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tripple quenching vs tripple normalising

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I was wondering if any of you knew of any comparisons and or data about grain size after triple normalising verses tripple quenching .

I understand the necesity of quenching over normalising in steels such as 52100 where the high alloying means that temperature reduction from the point where carbides are in solution has to be quick to keep the carbides small .

my question however is does triple quenching the normal steels I use such as W2 15n20 and 10 series just add stresses to the steel over the method of 3 normalisations .

I hear tripple quenching used a lot It seems to be an "It"phrase ,However conversations with other smiths have made me think twice aboutusing it as a method in preference to normalising with simple steel .

i would love to hear your thoughts .

 

I will put this question up on british blades and see what they come up with there .

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Thanks Owen, I think it's a great question. I'm curious about the W2 and 10xx steels that are above the .8 or so carbon range. Could anyone comment about quench thermal cycling, and if it's better to quench to pearlite rather than try to form martensite.

 

Take care, Craig

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I hesitate to use the word "better". You get similar things, but by different processes. If using simple carbon steels, I see no need to quench them.

 

If I am using L-6, or 5160, or something else that does not make pearlite well, I oil quench them, then sub-critical anneal (at least one hour in a pre-heated oven 1250-1300F) from the quench, and always do it twice (twice quenching, once sub-critical anneal). This will give you a severely tempered martensite matrix with an even distribution of very small spheroidal carbides, and be nice and soft. The final heat treatment is your third cycle and will give you the finest grain size you are going to get, with controlled austenitizing temperature.

 

Simple carbon steels can make spherodized structures from an air cool if the austenitizing temperature is controlled (must be less than 1430F for several steels .8-1%C). It is referred to as "divorced eutectoid" structure, and is quite similar to a spherodize anneal that is much more difficult to do with controlled cooling.

 

Neither of these things appear in "The Heat Treater's Guide" or text books. But they do work, I assure you.

 

You get new (and smaller) austenite grains every time you heat above Ac1. They don't grow until you dissolve all the carbides (exact temp. varies by chemistry).

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Thanks Howard,

that brings some dislocated bits of information together in my head .I appreciate the time it takes to constantly educate/re educate us!

thanks .

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Thanks also very much Howard.

 

Take care, Craig

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Howard, here's a quick related question. Have you ever run into a situation where the grain in the steel was made too small. The reason behind this is that master smith once posted an article that he had gotten the grain in a blade too small to hold an edge. Just looking for a second opinion.

 

Doug Lester

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With alloyed steels like 52100, the alloy carbides are very stable, and inevitable. So the heat treat cycles are to prepare the carbides appropriately for the final hardening cycle.

 

For a simple steel like 1080 modified with minimal impurities, minimal alloys, and close to eutectic composition, I believe the main point of the multiple normalisation cycles is grain refinement (homogenisation of Carbon and stress reliving can be achieved in a single cycle). Carbide preparation is not a concern. So, what is the best approach for _grain refinement_ - forming martensite, or forming perlite?

 

I think the main mechanism for grain refinement is that, at certain phase transitions, many new grains form on the boundary of a single original grain.

 

On heating from perlite, austenite forms on prior grain boundaries [and you get more sites of new grains, and better grain refinement, if you heat faster].

On cooling, ferrite/perlite/bainite tend to form on prior austenite boundries.

So you get grain refinement on the way up _and_ on the way down.

 

I believe that retained austenite, when heated, will not change much at transition temp. So we should avoid retained austenite during normalisation cycles as it does not contribute to grain refinement.

 

However martensite tends to be bounded by the prior austenite boundries. You don't get the same grain refinement on cooling that you do with pearlite. Unless the formation of austenite from martensite is special in some way then this would possibly suggest that martensite is not as efficient at grain refinement as pearlite.

I haven't read anything about how austenite forms from martensite. On the way up, I guess the martensite is tempered to a ferrite matrix with spheroidal carbides - similar to the DET Howard mentions? Now, does the austenite tend to mainly start to form on the grain boundries, or is there a significant tendency for it to form elsewhere as well, such as on the spheroidal carbides? If the latter, then maybe you get double grain refinement on re-heat even if you don't get any refinement on the quench.

 

So, there may be a theory to explain differences in the effectiveness of grain refinement between quenching and air cooling. I can't see much reason why quenching would be better. If I had to choose which was best, I would put my money on air cooling. But, I haven't read anything that suggests one is actually significantly better than the other. All my reading suggests that both seem to work adequately.

 

Adding the risk of stress cracks is a big incentive to prefer air cooling. The advantage of quenching would be speed, but we are only saving minutes which doesn't seem significant when you consider the overall effort invested in a blade.

 

Maybe other intermediate microstructures would be more efficient (in terms of refinement per cycle) at grain refinement, but these others are more tricky to obtain (like DET or lower bainite) and it would be much easier to just throw in another air-cooling normalisation cycle instead.

 

My conclusion is that for simple steels I will probably force-air cool until well past black, then quench in oil to save a little time, then re-heat with the temp transition through critical being as quick as possible (so high temp salts may be an advantage).

 

That's all reading, and no practice. So it isn't real, tested knowledge and could easily be wrong.

Edited by jhobson

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With alloyed steels like 52100, the alloy carbides are very stable, and inevitable. So the heat treat cycles are to prepare the carbides appropriately for the final hardening cycle.

 

For a simple steel like 1080 modified with minimal impurities, minimal alloys, and close to eutectic composition, I believe the main point of the multiple normalisation cycles is grain refinement (homogenisation of Carbon and stress reliving can be achieved in a single cycle). Carbide preparation is not a concern. So, what is the best approach for _grain refinement_ - forming martensite, or forming perlite?

 

I think the main mechanism for grain refinement is that, at certain phase transitions, many new grains form on the boundary of a single original grain.

 

On heating from perlite, austenite forms on prior grain boundaries [and you get more sites of new grains, and better grain refinement, if you heat faster].

On cooling, ferrite/perlite/bainite tend to form on prior austenite boundries.

So you get grain refinement on the way up _and_ on the way down.

 

I believe that retained austenite, when heated, will not change much at transition temp. So we should avoid retained austenite during normalisation cycles as it does not contribute to grain refinement.

 

However martensite tends to be bounded by the prior austenite boundries. You don't get the same grain refinement on cooling that you do with pearlite. Unless the formation of austenite from martensite is special in some way then this would possibly suggest that martensite is not as efficient at grain refinement as pearlite.

I haven't read anything about how austenite forms from martensite. On the way up, I guess the martensite is tempered to a ferrite matrix with spheroidal carbides - similar to the DET Howard mentions? Now, does the austenite tend to mainly start to form on the grain boundries, or is there a significant tendency for it to form elsewhere as well, such as on the spheroidal carbides? If the latter, then maybe you get double grain refinement on re-heat even if you don't get any refinement on the quench.

 

So, there may be a theory to explain differences in the effectiveness of grain refinement between quenching and air cooling. I can't see much reason why quenching would be better. If I had to choose which was best, I would put my money on air cooling. But, I haven't read anything that suggests one is actually significantly better than the other. All my reading suggests that both seem to work adequately.

 

Adding the risk of stress cracks is a big incentive to prefer air cooling. The advantage of quenching would be speed, but we are only saving minutes which doesn't seem significant when you consider the overall effort invested in a blade.

 

Maybe other intermediate microstructures would be more efficient (in terms of refinement per cycle) at grain refinement, but these others are more tricky to obtain (like DET or lower bainite) and it would be much easier to just throw in another air-cooling normalisation cycle instead.

 

My conclusion is that for simple steels I will probably force-air cool until well past black, then quench in oil to save a little time, then re-heat with the temp transition through critical being as quick as possible (so high temp salts may be an advantage).

 

That's all reading, and no practice. So it isn't real, tested knowledge and could easily be wrong.

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Great info, Howard. Thanks!

 

Hank, I assume the point of preheating is so that he can know (or at least come closer to knowing) how much time the blade actually spent at the target temperature.

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I think that a good method is to heat the steel little bit over Ac1 (for ipereutectoid steels) or Ac3 (for ipoeutectoid steels), quench it for 2 or 3 seconds in rapid oil (or maibe in water, but increase the risks of cracks or distorsions), extract the blade and cool it on still or forced air.

 

With this method you can obtain a structure formed by finer perlite (or, for carbon and plain steel with discrete hardenability a mixed structure formed by fine perlite and bainite), more finer than that obtained with a simple normalisation in still air.

 

More finer is the pearlite more finer will be the austenite grains (that form from pearlite) and consequently the martensite structure.

 

Best Reagards

Francesco.

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Howard, here's a quick related question. Have you ever run into a situation where the grain in the steel was made too small. The reason behind this is that master smith once posted an article that he had gotten the grain in a blade too small to hold an edge. Just looking for a second opinion.

 

Doug Lester

 

I just want to check what exactly you mean...

 

Was the smith unable to harden the steel properly, or was the abrasion resistance found to be inferior at a similar hardness to larger grain sizes?

 

I ask because I can verify that small grainsize lowers hardenability, so on a marginally hardenable steel you may become unable to harden it at small grainsizes. Can't really comment on grain size vs. abrasion resistance/edge holding at the same hardness if that was the case.

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From what I understand, the situation was that the steel, I think 1095, had such fine grain that it wouldn't harden or that it was so shallow and so thin that the hardened edge was ground away after hardening leaving only pearletic steel.

 

Doug

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Great info, thanks.

 

I understand that it seems triple normalizing is a safer, and just as effective method of grain refinement as triple quenching, but I'm currently using 1084, and cannot get very good temperature control with my current setup. So my question is, if i'm only able to triple normalize from critical, without being able to take the temperature down a bit each normalizing cycle, am i better off going with a triple quench?

 

And if the triple quench is the best option for my situation, should i be triple quenching at critical? Or do you still get the same benefits of grain refinement from a sub critical quench?

Edited by Saul Kokkinos-Kennedy

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Triple normalizing from a not very controlled critical temp will be just fine, no need to risk quenching. Quenching will always be more effective, but not necessarily worth the risk. A sub-critical quench will refine grain more than an air cool, but not nearly as much as super critical. If you were worried that you enlarged grains too much go ahead and do several (e.g. more than 3) normalizing cycles. Worst case scenario you are just wasting time and fuel by reaching the limit which your set-up will allow you to refine the grain, but it is so quick that you aren't really wasting that much, making it cheap insurance. Doing an air cool or two followed by a sub-critical quench or two would speed along the grain refinement and pre-heat your oil for you (which is good if you are going to be quenching right after normalizing). By sub-critical quench I mean heat above critical, air cool until you are sub-critical then quench.

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Ha! It turns out my impatience while normalizing is actually better than being patient. I always do the subcritical quench after the first two normalizations just to speed up the process. Using 1084 as well. And a WATER quench at sub-critical. Very sub-critical, I might add, I wait until all color is gone before quenching.

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Well, better for grain refinement. It does it more because you are introducing more stress. Not much, so it isn't likely to cause problems, but likewise it isn't doing very much for you either (comparatively speaking at least).

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Thanks Jerrod! nice and simple explanation.

 

I'm liking the sound of the double normalize followed by a double sub-critical quench. I have a hand held infrared temperature gun, that seems like it has ok accuracy, so for the sub-critical quenches, what temperature am i aiming for the quench as it cools from critical? 700 C?

 

Cheers

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I second Saul's question. I heat treat at night, so I am always looking for the recalescence. Could the sub-critical quench be done right after that? Does the sub-critical quench work better the closer you are to the critical temp? This is awesome info btw. Thanks everyone!

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I'd shoot for 25-50 degrees F below critical (which varies by alloy, thus I'm not throwing out a specific number) for both a sub-critical soak (if you are wanting a sub-critical anneal) and quench. Once you are certain you are below critical (no more austenite left) you should be completely safe. If you get it a little wrong and still have a little bit of austenite you may get a little bit of martensite. This will help with grain refinement and still only have a little added risk. I personally like watching de/recalescence, and often quench as soon as I have seen all of the shadow pass through the blade. I've been playing with W1 a lot recently, for what that is worth. Keep in mind that there are a lot of people that do triple quenching without catastrophic failure (of the blades at least, that can't be good for ones nerves!) so if you have done a couple standard normalizing cycles first, don't worry too much.

 

I homebrew and have read The Complete Joy of Homebrewing. One of my favorite things about this book was the repeated mantra: "Relax. Don't worry. Have a homebrew." Same vibe goes for grain refinement steps. Relax. Don't worry. Play with fire.

 

I also ran some specialized casting simulation software for a while . Best advice I ever got about approaching making changes was from one of the trainers: "There's nothing a complete re-install won't fix". She wasn't joking, Same goes with steel. We can always get a new piece. We do this for the experience at least as much as for the end result; many of us much more for the experience.

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I personally like watching de/recalescence, and often quench as soon as I have seen all of the shadow pass through the blade.

 

Me too. One of the reasons I do my heat treating at night.

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I had a chart form the 50's somewhere with grain size resulting from normalizing cycles with several alloys. I'll have a look.

 

The reality of these ideas is that most blade smiths can not control temp as well as they think so what is said to be done is not really what is being done.

 

 

Ric

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Around page 69 of this document you will find what triple quenching does. 

Metallurgy of Steel for Bladesmiths & Others

who Heat Treat and Forge Steel

John D. Verhoeven

Emeritus Professor

Iowa State University

March 2005

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