(10-25-2018, 11:14 PM)Bud Wrote: So I take it then that when we talk about over heating edges and softening the steel that we are talking about more like much higher temperatures and not tempering temperatures.
Well Mr. Bud, I seem to be hearing the same story of much higher temperature generation, so I'm glad I'm not alone.
Tempering a fully hardened blade is usually done twice, for two hours each time. Temperature is the variable. Simple carbon steel is tempered at significantly lower temperature than simple stainless. The very high alloy particle steel commonly used these days could take tempering temperatures as high as 600°F or more.
The point being most knives these days should be very heat tolerant compared to the simple carbon steels people have been using for hundreds of years. Surprisingly, virtually no one in the world seems to have noticed softened edges of simple carbon steel in all that time. If you consider how much sharpening has been done by people who literally lived or died by the quality of their edges, it's hard to imagine no one jotted down some notes for posterity.
Anyway, the first temper has a greater affect than the second temper, so my first temper is always at a lower temperature. With 52100 full hardness after cryo is regularly 65-66. A two hour soak at 360 brings hardness down 2-3 points. The second temper at 375 usually leaves me with RHC 61-62. That's pretty hard, which means relatively brittle. A typical blade might only flex 15° before snapping in two.
If I raise the tempering temperature to 400-425, the hardness would drop to RHC 57-58, but would increase the flexibility/toughness substantially. Perhaps the same blade would flex closer to 25° before breaking. The reason my blades are unbreakable is simple. I temper the spine a third time at a very high heat of around 600-700°F for maybe ten seconds before quickly quenching in oil. This produces spring tempered martensite with RHC 50 on the spine, while preserving HRC 62 on the edge.
Near as I can tell, the overheated edge theory we are hearing so much about doesn't seem to be based on a normal source of heat. I don't understand anything about extra heat coming into the picture from molecular degeneration. It sounds interesting, kind of like how splitting an atom releases energy, but I don't think that grinding steel releases any energy at all.
If there is anything to this theory of spontaneous high heat energy generation due to molecular separation or however you describe it, wouldn't someone be harnessing this energy resource?