Wow! I like it. In all the years of people wanting to heat treat a knife as if it were a pry bar, this is the first time I have heard somebody ask how to do a real pry bar!
This can be an excellent opportunity to clear up some confusion on the topic by coming at it from the opposite direction of how does one actually make a good pry bar meant for a pry bar. I wonder how many will then be ready to discuss how to heat treat a pry bar so that it can be used to cut things?:3:
I like your thought process Brad, you are going for a good homogenous heat treatment without going for uber-ductility. The main property of the pry bar is rigidity, you don’t want it bending or flexing too much otherwise it won’t be much use in its primary function of applying leverage. This is first and foremost accomplished in the shape and cross section. One can keep it from bending with a thorough heat treatment but flexing cannot be affected by any of our heat treating efforts, only designing its shape to be rigid will do that (incredibly important note to file away for knives).
I have forged out many 5 foot pinch point bars for local millwrights to move really heavy things and have always just left them in the normalized condition, mostly because those guys couldn’t afford the extra heat treatments. The only place that the geometry didn’t carry the piece through was indeed the very tip that would deform when jammed and wedged into tight spots involving concrete.
A bent pry bar is obviously useless, so heat treatment is there to keep the thing from permanently deforming should the geometry’s limits be exceeded. But if one gets carried away then there is the chance of brittle failure when forces are extreme enough to overcome the geometry; under such force the danger is flying shards and sharp fragments. It must also always be remembered how often we hammer on a pry bar to wedge it into position, bringing impact toughness into play in ways knives should never see. So we need some toughness to handle all of these things.
Harden the thing normally and then I would draw it back around 550F. This will not give any performance like you would want in a knife for edge holding, but it will give enough resistance to the bend while keeping it together under extreme or sudden loads.
The chart above is more for hardening operations and can only give you a rough idea of tempering hardness. I have no tempering harness numbers on my site for 5160 for two reasons- the stuff is pretty touch and go on such numbers and due to previous treatments and chemistry deviations should be dealt with on an individual basis, and secondly I don’t work with it that much at all any more so I would have very little personal data to stand behind for a solid recommendation. But for what it is worth, while it is not one of my first choices for a knife, it certainly would be one of my first choices for a pry bar!
