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An introduction and a question on Hamons


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Hello, I always find it a bit awkward introducing oneself to a new forum :) I have loved all things sword and knife related for a very long time and after lurking on this forum for a while and reading some great books on knife making (Wayne Goddard and Jim Hrisoulas to name a few). I have decided, as soon as I have the funds, to try and make some knives.

 

My question is other than the obvious application difference between a hamon (clay application and water quench) and an edge quench in oil (or Goddards Goo if you read his book). What is the difference at a steel level. A hamon if I am understanding it correctly is a Martensite edge but what does edge tempering produce? Is it as well a Martensite edge just not visible? Thanks in advance.

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You are right, edge quenching produces martinsite in the edge and the spine, which is not quenched, is allowed to form pearlite. However, with some steels a hamon will still be demonstrated with edge quenching along with proper surface preparation. You can also sometimes see a hamon with a fully quenched and uncoated blade if a shallow hardening steel is used because martinsite will develope on the thinner edge and the thicker spine will form martinsite. You also need to remember that a hamon only demonstrates the presence of differential hardening but does nothing on it's own. With appropriate heat treatment the soft spine and hard edge will still be there even though there is no hamon. The selection of steels has a lot to do with it. With some steels edge quenching is not as effective or is impossible because they will partially or completely air quench. It really takes a study of steel metallury to get a handle on this.

 

Doug Lester

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Thanks for your reply. And now I have more questions :) So isn't Air hardening usually denoted by A-1 or A-2? Or are a lot of steel partially air hardening due to high Chromium content (if I am wrong as to what element causes air hardening I apologize)? So if I use 1075 steel can't that be used for both a Hamon and edge quench?

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Thanks for your reply. And now I have more questions :) So isn't Air hardening usually denoted by A-1 or A-2? Or are a lot of steel partially air hardening due to high Chromium content (if I am wrong as to what element causes air hardening I apologize)? So if I use 1075 steel can't that be used for both a Hamon and edge quench?

 

As any steel alloy becomes richer in it's alloying elements it will begin to harden in air. Alloying elements of any kind always push the pearlite nose to the right in an I-T diagram allowing much more time to cool the steel and still produce martensite.

 

Your 1075 will be good for both edge quenching and making hamon. It is a simple eutectoid steel with some amount of manganese added. The quality of the hamon however will depend on how much manganese the 1075 has in it, manganese is one of the most common elements added to steel and increases hardenability. If the manganese content is low it will create nice hamons, if it is high the hamon will tend to be a bit plain and "muddy". Bear in mind that an edge quench will create a demarcation line between the martensite edge and the pearlite body but it may not qualify as a hamon per se. The combination of a clay coating combined with careful heat treating and a full quench allow a lot things to happen in the area between the two structures ceating the complexity that is revealed by careful polishing..

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