Inconel 718 Heat Treatment per ASTM A1014
ASTM A1014 fixes the heat treatment of Inconel 718 (UNS N07718) bolting in clause 5.2: a solution treatment followed by a two-step precipitation (aging) treatment. All tensile, hardness and stress rupture tests are made after aging (7.1), and the bolting must then meet Table 2: 185 ksi [1275 MPa] minimum tensile strength at room temperature and a 23 hour minimum stress rupture life at 1200 °F [650 °C] and 100 ksi [690 MPa].
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.
Inconel 718 is an age-hardenable nickel-chromium alloy. Solution treatment puts the aging constituents (aluminum, titanium and niobium) into solution; the precipitation treatment then forms the gamma prime and gamma double-prime strengthening phases in the matrix (Special Metals, INCONEL alloy 718 bulletin). ASTM A1014 controls aging temperatures and cooling rates within ±15 °F [±8 °C] (5.2.2.1).
- Temperature: 1725 to 1850 °F (940 to 1010 °C)
- Control: ±25 °F (±14 °C) (5.2.1.1)
- Hold time: commensurate with cross-sectional thickness
- Cooling: at a rate equivalent to an air cool or faster
- First step: heat to 1325 °F (720 °C), hold 8 hours minimum
- Furnace cool: to 1150 °F (620 °C) at 100 °F (55 °C) per hour
- Second step: hold at 1150 °F (620 °C) for 8 hours
- Final: cool to room temperature
- Control: ±15 °F (±8 °C) on temperatures and cooling rates (5.2.2.1)
Alternative cycle (5.2.2): furnace cool from 1325 °F to 1150 °F at any rate, provided the time at 1150 °F is adjusted so the total precipitation heat treatment time is 18 hours minimum.
When straightening is necessary, it is done after solution treating and before aging. Straightening after aging is prohibited, so bolting straightened after aging does not conform to ASTM A1014.
Threads are formed by rolling in one pass after oxides are removed from the area to be threaded (5.4). If the purchaser specifies supplementary requirement S6, thread rolling is done before the precipitation heat treatment; supplementary requirement S1 calls for heat treatment under a suitable protective atmosphere.
In addition to the ASTM A962/A962M requirements, the certification report states the solution treatment cycle time and temperature and the aging cycle time(s) and temperature(s).
For aerospace procurement, Inconel 718 bars, forgings and rings are bought to SAE AMS 5662 and AMS 5663, and bolts and screws to SAE AS 7467, which ASTM A1014 lists as a referenced document (2.3). Their heat treatment requirements are set in those documents, not in A1014.
Why does Inconel 718 bolting need heat treatment?
ASTM A1014 makes the solution and precipitation heat treatment of clause 5.2 mandatory, and all tensile, hardness and stress rupture tests are made after aging (7.1). The aged bolting must meet Table 2: 185 ksi [1275 MPa] minimum tensile strength, 150 ksi [1035 MPa] minimum yield strength and 331 to 444 HBW.
What is the solution treatment temperature for Inconel 718 per ASTM A1014?
1725 to 1850 °F [940 to 1010 °C] per ASTM A1014 5.2.1, controlled within ±25 °F [±14 °C], held for a time commensurate with cross-sectional thickness and cooled at a rate equivalent to an air cool or faster.
What is the double-age cycle for Inconel 718 per ASTM A1014?
Heat to 1325 °F [720 °C] and hold 8 hours minimum, furnace cool to 1150 °F [620 °C] at 100 °F [55 °C] per hour, hold 8 hours, cool to room temperature (5.2.2). Alternatively, furnace cool to 1150 °F at any rate with the time at 1150 °F adjusted so the total precipitation treatment is 18 hours minimum. Temperatures and cooling rates are controlled within ±15 °F [±8 °C].
Can Inconel 718 bolts be straightened after aging?
No. ASTM A1014 5.3: when straightening is necessary it is done after solution treating and prior to aging; straightening after aging is prohibited.
