Mitch
Normally hammers are made from 1040-1045, 4140 etc. Not normally good for blade steel. Files are normally 1095, W-1 or the like. The key word here is "Normally" Blue Dragon has a good point. If you are just playing around then use the files, If there is any remote possibility you will be getting more serious about knifemaking then buy known steels. I'm not saying files or "salvaged" steel won't make a good knife, it is just much harder getting a proper heat treat.
Chuck