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Ed Caffrey's Workshop Talk to Ed Caffrey ... The Montana Bladesmith! Tips, tricks and more from an ABS Mastersmith.

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  #1  
Old 01-29-2001, 04:48 PM
radnur22
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tempering


What is the advantage (if any) of tempering a blade for 3 one hour cycles verses 1 two hour cycle?
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  #2  
Old 01-29-2001, 06:23 PM
Ed Caffrey
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Tempering


OK, let's see here......First off, I would never recommend tempering a blade for only one hour, that's just not long enough for the heat to do it's magic on the grain structure, and after such a short duration in the heat, you will still have a good percentage of material, towards the core that will remain slightly more brittle than the material nearer the surface. Not a good thing. In reference as to why to do it three times......I could go into a long winded explaintion of temp curves and transformations in the matrix, but it all boils down to insurance. Through the multiple tempers you ensure that the entire matrix of the steel has been completely transformed/softened to the level that you desire. This becomes very important when dealing with steels such as 5160 or 52100. Both of these steels contain a very small amount of Chromium, which seems to be the key to why the multiple quench/tempers work so well on them. I cannot provide you with undisputable
scientific proof as to why this improves these blades' performance, but through the tests tha I've conducted where I have quenched/tempered blades 1, 2, and 3 times, then done destructive tests on each of them..........it makes a very noticable difference. Single quechned blades will rarely pass the 90 degree flex test, and will only cut about 35% of what a triple quenched and tempered blade of these materials will. Once you experiment with it, and gain a bit of experience with the materials, it is also very predictable.
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Old 01-29-2001, 10:06 PM
Sandspur
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Re: Tempering


Ed I make some parts out of O1 drill rod ,totally unrelated to knife making.These parts are subjected to a lot of shock and stress.Would triple tempering be benificial.I usally just heat treat and temper them by the manufactors recomendation but every once in a while I have one to break.
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Old 01-29-2001, 11:14 PM
Ed Caffrey
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Tempering


It would be worth a try. I would suspect that you would have fewer, and possibly no breakages by double or triple tempering. There is always that instance though, where a part is stressed past it's mechanical limits........so it's not foolproof, but it has certainly helped with the toughness of my blades.
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  #5  
Old 01-30-2001, 07:45 AM
radnur22
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Ed, I just finished heat treating a blade and tempering it in the oven at 375 deg for 2 hours. I then tested the blade. Here is a link to the test. Would the chipping of the blade happen to a properly tempered blade? Or is it normal after hitting a chunk of steel?
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Old 01-30-2001, 08:40 AM
Ed Caffrey
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tempering


If you whacked the chunk of steel, I would say that's pretty normal. I can't be sure, but from the picture the edge appears bent rather than chipped. My foumula for 5160 is triple edge quenching, triple tempering at 350. This will render an Rc of 57-59 at the edge and 38-40 at the spine. With this heat treat method I have never had a blade fail to pass any of the ABS tests, or the brass rod test. Also remember that your blade geometry plays into what tempering temps to use. from the cuts on the 2x4 it appears that the edge on that blade is fairly thick and heavy. With that geometry you can get away with a bit higher tempering temp. Not that that's a bad thing, it just tells me you designed that edge to chop. That's what's so neat about what we do.....using the concept of "The Overall Package" you can produce a blade to do just about anything you want. I use that "Overall Package" concept and try to get the best ALL AROUND performance that I can. Keep up the testing!! That's what gives you the answers you need!!
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