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tk59
05-18-2011, 03:02 PM
Correct me, if I'm mistaken but I remember seeing someone post somewhere that differential HD of 52100 does not produce a hamon but I've definitely seen something that looks like one on 52100 blades. Can anyone tell me what the deal is here?

StephanFowler
05-18-2011, 03:12 PM
it depends on how you define Hamon

this is reposted from a tutorial I did a while ago:


Firstly let's establish what Hamon "is".
Hamon is a Japanese word used to define the pattern that the hardened edge of a properly made sword. A common misconception is that Hamon refers to the hardened area, this is incorrect, the hardened area is known as Yakiba.

In modern knifemaking terms however Hamon has come to define the hardened portion of any knife which displays a differentially hardened edge.

There are many ways to achieve a differentially hardened edge but they all center around the same concept, getting the edge hard while keeping the back soft.

I use Satanite clay to insulate the spine area of my knives, thus preventing the spine from cooling fast enough to form Martensite (hard steel), while allowing the edge to harden. I use Parks #50 metallurgical quenchant with all of my blades but similar results can be achieved with any decent quenchant.
This tutorial assumes that you are using appropriate steel for creating a Hamon, a shallow hardening carbon steel is preferable.
1075, 1095, W1, W2 all do really well, 1084 is a little picky, O1 and 5160 are technically possible but a real bear.
Creating a good Hamon starts in the hammering and shaping phase. It is very important to have an understanding of what each heat is doing to the grain boundaries in your workpiece. If you are doing stock removal you should be pretty well set to go, if not you MUST make sure to properly normalize your work before HT.

StephanFowler
05-18-2011, 03:13 PM
I would actually term the differential hardened 52100 blades as having a edge quench or selectively tempered spine (each of which is a different process yielding different physical properties)

Marko Tsourkan
05-18-2011, 08:44 PM
Bill Burke gets a temper line on his 52100 blades by heat treating his blades with a torch.

l r harner
05-18-2011, 11:26 PM
in fact that would not by the terms be a temper line but thats not here nor there

Eamon Burke
05-19-2011, 12:56 AM
What is it then, Butch? I am interested.

StephanFowler
05-19-2011, 09:00 AM
in specifics, a temper line would be when you harden the entire blade and then go back and soften the back of the blade with a torch.

I would call it a hardening line or a quench line when you only heat the edge portion of the blade to 1450 and then quench.

Eamon Burke
05-19-2011, 02:22 PM
Is it easier to screw up a blade by doing the temper line? Perhaps by overheating too close to the edge? It just seems to be that it would be way easier to harden the whole blade and temper the back than to harden the edge with a torch.

l r harner
05-19-2011, 02:56 PM
that woudl be a fact


i ether HT in my kiln and harden the whole blade then temper the whole thing evenlt o0r i clay the spin(still using the kiln t5o controle the temps) and quench (the clay leaves the spine sfter ) then temper the whole blade again

Marko Tsourkan
05-19-2011, 03:35 PM
Is it easier to screw up a blade by doing the temper line? Perhaps by overheating too close to the edge? It just seems to be that it would be way easier to harden the whole blade and temper the back than to harden the edge with a torch.

:) it depends whom you ask.

l r harner
05-19-2011, 07:11 PM
so here is the next question for you guys then
in a kitchen knife what is the need to ahve a softer spine on a blade any how ?

mainaman
05-19-2011, 07:42 PM
so here is the next question for you guys then
in a kitchen knife what is the need to ahve a softer spine on a blade any how ?

isn't that how honyaky knives turn out to be?
I am not sure what the function of the hamon is? Stress relieve during HT?

l r harner
05-19-2011, 08:27 PM
true hamon happens during quench and temper has little to nothing to do to it then
in a nut shell unless you need a knife to be able to be bent to a set there is no real use other then to look nice (tradition trickle down from swords)

now then on a sushi knife that is single bevel being able to straighten a blade as you hone it would be mayber the one time a soft back is useful

JBroida
05-19-2011, 08:42 PM
true hamon happens during quench and temper has little to nothing to do to it then
in a nut shell unless you need a knife to be able to be bent to a set there is no real use other then to look nice (tradition trickle down from swords)

now then on a sushi knife that is single bevel being able to straighten a blade as you hone it would be mayber the one time a soft back is useful

shock absorption? If the entire blade is as hard as some honyaki blades are, wouldnt it be helpful to have that softer steel to help absorb shock from cutting?

Marko Tsourkan
05-19-2011, 09:40 PM
shock absorption? If the entire blade is as hard as some honyaki blades are, wouldnt it be helpful to have that softer steel to help absorb shock from cutting?

I got to agree with Butch that hamon on a honyaki gyuto (57-60RC) is all about look. Not sure about yanagi. I was under impression that you can't straighten honyaki, so not sure why it has a soft spine.

M

JBroida
05-19-2011, 09:49 PM
I got to agree with Butch that hamon on a honyaki gyuto (57-60RC) is all about look. Not sure about yanagi. I was under impression that you can't straighten honyaki, so not sure why it has a soft spine.

M

you can, but its a bit of a different process and they still break easily

also, i think it makes more of a difference at 62-64 hrc

l r harner
05-19-2011, 10:25 PM
I can and have shown 62rc blades bent 90 degrees with no fail and no blade set
Did I tell you that the blade was cpm 154

Eamon Burke
05-20-2011, 10:10 AM
I've yet to figure out what the function is of differential HT on kitchen knives.

Dave Martell
05-20-2011, 12:13 PM
I've asked this question to lots of chefs who have honyaki knives and some (not all) have mentioned that the knives feel more alive or springy in use compared to a more dead type feeling they note that kasumi construction offers. Now this says nothing for standard mono-steel knives not differentially heat treated and how they fair in comparison.

tk59
05-20-2011, 12:50 PM
I've tried a few differentially HT single steel knives and for the life of me, I cannot tell the difference. Maybe you can feel it more for a hacking knife like a cleaver or a machete...

Bill Burke
05-20-2011, 12:57 PM
I do it because I like the way it looks nothing more. A differentially hardened gyoto will bend 90 and pretty much stay there whereas a fully hardened and tempered 52100 blade will bend 90 and srping back to straight even at 62-63 rch.

StephanFowler
05-20-2011, 05:22 PM
I do it because I like the way it looks nothing more. A differentially hardened gyoto will bend 90 and pretty much stay there whereas a fully hardened and tempered 52100 blade will bend 90 and srping back to straight even at 62-63 rch.

I agree, for me it is an entirely aesthetic consideration.

I have found very little mechanical difference between fully hardened and differentially hardened blades in use (assuming there is no useful purpose for bending a knife 90 degrees)

I have always done Hamon up until I started playing with 52100 last year, every knife I ever did had Hamon. I just love the way it looks.