Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Inconel 718 Heat Treatment, Solution + Double-Age Cycle
Solution Annealing + Precipitation Aging per ASTM A1014 §5.2 / AMS 2774
The 185 ksi tensile strength and 23-hour stress-rupture rating of Inconel 718 (UNS N07718) bolting are only developed by a precise solution + double-age heat treatment cycle mandated by ASTM A1014 §5.2 and SAE AMS 2774. Untreated or improperly treated stock will not meet the mechanical thresholds in Table 2 of A1014. The cycle below is the authoritative reference; deviations void the certification.
Need certified-heat-treated bolting? TorqBolt heat treats every Inconel 718 bolt per ASTM A1014 §5.2 with documented furnace charts. Request quote at +91-22-66157017 or info@torqbolt.com.
Why Inconel 718 Requires Heat Treatment
In the as-rolled or as-forged state, Inconel 718 has roughly 130 ksi tensile and 60-70 ksi yield, comparable to a cold-worked stainless steel. The alloy needs two strengthening phases, γ″ (Ni₃Nb) and γ′ (Ni₃(Al,Ti)), to precipitate from a supersaturated solid solution. Solution annealing dissolves residual phases; controlled cooling then aging precipitates the γ″ / γ′ to coherent particles 5-20 nm in size. Particle size and distribution control yield strength, hence the tight ±15 °F aging temperature tolerance.
Stage 1, Solution Anneal (ASTM A1014 §5.2.1)
- Temperature: 1725 to 1850 °F (940 to 1010 °C)
- Tolerance: ± 25 °F (± 14 °C)
- Hold time: commensurate with cross-sectional thickness; typically 1 hour per inch of thickness
- Quench: air cool or faster
The solution-anneal temperature dissolves the γ″ and γ′ phases plus most of the Laves phase and δ phase. Cooling rate is not critical, but air cool prevents the formation of large incoherent precipitates that would inhibit subsequent aging response.
Stage 2, Precipitation Aging (Double Age)
- First age: heat to 1325 °F (720 °C), hold 8 hours minimum, ± 15 °F (± 8 °C)
- Furnace cool: to 1150 °F (620 °C) at a controlled rate of 100 °F (55 °C) per hour
- Second age: hold at 1150 °F for 8 hours
- Final cool: air cool to room temperature
- Total cycle: minimum 18 hours from start to second-age completion
An alternative furnace-cool schedule is permitted by §5.2.2.1: cool from 1325 to 1150 °F at any rate, provided the time at 1150 °F is adjusted so the total precipitation cycle still totals 18 hours minimum. The two ages are not equivalent: the 1325 °F stage nucleates the γ″ phase; the 1150 °F stage coarsens the existing precipitates and nucleates additional fine γ′. Skipping either stage leaves the alloy strength-deficient.
Straightening Constraint
Per ASTM A1014 §5.3, straightening of bolting components is permitted ONLY between solution treatment and aging. Straightening after aging is prohibited because the γ″ phase has no plastic reserve; the bolting would either fracture or develop unacceptable residual stresses. Bolt suppliers that straighten post-age are non-conforming.
Aerospace Equivalent Specifications
The same solution + double-age cycle is mandated by SAE AMS 2774 (heat treatment of nickel alloy parts) when bolting is procured under aerospace specs SAE AS 7467 or SAE AMS 5663. AMS 5662 covers the solution-treated condition only; AMS 5663 covers the final solution + age condition that matches A1014 bolting properties.
Related Inconel 718 References
- Full Inconel 718 mechanical and physical properties
- UNS N07718 chemistry and standards index
- ASTM A1014 master specification
- Inconel 718 Hex Bolts (B18.2.1)
- Inconel 718 Socket Head Cap Screws (B18.3)
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