I've been making my PB springs from 1018 mild steel for about 20 years. Never had a single problem. Usually I work harden the face of the bending part of the spring with a small ball peen hammer but the movement is so small that is hardly "necessary". I just think it looks cool. I'm not wild about burning it in, although that is more HC, so I use a short screw through a flared-out end I make with my hammer.
Best Regards,
JMC
John Cholin