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Shallow hardening vs. deep hardening


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#1 Joe Renner

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Posted 17 March 2003 - 02:33 PM

The answers are always right in front of us, but that doesnt mean we see them. But we do see the questions, bright as the fire that inspired them.

Shallow hardening, simpler steels are more controlable, the hamon can be controlled better. deep hardening steels will make the hamon jump back or simply the matter of time is not enough to leave you with both martensite and pearlite, they will simply go one or the other.
1084, I would call medium, especially considering the high manganese and carbon its been having lately, yea it seems to be on the high side. Because of this its hamon can lightly jump, even out(from each side) and if you are not carefull harden all the way through(ie: no pearlite).
5160 can take a hamon and even a controlled one, Ive done it and others  are doing it. I dont like 5160 done that way, however, and dont use it anymore.

-Joe

"If you do not pursue a genuine path to its consummation, then a little bit of crookedness will later turn into a major warp." -Miyamoto Musashi

#2 Guy Thomas

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Posted 17 March 2003 - 02:16 PM

I think I know the answer but what makes shallow hardening steels better at showing hamon than the modern deep hardening simple 10xx alloys? Does the varying depth of the hardened "skin" of the surface of the blade as you move up from the edge toward the spine create the showy hamon? And is this why Howard Clark had a special batch of 1086 made?

I'm thinking that the homogenous nature of the hardening of modern steels prevents the formation of varying visible structures in the hamon area of the blade even when using clay coatings. You will essentially just get a distinctive hardening line (what most people call a temper line) whereas on a traditional shallow hardening steel you get a wide band of transition from the hardened edge to the softer spine. This wide transition area would be the showy hamon. (I will be doing my first clay coat heat treat on a blade (an 11 inch tanto) this coming weekend so hopefully I will find out first hand how this works on 1084 steel.)

I'm not sure where I'm going with this, I just haven't found any good discussions of the differences between various steels and depth of hardening and how it affects the finished blade not only in appearance but in performance. For example, from what I understand, 5160 should not be used with the clay coating process because the resulting blade may actually break or separate along the hardening line. If I understand right the way to defeat this is to first through harden the entire blade and then do the clay coat heat treat.
1084, however, from what I've read, will respond favorably to the clay coat method, but I'm not sure why the same problem 5160 has doesn't occur. 5160 is obviously a deep hardening steel, but is 1084 a "medium" hardening steel, so to speak when referring to the depth of hardening?

Anyway, the puzzle pieces fall into place the more I learn. I'm getting to the point where I hate asking questions because I have the feeling that the answers are right in front of me. I would love to see more discussion on this topic however.

P.S. After submitting this post I realized it wasn't where I thought it was. I thought I had posted this in the metallurgy section. What can I say, I'm a dunce! :P

Guy Thomas




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