Quenching Swords

[SBranson]

There's actually a fair amount of useful information in this thread.
I think the question of Valar God's experience is valid in so far as to know if his ideas are from experience. They may be "commonly understood principles of metal working" to some but if you look around on this site, or many others, the interrupted quench is a pretty common practice, for better or for worse. I for one use these forums as a type of "research" so I for one would like to hear his experience and/or see his work for what he says goes against the practices of some well respected bladesmiths. That is very interesting to me, mostly because I agree with what Valar God is saying even though some "important" MS's are doing otherwise.

That said, I agree with everything he said and thank him and 1966c10 for some really useful information and the next time I try a sword I am going to leave it in and see if it cracks, and if so figure out why. I am one who learned from reading forums and books so I don't purport to have any real knowledge.
I do have to say though that the "stabbing" motion is a bad idea. Think of how fast the phase change is in something like W2 and water and I'm sure the quench is really uneven doing it that way.
As far as the short forge... is it possible to ever get a heat source perfectly even? Doing it in the dark with colour and experience is probably the best you can really hope for..

Forgive me if I'm misunderstanding some terms here but Valar God says that differential tempering process doesn't exist but you (1966c10) in the next post talk about differential hardening vs. differential tempering. Do you mean by differential tempering through hardening then drawing back the spine?
By that then, in say a W2 katana, one should forge in the sori then through harden, draw back the spine then toss 'er in the oven for an hour or 2? (for the best performance, hamon aside? ie, no clay)

Off the top of my head... Wally Hayes uses the interrupted quench in his tactical Katana video, Nick Wheeler suggested interrupted quench before abandoning water as a medium and I believe Walter Sorrells interrupts his quench in his videos. Howard Clark cites it as his method. Repected bladesmiths all.

Bill Burke is one of the few who doesn't suggest interrupted quench for water based on his experiences and his observation of Japanese smiths but he stresses this in a thread I started on a cracked blade.
"THE MOST IMPORTANT THING IS TO NOT OVER HEAT THE BLADE. even the upper end of the austenitizing range is too hot for a water/brine quench with some steels."

The difference I have found is that those who say to interrupt the quench (except maybe for Walter) are bringing the whole blade to austenitic either in an oven or high temp salts. If the spine never reaches critical, there is less likelihood of cracking. But I get the sense that that is not what is being suggested as the best practice.

Can't wait for my next quench...

 

[Valar God]

Forgive me if I'm misunderstanding some terms here but Valar God says that differential tempering process doesn't exist but you (1966c10) in the next post talk about differential hardening vs. differential tempering. Do you mean by differential tempering through hardening then drawing back the spine?
By that then, in say a W2 katana, one should forge in the sori then through harden, draw back the spine then toss 'er in the oven for an hour or 2? (for the best performance, hamon aside? ie, no clay)

Actually, I have said that differential tempering DOES exist, exist indeed,
but that it got nothing to do with differential hardening.

Many people are saying "tempering" instead of "hardening" or "heat treating", that was my remark.

Yes, that process of drawing back the spine of pre-shaped sword would be diff tempering.
Japanese swords have a constant "stress" in them between spine and cutting edge.

W2, tamahagane and similar steels expand during heating, then while quenching
the cutting edge cools rapidly and stay that long, while the spine cools slowly under the clay
and returns to previous lenght and therefore creates the sori.

So, in "interrupted quench" process you can't achieve this difference
if you let the cutting edge cool down slowly.

Unrelated to this subject,
if you look what is the shape of sori on most of katanas are Koshi Sori
and if you look how the clay is distributed and where the most of "stress" is created
you will see that the most critical part of the blade is near the hilt.
Not mentioning that Koshi Sori is an useless sori.
While in Saki Sori, the most stress is near the tip, while the curvature is also where you need it,
that is, at the part of the sword you use the most.

About the diff. tempering of the sword like you said,
I don't know why japanese haven't used that way.
So, it is either difficult to make or it has some other disadvantages, I don't know at this moment.


As for the process of heat treating certain steel,
all you have to do is to look at factory specification of that steel.
Perhaps you have to search in several places to get all the details but it says all there.

Certain elements of the steel like Mn, Mo, W, ... are moving the temperature points of that steel
like the point to which a steel should be heated, the point under which the transformation starts
and the time of how fast that steel should be cooled down in order to achieve that transformation.

Therefore, you have water, oil or air quenched steels.

If you air quench a W2, you will not quench it.
If you water quench D2 it will crack.

So, if an defect occurs while quenching a steel in a way it is meant for that steel
then it isn't an error in the process itself but in the work piece.

That is the reason why I am doing stock removal instead of forging.
Forging will not make the quality of that piece any better than it was in new piece of steel stock.

It might save you some money or time on machining process, but that's all.
It is more likely that it will create some defect in the working piece.
Which is most likely by forging when the piece is cooled under the temperature point
where it is not allowed to forge it any more.

There are a lot of different information out there and most of them are coming from people with long experience.
But that is not necessarily reliable information.
My info is from such source too, but from those who work in large industry not from individuals.

And, I am not saying that I would perform error-less in my work.
But, if I make mistakes has nothing to do with the reliability of my info.

In the end, I don't take other people's info for granted so I don't expect others to take mine that way too.
Please, read what I have wrote and make the decision for yourself.
Always do your own research.

Cheers.

 

[SBranson]

Actually, I have said that differential tempering DOES exist, exist indeed,
but that it got nothing to do with differential hardening.

My apologies. I read that as "does not exist for some reason.. Maybe I need glasses. I was confused but I read it wrong several times. Strange.

W2, tamahagane and similar steels expand during heating, then while quenching
the cutting edge cools rapidly and stay that long, while the spine cools slowly under the clay
and returns to previous lenght and therefore creates the sori.

So, in "interrupted quench" process you can't achieve this difference
if you let the cutting edge cool down slowly.

I think this comment may the be the source of some of the confusion in this thread because it is wrong. Unless you have a misunderstanding on how to do an interrupted quench or I misunderstand your comment, every water quenched blade I've done has developed sori solely from the quench, an interrupted quench. I use W2 and the "nose" on this is so fast that 3-4 seconds in water and you are well past the phase change. The interrupted quench slows the cooling process which presumably leads to fewer failures.

Yes Japanese smiths do not interrupt the quench and that may be for many reasons but tamahagane is a very different steel than modern mono-steels like W2 from all accounts I've read. Add to that that many Japanese blades are constructed very differently, with the soft core in a hard shell, you have a completely different scenario in heat treating.

About the diff. tempering of the sword like you said,
I don't know why japanese haven't used that way.
So, it is either difficult to make or it has some other disadvantages, I don't know at this moment.

I think they didn't do that historically because of the type of steel they used. They needed to forge it to distribute carbon evenly. And in modern times, I believe that Japanese smiths are not allowed to use anything but tamahagane or orishigane for cultural reasons.

As for the process of heat treating certain steel,
all you have to do is to look at factory specification of that steel.
Perhaps you have to search in several places to get all the details but it says all there....

...
So, if an defect occurs while quenching a steel in a way it is meant for that steel
then it isn't an error in the process itself but in the work piece.

It should be that simple but in practice, the thinness of a blade and the requirements of the steel in different applications do change some factors.. Since this thread started with water quenching Japanese style blades. I doubt you'd find information on how to achieve sori and a hamon in W2 in factory specifications.
In practice it's not quite that simple because the desired results are different. Some of those desires are what leads to failures, so they are failures of process in what could be a fine work piece. Just pointing out that you can follow the industry rules but sometimes pushing the "edge" in another direction can have great results. Look at the L6 Bainite used for swords as an example. You don't have to HT L6 that way and I'm not even sure what the industry standard is for L6. Anyway, just picking nits here to make the point that HT can be as much a part of the creative process as the knife itself.

That is the reason why I am doing stock removal instead of forging.
Forging will not make the quality of that piece any better than it was in new piece of steel stock.

It might save you some money or time on machining process, but that's all.
It is more likely that it will create some defect in the working piece.
Which is most likely by forging when the piece is cooled under the temperature point
where it is not allowed to forge it any more.

Now this I disagree with. I don't think that forging "magically" makes steel better but the steel has already been through a forging process in making it and getting it into bar stock size. The steel may be full of stresses coming from the steel mill as their forging processes may have had deleterious effects, maybe not for industry, but certainly for knifemaking. I've had more warps from stock removal than from forged blade and it's not because of how I ground it. Perhaps you do your own heat treat but the thermocycling and grain refinement cycles that a common for most bladesmiths put the steel in a proper form to suit the purpose of a blade. Not that you can't as a stock removal maker but I'm not sure that as many do this as do smiths.
The smith is all too aware of the stress he has put into the steel and I think many if not most stock removal makers don't think of the steel from the knifemaking supply as needing work to be good blade steel. I don't know about stainless steels at all though.
I'm not specifically referring to you as I don't know what you do.

Forging, for me, is as much the enjoyment of the process as any part. It is the tie to the history of the process and allows me a little more freedom than trying to fit within the confines of a given piece of bar stock.. I have nothing against stock removal, I just enjoy forging.

There are a lot of different information out there and most of them are coming from people with long experience.
But that is not necessarily reliable information.

This I completely agree with.


Anyway. that all said, I thank you for your ideas as I find myself in agreement with almost all of what you say, in principle, if not in practice. This has been a good thread not only for instruction but for me to try to think through all the information that has been piling up in my head.

Well back to the research.

Regards.

 

[cbr900son]

from semi argument to information overload! LOL Some good reading in there!

 

[Bo T]

I am new to knife/sword making. I am trying to get the basics down before I start on my first stock removal knives. I have read some of Kevin Cashen's information on heat treating. Please feel free to correct any misconceptions that I have. I have to limit myself to the high carbon steels 10xx as those are the only ones I have studied.

By placing clay on the back of the blade it seems that the rate at which it is quenched is reduced so that pearlite is formed from the austenite during the quench. Below the clay, the temperature drops fast enough to avoid the pearlite nose. As the quench continues the austenite along the edge converts to martensite hardening that part of the blade and since martensite takes up more space than either austenite or pearlit the tip of the blade moves upward, causing the bend to the blade. After the quench, the back of the blade is soft but the edge of the blade is hard and stressed from the untempered martensite. Upon tempering the martensite, the stress is reduced as well as the hardness of the edge. I don't know what happens to the back of the blade. Does the pearlite change to bainite?