43-13 says "Reheating of 2017 and 2024 alloys above 212 degrees F tend to impair the original heat treatment. Therefore, reheating above 212 degrees F including the baking of primers, is not acceptable without subsequent complete and correct heat treatment."
I screwed up and did heat my HS to about 400 F for a short time. I had a 35,000 BTU propane heater standing on the floor beside my work table and laid the HS on the table. After maybe 30 seconds I realized the HS was above the heater, shut off the heat & moved the HS so it would not be above the then cooling heater. It wasn't hot for very long.
With a scrap piece, I reproduced the situation and measured the temp. It came to something over 400 degrees. Consulted Van's, 43.13 and the internet and was unable to get any help. Ken Kruger had not encountered the problem before.
In cFortunately, I had retired from the Air Guard and the shop I worked in did non-destructive testing. We had equipment that could discern differences between alloys, including heat treatments, although we never had occasion to use the equipment for that purpose.
Off to the Guard I went. By dumb luck, the Reserve unit on base had just had a requirement to check for heat treatment and the gal that worked there was visiting my old shop when I arrived. So we set up the equipment, checked a test piece that I had heated longer and hotter than my HS & yes, we found changes. Then we checked my scrap piece that I had used to duplicate the situation and found a small change over a very small area, maybe 2" diameter. This difference was not great enough to classify that spot as a different temper, but it was slightly different from the surrounding area. Lastly, we checked my HS & found no changes. Whooee!
In conversations with some engineers later on I learned that it would have to have been heat soaked longer to produce significant changes.
