Is differential tempering necessary for such a knife?

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Jan 28, 2000
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hi everyone
I have a hand-forged 5160 knife with 10" blade and use it only for chopping.I am quite satisfied with its performance.But it is not differently tempered.I'm curious how much improvement can be made by
differential tempering on such a knife?
Thanx.
 
I Am Not a Knife Maker, but...

My understanding of it is that differential tempering allows the blade to flex a bit more, so it's less likely to crack or break. Because of that, I think it would be possible to harden the edge a teeny bit harder without worrying about the whole thing being too brittle and snapping in half. But, if it seems to be holding an edge okay and hasn't broken, it's probably fine as it is.
 
With any luck, Bill Siegle will pop-in with his views on your question. I have a "Bowie" with an 11 inch-long blade that he made (5160 steel that is differential tempered), and it's holding-up very well.
 
Have there ever been any controlled, scientifically rigorous or otherwise convincing tests of the benefits of differential tempering?
I know the Japanese have taken it to the level of High Art and it was battlefield experience, especially with the Mongols, that motivated that development yadda yadda yadda, but are there any tests with modern materials? Cliff? Mastersmiths? Lurkers? :)
 
Crayola,
Names noone could argue with, for sure. I'd give alot for a knife of theirs, especially a 52100 by Ed. Wow! [and the crowd begins to chant, "pronghorn, pronghorn..." :)]But have they done controlled tests that would show even a dummy like me quantitatively and qualitatively what the improvements are?
 
HJK,
What exactly is the type of performance are you wanting to test. A differentially heat treated blade is one that is hardened on the edge. The performance of the cutting edge has been tested time and again for ease of sharpening, ability to stay sharp, and usability of the blade. The soft back is to keep the blade from breaking in half and loosing its ability to function as it had before breaking. Basically, that is why I differentially harden and temper my blades.
 
Exactly what you said, I suppose. The superior impact resistance or resistance to breaking of the blade as a whole. I suppose it stands to reason that a blade that has, say, a 60 Rc edge and 48 or whatever back will have a springiness to it and that with a proper hamon etc the edge could even be repaired. Hey, I'm a fan of you guys who do it and I lust over some of the beauties made that way, including a few of my own purchases. But I bet there are some doubters out there who would say that with modern materials like CPM 3V and the like, you don't need to do this: the entire blade can be harder, or maybe the effect of differential hardening isn't what its cracked up to be, at least with better steels. I sure as heck don't know. I don't pretend to know. I'm asking. I think the question makes sense. It surely isn't meant as an insult to the great forgers and folders out there, and no doubt you are among them. The performance of your blades is well known and roundly admired.
I would never risk pissing great smiths off - they might never build me any more blades :)
 
I think that the word "necessary" may be what you need to know. On the blades that are completely hardened, which is easier to do, they can be tempered to the specific use of the blade. A big chopper would not need to be a 60 Rc. A small caping knife probably would. Carving knives tend to be harder as they need the edge holding qualities of the harder edge. Not too much twisting and chopping for them. A 10" to 14" camp or bowie, would be tempered softer, whether or not the back is soft or not. Basically, the knife maker knows his steel and will heat treat it according to the requirements of the customer.
Don't worry about upsetting someone when you ask a question. Sometimes the question is not understood so it is hard to get the answer you need.
A closed mind is about the only thing that really upsets me.
I hope I have helped answer your question.
 
I have seen claims that a softer spine will increase the edge holding over a fully hardened blade with the same edge heat treatment. The reason being is that the softer spine will act to absorb the shock on really heavy use and thus prevent crack formation and migration along the edge. I never tested this, but have spoke to engineers who have and they agree, however they were working with much larger "blades" and didn't think that the effect would be significant on a hand held knife.

In regards to modern steels, the point has been made correctly that there are current steels that have a very high impact toughness and ductility even at rather high hardness like 58+. This means that you can run them at full hardness and not have to worry about premature breakage. This means that you don't have to deal with the drawback of differential tempering which is that you significantly weaken the blade. This is not a small effect either. Roughly, since strength is proportional to hardness and the contribution to the overall strength is actually maximum near the spine, you can see a strength drop of 25-50%, depending on how much you soften and to what extent .

-Cliff
 
This means that you don't have to deal with the drawback of differential tempering which is that you significantly weaken the blade.

Cliff, by "weaken" do you mean decrease the blade's elasticity such that plastic deformation would take place at a lower stress level?
 
The difference between differential hardening and differential tempering is great. We have tested the influence of many variables. Most have been discussed in the forums and atricles in Blade Magazine.

Multiple tempering is better than single heats as it allows a greater uniformiy and hardness than a single higher temper heat. Come to the desired temp slowly, hold for two hours and cool down slow. Wait 24 hours between heats, place in home freezer between heats. This pertains to 52100 and 5160. The difference is ever so subtle, but measurable when the hemp rope slice test is used. Another consequence is greater toughness. What we seek is uniformity.

The more the previous thermal and working cycles are specifically appropriate for the steel used, the greater all following steps influence the blade.

We have developed many thoughts on the subject and I am working on a book that will describe the subject thoroughly. Over 100 pages and growing. There are no simple descriptions. When pushing a steel to the ultimate leves of performance, every little bit helps.
 
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