Can any one school me in the proper use of heat treating foil. Does it work? Is it a time saver? Can you use it on a blade in a propane forge, or is it only usfull in a inert gas injected furnace? What does the steel look like after quenching? And finally can you still use conventional quenching mediums? Thanks in advance; Bob @ Frontier Forge Works
The heat treating foil works to reduce decarburization and oxidation. If you are using an inert gas set up, you do not need the foil. The gas is designed to fill the chamber, constantly pushing out oxygen so it cannot react with the steel. The foil keeps out the oxygen (by forming a barrier) present inside kilns and other heat treating devices, that do NOT use inert gas set ups. There is no reason you couldn't use it in a forge, but typically only carbon and low alloy steels can be accurately heat treated in such an environment. The foil is for higher alloy steels. And as Mike was indicating, you need critical cooling rates and foil may pose a problem in that department for low alloy and carbon. Plus, judging temps with the foil on may prove awkward. It would be best to avoid I feel.
However, tool steels, stainless steels and others similar steels typically require soak times, preheats and critical, minimal temperature deviation. So, precise heat treating kilns are required in most cases. These common HT temps are often high and long, creating a world of problems with decarb and scale. 1500°F scale is very different from 1900°F or 2000°F for example. Something to keep in mind, many of the steels that must go into those HT kilns need a much slower quench and can cool in still or forced air. So, unlike the carbon and low alloy, they do not have to be cooled in seconds. It depends largely on the steel and subsequent chosen HT.
If you have wrapped it tight, the knife will have some very, very slight scale on it. Its unavoidable. But its a piece of cake to remove. If you do not use foil, well the scale formed at such high temps required for many (not all) stainless steels and tool steels will form a HORRIBLE mess. You will get so much decarb and scale, you might as well make another knife. Take it from someone who has tried and failed, DON'T!
I wrap paper grocery bag pieces around each blade inside the foil. This helps to burn off some of the oxygen inside the foil. Well hope that helps answer some questions.
