Quenching At Non-magnetic

LRB

Well-Known Member
Concerning the simpler carbon steels, why is it that so many persist in this practice, and continue to recommend it to be the critical temperature at which a blade should be quenched in the hardening process? Non-magnetic happens at 1414° in all steels, and is only the second phase of fully Austenitizing steel. Phase three, or actual critical temp, varies with the type of steel, but 1450° is about as low as any can achieve full austenitization, with 1475° to 1500° being most often more ideal, depending on carbon content and other alloys, which may require even higher heat. Between these two temps, grain growth is insignificant if at all. Those not having an oven, or other way of controlling heat can simply heat to one or two shades of red above non-magnetic and be close enough to produce a good solution of the iron and carbon with a reasonably good carbon dispersion. Of course even a short soak at temp will benefit even more, but without heat control is not easily done.
 
I agree Wick. I think its because magnetic is an easy gauge without other methods to determine temp.. If I were doing H/T without an accurate way to monitor temps., I would buy 1450 & 1500 degree Tempilstiks. I would learn what color would melt the 1450 degree but not the 1500 degree. I believe that would be good enough for a decent H/T on steels that don't require much of a soak. I do agree that just taking steel to non-magnetic will not produce a good blade. Just my $0.02.
 

Rudy Joly

Well-Known Member
LOL. good subject Wick.
This subject comes up almost on a weekly basis either in person or on the phone. When I ask them to review their proceedure, non-magnetic is always the point of quench, almost like it's an act of desperation. I always advise a count of at least 50 after non-mag , while moving the blade slowly. At least the count will get them closer to the target regardless of the type of steel. The other misconception that goes directly hand in hand with non-magnetic is time to quench. They persist in thinking it's a race to quench when the target temp is reached, to a certain degree it is. It takes a while to understand that it's the steel that has the time limit for phase change upon quench, not you getting it to the quench. In their defense, I can remember a time when this was all new and confusion and anxiety of the procedures ruled the day. Relax and think.

Rudy
 

Kevin R. Cashen

Super Moderator
The Currie point method is so prevalent because there are so many folks who use forges and other non-controller run heat sources, not that I am criticizing this but instead simply pointing out that if one has a controller ran heat source one simply puts in the desired temperature numbers for the alloy; so for folks with controllers it is a moot point. If any folks get a lot of e-mails and phone calls regarding heat treatment issues, they are welcome to trade places with me anytime:3:. And I know the reason for this. We can see, with our own eyes, if we got everything else the way we want it with a knife, but not so with the heat treatment. It is this mysterious, doubt creating, nature of one of the most critical aspects of knifemaking that makes us desperate for answers, reassurance, and any kind of indicator, guideline or reference point and the more foolproof we can believe it is, the less anxiety we have. You should see me when I am working with a new alloy that I cannot get Rockwell numbers off from, I am like Sheldon Cooper trapped in a poorly maintained porta-potty.

If you follow the Fe/Fe3C phase diagram the Currie point all makes sense and works, but that diagram is based on equilibrium conditions and cannot apply to a dynamic system that involves heating or cooling without holds. It also only applies to basic iron/carbon systems, any alloying present completely invalidates it. I have done tests where I actually quenched steel from exactly 1414F, something you can't do without very precise controls, and the lower Rockwell and mixed phases were not pretty, but it would skate a file just fine.

But here is what the guys who work with forges have going for them- guys who forge prefer simpler alloys, and so they are much closer to the basic iron/carbon system described in the Fe/Fe3C phase diagram. The second thing they have going for them is the lack of control one has with such a heat source. Yes, I did say the lack of control is a benefit there:3:. With a heat source such as a forge it is nearly impossible to nail the Currie point dead on and you will almost invariably overshoot it by the time you get the entire blade up to heat. So in this case the magnet is an excellent tool to keep from overshooting the temp since you will often overheat about 50F -75F. So 1414F plus about a 50F-75F margin of error puts you right in the sweet spot for most basic carbon steels, but if you had shot for 1475F to begin with your margin of error would have you much too hot by the time you had things worked out.

Guys who use the magnet with something like 1084 heat it, check it, quench it and are happy. The forge fire gave them a pretty nice knife with that simple steel with one simple operation; with the exception of some Mn, it is that simple iron/carbon system. Now add just a little chrome and watch what happens to the simple magnet approach, suddenly folks using the magnet are finding better results by having to have a second or third go at the hardening operation. The added alloying pulls all the numbers much farther away from the system where the magnet and no soak times work so well. Now, without a controlled soak, you have difficulty obtaining full solution without taking the temperature beyond the safety zone surrounding the Currie point; rather than risking overheating, the safer route is to repeat the operation inside the safety zone until you have proper solution.

The more accurate method is to watch for decalescence, but that is something that takes time and patience to develop the skills to do, the magnet can be done your first time heating steel. In training your eye to recognize proper temperature you will then see the actual transformation as it occurs and you will develop a much closer working relationship with your steel of choice, but we are all human and you will have your bad days. The magnet gives more of a feeling of a safety net. And the controller, of coarse, is the ultimate safety net by eliminating human error altogether; it is for this reason that I encourage all makers to learn to heat treat by eye before moving onto controllers. Then when they combine their knowledge of color with what the exact temperature really looks like, they are practically human pyrometers. I have had some say they doubt I know how to heat treat without my fancy gadgets; they obviously are not aware of the years I did it by eye with a forge, and are quite surprised when I show up to a demo somewhere across the country and move and oven or a gas forge out of the way so I can demonstrate heat treating in a coal forge.

I don't have any problem with folks recommending or using the magnet since, for the reasons I mentioned, it can work. I do have a problem with calling it a perfect, or foolproof, method for determining temperature, because that just is not true. One more huge issue can be summed in one word- "hysteresis". Rather than typing another dissertation I will allow those interested to look it up.
 
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LRB

Well-Known Member
So Kevin, what you're saying, more or less, is that sometimes, under some situations, ignorance not only can be bliss, but also productive though in an incomprehensive manner. I get that. A good explanation.
 

Knifemaker.ca

Dealer - Purveyor
Hysteresis: is the dependence of the output of a system not only on its current input, but also on its history of past inputs. (Credit Wikipedia)

FWIW, I got to that understandable definition after several painful excursions through verbal diarrhea. (..or what others might describe as appropriate technical precision) :3:

Rob!
 

samuraistuart

Well-Known Member
I have never heard anybody say that a carbon steel should be quenched AT non magnetic. When I first got into this, I was ALWAYS told (and I understood why), that you had to go "a shade or two more", than when the magnet stops sticking (1414F). Maybe someone somewhere is saying to quench AT the point the magnet fails....but it sure isn't right. And, like Kevin said, this recommended with those heat treating in forges, where exacting control of temps is difficult at best, if not impossible.
 

scott.livesey

Dealer - Purveyor
temp sticks would work for gauging temperature. for control, a muffle(a piece of square steel tube) would help in two ways. the temperature inside the muffle will rise and fall slower than just sitting in the fire. it is also dark inside, so i would be easier to judge color.
Kevin: saw the Nova piece you were in this morning. was the sword done just by color or was there a thermocouple hidden somewhere?
 

scott wheeler

Active Member
Being new and only heat treating for a year or so with a forge the magnetic approached has work ok for me. I don't use it as a benchmark for the quench but what it has taught me is better understand temp colors when HT so I guess ignorance is bliss.
 

Kevin R. Cashen

Super Moderator
temp sticks would work for gauging temperature. for control, a muffle(a piece of square steel tube) would help in two ways. the temperature inside the muffle will rise and fall slower than just sitting in the fire. it is also dark inside, so i would be easier to judge color.
Kevin: saw the Nova piece you were in this morning. was the sword done just by color or was there a thermocouple hidden somewhere?
The only thing I can say for certain is that the Ulfberht heat treatment was done without any Cashen; I don't do flaming quenches. Due to my principles on such things, the film crew found me a little more difficult to work with than Ric, and I sort of got the title of the "uncompromising artist." I was originally just a consultant until Ric asked that I be present for the shooting because that is the kind of guy Ric is, i.e. willing to share the spotlight with friends, so despite my being difficult to work with the filmmakers still included my face a couple of times.

Back on the topic of the magnet, I think it is great practice to watch the shadows of decalescence and to explore them with the magnet, you will then get an idea of where the transformation effects are related. Also, it is very enlightening to watch where recalescence occurs in relationship with decalescence and ask yourself if you would want to quench from that color/temperature? I is the Currie point of Fe that is 1414F so just remember that what is occurring in the electron cloud of the iron atoms to bring about the ferro-magnetic changes does not reflect what is happening with any of the other elements present.

I did a study about three years ago regarding the Currie point and solutions in the most commonly used blade steels (5160, 1084, O-1, L6, W2, 52100 etc...) and found a range from 1414F up to 1428F where the magnet starts to let go and you need to then achieve the solution that this shift makes possible but does not guarantee.
 
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Smallshop

KNIFE MAKER
I see that show listed on netflix. Haven't had time to watch it yet. What is a "flaming quench"? Something they used to do, or something hollywood has found more interesting for viewers?
 

Doug Lester

Well-Known Member
I think it was done for dramatic effect. The sword blade in question was quenched in a normal fashion and the flame flashed up around it in the tank. Ric then removed it from the tank so that the oil on the blade flamed up. I doubt that it supplied enough heat long enough to temper the blade. Actually there is some question if and how this was done. Much of what was done in this period is open to debate because there is little written down.

Doug
 

scott wheeler

Active Member
Guys, I'm a little confused, did I miss something? Was the blade not quenched enough in the oil, and Kevin I apologize for my ignorance but what is it that your protesting? Was there some inaccuracies? I watched the entire program and thoroughly enjoyed it.
 

Kevin R. Cashen

Super Moderator
The program was fine, I have been involved behind the scenes with a few T.V. things now and this one was probably the best yet. But in any film endeavor there seems to be this inexplicable struggle between educating the audience and entertaining the audience, I don’t understand why good information can’t do both and thus I tend to be more difficult for the producers to work with.

Let me focus on a positive example from the show. John Clements did wonderful job in explaining and demonstrating how the katana is a fine sword, but not the nonsensical ultimate weapon that Hollywood has so grossly overhyped it as, and how the Ulfberht or any number of wonderful swords are easily its equal. You won’t see that awkward bit of truth touched on in many other T.V. shows.

Also to their credit, they got Ric Furrer, somebody who is actually an expert in crucible steel and can make it, rather than some joker who could keep them entertained while making it up as they go.

I could tell many stories about the filming, but it would only amount to so much thread drift in a thread that is supposed to focus on the Currie point in steels.
 

scott wheeler

Active Member
The program was fine, I have been involved behind the scenes with a few T.V. things now and this one was probably the best yet. But in any film endeavor there seems to be this inexplicable struggle between educating the audience and entertaining the audience, I don’t understand why good information can’t do both and thus I tend to be more difficult for the producers to work with.

Let me focus on a positive example from the show. John Clements did wonderful job in explaining and demonstrating how the katana is a fine sword, but not the nonsensical ultimate weapon that Hollywood has so grossly overhyped it as, and how the Ulfberht or any number of wonderful swords are easily its equal. You won’t see that awkward bit of truth touched on in many other T.V. shows.

Also to their credit, they got Ric Furrer, somebody who is actually an expert in crucible steel and can make it, rather than some joker who could keep them entertained while making it up as they go.

I could tell many stories about the filming, but it would only amount to so much thread drift in a thread that is supposed to focus on the Currie point in steels.
Thanks for the explanation Kevin, I understand about the entertainment part but I'm really interested in the science. It's PBS/Nova its suppose to be about science and not meant to entertain, I'm glad you kept focus on the topic at hand. That's why I joined this forum!
 

Doug Lester

Well-Known Member
The NOVA and other PBS programs are supposed to be educational but they also have to be entertaining to keep you in front of the TV. They try to keep things accurate but don't forget that there can be differences of opinion-like did Shakespeare or Bacon write Shakespeare's plays. Even the above show on the Ulfberht sword stated that there was a dispute as to whether or not these things were tempered.

Doug
 

BossDog

KnifeDogs.com & USAknifemaker.com Owner
Staff member
does anyone have a good video showing decalescence and/or color shades of the proper quenching temp?

ok...back after a quick look on youtube

recalesence video

[video=youtube;33neAGXxZ94]https://www.youtube.com/watch?v=33neAGXxZ94[/video]
 
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Kevin R. Cashen

Super Moderator
That is a great video!:s11798: It is always easier to show recalescence since all you have to do is remove the heat and watch it happen.
 
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