Triple Quench 0-1?

Kevin (C).....what would you recommend be an approriate time to soak.

I am currently soaking 52100 for 10 mins at 1550F in a digital oven ..should I extend this?

Thanks.
 
Dewweyknives,
One thing that may help with the temperature control on the coal forge is better air flow control. You should be able to get it from a faint glow to a big roar with proper air control.
Stacy

Kevin,
You make people THINK,and THAT is what makes for better knifemakers (not just better equipment).Thanks for your input.
Stacy
 
Kevin - can you confirm (or refute) the idea that reheating O-1 to non-magnetic after quenching "wipes the slate clean"?


(respectfully quoting a post above)
 
Perhaps if I had a high spec heat treating oven designed for knife makers I would have a higher opinion of ovens for cycling.:) A poorly designed or made tool is never going to leave the best impression. I just didn't realise, until I read the reactions here, that the tools I used were THAT bad;)

I wanted to move a blade rapidly between critical and non-critical three or four times and every time I opened the door of the oven the temperature plunged, then took a very long time to come back up and invariably had some over-shoot before stabilising. Even if the response was twice as good it wouldn't have been satisfactory. On top of that, the amount of decarb I got was astounding :eek: The door didn't seal and I didn't have any carbon bearing material in there with the blade.

I have spoken with a couple of (possibly) full time makers and a couple of professional heat treaters here in the UK and they all looked at me like I was an idiot when I asked about cycling with an oven. So, I assumed that my experience wasn't an aberation.

Had I just been able to put the blade in and soak it I think the oven and I would have got on a lot better:D Fortunately it wasn't MY oven :D
 
Chris Meyer said:
For those of you with the time and interest, John D. Veerhoeven PhD has written, and generously posted (in .pdf format) for free, a book entitled Metallurgy of Steel for Bladesmiths & Others who Heat Treat and Forge Steel. I am in the process of reading this book, which is written for Bladesmiths and Blacksmiths, and it's quite fascinating. I strongly recommend it to everyone in the forums.
Click to expand...


I just downloaded and printed that book myself several days ago. I'm about a fourth of the way through. It's very interesting, though some parts are a little over my head. :)
 
C_Claycomb said:
Perhaps if I had a high spec heat treating oven designed for knife makers I would have a higher opinion of ovens for cycling.:) A poorly designed or made tool is never going to leave the best impression. I just didn't realise, until I read the reactions here, that the tools I used were THAT bad;)

I wanted to move a blade rapidly between critical and non-critical three or four times and every time I opened the door of the oven the temperature plunged, then took a very long time to come back up and invariably had some over-shoot before stabilising. Even if the response was twice as good it wouldn't have been satisfactory. On top of that, the amount of decarb I got was astounding :eek: The door didn't seal and I didn't have any carbon bearing material in there with the blade.

I have spoken with a couple of (possibly) full time makers and a couple of professional heat treaters here in the UK and they all looked at me like I was an idiot when I asked about cycling with an oven. So, I assumed that my experience wasn't an aberation.

Had I just been able to put the blade in and soak it I think the oven and I would have got on a lot better:D Fortunately it wasn't MY oven :D
Click to expand...

You're right, it is slow, and it does decarb like crazy. :( I'd use salt pots if I had them, but right now I don't have room. Fortunately, I'm fairly patient, so the slowness doesn't bother my too much. And I've learned to leave on plenty of extra steel to account for decarb. I also do all the thermal treatments right after forging, before any grinding.
Speaking of bad ovens, you should see the one I built from scratch several years ago. It weighs about 400 pounds, took about 2 hours to get to 1500, and the elements burnt up after only several firings. :eek: I'm very happy with my Evenheat. :D
 
Im thinking more and more about using brownells PCB. It seems more and more like its a necessity with carbon steels in ovens. I am too lazy to order some and find I can get through the decarb pretty fast in my final grind. Since I etch my carbon blades, its easy to see the decarb from the good steel as they etch vastly differently.
 
Thanks to all for the responses.

Stacy, yes I can go from smothering my fire out to blasting ash and ambers in my face. My issue is how consistant I can maintain heat over a specified time period and determining heat once I'm beyond nonmagnetic. Once beyond nonmagnetic,there is quite a temp range before there is any color change.I'de like to ask, How much fluctuation is acceptable during a soak?
Thanks Chris, for the link to the online book. Took a quick look and is a definate "must read".
Thank you Kevin, for provoking thought and some direction to carry on the persuit. Read,test,learn! I think I'll continue on with 0-1 now that I have a path to follow and see where it takes me.
Thanks to all and best holiday wishes
 
This is a good thread, there are two types of threads that seem to stretch out into 3 pagers, one that stirs up the hornets nest and has mud flying, and those that are loaded with answers to the great questions they inspire, this one seems to be the later which is a much rarer and more valuable thing. It would also seem that if one wants at least a 3 pager all they need to do is put the words “triple quench” in the title, which often are of the former category unfortunately. One can tell how much I enjoy a thread by how verbose I become, this one should reveal my attitude shortly.

So where to begin…
 
Kevin Davey said:
Kevin (C).....what would you recommend be an approriate time to soak.

I am currently soaking 52100 for 10 mins at 1550F in a digital oven ..should I extend this?

Thanks.
Click to expand...

Kevin, almost as important a factor in determining heat treatment as the chemistry is the heat treat history. In soak times, what has been done to the steel prior to austenitizing is very influential, so I may recommend a minimum soak that would work in my shop that may not get it in your shop. With the alloy you mentioned you have chromium carbides and loads of proeutectoid cementite, this makes it easier to get into solution than if you have something like tungsten or vanadium. My recommendation would be to do just what I do all the time myself, make up some tests samples with the exact treatments that your blades get and soak them all and begin to quench the first one at the time you feel is your minimum and then quench another in 2 minute intervals after that, be certain they are labeled so you can identify each (I use number stamps). Leave them fully hard and get them Rockwell tested. If you find no significant increase in HRC from the first to the last, be happy with what you are doing, if there is an increase find the number of minutes the increase leveled off and add a couple of minutes. Finally break the test samples and see if the grain is where you want it, and thus your control of the temperature will give you the freedom to soak as you please.

You are never going to get 100% of that carbon into solution, nor would you want to. In my opinion the ideal situation is to get at least .7% -.8% of that carbon into solution and leave the rest in many very tiny little chromium carbides scattered evenly throughout the martensitic matrix, the finer the better.

From my experience 10 minutes should be fine but, as laid out in the above paragraph, don’t hold me to that. The most important thing to remember is that if you have control over that temperature, the minimum is all that need keep you awake at night, going beyond that will use more electricity but if the temperature is constant the steel doesn’t seem to care.
 
Daniel Koster said:
Kevin - can you confirm (or refute) the idea that reheating O-1 to non-magnetic after quenching "wipes the slate clean"?


(respectfully quoting a post above)
Click to expand...

Daniel, as with most of this stuff, there are no absolutes, so it depends upon what areas you look at. In the terms of prior austenite grains and the new martensitic structure, it will begin recreating itself as soon as you approach “critical”. Carbides, even simple cementite (iron carbide) requires more effort to “wipe clean” , that is why there is an Accm line on the iron carbon equilibrium diagram.:

fefe3c.jpg


on the diagram there are three lines to the far left, A1, A2, and A3, since we are talking about heating so they could also be called Ac1, Ac2, Ac3. A1 is the point at which the transformation (alpha iron to gamma iron) begins. Before this you get degrees of tempering carbide formation and then formation of spheroidal cementite in increasing degrees. As you reach Ac1 the pathways for the carbon to move begin to open up and you get much more diffusion and as more gamma iron is formed the carbon is dissolved in it. Hanging around or just below Ac1 can allow the carbon to move, but to find its own kind and pool up and segregate, this is how spheroidizing works. If there are carbide forming elements that can grab onto that carbon they will gorge on it and this is how you get banding and heavy segregation.

Continue to heat the steel and you will reach Ac2, the Currie Point or nonmagnetic, which, believe it or not, is not all that significant for this conversation. But now since we are talking about carbides lets jump to the other side of the “V” on the chart, the portion that rest between .8% and 2% carbon and would describe a higher carbon steel. The next line up is Acm. Between Ac1 and Acm is a whole field of varying degrees of solution for simple cementite, stop at any point in there and you will have undissolved carbide that is leftover from the last heat, pass the Acm line in temperature and you will dissolve it all and have all fresh austenite, unless…

Unless there are carbide formers, then you will need to soak for an extended period to peel some extra carbon off them or increase the temperature high enough to break the chemical bonds ( for something like vanadium this can be in excess of 1900F.)

Are you starting to see how this is not so black and white?:(

The first thing to be wiped clean on a reheat is residual strain from forging, cold working, thermal treatments etc. In a process known as “recovery” the dislocations will be rearranged in a configuration more conducive to lower stored energy, this is how stress relieving works and why the idea of “stresses” or “strengthening” from previous deformation, be it hot or cold, surviving through a heat treatment is nonsense.

The next thing to go (I am probably missing some) would be the original even grain configuration as new grains begin to nucleate and from sub grains at the old grain boundaries, you would now have a mixed grain size between the remnants of the old grains and the new. When the process is complete there will be fresh austenite grains that will then set to consuming any extras carbon it the grain boundaries as heat increases. Grain growth cannot occur until those boundaries are depleted and destabilized, above Acm. But if there are alloy carbides they will arrest this and that is why that 5 hour soak was possible.

Finally the last thing to go, and would probably survive most of our heat treating operations would be those richer alloying carbides.

So, in short, ;) the answer to your question is YES! ... and NO!
 
C_Claycomb and Phillip, I have kilns and have always cringed at the amount of scale they produce if efforts are not made to overcome it, and the insulating effects of the open space in them makes heat time a little slow for my liking. The salts may sound great but, to fire them up (no small undertaking for mine) just for a few quick heats is prohibitive, but what really concerns me is decarb. Yes I did use the “D” word in reference to salts. As long as my pieces have remained under the surface, and the salt was in good shape, I get none of that nasty stuff, but pieces that I have removed and allowed to air cool and put back into the salts gave me a heart attack when I etched the Damascus. The worst part is that it is an insidious unique kind of decarb in the salts, nasty little polka dots all over the pattern welding, as if some knit wit got happy with a spray bottle of WD40 near your blade right before you etched it.

Having tight control over normalizing is probably best and I am dropping the ball here myself, but with all of these factors it is easier for me to just normalize in the forge, since it is there and still hot from forging. Plus I really have no set temperatures that I use in every normalizing, I often will change heats on the spur of the moment depending upon how the forging went that day, if I saw something that give me concern, how on the ball I was etc…
 
Deweyknives, I have been working with forges for a quite a few years now and I don’t bother with attempting a 10 minute soak in them, I just switch to a steel that can handle a 1 minute soak instead, heck a coal fire would burn out and get tired before you could finish such a soak. I feel a person could do more harm than good by trying to cook a piece of steel for that long in such and unstable heating environment. Even if you kept the whole thing evenly hot, you would also need to watch your atmosphere the whole time to keep the carbon in the blade. There are just too many things for human hands to juggle. Under these circumstances the best bet is to match up the steel and the tools, if not that then I would be willing to say that quenching it more than once may give a little better performance over once, in a richer steel, but for me nothing beats doing it right the first time and knowing you nailed it.

Fluctuation in soaking is less of a problem if you err on the cool side, you would need to drop quite a ways to effect a change that would set you back, you just wouldn’t be accomplishing much in the time you were cooler than the set temperature. The real killer is having the temperature go higher, then you would get grain growth or worse, and the results would be worse than no soak at all.

It is also worth mentioning that if one had the luck of a god and the faculties of a computer with a thermocouple plugged into it, it is theoretically possible to eliminate the soak by very rapidly heating to a temperature just a few degrees below the grain coarsening temperature achieving complete solution throughout and then quenching. The temperatures would be a little higher than we are used to and the margin of error would be nil, but anything possible (just not likely;) )
 
Kevin R. Cashen said:
In my opinion the ideal situation is to get at least .7% -.8% of that carbon into solution and leave the rest in many very tiny little chromium carbides scattered evenly throughout the martensitic matrix, the finer the better.
Click to expand...

I've been wondering for awhile, how to you control carbide size? Does carbide size become refined at the same time you're refining austenite grain size?

Kevin R. Cashen said:
C_Claycomb and Phillip, I have kilns and have always cringed at the amount of scale they produce if efforts are not made to overcome it, and the insulating effects of the open space in them makes heat time a little slow for my liking. The salts may sound great but, to fire them up (no small undertaking for mine) just for a few quick heats is prohibitive, but what really concerns me is decarb. Yes I did use the “D” word in reference to salts. As long as my pieces have remained under the surface, and the salt was in good shape, I get none of that nasty stuff, but pieces that I have removed and allowed to air cool and put back into the salts gave me a heart attack when I etched the Damascus. The worst part is that it is an insidious unique kind of decarb in the salts, nasty little polka dots all over the pattern welding, as if some knit wit got happy with a spray bottle of WD40 near your blade right before you etched it.

Having tight control over normalizing is probably best and I am dropping the ball here myself, but with all of these factors it is easier for me to just normalize in the forge, since it is there and still hot from forging. Plus I really have no set temperatures that I use in every normalizing, I often will change heats on the spur of the moment depending upon how the forging went that day, if I saw something that give me concern, how on the ball I was etc…
Click to expand...

I'm not in any hurry to get salt baths. I think right now they're a little out of my league. :)
 
Kevin; Again,thanks for getting involved.Lots of great info for us that are "less informed". I have a propane/gas forge that I began to build a couple years back.Will dig that out and figure my burner so I can fully use this info.Went to a charcoal forge as playing in fire just "makes my day" but if proper heat treat requires other methods,that's where I have to go.Thanks .
 
This is a great thread. I cant get enough of this stuff. Its good that people are so interested in knowing what is actually going on. Too often fit and finish are focused on when in reality, we could all be making knives with mild steel and be worrying about that. Id rather have an ugly knife that performed like a dream than a beautiful art knife that couldnt cut a piece of cardboard without dulling
 
David Schott said:
Id rather have an ugly knife that performed like a dream than a beautiful art knife that couldnt cut a piece of cardboard without dulling
Click to expand...

That's something you're entirely incapable of, Dave... having put hands on your work, your attention to detail is incredible. As is evidenced by your participation in this thread, it's obviously deeper than that, too!
 
Thanks man! Who paid you to say that? :)

Im partway through the book. Im soaking this stuff up and my brain is spinning with ideas....maybe too many ideas...
 
I agree with these thoughts,David. There's no excuse to make an ugly knife with what is available today but at the same time,why put the effort into something that will let you down when you NEED a knife? I guess it comes down to knife or art. It takes a real craftsman to accel at both and there are a number of them around. With the advise and info from all involved with this thread,I'm certian my knives will improve as I'm still concentrating on very good quality users that look good. Incredible art may or may not follow!
 
You must log in or register to reply here.
Back
Top