Inconel 718 High-Temperature Bolt and Fastener Stock

Inconel 718 (UNS N07718) is a precipitation-hardening nickel-chromium alloy supplied as bar, forging stock and machined blanks under ASME SB-637. It is the material behind most high-temperature bolting in turbines, exhaust systems and chemical process plant, and it is the alloy we are most often asked to supply in cut-to-length bar for fastener manufacturers. This page covers the composition, the age-hardening route, and the specification boundaries that buyers need to get right.

What Inconel 718 Is Used For

718 is used where a fastener must carry substantial preload at elevated temperature and resist oxidation, chloride and hydrogen embrittlement. Typical applications include turbine and compressor bolting, rocket and turbine engine components, high-temperature springs and fasteners, nuclear reactor internals, and downhole completion equipment. The combination of nickel, chromium, niobium and titanium gives age hardening plus good corrosion resistance, which is why it replaced solution-strengthened bolt alloys in most high-temperature classes.

Two facts matter for procurement. First, 718 achieves its strength through an ageing cycle, so material supplied must be in a defined condition and the fastener manufacturer must complete the heat treatment on finished parts. Second, because it is age hardenable and corrosion resistant, it is frequently substituted for A286 or other iron-based high-temperature bolting without a check that the design allowable stress still applies. Confirm with the design authority before substituting.

Grade Comparison

The genuine comparison is against A286 or austenitic stainless: austenitic stainless is adequate where creep is not the limiting factor, but the nickel alloys are chosen when bolt preload retention at temperature matters.

Chemical Composition (ASME SB-637)

The niobium plus tantalum and the aluminium and titanium contents drive precipitation of the gamma double-prime phase responsible for the strength. Boron, though small, is deliberately controlled because it assists grain-boundary strengthening and hot ductility.

Product Forms and Ordering Conditions

SB-637 covers precipitation-hardening and cold-worked nickel alloy bars, forgings and forging stock. Product forms available include hot-rolled round bar, cold-drawn round bar, cut-to-length bar, forging billet, and machined blanks to a drawing. For bolt and fastener manufacturing the usual route is hot-rolled or cold-drawn round bar in Condition A, then heading and heat treatment by the fastener maker.

Applicable Specifications

Important boundary note: neither ASME SB-366 (wrought nickel alloy fittings) nor SB-462 (forged flanges and fittings) lists UNS N07718. If a project combines 718 bolting with nickel alloy piping components, the bolting is specified to SB-637 and SA-962 while the piping components are specified to their own SB-366 or SB-462 grade lists. Confirm the correct specification for each component family separately.

Inspection and Documentation

Mill test certification to SB-637 includes chemical analysis, mechanical properties in the delivered condition, heat number, grain size and dimensions. Because 718 is age hardening, mechanical properties depend on the delivered condition, so the certificate must match the condition ordered. For critical bolting we can supply hardness surveys, microstructural examination and full traceability from melt to finished bar.

Ordering Information

Please include the following when requesting a quotation:

• Grade: Inconel 718 or Incoloy 718, UNS N07718
• Product form: hot-rolled bar, cold-drawn bar, cut-to-length, forging billet, or machined blank
• Diameter or section size in inches or millimetres, and tolerance class
• Delivery condition: Condition A, Condition B, or solution annealed and aged
• Length requirement and straightness requirement
• Quantity and annual usage pattern
• Certification: EN 10204 3.1 or 3.2, plus any supplementary tests
• Destination port and required delivery window

Send your sizes, condition and quantities and we will return pricing, calculated weight and lead time. If you need a fastener machined to a drawing, send the drawing and we will confirm the bar size required and quote both bar and blanks.

Related ranges: dimensional and standards background for this product is set out in our Inconel 625 fittings. See also our Fasteners. Both are supplied to the dimensional standards quoted above.

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