Double-End Studs in Inconel 718: FAQ
What are Inconel 718 Double-End Studs per ASTM A1014?
Double-End Studs made to the dimensions of ASME B18.31.2 in UNS N07718 (Inconel 718) bolting to ASTM A1014/A1014M, the specification for precipitation-hardening bolting for high temperature service. ASME B18.31.2 sets the dimensions; ASTM A1014 sets the melting practice, heat treatment, tests and marking, with ASTM A962/A962M as the common bolting requirements (4.1). After aging, the A1014 Table 2 room temperature minimums are 185 ksi [1275 MPa] tensile strength, 150 ksi [1035 MPa] 0.2 % offset yield strength, 12 % elongation, 15 % reduction of area and 331 to 444 HBW.
What heat treatment do Inconel 718 Double-End Studs need per ASTM A1014?
Solution treatment at 1725 to 1850 °F [940 to 1010 °C], 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 (5.2.1). Precipitation treatment: 1325 °F [720 °C] for 8 hours minimum, furnace cool to 1150 °F [620 °C] at 100 °F [55 °C] per hour, hold 8 hours, cool to room temperature; or furnace cool at any rate with the time at 1150 °F adjusted so the total precipitation treatment is 18 hours minimum (5.2.2). Aging temperatures and cooling rates are controlled within ±15 °F [±8 °C]. Straightening is done only after solution treating and before aging (5.3).
How are Inconel 718 Double-End Studs tested per ASTM A1014?
All tensile, hardness and stress rupture tests are made after aging (7.1). Studs with a body length of three times the diameter or longer are full-size tensile tested to the Table 2 tensile strength, using the ASME B1.1 stress area (7.3); one tensile test is made per lot (9.5). Shorter components may be tested on a separately forged bar heat treated with them (9.2). At 1200 °F [650 °C] the Table 2 minimums are 145 ksi [1000 MPa] tensile and 125 ksi [860 MPa] yield strength, and the stress rupture test at 100 ksi [690 MPa] must last 23 hours minimum with 5 % elongation (7.2, one test per lot per 9.2).
