Triple Zone hardening

[Dave]

Could one of the knife makers, explain to me, what Triple Zone Hardening is please?

Is it Japanese in origin?

Thanks.

 

[Dave Budd]

Never heard of triple zone hardening.

It may be a reference to a hamon; which has a soft back, hard edge and a band in between of different structures.

Or it could be a mistranslation/understanding of triple hardening that some people do as a way of refining grain size in a blade (although triple normalising at the correct temperature achieves at least as good results but with none of the negative aspects)

 

[Dave]

Never heard of triple zone hardening.

It may be a reference to a hamon; which has a soft back, hard edge and a band in between of different structures.

Or it could be a mistranslation/understanding of triple hardening that some people do as a way of refining grain size in a blade (although triple normalising at the correct temperature achieves at least as good results but with none of the negative aspects)

Thanks Dave. I got the info from an article in Gunmart, the Bushman knife has been my main user for years now, and I just wondered what he meant by it.

Paul Baker of Bushman UK is celebrating 40 years of knife making, he uses a triple zone hardening system exclusively with the BUSHMAN and the BUSHMAN scout. Materials used are straight carbon steel, 1060, cs70 , cs80 and 01 tool steel. Paul favours traditional Japanese methods for finishing and polishing, he uses both forge and stock removal methods or a combination of both.

http://www.gunmart.net/accessories_review/knives_uk_2008_part_i

 

[OldJimbo]

I'm just throwing up ideas as even with having many zone hardened blades, I've never heard of triple zone hardening. While zone hardening is essential in making heavy duty chopping blades, I wouldn't have thought it likely in western knives.
So with a kukri it is forged to shape, then heated and the edge suddenly cooled to harden it, often by simply pouring water on it from a kettle. The rest of blade cools slowly and is soft. Where the hardened steel of the edge meets the softer steel a line called the hamon develops with etching solution and polishing.
Indonesian blades are forged out in the same fashion, but are covered in a variable thickness of clay which is dried, then the blade heated and suddenly cooled. The edge cools suddenly and is hard, but the remainder back to the spine cools in a graduated manner depending on the thickness of the clay. You still have a well marked hamon line between the hard edge steel and the softer steel behind it, and this can be controlled by the application of the clay to be in various wavy patterns as seen in Japanese swords. I guess it could be called triple zone since there are three distinct hardnesses from edge through middle to spine - but I've only ever known it as simply zone hardening.
If you have one of the knives, then polish the blade a bit and rub on some vinegar. If it's zone hardened then you will see a hamon line behind the edge.

 

[Shinken]

For years bladsmiths have been coming out with fancy names for something that is quite simple. It is probably just edge quenched

 

[Dave Budd]

sounds like the article writer not knowing what they are taking about and miss understanding that Paul told them that heat treating is a 3 stage process: normasing, hardening, tempering.

 

[OldJimbo]

sounds like the article writer not knowing what they are taking about and miss understanding that Paul told them that heat treating is a 3 stage process: normasing, hardening, tempering.

I'd agree. There is one western knife with a hamon line, the Lauri PT, but the PT stands for precision tempering. These knives have an an extremely hard edge (R63), but the rest of the blade back to the spine is R55. Some people have called these zone hardened (all in one quenching/hardening process) because of the hamon line, but in fact they are first hardened then tempered in a multi stage process, as normal western blades - just more extremely so. Thus the name PT.
Most vintage axes have a well defined hamon line at some point on the blade since the ramp, eye and poll areas need to be much softer to absorb shock. But these get lots of specialized heat treat after the initial hardening, so they really couldn't be called zone hardened due to the multi stage process.

I guess most people are wondering what all this zone hardening versus tempering is all about. Back at the start of this century, many of us were wondering about large blades which would chop well and unlike an axe could be used for clearing finer but incredibly tough stuff like hardhack. That was before we learned about precision profiling of machetes which then stuck in wood and bounced off hardhack. Pretty simple, we wanted a machete blade made out of harder steel with a better convex grind. And we were told by highly qualified western makers that such a blade could not be made with normal western methods because it would break, or if made thick enough to withstand breakage, would be heavy and far less effective. Looking toward places like Nepal and Indonesia, we found that effective blades did exist but they had two things which defined them. They were hand forged and zone hardened. So the blades were effective choppers of everything due to their shape and profile - but the blades were soft with only the edge hard. So the blades are unsuitable for extensive batoning and prying with them is totally out of the question. Anyway mine have been cutting thin flexible stuff to seasoned wood for over a decade with no breakage. I do have a Cold Steel LTC which is a thin chopping blade styled after a kukri and made by western methods. I also have had more than a few emails by people who started chopping bigger wood with one and ended up with the blade breaking and flying. So while I treasure my zone hardened goloks etc. for chopping and clearing, I equally treasure my small tempered and heat treated knives for their virtues. Horses for courses..

 

[mjojom]

For years bladsmiths have been coming out with fancy names for something that is quite simple. It is probably just edge quenched

yup, just like apple using fancy names to promote there crap. eg retina display...

 

[Dave]

Thats a poor choice of adjective to describe good work. He's on here, you know, but doesnt post much.