Benefits of Hamon?

S

stax

Joined
Jan 6, 2009
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Can anyone tell me what the benefits are of Hamon? I've seen it on a lot of knives in here. I also saw a special last night on the making of Samarai swords which was pretty cool but I failed to hear what the Hamon was for. Does it get the part that the clay is on hotter and make the steel hard there? Why don't more people use it? Thanks
 
With modern steels, tools and techniques, the hamon is mostly just for aesthetics. It developed out of necessity in Japanese (and, in my opinion, Chinese) weaponry. The clay holds heat longer, allowing the part with clay to remain softer and more resistant to impact than the harder, unclayed edge.
 
The hamon is a side effect of differential hardening techniques. It is the transition line between the harder edge, usually martensite and a softer back, usually pearlite. It has no function per se, it is very attractive however! A blade that has been fully hardened will obviously not have a hamon and some blades that have hamon aren't polished or etched in a manner that makes it evident.
 
So if the blade is heated correctly, the discoloration goes all the way through? Although it may not be seen if not pollished etc.?
 
I think the point of the hamon (back in the days) was for a harder cutting edge to cut stuff (like human bones) and for a softer back spine so as a blade could take the blow from another blade incase you needed to block your opponents blade from slashing you in half. Having a harder edge and softer back allows the blade to flex and at the same time be a lethal killing weapon that can cut through limbs, etc etc.

Mainly the hamon is just pretty to look at. It's a form of ART/Painting with the katana blade being the canvas.
 
Ken Hurst said:
Great program --- did anyone notice that the clay was mixed with charcoal ash ?
Click to expand...

Its also mixed with sand. The clay acts as the insulator, the sand helps keep the clay from shrinking/cracking and falling off the blade, and the charcoal ash helps keep decarb to a minimum. :)

As for the purpose of the hamon, in modern steel with modern tempering it just looks pretty. For tamahagane with traditional tempering (using the charcoal forge) it helps keep the blade from being hard all the way though to prevent the blade from breaking.
 
Dan Seaver said:
Its also mixed with sand. The clay acts as the insulator, the sand helps keep the clay from shrinking/cracking and falling off the blade, and the charcoal ash helps keep decarb to a minimum. :)

As for the purpose of the hamon, in modern steel with modern tempering it just looks pretty. For tamahagane with traditional tempering (using the charcoal forge) it helps keep the blade from being hard all the way though to prevent the blade from breaking.
Click to expand...


what does a charcoal forge have to do with it? The defferential hardening with clay is what keeps the blade from bein through hardened, not the tempering
 
That special is interesting, but has several inaccuracies.

As far as the function of the hamon, it originally showed the differential hardening to the prospective owner. Then it evolved into the showing of the skill of the smith in controlling the hardening. Now it shows that the smith can still control the aesthetics and the hardening.
Stacy
 
SShepherd said:
what does a charcoal forge have to do with it? The defferential hardening with clay is what keeps the blade from bein through hardened, not the tempering
Click to expand...

Because traditionally a charcoal forge was used to temper the blade which is no where near as accurate as a kiln. This created spots on the blade that were harder than others because the blade was not evenly tempered after it was hardened. This increased the need for having a differentially hardened blade.
 
BTW, stax, the hamon does not result from different colorations in the steel, but from different hardnesses. When only hand polished, you will see a difference in the softer and harder portions of the blade which will cause the hamon to faintly "appear". Many hamon'd blades are etched as well. This helps the hamon really stand out as the difference in coloration of the soft/hard steel results from differences in how the etchant attacks the hard vs. the soft steel.

--nathan
 
There are two uses for a hamon that nobody has mentioned.

One, martensite is less dense than pearlite. So it wants to take up more room. A martensitic edge and a pearlitic spine will put the edge into compression. Industry frequently employs things such as shot peening and burnishing to create surface yielding to put the surface of components into compression because it tends to prevent cracks. It stands to reason to me that a similar mechanism may be in play here also. A hamon might indicate a more crack resistant edge.

And secondly, soft steel might transmit shock differently than hard steel. Bounce a bearing off a hard anvil and a soft anvil to see what I'm talking about. A soft spine and tang might jar less in chopping due to a damping effect from minute yielding.


Edit:

That said, I feel no need to incorporate one in my knives. It does not affect edge retention or the way a knife cuts (which, in the big picture, is what generally matters), and there are disadvantages also, such as a blade that is overall less stiff (because you get into yielding, not due to a change in flex modulus) and generally weaker (as defined by force required to ruin it)
 
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Nathan the Machinist said:
There are two uses for a hamon that nobody has mentioned.

...And secondly, soft steel might transmit shock differently than hard steel. Bounce a bearing off a hard anvil and a soft anvil to see what I'm talking about. A soft spine and tang might jar less in chopping due to a damping effect from minute yielding.
Click to expand...

An interesting point, and one that would apply to many western swords as well. As of the concept of compressive preloading, it has been a bit over-blown and stretched itself when applied to katanas, in my opinion.

This forum continues to be a beacon of common sense for blade matters on the internet. Almost any other place this topic is addressed you would have gotten a litany of overblown myths about the Japanese heat treating method, the replies in this thread have been extraordinarily level headed and refreshingly grounded in reason. Kudos to all the folks here who value common sense over Hollywood fluff. :thumbup:
 
Don't forget that a hamon adds +20 awesomeness to the blade! In all seriousness though, despite not needing one I cannot seem to get over them. The more active and patterned ones still make me drool like a 12 year old watching ninja movies.
 
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I do it cause I like it :D

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Don, You didn't know this but we had a pool going on how long it would take before you posted one of those W2 blades with that beautiful hamon you are so good at.
I make them because like Don I love the way it looks.
 
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