How deep is the hardness of oil hardening steels vs 10xx steels ? Awhile back, I bought two sledge hammers at a garage sale, cheap. The face of one had spider web cracks all over the face so I wanted to cut that off. Knowing it was probably cheaper, water hardening steel, I scored a line about .030" deep then band sawed thru it. The band saw cut it quickly and easy. Curiosity, so I cleaned up the cuts and etched. The hardened steel was very thin, maybe .010- .020. So now I always wonder how deep my heat treats get and can I grind thru to soft steel ?
A lot of tools today are case-hardened mild steel. What's a spark test say about the rest of the head?
The hammer head is not my concern. I wonder how deep the hardness gets on our knives and can we grind thru to soft steel ?
The hardness depth is going to depend on a number of factors, but we deal with much thinner material than tools like hammers. So the heat treatment you see for knives is primarily done to get even hardness through the entire blade, or a differential hardness where everything underneath the hamon/DH line is of the right hardness. If I recall correctly, hardenability tests to determine if a steel is deep or shallow hardening is done with a 1" rod. So until you start to approach that thickness it's not much of a concern.
Most case hardening is done on lower carbon and thicker steels, where through hardening would be near impossible or cost/efficiency/task prohibitive.
If you're worried about your knives in particular:
Something I was taught to do, and I believe a lot of other makers do, is to intentionally break test knives and/or a "coupon" when dialing in heat treatments. This allows you to look at the internal grain and you can etch it to check for things like hardness penetrating all the way through. It's also a good idea to use coupons when heat treating even after you've got it dialed in, so you have something to quality test.
Thank you. I've often thought about breaking a blade, did not know it was common practice.
