Did some research. Some info. on Wikpedia says 450 degrees F., but our tech gut a work opened his magic book. I don't know the exact material Ford springs are made of, but most springs (industry wide) are tempered at 850 degrees F. to 1050 degrees F.
where do you get a big oven and how much are they? would a heat gun do the job? one that goes up to 1000 degrees
do a search on Summit Eastwood Caswell They do sell heat lamps for bigger pieces. Its all about the heat, so sure a gun would work.....as long as you can control the temp. Would suck to hold it for 30-40 minutes :16suspect
It is probably the machinists handbook and the temperatures he gave you is commonly used to anneal or normalize your material. "850 degrees F. to 1050 degrees F" at this point the metal starts to become a maleable state and the granular structure starts to realign itself. The 400 degrees F. won't hurt it
