Stock removal on a file blade has one good advantage. The grain structure and grain size is at just about as good as it will ever be, unless the file is over heated. If, in a darkened area, you raise the heat on the file until you begin to see a low red color, and try to hold that level of color for a minute or so, the carbon will form into balls in the steel. This allows cutting tools to slide past these balls. I would say, repeat this a few times, and the file should be soft enough to work with, without a common annealling process, which does not do well on steels of high carbon content. If a common anneal is used, the carbon forms layers which will resist drill bits, and other cutting tools. The process is known as spheroidizing annealling. Then shape into what you want by grinding or filing. When ready to heat treat, bring the heat to a red-orange, hold at that color for a minute, or a few minutes if possible, and quench in warmed canola oil. File steel requires a fast cooling quench, and canola is the fastest other than commercial quench oil. At this point, a good file should not even scratch it in the least. Then temper at 450°, twice, for one hour each time. Just use your kitchen range, governed by a separate oven thermometer. When you file check for hardness after the quench, you will have a few thousandths of decarb on the surface, burned away by the heating. Be sure and file check deep enough to get below the decarb.
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