In Ancient Times, circa 1980, Nicholson made their regular files of 1095 steel. This is nominally 0.95% carbon, which is high carbon. It was heat treated - well, File Hard - all the way through.
Generally when filing a piece of metal one gets no back-talk.
Farriers have to deal with horses. Now & again the farrier must get the horse's attention. This he does by a sharp rap on the hoof.
If his rasp were 1095 hardened all the way through it would break, at least occasionally
So Nicholson made farriers' rasps of a medium carbon steel, 1035, and put a light case on it. The 1035 (nominally 0.35% carbon), even though used as-water quenched, was tough enough to withstand a little pounding.
Which means if you wish to forge a throwing knife, a used farrier's rasp is a good choice. You can get it hard enough to stick in wood when thrown. It is not likely to HOLD an edge for long, but it is also unlikely to break.
If you plan to skin bears or cut a lot of rope with your knife, you will be happier using a used 1095 metal file for your starting stock.
Maybe the files & rasps mentioned above are made differently today, I dunno.