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Post by freq on Oct 9, 2016 2:17:59 GMT
this has been kicking around my head for a few weeks now, whats with modern smiths and their fear of the water quench? have been watching forged in fire and it seems like every time anyone puts a hot blade in the water the judges loose their proverbial, which i cannot for the life of me understand, since water quenching has been around a long, long, long time, not so long ago (pre crude oil/1850s ) the idea of plunging a hot blade into oil would have been an anathema to smiths (not to mention serious expensive) i cant imagine that you would waste oil you could use for fuel, lighting etc to harden a blade when you have a free resource that falls from the sky, it also seems strange to me since its still the accepted way to make Japanese blades, in fact its what gives the blade its curve, so what is it that makes western smiths freak out about the water quench, could it be that they have been told this is how it had to be done by the person teaching them, ergo thats all they know so thats the "right" way to do it?
p.s. i know this is opening up a can of worms lol
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Post by Brendan Olszowy on Oct 9, 2016 5:06:22 GMT
Hi freq There is no can of worms, just a lack of understanding. Water doesn't give katanas their curve. The molecular volume of the hardened steel at the edge is higher than the unhardened steel. Thus the hardened edge expands in comparison to the unhardened spine, creating the curvature. It will happen in any quench medium which is sufficient enough for martensite formation. It also happens when you don't want it too. Many double edged blades will "sabre" in the quenching process. Many modern high carbon alloys will simply crack in a water quench, as it's far too aggressive (removes heat too rapidly). Salt water is even more aggressive as it evaporates at a higher temperature allowing better contact with the steel (less vapour jacket). So most modern alloys need to be quenched in oil to prevent cracking - some even air quench. Simple as that. My 9260 will sure as hell crack if quenched directly in water. Except rarely I get a stubborn piece which won't harden sufficiently in oil, so I'll pass it from a very quick oil quench to a water quench, or if that fails, go straight into water. But usually I give it about 15 seconds in oil, then into water. In days of yore they were less likely to achieve the very high carbon contents we have at our disposal today - and steels lacked the alloying components added to high tech foundry steels to enhance hardening characteristics (manganese, vanadium, silica etc). This meant they needed a more aggressive quench to get any martensite formation from their low carbon steel. Thus they could use water, or you'll often hear stories of them using Urine to quench in - ie. salty water. However if they had very high carbon steels (which would only have been used on the edge of a blade with a softer iron spine), they could use oil. Oil can be sourced from animal fat, as well as pressed from vegetables and grains. Not just mineral sources. Correct, it wouldn't be cheap. But swords aren't cheap and it would be a cost of business. Just like today, a quality quenchant is not cheap - a 200L drum of Parkes quenchant is around $1000. Thus we get by with old cooking oils, or used motor or transmission oils. Try buying 100L of Automatic Transmission fluid, it aint cheap. But it's good because it is high in detergents which allow better surface contact with the steel, speeding up the quench, but still gentler than water. Water however cheap, is still expensive when you calculate the cost of having to remake a blade every time you quench it and it cracks. That said there are modern steels which are designed to quench in water, they may start with a W- prefix. Or some smiths may make their own steels the traditional ways. The smith needs to know the behaviour of his steel is, and what he needs to get the results he's after. As for the hesitation of the judges and bystanders, though I've never seen the TV shows, I imagine it's one of a few sources of drama they can use to create suspense, just like all those reality shows. Cooking shows do it all the time with unset jelly, undercooked meat, and overcooked pasta - acting like it's the end of the world. Cheers :-)
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Post by freq on Oct 9, 2016 6:06:58 GMT
thanks Brendan a well thought out and explained answer, was familiar with the effect of curvature in katana was simplifying it a lot so question wasnt a mile long lol. so if im getting the overall gist of it its that steel got better so quenchants got "oilier", where my interest arose from is reading a lot of old blacksmithing/tool making books they all reference either brine of water quenchants for took making, and a knife is just a form of tool, my other query is that it seems that alot of the old books mention quenching at lower temps than most smiths use now, some even saying red heat in a dark environment then into water which would seem right on for approx 1500f, where as ive seen people on the aforementioned show/ youtube putting visibly glowing (bright yellow/white) blades into quenchants and wondering why thermal shock has cracked them, so would it be possible to heat lower and quench faster to get hard blades with modern materials?
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Post by Brendan Olszowy on Oct 9, 2016 9:24:17 GMT
Hi Freq For regular blacksmithing of mild steel, to make tools such as Tongs, then plain old water is fine. It's only regarding high carbon steels you have cracking problems. Modern steels each have a specified quench temperature range - they vary depending on steel types. When you film forging or quenching, the camera really exaggerates the glow. Even a dull red can look bright orange. While a strong red to orange (forging temp) will look bright yellow. You can't believe what you see on film. Cheers
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Post by aussie-rabbit on Oct 9, 2016 10:22:37 GMT
The most critical stage of the process, the zone hardening with slow water quench. Here is where the years of experience will help Nara. Look at the intense expression on Nara's face. He knows only too well if he misses his mark here the entire project is a loss. (full story) www.himalayan-imports.com/kami.html[Image]
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Post by demonskull on Oct 9, 2016 16:46:35 GMT
Interesting question and great answers, thank you gentlemen.
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Post by brotherbanzai on Oct 9, 2016 17:13:35 GMT
Brendan's answer is spot on.
To reiterate and maybe simplify a bit: Different steels are made to be quenched in different mediums. There are even fast, medium, and slow oils for quenching. Using a quenchant that is too slow will result in the blade not hardening, using a quenchant that is too fast can result in the blade cracking, using a quenchant which is slightly off can result in a still functional blade with suboptimal hardness.
Most high carbon steels will harden in a medium or fast oil even if they are meant to be water quenched, though they may end up with less than their maximum hardness. There's no real advantage to hardening a steel meant to be quenched in oil in water, but it could easily crack and be ruined, which is a far bigger loss than slightly lower hardness.
On the show, the judges reaction to someone quenching in water, specifically with an unknown steel, is justified because doing so is a really dumb move when oil is readily available and they are in a competition where a broken blade will knock them out of the running regardless of anything else.
Heating a blade below the point where austenite forms will not allow the blade to harden when quenched. This temperature varies with different steels. It's not the heat and rapid cooling that specifically makes a blade hard, it's the transformation of the steel structure from ferrite and pearlite at room temperature to austenite at a specific critical temperature and then cooling rapidly to cause the austenite to become martensite. Without first heating to that critical point to change the structure to austenite, it doesn't mater how fast or slow the steel is cooled, it won't end up as martensite.
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Post by Croccifixio on Oct 10, 2016 5:06:48 GMT
J and David are simply emphasizing the context. Water quenching is all well and good in your backyard even with oil quenched alloy steels... But there are $10,000 on the line. Risky stuff like that have minimal reward. I know they get a lot of flak from other smiths for being snobs, but the reality is that less mistakes = much higher chance of making it into the next round, so it is quite perplexing to see smiths take huge risks with that money on the line. Sometimes they get proven wrong, but they have always been able to point out the times when smiths make risks that do not pay off (hell, Burt Foster himself overheated a blade in the champions round trying to correct warpage).
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Alan Schiff
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Post by Alan Schiff on Oct 10, 2016 17:25:30 GMT
Brenno and Jeffery are spot on. While it IS possible to harden properly with a water or brine quench, for small pieces or those with thin cross-sections, it's easier to get good results (and therefore safer) to use oil, even for a lot of steels marketed as water quenching. I've read/seen a few smiths/knifemakers that only water quench, but again, with oil quenchants readily available, why take the chance?
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Post by DigsFossils-n-Knives on Oct 11, 2016 13:37:33 GMT
I agree with pretty much all that is stated above, why take a chance when there is $10,000 on the line, or loosing the reputation/title of being a Forge in Fire winner. But if that is not on the line then some smiths will take a chance with a water quench so that they can repeat the ancient methods of the past. And I have heard and seen that water quench produces better (aesthetic) hamons.
But why does a water quench produce a sori but oil does not (or very, very slight sori)? I'm sure I can google it, but I think it would be good to include this in this thread.
Another question, does it affect the sori if you thermally anneal or 'differential tempering' the spine of a TH blade? I don't think so, perhaps because the edge half or bevels are too hard to allow the blade to bend/curve. So does that mean differential tempering produces stress in TH blade?
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Mikeeman
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Post by Mikeeman on Oct 11, 2016 15:17:02 GMT
I'm sure someone with a brain will be along shortly, but I THINK the reason you get the sori from water is because of how fast it can cool steel as opposed to oil. When the less clayed edge hits the water, you see the blade pull towards the edge because that part of the blade has shrunk from being cooled. But it is to my understanding that it was not able to shrink completely due to being cooled so fast and is sort of "locked in" in a slightly expanded state. As the back cools off, it pulls the blade back toward the spine. And since it is cooled slower, it is able to shrink more.
If I'm wrong, someone please correct me. Because this is just my theory. Here's a good video where you can watch what happens.
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Post by Croccifixio on Oct 12, 2016 10:24:56 GMT
Someone also posted in the FB group that you get a reverse curve in oil. Anyone care to enlighten me as to why that would be? Can't load bladeforums/bladesmithsforum right now.
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Post by Brendan Olszowy on Oct 16, 2016 12:12:22 GMT
Someone also posted in the FB group that you get a reverse curve in oil. Anyone care to enlighten me as to why that would be? Can't load bladeforums/bladesmithsforum right now. I've already addressed this in my first post in this thread. It has nothing to do with the quench medium. *efit* Oh hang on, are you saying it curves forward, like the other way???
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Post by Croccifixio on Oct 16, 2016 13:29:32 GMT
Someone also posted in the FB group that you get a reverse curve in oil. Anyone care to enlighten me as to why that would be? Can't load bladeforums/bladesmithsforum right now. I've already addressed this in my first post in this thread. It has nothing to do with the quench medium. *efit* Oh hang on, are you saying it curves forward, like the other way??? Yep, I read that in one of the FB comments. It further stated that's the reason why you should pre-curve when quenching in oil if you wanted it straight, and put more curve before quenching in oil if you wanted a sabre-ish blade.
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Post by AndiTheBarvarian on Oct 16, 2016 14:49:01 GMT
I've read in an article about material science that this concave bending can happen if the edge is already cold and the spine still so hot, that it has more volume. Even when the spine colds out too, a single edge sword can remain concave. This seems to happen in the beginning of every katana quenching process to a small degree, but when done right the convex form develops.
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Post by Brendan Olszowy on Oct 17, 2016 1:21:06 GMT
If it's not coated in clay it's likely to curve forward, as a through tempered blade will all transform to the larger volume of martensite. And the extra mass in the spine means extra expansion along the spine, which means it is likely to curve forward (toward the edge). If however it is coated in clay to prevent martensite formation at the spine, it will still curve backward, as only the edge material expands in volume. NB: *Again noting that when you shape the blade you're shaping it in pearlite and ferrite. When you harden steel it becomes martensite which occupies more volume in space than the molecules you formed it from - hence the post HT expansion/ new shape. *Also note that the volumes I'm referring to are all in the steels' cold states. Shape when hot is irrelevant to this outcome, but fun to watch when quenched in fishtanks. *I still believe that quench medium is irrelevant except in the discussion of cracking and/or suitable martensite transformation, as discussed above. *The most fun thing about single edged blades is that it's ok if it sabres a lot or a little (forward or backward), you just have a fun shaped blade, always nicely curved and sexy. When it happens to double edged blade you have a hassle, any which way you slice it. :-D
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Post by Croccifixio on Oct 17, 2016 9:01:52 GMT
Nice pun :) Since you're here answering questions, can I also ask something I've done research about: edge quenching.
I've seen in bladesmithing communities that edge-only quenching or edge-only heating is poorly thought of. The common answer is that a full quench plus differential tempering of the spine is still better. However in my country (which has the use of blades as part of everyday life for a majority of the populace), almost all edged tools are just edge-quenched (and almost all of them are made of used leaf-springs so mostly 5160). A majority also quench in water. Now I wonder, is it just the lack of education about metallurgy? Is there a real benefit to an edge quench over a full quench with differential tempering except the speed at which one can do it?
Thanks for anyone answering (and especially Brenno)!
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Post by AndiTheBarvarian on Oct 17, 2016 15:22:54 GMT
*The most fun thing about single edged blades is that it's ok if it sabres a lot or a little (forward or backward), you just have a fun shaped blade, always nicely curved and sexy. When it happens to double edged blade you have a hassle, any which way you slice it. :-D You still can call it a "flamberge"
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Post by AndiTheBarvarian on Oct 17, 2016 15:47:21 GMT
www.tf.uni-kiel.de/matwis/amat/iss/index.htmlCroccifixio: I can only assume that for a tool reworked from already used spring steel an edge quenching is sufficient and less work or risk of failure. If you're interested in sword metallurgy here above is a nice and funny script from a german university professor and swordfan.
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Post by Croccifixio on Oct 17, 2016 16:01:32 GMT
Yes thank you I have read that quite a bit. Also plenty on bladesmithing in books and forums. However, edge quenching seems to be a controversial topic without much positive support for it other than traditionalists.
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