Some years ago, I was machining the laser-cut blanks for my engine-gearbox mounting plates. I wondered why it was so damn difficult to cut, some of the time. It was some time later that I was talking to the laser guys and they told me that the material they had to hand at the time was high-Carbon steel
. I guess that I was having the same problem as with stainless, in that it was work-hardening if I didn't immediately get to cutting a decent amount with proper chip loading. When machining stainless, you need a really sharp tool. Machining mild steel
, you get a better finish with a slightly dull one.