Hamons

[Thomason]

I kind of feel like a doofus for asking this and I'm pretty sure the answer is yes, but I have to ask. Is a hamon and a temper line the same thing?

 

[mete]

Yes but 'temper line' is not a proper term since it has nothing to do with tempering. It's from differentially hardening with clay or differentially quenching [quenching just the edge]. The spine has a structure of pearlite and the edge has a structure of martensite . The two polish and etch differently.

 

[hammerface]

Thomason,

You're not alone - I wasn't totally sure either

 

[krept]

Interesting note: I spoke to the maker of Mad Dog Knives (Kevin) and he said that his blades actually have a temper line. He uses precision ground O1 and after the quench, he said that the knife is selectively hardened during the tempering cycle...

He was using the term "temper line" and that is what started the discussion.

I asked him to clarify on what someone else said:

The usual methods that I am aware of either (a) involve clay coating the spine, bringing up to critical and doing a full quench... (b) using a torch to heat the edge & tip to critical then doing a full quench or (c) heating the entire blade to critical and then only quenching the blade portion.

(added: I didn't mention full quench then drawing back on the spine with a torch)

This was how he answered:

All of those listed above are selective hardening processes. High tech stuff about 500-700 years ago, but steels have evolved a lot since then. So has heat treatment.
I harden the entire blade from tip to tang end and then I use a selective tempering process which is more precise and yields better results in strength and edge holding.

The hamon on these blades is relatively straight and usually does not go to the tip. A decent example is seen here:

http://www.mdenterprise.com/popups/maddog/taiga.htm

I didn't ask what procedure he uses, but it makes for an interesting discussion nonetheless... I'm thinking that some circulated liquid stream might be used to keep the edge section cool, while the rest of the knife sits at 400F (or whatever is used).

I'm interested in your thoughts regarding this mete.

cheers

 

[mete]

He's talking about selective tempering .But even with the edge in water as the spine is heated you will not get a distinct contrasting line since it will be tempered martensite edge and higher temperature tempered martensite spine. The typical katana will show hamon even without etching.

 

[Mark Williams]

On shallow hardening steels, You will get a line if you etch after drawing back the spine on a fully hardened blade. It is just very faint.

 

[Jason Cutter]

I agree with Mark - I have been able to produce a visible difference in finish with differentially tempered blades of 1095 and 1084, but it was a mistake - I never intended the spine to become so soft in the first place. Nonetheless, the effect is so difficult to see, its pretty much visually insignificant to anyone not looking carefully for it.

The term temper line is often used incorrectly. It comes from centuries of lay-people calling all heat treatment "tempering," rather than differentiating between hardening and tempering.

The term "temper line" could be better called "Hardening line" and yes, thats what a hamon is.