Hi Brian, there is a chapter in The Craft of the Japanese Sword (which should be in your library), that offers some excellent information including very good photos and diagrams on this topic, see page 80 in particular. Another term related to this topic worth researching is ' nioi giri '. It is wise when it comes to nihonto to build complete pictures and understanding of what exactly is taking place, cause too often those little missing pieces of the puzzle have a way of returning and biting when you least expect it.

The cross section pictures quite clearly show that the hardening can reach into the steel more than 1,5 mm (the darker areas), as far as I have learned it is about 4 mm. These very clean steels used by Japanese smiths are able to change their molecular structure very rapidly which is the reason why they should be quenched in water. Modern industrial steels - even if they are called carbon steels - contain small amounts of alloy metals besides carbon and are likely to crack when cooled down rapidly in water, so they are quenched in oil.

From the technical point of view a YAKIBA will always go through the material of the blade as long as the cross section has a sufficient carbon content to be able to harden. A HAMON may change it's appearence if polished many times but as long as it is not polished away from the HA side because of age or chipping or damaged by fire or heat it will be visible.

@ Franco


I just got off the phone with Barnes & Noble, I ordered that book , they said that book has an re-release date for next month, so I will have it next month, thanks for the heads up on another book that I will need.

Brian

Hi,



Do you have the measurements of theses cross sections ? When nioiguchi is near the shinogi do you think hardening goes trough the entire blade shingane include ?

That depends on the construction used and the carbon content of the shingane. Steel below a certain carbon content will not form martensite. Hagane will all be transformed to martensite so it depends on how far into the blade the hagane extends. Usually shingane is mostly in the center of the blade.

In any case, your original comment that the yakiba is only on the surface is simply incorrect. The habuchi may not penetrate completely through the blade on a wide hamon, depending on construction, carbon levels, and cooling rate, but the vast majority of the yakiba, in most blades made well, is through the blade.

Cross section images clearly support Chris on this where you can actually see the depth of the hardening going all the way through and rising quite high on some examples.

Jacques, if you read through the second link I posted earlier, he states that 1.5 mm of material was removed from the one side of the tanto. As you can see, the nioi-guchi is still very much present, although it is not as narrow and bright.

If anyone didn't read the 2nd Usagiya article, I would suggest reading it when you have the time. It is directly about this very subject, and very eye opening as to how much material loss from polishing can affect a sword's appearance.

Well, Brian (bmoore1322), you have certainly taken your lumps on this Board and I admire your tenacity and thirst for knowledge - that augurs well for your future as a connoisseur of Nihontô that I think you will eventually become. And continuing that thought, I highly recommend The Connoisseur's Book of Japanese Swords by Kokan Nagayama - this link will take you to the Amazon offerings that include new and used copies and also includes customer reviews. Of course, there are other vendors that might offer better prices.

I envision you being a young man, Brian. If you keep asking thought provoking questions similar to the one that started this thread and deflect "the slings and arrows ....." like you have so far you will do well!

Hi James,

Right, no "rub"

Hi,



Cross section is juste cross section nothing more. It only show an inifinite part of steel, it's the same when you look at water of a river or a lake that you see is only surface but not that there under surface, when you are front of a closed tunnel, you see the door not the tunnel. On the over hand, if you look at the picture 9 or 10 on this link below you will see a little triangle just above the edge, we can reasonably speculate it is the hardened part of the blade; how thick is the upper part of this triangle ? a blade has usually a wideness of around 3cm and a thickness of around 7mm at the mune. I guess it is not more than 3mm.

http://legacyswords.com/nihontoCS/crosssections.htm



True, and which percentage please ?



Top layer was not the best term yes, but further, i precised not more than 1.5 mm depth.

Craft of the Japanese Sword - 20 Bucks http://www.japaneseswordbooksandtsuba.c ... -yoshihara
I regard this as the first book that any enthusiast should purchase. You need to know what goes into the making and crafting of a sword before learning about the features and intricasies. Grab it...it's a great read.
There are also numerous other copies available:
http://used.addall.com/SuperRare/submit ... store=ZVAB

Brian

Which was also incorrect... apparently you still haven't read the 2nd Usagiya article I posted

I was watching some Youtube video's on sword polishing, and they had some great polishers on there, but none of them answered the question I asked, I heard them all say that polishing takes away metal , and needed to know if they polish a blade too much, would the hamon eventually disappear completely.

I did look through some books, and did a Google on it, but could not get a good answer, and I knew that there would other collectors in here that would know the answer to my question.

I was thinking that is why some great polishers will look a blade over for weeks before they attempt to polish it, would it take off too much metal, has it been polished too many times, that it could destroy the blade, does it have it fatal flaws, may be that is what they were looking at also.

Brian

Hi,


Yes, they say 1.5mm steel was removed, but it is modern steel with a higher carbon content and hamon becomes less visible. What will happen if you remove 0.1 or 0.2 mm steel more ? An example is not a generality

Insructive but in french, maybe Jean who is fluent in english can make a synthesis.

http://www.otua.org/acier_outils/non_al ... _froid.htm

Sorry, I had to be able to read this, and some really good reading.

Thanks for posting it.


Brian





First paragraph ;

These are the simplest since they contain only iron and carbon, other elements being present there in residual content vary according to raw materials and the method of production used.

A carbon content equal to acquire these steels tempering hardness as high as those of alloy steels. They differ, however, the latter by a lower hardenability, which limits their use in parts of sections relatively narrow

Their limited hardenability also leads to the use of energetic quenching means: pure water or salt water, and more rarely for small section parts, oil.

In exchange, carbon steels are easier to anneal and are softer in the annealed and consequently has a machinability and cold forming ability much better.

Second paragraph :



hardness:


The hardness of non-alloy tool steels for cold work is relatively high because it is given by the carbon content.
However, deep hardening steels is very low because this property is given by the alloying elements that are present in very small quantities.
For a given tool, there will be gifts just a few millimeters of surface film thickness of martensitic structure of a heart unprocessed lack of hardenability.

tenacity:


Carbon steels, after quenching in water, have a low hardening depth and a heart not hard.
The toughness is partly a function of the large volume of untempered piece that enables it to withstand some shock loads.
The tenacity of a carbon steel is also a function of grain size obtained after quenching. More grain will end it, the better the toughness.
The evolution of grain size and hardness depth as a function of austenitizing temperature is much more dispersed in steels for general use and in extra-fine steel, because of differences in levels residual elements.
Furthermore, the temperature range that is available for tempering is relatively narrow in steels for general use and because of the sensitivity of these steels to overheating phenomenon.

Wear resistance:


It is weak-but can be improved by increasing the carbon content (Minimum: 1%). This is one of the weakest characters of carbon steels, which may not be successfully improved by the addition of carbide-forming elements.


Third, and last paragraph :



Temper resistance:


Hardness of 60 HRC obtained after water quenching from 790 ° C and tempered at 200 ° C decrease very quickly as soon as it exceeds the tempering temperatures of 300 ° C (50 HRC after an income of 2 h at 350 ° C). This reduction is significant regardless of the carbon content of steel.

Deformation heat treatment:
Distortion due to the change in specific volume of the hardened layer of a carbon steel varies in proportion to the volume tempered and lead to the expansion.
These deformations are therefore even lower than the hardness depth will be smaller. During heat treatment, deformation most to fear are not those concerning the volume change, but change of form; these shape changes are often significant and lead, for example, arrows or curtains and that of especially since the mechanical properties of these steels heat is low.
This is what gives carbon steels reputation deform easily to treatment.

Shades
EN ISO 4957 in May 2000, defines six shades. These grades correspond to existing nuances in the NFA 35-590 of December 1992.

(For the record we will resume the match shades and field of use included in the NFA 35-590 December 1992)


Field following NFA 35-590 (1992)


Shades following
NF EN ISO 4957
(2000)


Shades following
NF A 35-590
(1992)

Steels for general purposes
C45U C48E4U

Carbon steel extra fine
C70U C70E2U

Carbon steel extra fine
C80U C80E2U

Carbon steel extra fine
C90U C90E2U

Carbon steel extra fine
C105U C105E2U

Fine carbon steels
C120U C120E2U