Heya. I've read most of the posts about heat treating 5160, and you mention that most of the time drawing back hardness on a fully hardened blades does more harm than good(taking a torch and painting the colors). What would the correct way to draw the blade when the entire thing is hardened?
I normally use the forge to heat treat my blades, and only get the cutting edge to critical. I get a wonder temper line. Say for instance, I was to use salt pots instead and got the whole blade to critical. The entire blade would harden which seems too hard overall. What would be the best way to temper the back?

I'm not doing this, but I might be setting up salt pots soon and am just wondering. I'll probably stick to the way that I'm doing it since I like the results. (In terms of strength and durability, not to mention the temper line.)

Jamie

I think that you might be able to use clay hardening techniques. You could put a layer of clay on the back of the blade and work with your time in the high temp salts to make sure that the back didn't have time to reach the critical and if it did, you could still edge quench to get a temper line.
If the blade is not in the salt long enough to heat the back, it shouldn't be able to get hard and that would also leave you a temper line. I have been thinking about doing this with the 52100, but I don't know how much contamination the clay would do to the salt or if it would float out and you could skim it off. I have seen the high/low salt pots work and they do work very well. The blade can be finished before heat treat and the scale will be non-existant due to no oxygen to scale the steel.
I don't make a lot of knives so the time saved would be small in the heat treat part but would save a lot of time on the hand sanding because of the softer steel (before treat).
Let us know how it works out.
Ray Kirk dba Raker Knives

I know that clay coating has been in in the salt pots, and I've never heard people complaining about it contaminating the salts. I was just curious. I'll probably continue using the forge to heat just the cutting edge and magnet to determine the correct temperature if clay coating would be the only reliable way to do this with salt pots.

Jamie

Jamie, I usually harden the entire blade then draw the spine. After tempering, freezing, temper again; I put the edge in a metal ice cube tray full of water and heat the spine with a propane torch 'til it turns purple/blue. Allow the heat to stay with the blade for awhile before cooling it. Your blade should bend and return straight.