differential hardening question

M

martin j

Joined
May 16, 2001
Messages
692
Hello,
I have been wondering, is there qualitative differences between blade which has been edge quenched, one which has clay temper, and another which has been fully hardened then had the spine softened with a torch? (Perhaps there are other methods I have neglected, my apologies). Assuming the same steel ,even stell from the same batch. There is aesthetic difference, I understand, how the temper line appears. But is there a difference in use for the "end user"?
Also, is one method preferred or required vs. others for ABS journeyman test and master smith test?
Thank you-
Martin
 
That's a loaded question if I ever heard one. For the purest I expect the answer is yes because in a perfect world the edge absorbes something from the clay as well as being in a somewhat controlled enviourment during heat treating. Out here in the real world I would say no assuming the spine treatment is done well.:confused:
 
The main difference in edge quench (if the edge is all that is brought up to the hardening temperature) and the clay temper quench, is that there is more control in the area that is to be hardened. Also with the clay temper, when using a heat treat oven, the critical temperature is evenly distributed over the exposed area and the back will not reach the critical temperature. Even if it does, the clay will slow down the rate of temperature drop so that it will not harden. This is what I believe is called differentially hardening because only the edge will get hard and the back remains soft. After the tempering process, the back will remain the same (soft).
When the whole blade is hardened and the back is softened, I believe this is called differentially tempering. The back will be springy if done correctly using the torch. You will need to really know the oxidizing colors to get it right. On some steels, When it has gotten too hot, it will air harden and actually be harder than the edge. A file will usually tell the difference.
To the end user, it would matter only if the process was done incorrectly and the back remained too hard.
I prefer differentially hardening because it is more consistant for me. Aftr a light etch, 20 seconds, you can tell exactly where the hardened area is and if not as large or as high as you want, do it again. The steel I use most is 52100 so that may make a difference on some of my preferences.
Hope this helped some.
 
Raker,
FYI for your brain database :cool: my preferred method is to clay the blade in Japanese fashion. I raise the entire blade to a homogenous heat and quench. I do this to obtain a fine pearlite body, martensitic edge and martensitic spine. Then I give a fully even temper over the entire piece. This is with 1045 by the way.
Depending on your desired method, steel, skill level and tools available you can get a host of metallurgical effects and limitations. I for example use dual electric kilns for heat treating, even though I forge my diff hard blades in a propane forge. Just some info to compare and contrast ideas. Everybody is different. :cool:

-Jason
 
Thank you for the information, also I apologise if it sounds like "trolling," as outsider to blade smithing I am honestly unaware of controversy among different approaches to differntial hardening /tempering. I am only curious of makers opinions-
Martin
 
Jason,
On the small knives, I like to use the torch to bring the edge up to critical. I prefer to use clay on the larger ones as the heat is easier to control. I do not harden the whole blade and draw the back.

Martin,
I understood, I think, what you were trying to find out as to the different types and methods of "edge hard, soft back". I used clay on 52100 for my JS test knife and it performed beautifully. I think that if the knife maker is comfortable using one method, then they will be more proficient at it and have repeatable results.
If you don't ask, you can't get an answer :). Have a nice day.
 
Raker,
I am sorry I meant to address Martin! :( Sorry that probably came across really rude. I meant to just fill in martin on my preferred method. Wasn't questioning you I swear. Oops! man, i gotta pay more attention LOL!

-Jason
 
Jason,
No problem, I didn't take offense.
I am curious as to the dual electric oven set up. I am going to go with salt bath for my heat treat as soon as I can get everything else set up. I like the idea of no scale after the heat treat. A soft blade is a lot easier to hand sand to the finish I want.
How do you get a martensitic spine with the clay on it? I watched Mr. Mike Bell do a sword form cable that had been folded about 10 times. The clay was about an 1/8" thick and the blade was quenched in a bath tub of tap water that had just been filled. It was great watching the blade curve on way and then curve back. What was very interesting was that he didn't temper it at all. That may be one reason for the type of hamon lines and other visual effects that he produces in the blade.
 
Thank you for more responses and information, yes Raker, that clarifies. It is very nice to be able for "know-nothing" like me to have thoughtful replies from excellent well regarded makers like yourself (even to "dumb questins" :)). I only was curious if there were major differences between the different approaches to getting the 'hard edge/soft spine," not surprising that more important it skill of the maker in any given approach.
Thanks-
Martin
 
And yet another method.Guys,I heat mine with a torch or propane forge.Then full quench, and temper using a propane torch.I use mostly O-1 and some 1095.I have had good consistent results, but I have welded for years and read the colors pretty well.I would like to try the clay method though as I have heard many good things about it.As far as the difference between methods, I think Ray and Jason covered it pretty well.Dave:)
 
Color painting with a small propane torch is also effective on carbon blades. Oil quench as usual. A straw brown color at the edge equates to 400 F. The blade is progressively softer toward the spine. that progrssion makes a very tough blade. Just another thought. Terry
 
Raker,
No scale would be a beautiful thing actually. I may go for a gas injection device some day to get that result. I decided on two kilns just cause it works well. Salt bath is an excellent choice and much more affordable. I would have gone with that as my next option, but my methods really demanded a kiln-like atmosphere for some of the heat treating I'm doing.
For the martensitic spine I just don't cover the spine. I need wire to hold the clay on though. I use 19 gauge, black annealed and I have to use less than 1/8" clay, otherwise my blades will crack at the edge. I underestimated the insulating properties of Satanite for a long time.
Some questions for you... when watching Bell, did he put a thin layer of clay along the cutting edge? Or leave it bare? How well did the clay stay on? I'm curious.
You are right by the way about the effects in the hamon. It will depend upon your steel and methods but, tempering essentially reduces some of the effects at times. Its like going in reverse, if that makes sense. Again, it depends on the steel and method as to whether or not you will notice anything.

-Jason
 
Jason,
When he put a wash on the blade, it was as if some muddy water had splashed on the wind shield and dried. He put this on all the blade. When it dried, because of the etching effect of satanite, it would hold the rest of the satanite. The first thing he did was take a thin piece of material and put small lines from the center to the edge of the blade. This would prevent stress risers from forming in the blade. This was done on both sides. When that dried, he put about an 1/8" thick layer on the rest of the blade. The next day was hardening time. He used an upright propane forge and would run the blade through the heat. The closer he got to critical, the faster he would move the sword, until the blade was all brought up to hardening temperature. Then he submerged it in a tub of water, freshly drawn, for a few seconds and would look at the blade. He submerged it again and would look and then he was done. The blade bent one way and then bent back the other, as the back shrank from cooling. No cracks, breaks, or loud noises.
I loved it all.
 
Very cool. Thanx Raker, I wish I could see Bell work in person. I'm still trying various tsuchioki methods and may try his just 'cause. Thanks again!

-Jason
 
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