Another area you may want to investigate is the actual ageing heat treat practice used. I am assuming that AMS 2759/3 was the heat treat specification utilized. When I was a Nadcap Heat Treat Auditor I saw quite a bit of variation in how AMS 2759/3 was applied. Given the low ageing temperature of 900F I would focus on how soak times were actually determined. Was Furnace Instrumentation Type C or Type B used? Weight of the furnace load and ramp-up cycle are also significant factors to investigate.
I have seen a lot of interesting heat treat practices in my career. Just because a specification may allow you to do something does not necessarily mean it is a good idea to do so.
Robert Werber, PEPlanish Inc.
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