Gentlemen,
FWIW, stick with
old files.
Don't know the reason or the metal but some newer files, made in the last 10-12 years or so will
NEVER make a usable knife.
Started hearing that about 10 years back, don't know the details as I've made no new blades since then.
Good luck to all, it's a great hobby/pastime!
Regards,
...