I was reading my blacksmith group newsletter, and somebody wrote up about a homemade temperature controlled propane oven using industrial controls to turn the propane on and off. He used an Omron E5CN controller with a Type K thermocouple. He warned you about the safety issues, never run it unattended, be sure you have a pilot light to ensure relight of the burner, etc., but it still seemed scary to me. I would feel safer with an electric furnace, potentially using the same controller.
I built a simple (5 gallon bucket) propane forge with a Reil burner, it works fine, but of course no temperature control other than keeping an eye on the color of the steel.
A friend of mine took a used household kitchen oven ($25), put on his own controls, and uses it to bake powder coating on metal parts. I think he goes up to 450F or so. Not sure how hot the self-cleaning ovens will go, I tried to look it up on the web but came up dry after a few google searches.
I am not necessarily interested in heat treating tool steel, but I am interested in forging aluminum, which I understand has a narrow temperature range for forging, 600 to 800 F. On the other hand, if I am going to the trouble to make a temp-controlled oven, I might as well go all the way and design it for a wide range of temperatures, to allow it to be used for multiple purposes.
I understand that ceramic kilns can be used for that purpose, and perhaps a used kiln would be a good place to start modifications. However, for forging, one would need to take the part out and put in back in multiple times, especially since I am not a skilled blacksmith.
I did notice that some knifemakers use nitrogen to reduce oxidation.
Comments? Useful web pages?
Richard Ferguson