Just heat treated my first piece of metal. It's a mandrel for expanding exhaust pipe for slip fits. Worked before but it was hard to push in and pull out because the pipe would grab hold of it pretty good, and it was starting to show some signs of wear.
Heat treated that baby and now a file slides on it like it's made of glass. It's 1" thick so I don't have to worry about it cracking...and it's not under any bending loads anyway.
Tried it on another mandrel...didn't work...then I noticed I didn't make the other mandrel out of "hardening" steel like the first one.
Just had to tell someone.