.010 | ≤0.5 |
Chemical & Petrochemical||High-temperature spring elements|Preload bolts for reactor vessels|Heat exchanger fasteners|Spring clips for high-temperature piping systems
Nuclear Power||Reactor hold-down springs|Core internals fasteners|Spring assemblies
Automotive||Turbocharger retaining springs|Exhaust valve springs
Technical Standards | Product Form |
ASTM B637 | Bar, Forging, Forged Billet, Ring |
AMS 5542 | Bar, Forging, Ring, Wire, Spring Wire |
ASTM B805 | Wire, Spring Wire |
Product form | Size range (mm) |
Forged bar | Dia.70-500 |
Rolled bar | Dia.2.0-70 |
Flat bar | T4-50*W60-300 |
Wire | Dia.0.25-18.0 |
Q1: What is the main advantage of Alloy X-750 for springs and fasteners?
A: Alloy X-750 delivers excellent high-temperature stress relaxation resistance. It maintains stable preload and elastic force under prolonged heat. It is cobalt-free, making it suitable for nuclear applications.
Q2: What is the maximum continuous operating temperature?
A: Long-term continuous service up to 700°C. Short peak temperature can reach 815°C. Stress relaxation worsens above 700°C.
Q3: How does Alloy X-750 compare with Nimonic 90?
A: X-750 has no cobalt and is acceptable for nuclear service. Nimonic 90 shows slightly better anti-relaxation performance at very high temperatures but cannot be used in nuclear environments due to cobalt activation.
Q4: How does Alloy X-750 compare with Inconel 718?
A: X-750 retains strength and elastic properties much better above 650°C. Inconel 718 loses performance rapidly beyond this temperature.
Q5: Can we age the wire first and then coil springs?
A: No. Wire should be supplied in solution-treated condition. Spring coiling must be completed before final aging, otherwise cracking will easily occur.
Q6: Which standards apply to Alloy X-750 bar, forging and spring wire?
A: ASTM B637 for bar, forging and ring. AMS 5542 covers bar, forging, ring, wire and spring wire. ASTM B805 is available for spring wire. MTC can be issued per these specs.
Q7: What melting options are available?
A: VIM+ESR for general industrial use. VIM+VAR for high-end aerospace and nuclear requirements to reduce inclusions and gas content.