Hi... Just want to mention something related to heat treat ovens... When the heating element wire is active, it's very susceptible to chemical attack that can lead to rapid failure. Any kinds of chemicals, salts or chemical-based fluxes used inside the oven will shorten the life of the elements. There are various recipes and products on the market for carburizing compounds and every time I ever used them, I could see the junk crusting-up on the wires and they usually fail soon thereafter. I often use argon gas to purge the oven and when I do so regularly, the elements seem to last about 2-3 times as long.
Merry Christmas...
Ray C.