ladybug93 wrote: ↑Tue Jan 24, 2023 8:30 pm
but that's what they do on forged in fire...?!
Heh, to be fair I wasn't saying that oil-quenching a blade of a certain temperature and then tempering in an oven can't make for a great heat treat.
I was just trying to point out there's no way of telling if that's all someone did. I could TELL you that I annealed, normalized, thermocycled, and did cryogenic cooling... But you have no idea if I really did all that, or if it was just me out in the backyard with a fire pit, a tank of motor oil and mom's old oven.
But to be fair Brock O Lee was absolutely right to walk away from that deal. Depending on the steel, the temperature at quench, etc. those blades could have even been well up to 66-68 HRC! Basically way too brittle for most simple carbon steels and most use cases for them, particularly a pocket knife. Using a blade at it's quenched-hardness is almost never a good idea unless you just didn't get it hot enough to get very hard, and that raises all sorts of other issues with things like grain structure.
File-testing hardness goes down a lot on Forged in Fire because it's a really simple way to tell if the quench hardened the blade at all (not that it got as hard as it should), and it's a competition format. But as someone else mentioned they usually never show the tempering process, which is hugely important... Arguably much more important. I don't think the file test is actually that practical outside of that contex. There's also been a few times on that show where they will use steels that don't actually get harder than a file, or the smith neglects to remove forge scale, and their file skates on a hardened blade and they re-quench it unnecessarily thinking it wasn't hard. In my (very limited) experience the way to do it is to get it to its critical temp, quench it, then test the hardness after the temper.
But anyway, I studied a lot about heat treating 108* series carbon steels, and it's really not exactly rocket science to get a serviceable, hard blade with steels like that even without specialized equipment or processes; there's a few cool videos around showing you how to make blades with a campire that actually do work. BUT that's just the 108* carbon steel series; things even get trickier just going up to 1095. Other steels might be air quenching instead of oil, and there's differences between martensite and austenitic, etc. Especially when you start talking about highly-alloyed steels. All steel is technically an alloy of iron and carbon, but once you start throwing things like chromium, vanadium, tungsten, molybdenum, nitrogen, etc. things get really complicated. I'd be speaking out or turn if I commented on anything but doing simple oil quenches on low-alloy steels. And then there's things like annealing and normalizing...
Anyway I got sidetracked. Like I said before, without special testing equipment, verifying the quality of a heat treat isn't really that feasible for the average consumer. Even using some of those hardness testing files, or even a Rockwell machine, aren't going to really tell you anything about the grain structure. Only way for the end user to really verify is to have that equipment and/or do very controlled testing. It's pretty much all a game of trust for us. Personall, I think a lot of the qualities or shortcomings people tend to attribute to the heat treatment are more likely differences in blade geometry.
I should have linked to these videos before when I mentioned Shawn Houston talking about this stuff
https://youtu.be/abaR6fE3MUA
https://youtu.be/pgASlsQRDAo
So yeah, any time someone says a heat treat on one knife isn't as good as a heat treat on another, I think it should be taken with a real big grain of salt unless they're testing work identical geometry and have the calipers and goniometers to prove it.