# Inconel 718 Bolts

*UNS N07718 · 2.4668 · GH4169*

**Category:** Nickel-Based Superalloy

Inconel 718 (UNS N07718, GH4169, 2.4668) is a precipitation-hardened nickel-chromium bolting grade rated to 700°C and supplied to ASTM B637 and AMS 5662 at 1275 MPa tensile and 1030 MPa yield in the aged condition. Strengthening comes from gamma double-prime (γ″) Ni₃Nb precipitates, which gives inconel 718 bolts and inconel 718 fasteners the highest room-temperature strength of any common superalloy fastener together with good creep-rupture behaviour to 700°C.

Every bolt we ship starts as our own VIM + VAR ingot. Vacuum induction melting removes oxygen and nitrogen, and vacuum arc remelting refines the solidification structure so the niobium segregation that causes Laves phase, and with it premature fatigue failure, never forms.

Bars are hot forged into inconel 718 stud bolts and inconel hex bolts with continuous grain flow through the head-to-shank fillet, solution treated, double aged, and thread rolled after aging for maximum fatigue life. Every UNS N07718 bolt and alloy 718 bolt lot carries an EN 10204 3.1 or 3.2 certificate tied to the head marking.

## Standards

- ASTM B637
- AMS 5662
- AMS 5663
- AMS 5832
- UNS N07718
- GH4169
- 2.4668

## Chemical composition (wt%)

| Element | Min | Max |
|---|---|---|
| Ni (+Co) | 50.0 | 55.0 |
| Cr | 17.0 | 21.0 |
| Fe | Balance | - |
| Nb + Ta | 4.75 | 5.50 |
| Mo | 2.80 | 3.30 |
| Ti | 0.65 | 1.15 |
| Al | 0.20 | 0.80 |
| Co | - | 1.00 |
| C | - | 0.08 |
| Mn | - | 0.35 |
| Si | - | 0.35 |
| S | - | 0.015 |
| P | - | 0.015 |
| B | - | 0.006 |
| Cu | - | 0.30 |

## Mechanical properties

| Condition | Tensile (MPa) | Yield (MPa) | Elongation (%) | Hardness |
|---|---|---|---|---|
| Solution Treated | 965 | 550 | 30 | ≤ 30 HRC |
| AMS 5662 Aged | 1275 | 1030 | 12 | 36-44 HRC |
| AMS 5663 Premium Aged | 1310 | 1100 | 12 | 38-44 HRC |

## Applications

- **Aerospace**: Inconel 718 bolts for turbine disc bolting, compressor casings, afterburner hardware and engine mount fasteners qualified to AMS 5662/5663.
- **Power Generation**: Gas turbine hot-section bolting, transition duct hardware and steam path fasteners in continuous 650°C service.
- **Oil & Gas**: Inconel 718 stud bolts for wellhead components, subsea connectors and Christmas tree studs where NACE-compliant strength is required.
- **Nuclear**: Reactor internals, fuel handling tooling and control rod drive mechanism fasteners with full lot traceability.

## FAQ

### What is the maximum operating temperature of Inconel 718 bolts?

Continuous service is limited to about 700°C (1292°F). Above 650°C the γ″ strengthening phase begins to over-age and transform to the stable delta phase, so long-term creep strength drops. For sustained service above 700°C we recommend Nimonic 80A (815°C) instead.

### What is the difference between AMS 5662 and AMS 5663?

Both cover solution treated and aged bar. AMS 5662 specifies solution treatment at 954-982°C, while AMS 5663 adds a tighter aging schedule and higher minimum properties (1310 MPa tensile, 1100 MPa yield). AMS 5663 is normally specified for rotating aerospace hardware.

### Can inconel 718 bolts and inconel 718 fasteners be used in seawater?

Yes for general marine structures, but in stagnant chloride or crevice conditions UNS N07718 bolts trade some corrosion margin for their much higher strength. Inconel 625 or Monel K-500 perform better in aggressive chlorides.

### What is the lead time for inconel 718 bolts and inconel 718 fasteners?

Standard M6-M36 inconel 718 bolts and inconel 718 stud bolts from stock bar ship in 2-3 weeks. Fully melt-to-bolt orders (new VIM+VAR heat, forging, aging and certification) take 6-8 weeks. Trial runs start from 50 pieces across all inconel bolts grades.

### How are inconel 718 bolts heat treated?

Solution treat at 954-980°C with rapid quench, then double age: 718°C for 8 hours, furnace cool at 55°C/h to 621°C, hold 8 hours, air cool. Alloy 718 bolt threads are rolled after aging so the compressive residual stress stays in the root.