Metalguy’s link has a typo (blank space); should be
This data sheet gives the single step aging:
“HEAT TREATMENT
The heat treatment consists of solution treating followed by a single aging treatment. Solution treat at 1,850 - 1,900° F (1,010 - 1,038° C) for 1 hour. Rapid cool. Age at 1,425 - 1,475° F (774 - 802° C) for 6 -8 hours hours. Air cool.”
[The two stage aging procedure is also given, on page 2.]
“HARDNESS
The hardness in the solution treated condition is about 20-25 HRc which increases upon aging to about 40 HRc max.”
The 4-page technical data sheet at
gives the two-step aging procedure and a few more details:
“The optimum temperature for annealing or solution treating Altemp 718 alloy is determined by the relative importance of short or long time elevated temperature mechanical properties….best long time stress rupture or creep properties are obtained by solution treating at 1900 to 1950°F (1038-1066°C) and aging. If excess phases are present in the microstructure, they are more readily dissolved by the higher temperature solution treatment.
The best aging treatment following solution treatment is to hold the alloy at 1325 to 1350°F (718-732°C) for 8 hours, followed by furnace cooling to 1150 to 1200°F (621-649°C), holding for 8 hours and then air cooling.”
This is also the procedure given in
ASM Metals Reference Book, 3rd Edn.
Also,
“Altemp 718 alloy is subject to Laves phase (Fe
2Cb) formation during solidification. This phase reduces the strength and toughness of weldments. This phase is dissolved by a 1900-1950°F (1038-1066°C) solution heat treatment.”
COKA’S results suggest that the welding resulted in the formation of undesirable precipitates which grew during the over-aging. The HRC 28 value is way, way below the max. achievable, HRC 40 (roughly, a UTS of 130 vs. 180 ksi). My recommendation is to solutionize and re-age
after approval of the APU Engineer. Possibly, an Engineering Change Order has to be run past the FAA, so mind your Ps and Qs!!!