[jimmontg]

Well the ferric acid turning dark fast means if there is nickel in it it's less than 1%. I couldn't tell very well, but the grain looks good in the high temp center one. Looks like it broke consistently too. You might have some chrome in it. Try what Doug said, but since you have a limited amount of material try two hours at 425 which I have found to be good for a lot of Nicholson files which are basically W2 steel. If it's still brittle try 2 2 hour tempers.

If you decide to use brine heat it up to 80C+ to help, note help prevent cracking, but it's no guarantee. You have oil use it at 45-54C (115-130F) as oil should be heated up some and not used at room temp, because too cold oil will also make some steels brittle and/or warp. You have a mystery steel and it could be 5160 for all we know without spectral analysis.