Damascus Steel Problem

[huntingsgr8]

A few years ago I decided to try my hand at making damascus steel, and after rigging up a forge, I successfully managed to weld 3 pieces of medium carbon steel together. I did as I had read to the letter, I cleaned up the pieces, wired them together, put them into the forge until red, applied enough borax along the edges and ends to give it a wet appearance, repeated when it got to a bright orange, then when I saw a few sparks coming from the forge I pulled it out and welded it solid, then allowed it to cool in open air. After it was cool I went to file the edges to examine my welds......but I couldn't. The steel somehow became so hard that even a file refused to bit into it. So I tried again, this time I used mild steel, and 7 layers. It welded at one end, and I ran into the same problem, however where the block had not welded, I was still able to file. Has anyone got as clue as to why this happened? I figure it's worth mentioning that I was using coal at the time too. I haven't tried since and have accumulated the parts for a propane forge, but before I go trying again I figured I'd ask.