What Is nickel alloy UNS N07718 Threaded Rod?
nickel alloy UNS N07718 threaded rod is a fully threaded fastener bar made from nickel alloy UNS N07718, an age-hardenable nickel-chromium-iron superalloy designated UNS N07718 in the Unified Numbering System and 2.4668 in the German material numbering system. Unlike ordinary carbon steel rod, the alloy retains high strength from cryogenic temperatures to approximately 1300°F (704°C), resists oxidation and chloride-induced attack, and develops its full properties through precipitation heat treatment. Because it is threaded along its entire length, this product form is used to build stud assemblies, anchor rods, and tension members in applications where a combination of high strength, corrosion resistance, and elevated-temperature capability is required.
Chemical Composition and Mechanical Properties
nickel alloy UNS N07718 derives its strength from a carefully balanced composition. Nickel (50.0%–55.0%) provides the austenitic base and corrosion resistance, chromium (17.0%–21.0%) provides oxidation resistance, and molybdenum (2.8%–3.3%) together with niobium (4.75%–5.50% Nb plus Ta) drives precipitation hardening. Carbon is limited to 0.08% maximum, manganese and silicon to 0.35% maximum each, and phosphorus, sulfur, copper, and cobalt are held to 0.015%, 0.015%, 0.30%, and 1.00% maximum respectively. The table below lists the composition limits that apply to rod and bar under ASTM B637.
| Element | Weight % |
|---|---|
| Nickel | 50.0–55.0 |
| Chromium | 17.0–21.0 |
| Niobium + Tantalum | 4.75–5.50 |
| Molybdenum | 2.80–3.30 |
| Carbon, max | 0.08 |
| Manganese, max | 0.35 |
| Silicon, max | 0.35 |
| Phosphorus, max | 0.015 |
| Sulfur, max | 0.015 |
| Copper, max | 0.30 |
| Cobalt, max | 1.00 |
Typical annealed values for nickel alloy UNS N07718 rod are a tensile strength of 135,000 psi (930 MPa), a 0.2% offset yield strength of 70,000 psi (482 MPa), and 45% elongation; density is approximately 8.2 g/cm³ and the melting range begins near 1350°C (2460°F). After full age hardening, the alloy develops considerably higher strength: ASTM B637 specifies minimum tensile strength of 180 ksi (1241 MPa) and minimum yield strength of 150 ksi (1035 MPa) for age-hardened bar, with lower elongation reflecting the hardened condition.
Standards, Sizes, and Specifications
nickel alloy UNS N07718 threaded rod and bar are manufactured to ASTM B637, which covers hot- and cold-worked rod and bar of precipitation-hardening nickel alloys. Threaded rods are commonly produced to DIN 975 thread rod geometry, and thread fit and tolerance follow ISO classes such as h8 through h11 for ground or drawn finishes. Typical metric sizes range from M6 to M52 (10–75 mm) and inch sizes from 1/4 to 2 inches, in cut lengths from 1000 mm to 3000 mm or 1 to 12 feet; longer continuous lengths of 2000–6000 mm are available on request. Surface options include plain, galvanized, hot-dip galvanized, and yellow zinc finishes.
Temperature Limits and Forging Practice
The practical service range of nickel alloy UNS N07718 extends from cryogenic temperatures to about 1200°F (649°C) for long-term continuous service, with short-term capability to roughly 1300°F (704°C). The alloy keeps its strength and toughness far below zero, which is why it appears in liquid-hydrogen and cryogenic-pressure systems. For hot working, the maximum furnace temperature is 2050°F (1121°C); the recommended hot and cold working range is 1700–1850°F (927–1010°C), and extended holding time at forging temperature should be avoided because it can coarsen the grain structure. After forging, the material is solution treated and age hardened, typically with a double-aging cycle, to develop the precipitation-hardened microstructure that gives 718 its mechanical signature.
Applications of nickel alloy UNS N07718 Threaded Rod
Because it combines high strength, corrosion resistance, and thermal stability, nickel alloy UNS N07718 threaded rod is specified in aerospace and aviation fasteners, gas turbine and exhaust systems, oil and gas wellhead and subsea hardware, power generation equipment, cryogenic pressure vessels, refining and chemical plants, and marine construction. The alloy also resists pitting and crevice corrosion in seawater and aggressive process media, extending the service life of bolted joints that would fail quickly in conventional fastener steels.
Frequently Asked Questions
What is the UNS number for nickel alloy UNS N07718 threaded rod? nickel alloy UNS N07718 threaded rod is designated UNS N07718 in the Unified Numbering System and 2.4668 in the German DIN material numbering system.
Which standard covers nickel alloy UNS N07718 rod and bar? ASTM B637 covers hot- and cold-worked rod and bar of nickel alloy UNS N07718 and other precipitation-hardening nickel alloys; threaded rods are commonly made to DIN 975 geometry.
What is the composition of nickel alloy UNS N07718? nickel alloy UNS N07718 contains 50.0%–55.0% nickel, 17.0%–21.0% chromium, 2.8%–3.3% molybdenum, and 4.75%–5.50% niobium plus tantalum, with tight limits on carbon, manganese, silicon, phosphorus, sulfur, copper, and cobalt.
How hot can nickel alloy UNS N07718 threaded rod serve? nickel alloy UNS N07718 is rated for long-term service up to about 1200°F (649°C) and short-term exposure to roughly 1300°F (704°C); it also retains strength at cryogenic temperatures.
What are the mechanical properties of nickel alloy UNS N07718 rod? annealed rod typically shows 135,000 psi (930 MPa) tensile strength and 70,000 psi (482 MPa) yield strength; age-hardened bar must meet 180 ksi (1241 MPa) tensile and 150 ksi (1035 MPa) yield per ASTM B637.
Why is niobium important in nickel alloy UNS N07718? Niobium combines with molybdenum to precipitate the gamma double-prime phase during aging, which is the source of nickel alloy UNS N07718 high strength and creep resistance.
