Hello folks, I hope this thread is not old enough to warrant me starting a new one but I am having a similar issue.
I am currently trying to HT a rasp knife using a old Willie-Charlie rasp. My research indicates its from the 40's or 50's and should of been made of decent steel. I saved all of the chunks of extra material to practice my HT. The first piece was ramp to 1450, hold for 15, oil quench with oil heated to 150. I took the sample and put it in the vice and wacked it, and it bent over. Second piece was ramp to 1475, hold for 15, oil quench in same oil. Wacked that piece and had the same results. I took those chunks in and hardness tested them and it was sub-20. Switching assumptions I took another piece, ramped to 1450, soaked for 15, and then quenched in water. Wacked it and it snapped right off. Good results until I hardness tested it and it was all over the place depending on where and what side was tested from 35-55. The last test I did today was to put one more piece in and ramp to 1450 and soak for 30, thinking that it was possible I did not have a enough soak time for the conversion but I want to hit it on the surface grinder tomorrow and clean it up to see if it makes a difference.
The customer called for a hollow-ground skinner out of a file, otherwise I would be using O-1 or something known. I did explain to them at the time that the metallurgy of the rasp would be the deciding factor of its performance and they accepted that fact in order to get the "rasp look" they wanted. I know hawks are commonly hardened to a lower HRC and have decent edge retention and cutting ability, and people make camp knives out of 4140 which does not HT to very high hardness either. I guess what I am wondering is should I invest in some new rasps like Nicholson, Bellota, or Heller in the hopes of better (known) metallurgy, or just work to achieve the best HT with my samples and hope that 45-55 HRC gets the job done? I know the HRC will change post-tempering but I am unsure how much. I wouldn't think it would get harder.
Thanks,
Morgan