Was in the process of drifting a slit for my first hammer eye punch in a rectangular piece of 4140 about an 1 1/4 deep and 3/4 of the way one of the corners chipped off (about 1/4" of a 1"). I was cooling in my water quench bucket after every second/third hit, I didn't work the material cold (good orange heat), used a 2/5lb hammer.
What did I do wrong? I should be able to salvage the chisel by regrinding and re-heat treating, I just don't want to repeat my mistake.
Any advice (pertinent to my slitting chisel) is welcomed.
Edit: Should also indicate that the 4140 billet was annealed in vermiculite for a couple hours after I pressed it from round into rectangle.