Differential Tempering, a waste of time and money?

Jonniet: I have never worked with true laminated blades. The multiple quenched differentially hardened blade forms a marteinsite cone pointing to the spine surrounded by the unhardened matrix. This in effect forms a structure similiar to the laminated blade, except it is of all the same parent steel. Rather than two different steels, this is two and more forms of the same steel, with a reciprocal relationship between the two, I feel each influences the other to a degree that provides the opportunity to push the steel to high levels of performance than we have realized at this point. It is an open door waiting.
 
One may also ask if Damask steel is in the same category? Need with modern super steels or just a darn attractive option asthetically?

I have yet to own a diff tempered blade and I will in time (prob a practical Katana)

In truth even in a blade of 10" or so I see little value to myself in a differental heat treat. I just don't use a knife in a manner that would require the extra flexability afforded by this process.

I would buy one if it happened to come with the blade or it was a blade I happened to like.

It just does not wildly excite me unless its in a sword.
 
J.D.,

Thanks for the clarification. I admit to quoting you out of context, sorry. Interesting that when we refer to chisels and gouges as "tools" we do so, I am assuming, due to their single, or at least limited, usage(s). I guess what I was getting at was that some posit the same thing for a knife: "A knife is for cutting, period!" This makes it closer to a "tool," because some people believe it will/should never need to do anything but cut well.

Bill's point is interesting because he gives us a hypothetical situation in which we see the opposite extreme--the knife needs to be sharp enough to cut, strong enough not to deform, tough enough not to bend beyond a usable shape, be accessible with one hand (and upside down?), etc. This, of course, is also a tool, much more than a weapon, if we stay with the tool/weapon dichotomy. It is simply a multipurpose, as opposed to specific purpose, tool. Bill's point is also interesting in that it assumes the knife is carried on you at all times--the best knife in the world will not save you if it is in your safe collecting dust.

Ed,

This goes back to something you wrote a while ago on the odd but significant relationship among multiple quenches, fine grain, relative softness, chromium carbides, etc. I was looking through a book titled "Principles of Heat Treatment" by Grossman. In the chapter titled "Grain Size" he provides some possible answers. He refers to fine grained steels as "abnormal" due to the fact that they do not get as hard as coarse grained ("normal") steels. But, he writes later that when they are hardened, they are much tougher than coarse grained steel. Also, coarse grained steel fractures along grain boundaries, while fine grained steel fractures transgranularly, making them much tougher. All of this would be consistent with your observations concerning 52100 getting slightly "softer" with each successive quench, but also gaining in toughness and edge holding.

He also writes that low temp forging, normalizing, and cold forging (J.D. has done some work in this area too) all reduce grain size BUT all of them also lower the coarsening temperature (at which grain size starts to grow). This means initial austenite grain size can be made very small through proper thermal treatments and physical manipulation BUT you have to be much more careful when heating before the quench as these same treatments have made your grain ready to grow more rapidly if you get your steel even a little too hot.

There is no end (and I'm glad),

John
 
John and JD: Excellent observations and comments, I appreciate your thoughts! As long as we use the magnet, a simple instrument to predict decalesencce,the actual temperature doesn't matter, it is the relevant temperature,(allotropic phase change temp) we seek. When we use the multiple quench, grain growth is minimal due to a negligable soak time. Heat up slow to critical, hold only a few seconds to even up heat had quench we have the best of both worlds and more.
 
Bill Burke mentioned the rope cutting competition at Eugene Or. Ed Schemp cut 9 ropes and when asked about his knife he said it was 52100 made by stock removal. I do believe he said it was differentially heat treated. As to whether the differential HT is a must have I would say no. But I differentially HT my knives because it does according to tests I have performed, make a stronger blade. I look at it like this, not every user will need it but when they do it is there. Kinda like the bumper on your vehicle or the insurance card in the glove box. I have been told by some makers that they prefer to fully harden a blade and temper to a lower RC for toughness and sacrifice a little edge holding. I would rather have the best of both worlds. Even if I never need the extra strength.
 
I have just one Question for everyone; If you were stranded upside down in a vehicle with no way out but through the sheet metal and the only tool you had with you was a knife with a four inch blade that you had to use to cut yourself free then which would you rather have a knife that was made to be as nearly indestructable as the maker was capable of or one that was not made to be used for anything but cutting?
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Bill,

Would you like me to give the answer here or wait ? I know it very,very well!!!!


If you have an easy answer for that, then what if you had a fractured arm and fuel leaking into the passenger compartment at the same time?
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And one knife that had already let you down in the same emergency
 
General: I have never been able to push Damascus steel to the high levels possible with some modern steels. It would be pretty hard to make your own steel and come up with a knife that could match some of the high quality steels that are made to tight specifications as to chemistry, purity, lack of inclusions or occlusions and thermal controls.

Damascus is an art form, style, beauty. Many Damascus blades will cut pretty good, some are fairly tough. It all depends upon the goals of the maker.
 
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