Water-Quenching vs. Oil-Quenching

[Martin]

Hi all,

 

maybe a silly question for some members - but what (apart from the tradition of swordmaking) makes the difference between water-quenched swords and those who were oil-quenched?

I heard, that the quenching method is even visible on a finished blade and that some Hataraki do not appear on oil quenched blades. But that´s about all I know.

 

- Are there any additional effects on i.e. the cutting ability or firmness of a blade?

- And what are optical indicators of an oil-quenched blade?

 

many thanks in advance,

[Curran]

Quick answer from more of a fittings collector ?:

 

Think of it in photography terms-

 

Water: high speed / short exposure shot.

click- the millisecond of existence is burned or crystallized.

 

Oil: slower speed/ longer exposure

click- slower cooling speed, the resolution is much more blurry and less defined.

 

 

Water: you get more. But the high stress of the rapid action can also mean a lot more goes wrong. *Tink!* blade breaks in quenching.

 

Oil: Makes a weapon with less or little artistic value. But chances of it surviving the process are much higher.

[paulb]

I like the analogy Curran, I'd like to use it sometime when trying to explain the differences.

Basically oil tempering is a more gentle process which is less likely to damage but is unable to produce the dramatic crystal structures and actvity that can be achieved through water quenching.

Interestingly I was reading an interview with the last surviving Yasukuni smith regarding the story of some years ago that Yasukuni smiths tempered in oil. He said this was definately not the case. However they did reheat blades after water quenching and cool them in oil. obviously this was at much lower temperatures so as not to destroy the crystal structure achieved with the original temper, but it releaved some of the stresses inherent in the water quenched blade.

[Curran]

Paul,

 

Was that in the Yasukuni book? I seem to remember reading something similar and wondering about how that would all work out.

 

There is always a lot of debate about mizukage = saiha , but I've seen various things done... use of scalding water from a steam kettle, use of heated copper block (with and without meter so as to get the desired temperature for softening the machi for shortening) etc..

So the use of oil and water cooling troughs in conjuction with these other tricks can produce some odd results of all sorts.

 

Feel free to use the photography analogy. The wife is the classical photographer. I hoped I got the analogy right, as I didn't want to wake her to ask if I was mucking it up.

 

CCC

[paulb]

Hi Curran,

The reference was in the new generation of Japanese swordsmiths by Tamio Tsuchiko which contains an interview with Osaki Yasumune who was the last living Yasukuni smith. I believe he died in 1997.

[Martin]

Curran & Paul,

 

thanks for your replies so far.

Especially the photography comparison makes it very comprehensible.

 

cheers,

[Curran]

Paul,

 

Thanks. I have that one on my shelf. I felt I had read that before.

Good luck Martin.

[george trotter]

Hi Paul and Martin,

I read that interview and very interesting it is too (oil in the Yasukuni forge!...that will unleash a whole raft of rumours).

I presume you are also interested in the "look" of oil quenched blades?

Over the years I have seen many and 99% of the time it is relatively easy to tell.

Firstly...the shape is 99% of the time that very distinctive gunto/seki/showato shape...

Secondly....always with the same standard of polish (usually no ACTUAL yokote (only cosmetic)...when you look at the ji surface there is 99% of the time just muji. There is no distinct nie present and the hamon is often a wider nioiguchi without distinct hataraki anywhere.

That these hamon have bright/pointy spots in the niouguchi line is often seen....I think this is strongly a pointer to oil quenching...BUT, I have seen these spots on rare occasions on gendaito by good WWII makers...eg Watanabe Kanenaga (see pic).

 

I raise this point as currently on another thread is a NTHK papered blade with a seki stamp...members commented that it must be showato because it had the bright spots...while I agree that the spots are a pointer, as I have also seen them on obviously gendaito blades, I think we should just rememeber that "there are always exceptions" in nihonto.

Whether this means that some gendaito ALSO are quenched in oil I can't be sure, but it might be so...or maybe the result of a post water quench "de-stressing" like in Yasukuni forge.

Regards,

[ROKUJURO]

I would like to add that a smith does not have a free choice of his cooling liquid. The respective steels are different, and while a pure TAMAHAGANE based carbon steel is very likely not to get hard in oil, an alloyed tool steel may crack when cooled in water.

 

Until recent times, there was no metallurgical knowledge in Japan, so the safest way was to follow the master's instructions. Everything in this field was - and is - practice and experience, and that is why Japanese craftsmen generally cling to their traditional methods.

[John A Stuart]

While most heat transfer is done in the change of state there is some leeway achieved by the initial quenching water temperature. This is why you see seasonal reference to quenching with the water at a specific time. A hotter quench medium will reduce shock. John

Oh, BTW oil quenching is achieved by a layer of oil over water. The initial oil layer reduces the temperature somewhat to reduce shock with water being the true quench under the oil. Oil does not facilitate a rapid quench to produce martensite if used exclusively. Heat transfer to oil alone is too slow. J

[cabowen]

Formation of martensite depends on the amount of carbon in the steel, the presence of other alloying elements, the temp of the heated blade, and the cooling rate of the quench. Oil is a slower quench than water. Slower means less stress. Less stress means less cracking of the blade.

 

Tamahagane is a rather pure from of steel, having small amounts of other elements. It forms lots of martensite when heated correctly and water quenched. It takes skill and experience to do so without the stress cracking the blade. Oil is easier on the blade, and while it doesn't form as much martensite because of the slower quench rate and the presence of other elements in western steel, it does permit one to harden blades with a greater margin of error and thus less cracking. It is nice for mass production. One usually won't see much, if any, nie in an oil quenched blade because nie is formed by the rapid cooling rates associated more with water quenching.

[Jacques D.]

Hi,

 

Tamahagane is a rather pure from of steel, having small amounts of other elements. It forms lots of martensite when heated correctly and water quenched. It takes skill and experience to do so without the stress cracking the blade. Oil is easier on the blade, and while it doesn't form as much martensite because of the slower quench rate and the presence of other elements in western steel, it does permit one to harden blades with a greater margin of error and thus less cracking. It is nice for mass production. One usually won't see much, if any, nie in an oil quenched blade because nie is formed by the rapid cooling rates associated more with water quenching.

 

False. Japanese sowrdsmiths used water only because they didn't know another method. You can obtain martensite with all steel which are eutectoid and with oil quenching. The difference between oil and water ist that oil didn't produce vapor and the cooling is more homogeneous.

 

http://academic.uprm.edu/pcaceres/Cours ... MSE8-2.pdf

 

http://imperialoil.com/Canada-English/F ... SFenso.pdf

[george trotter]

Edit: erased first message.

 

Jacques, please post pics of the oil-quenched blades with nie that you are talking about.

[Jacques D.]

Hi,

 

Jacques, please post pics of the oil-quenched blades with nie that you are talking about.

 

I don't speak about nie but martensite, that's all. Saying you cannot obtain martensite with oil quenching is wrong. Yakiba is made of martensite. Nie needs a more complicated process (and water vapor).

[John A Stuart]

The point I was making, Jacques, is that oil quenching has too slow of a quenching velocity to form adequate martensite in swords, I'm thinking. A mixture of oil and water must be used to raise the rate of quenching velocity. A modern example is the use of varying % UCON heat transfer fluid 500 with water. The % varies the quench velocity for optimisation according to material. This is a polyalkylene glycol and is not an oil, but, replaces the typical diferential quenching bath. I wonder is there documentation of the quenching baths used for oil quenched gunto that can determine if it was oil over water used or was oil alone able to produce martensite enough to create an hamon on thin sword steel. When I was heat treating steels in my apprenticeship I learned that the oil created a barrier on the steel before water interface and reduced the shock. Of course I was treating webs, cranks and spindles in the tonnes of weight. John

[Jean]

That's why Stanley's tools, like hammers, are quenched in oil and not water.

[cabowen]

 

I don't speak about nie but martensite, that's all. Saying you cannot obtain martensite with oil quenching is wrong. Yakiba is made of martensite. Nie needs a more complicated process (and water vapor).

 

Reread my post Jacques. I did not say oil quenching does not produce martensite.

 

The oil quench used during WWII using non-tamahagane steels produces finer martensite (nioi) and little if any coarse martensite (nie) because of the quench rate.

 

It isn't the water vapor that creates nie, it is a function of the cooling rate. Notice the attached TTT graph does not mention quenchants. Any cooling rate to the left of the "Nose or Knee" will produce martensite. For any given steel, it is all about cooling rate.

 

Here is another TTT with cooling lines for various processes, as well as for oil and water. Notice oil quenching produces martensite and pearlite while water produces pure martensite. attachment=0]ttt-quench.jpg[/attachment]

 

The quantity and size of martensite produced depends primarily on the quench rate and steel used. The oil quenching process used on WWII era blades was not fast enough for the steels used to produce pure martensite in what is called "nie" sizes.

[John A Stuart]

Yes Jean. When steel at the austenising temperature is cooled slowly ferrite, pearlite and cementite are formed. Rapid cooling forms martensite and bainite. If a hammer head is over a 50RHc it will shatter and take out an eye. I have had hammers that have been too hard and pieces have broken off. Maybe I should explain something here that may be useful. When steel is quenched after having reached the austenising temperature (homogenous) there are three phases. 1) the vapour blanket stage; here vapour will form around the steel and slow the cooling rate 2) the boiling stage; here when the steel falls below 400F the water vapour destabilises and allows liquid contact with the steel; this is where martensite starts forming 3) the liquid cooling stage; at boiling point 212F; here is where the most advantageous martensite production occurs, having less residual stress, cracks and distortion. Anything that makes the % formation of martensite increase in the liquid cooling stage is best. Hence quenching in oils, oil/water or thermally buffered water. John

[cabowen]

Agitation is another technique commonly used with liquid quenchants to alter the cooling/heat transfer process.

[ROKUJURO]

.....Japanese swordsmiths used water only because they didn't know another method......The difference between oil and water ist that oil didn't produce vapor and the cooling is more homogeneous......

Jacques,

 

I don't think you can say so. Instead, Japanese swordsmiths used water because the method was working to their satisfaction. Pure high-carbon steels require a rapid quenching to produce martensite, and this can be obtained by water quenching. In the West, we don't use these steels any more, except for special purposes, so industrial alloyed steels are dominating.

 

Quenching a modern toolsteel item in oil at appropriate temperatures will of course produce vapour in the first few seconds! You can also see bubbles, and that can only be reduced by agitating the workpiece in the liquid. The same is done when you use water, but this is rarely seen with Japanese swordsmiths.

 

Interestingly, warm oil provides a faster cooling rate than cold oil, which has to do with the viscosity. Warm water (the temperature of which was kept as a secret by the master!) as used in swordsmithing reduces the cooling shock and helps to reduce the risk of HAGIRE.

[Jacques D.]

Hi

 

Mister Bowen, you wrote :

 

Tamahagane is a rather pure from of steel, having small amounts of other elements. It forms lots of martensite when heated correctly and water quenched. It takes skill and experience to do so without the stress cracking the blade. Oil is easier on the blade, and while it doesn't form as much martensite because of the slower quench rate and the presence of other elements in western steel, it does permit one to harden blades with a greater margin of error and thus less cracking. It is nice for mass production.

One usually won't see much, if any, nie in an oil quenched blade because nie is formed by the rapid cooling rates associated more with water quenching

 

All that is emphasized is wrong. Oil or water it's only matter of difference between temperatures, you will have less martensite with a water at 25° than oil at 18°.

 

Tamahagane is a rather pure from of steel

 

 

that depends of the carbon content, all tamahagane cannot be hardened, but it is still tamahagane.

[John A Stuart]

"All that is emphasized is wrong. Oil or water it's only matter of difference between temperatures, you will have less martensite with a water at 25° than oil at 18°. "

 

Where did you learn that?? It is patently absurd. John

[John A Stuart]

Anyway, Jacques, I should explain myself and hope this helps. When water changes state from liquid to vapour there is in that instant where temperature does not increase, but, energy absorbed. This is what I am used to calling the Latent Heat of Evapouration, more properly called the Latent Heat of Vapourisation. This is the fundamental principle of steam source power. Water has a LHV of 2257 kJ/kg. This is a huge energy sink. Most organic hydrocarbons of petroleum distillates are between 700 and 200 kJ/kg. What this means is that at the boiling stage and into the liquid cooling stage heat is more efficiently absorbed and eliminated providing higher quench velocity with water. John

 

Oh, while I am at it google Mouromtseff number. It is used to indicate the heat transfer rate of liquid coolants. In the chart below look at the rate for water (highest) compared to the aromatic and aliphatic hydrocarbons (found in oil). Again showing waters superiority. J

[cabowen]

 

All that is emphasized is wrong. Oil or water it's only matter of difference between temperatures, you will have less martensite with a water at 25° than oil at 18°.

 

l

 

 

You are incorrect. It is not only a difference between temperatures. We are talking about a rate of heat transfer. It is impossible to get more martensite with oil than with water unless the water is in fact super heated steam. You can see this if you understand the TTT curves I posted above.

 

The first variable affecting the rate of conductive heat transfer is the temperature difference between the two locations. The second variable of importance is the materials involved in the transfer. The effect of a material upon heat transfer rates is often expressed in terms of a number known as the heat transfer coefficient. The higher that the coefficient is for a particular material, the more rapidly that heat will be transferred through that material.

 

So clearly, it is dependent on quench rate, which is a function of time and heat transfer coefficients. Oil can not transfer heat fast enough to miss the nose of the TTT curve and form pure martensite. Water has a greater heat transfer coefficient than oil and can transfer the heat faster, thus missing the nose of the TTT curve and forming pure martensite.

 

 

that depends of the carbon content, all tamahagane cannot be hardened, but it is still tamahagane.

 

Of course Jacques, some tamahagane is too low in carbon content to form martensite. I would have thought it obvious that this discussion concerned only hardening steels. I guess I should probably add "liquid" water when I mention water as a quenchant or you will tell me that swords can't be quenched in all water (ice) next....

[cabowen]

John has provided a more advanced description of the actual mechanism (phase change) but the basics are the same: it is all about the rate of cooling, and this depends on more than just temperature differences, as you have indicated.

 

Also, Japanese smiths had, historically, many choices for quenching their blades, not only water. There were a variety of oils, both animal and vegetable, as well as crude oil later in the Edo period. They also had the option to use salt water, which is a slower quenchant.

[ROKUJURO]

.....They also had the option to use salt water, which is a slower quenchant.

Chris,

 

this I learned the other way round: saltwater is a faster quenchant.

[cabowen]

sorry, that is what I meant to say....salt water quenches permit a higher rate of heat transfer. Thanks for catching that...

[Jacques D.]

Hi,

 

The oil quench used during WWII using non-tamahagane steels produces finer martensite (nioi) and little if any coarse martensite (nie) because of the quench rate.

 

I missed that, martensite is not only nioi or nie, almost all the yakiba (at least 90%) is made of martensite.

[cabowen]

Not only nioi or nie? What else is it? Nie and nioi are both martensite, they only differ by size. The yakiba is considered nioi, that is why it is often said that all swords are nioi-deki. There is no such thing as a pure nie yakiba. Nie exists at the habuchi or in the ji. When the habuchi contains large amounts of nie, the sword is said to be nie-deki. Of course the yakiba is martensite,

[runagmc]

Yes, the yakiba is normally made up of mostly small martensite (nioi), but sometimes larger martensite (ko-nie, nie) can be present too. Here's some pics and info about nie/nioi... http://www.ksky.ne.jp/~sumie99/hamon.html#nie/nioi