David,
I was a high school kid when I made the blade for this knife in 1970 and, at the time knew next to nothing about heat treating steel. But I did know how to anneal the file to get ready to shape the blade. After it was shaped, I heated it to a very bright orange in a home made forge and quenched it in brine water. It was very hard after this and a file would skip across the surface like it was glass. I also knew enough to draw the blade back some, so I used a propane torch to bring the blade back to a straw color and then let it cool slowly on a block of wood.
I am sure that this was not the correct or optimum method to use, but I didn't even know what kind of steel the file was originally made of, and I sure as heck didn't have the internet to search for information. Whatever, the process I used worked for this knife and it seems to hold an edge well.
Better files are made of 1095 steel and sometimes W-1. I would suggest that you look up the correct heat treating process for whatever kind of steel you are using. Now days, it is really easy to get too much information (some of it wrong) via the internet. I still use my old dog eared copy of the "Machinery's Handbook, 21st Edition" for almost everything.
Dave C