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Angle grinder plus unknown steel equals spark testing.

Here's a start: Spark testing - Wikipedia, the free encyclopedia (there is a pending SOPA blackout).

Another: The Spark Test and Spark...

Ruined? No. You can always re-heat treat it and re-temper it. Steel can be very forgiving at times and other times it's a surprise. Like this one. It is entirely possible that it behaves in a...

Okay, one more thing. Try to gently file on this blue blade with a brand new file before doing anything else. Old files with the teeth partly used do not necessarily cut the same way as a new file....

Two things come to mind Jeff.

The first is that the file was probably overheated at some point if the grain size was large. It is possible with some simple techniques of thermal cycling to reduce...

I think you're off to a good start. Simply increase the temperature by 25 degrees for one hour. If you are patient and take that in steps you'll arrive at a hardness you like that won't abrade your...

400 C (750 F) would be much too high a tempering temperature for O-1. It should not skate a file. Most old files are W-1 or the like, that explains why it survived a water quench. The O-1 would...