details for heat treating 5160?

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Smallshop

Smallshop

KNIFE MAKER
The most detailed info I could find on heat treating 5160 was from Ed Caffrey on another forum 13 yrs ago:
(Thank you Mr. Caffrey! I appreciate this kind of detail and the analysis you did to prove your reason for multiple quench.)

"Over the years of experimenting I have found that steels that contain a SMALL
percentage of Chromium will benifit in two ways from doing a multiple quench,
and allowing the blade to cool down in the oil (completely) between
quenches.
The first is obvious, three quenches ensures that the steel is
completely converted. The second, and what I believe is the greatest benifit is
the reduction in grain size that is achieved by allowing the blade to cool down
in the oil between quenches.
A few years back I did some experiments where I
quenched four blades of 5160. I quenched the first blade once, the second one
twice, and so on. Once each blade was quenched I never took it out of the oil. I
simply set it on edge in the bottom of the tank, and allowed to cool down with
the oil. (which took overnight). I continued the process until the final blade
had received it's fourth quench. I then tempered each at 350F for three two hour
cycles, allowing each to cool to room temp between quenches. Once all the blades
were done, I sent them to be spectrographed. As a base line I also sent a blade
of 5160 that had been single quenched, and then immediatly tempered (not allowed
to cool in the oil)
The results made a believer out of me. Each blade, 1
through 3, had successivley smaller grain size, the blade that had been quenched
four times had the same grain size as #2. The final result was that the grain
size in the blade that had been quenched three times, and allowed to cool in the
oil was .79 microns, as compared to the single quenched blade, which had a grain
size of 1.91 microns.
The only thing that was done differently was allowing
the blades to cool down in the oil between quenches.
Afterwards I made a few
more blades to destroy, using the same basis and found that the blades that are
cooled int he oil between quenches usually display approx. 15% more cutting
ability, and much more durability. If you add a sub zero quench to that, cutting
increases another 5-10%! That may not sound like much to some, but it's a pretty
dramatic increase. I still have one of those blades hanging in the shop. It has
been through the ABS tests 18 times, including the 90 degree bend, and the edge
has not yet cracked.
Don't get me wrong, everything has to be done correctly
up to the quenching point to achieve what I've talked about. But with proper
handling including, forging, normalizing, annelling, and then heat treat, it is
very doable."

I know this was a while ago. Have any of you also used this method? Mr Caffrey, if you happen across this, have you modified this technique any? It sounds well worth the extra work. Would you use the same oil for all three quenchs? And if so, which would be best for 5160.

Thanks for any input from you experienced heat treat/knife making guys. I'm thinking of playing with this to learn my new furnace (if it ever arrives....) It's fairly cheap to buy and while the triple quench is more work I think perhaps more forgiving if I'm off a bit on something. (time/temp/quench motion/etc)

I do have a Rockwell tester so I can at least test for final hardness.
 
First and foremost, keep in mind that what you copy/pasted is 13 years old. I say that as a preamble to the following statement: Knifemaking is ever evolving. That being said, pretty much all that information is still valid, but by "tweaking" the process here and there, I've managed to make some slight improvements over the years.

The main point of that information, at the time I wrote it, was to make the point that it's not about any single step in the knifemaking process....it's about ALL the steps, done in a specific manner, and a specific order, and dealing with all the variables that occur within each step that determine how "good" or "bad" the finished product come out.

Mr Caffrey, if you happen across this, have you modified this technique any?
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Yes, nothing major, but as I mentioned, it's all about making "little" tweaks here and there....all based on variables that can be slightly, or even majorly different from shop to shop. I would hope that others would take that information, use what portions that fit their needs, and add their own "tweaks" to achieve their desired results.

Would you use the same oil for all three quenchs?
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Yes, as a matter of fact, several years ago I switched over the Parks 50 quenchant for most of my steels, however, I kept a seperate tank of mineral oil in the shop, that I use specifically for multiple quenching 5160. I tried to emulate 5160 results using Parks 50, but never was able to match all of the characteristics that I valued.....so the Mineral oil tank stays! :)

I'm thinking of playing with this to learn my new furnace (if it ever arrives....) It's fairly cheap to buy and while the triple quench is more work I think perhaps more forgiving if I'm off a bit on something. (time/temp/quench motion/etc)

I do have a Rockwell tester so I can at least test for final hardness.
Click to expand...

I'll caution you on something....I assume you're talking about a "heat treat" oven? If so, I can tell you that you will not realize the same results using a heat treat oven....the results I achieved where using a torch...and I have tried to emulate it using a heat treat oven. Without writing a huge explaination, I can tell you that it's way different using an oven versus using a torch.

Finally, Your rockwell tester will be of little use when it comes to a multiple quenched blade. It's simply because to achieve correct readings from the tester, the impact point MUST be flat/square/true.....anything with a bevel or angle of any kind, will skew a hardness test results.....you're also dealing with a single piece of steel (blade) that has (hopefully) a hard edge, and a soft back......so unless you do the following, it will be impossible to achieve accurate Rc numbers. The pieces of 5160 that I had tested were (give or take a few thousandth) .125" and .250" thick X 3" square. This was done after many months of preliminary work/experimenting, using rough ground blades (finished out to 120 grit prior to the heat treating process)

In the end, you MUST remember that knifemaking is every evolving. It's not a matter of finding a specific heat treat, grind, or anything else, and sticking with it....it's about constantly seeking improvement throughout the entire process. It's also about understanding that the knifemaking process is "fluid" and is not constant from shop to shop, or person to person...what works for me, is not necessarliy "cast in stone" for myself or anyone else.

I might get boos and hisses for this, but in recent years there has been what I consider a serious issue with people and knife forums....that being a lot of what I call "arm chair experts". Those people who have read a book, or read a bunch of posts that someone else has written, concluded it as fact, without ever having tried any of it for themselves, then posting/spreading it as "knowledge"....therein lies the trap for other who search for answers on various forums.... you cannot take anyones word (including mine)....but rather you must take the information, find out for youself if it's valid for YOU, and make your conclusions based on YOUR results.

I've actually stopped visiting a couple of online knife forums for that very reason.....because I got so tired of being "called to the carpet" by people who I know have zero experience, but yet are willing to tell me that I'm "dead wrong" in how I do things. Even now I get a bit riled when I think about it......and without trying to be a pompus butthead, I have both a JS and an MS stamp, with 30 years of experience to lend validity to may claims. OK, I'll stop now.... :)
 
Thank you for the thoughtful reply Mr. Caffrey. I hesitated quoting something that old but it was the one post I had found that wasn't just generalizations.

Perhaps using the oven heats more of the tang than necessary and affect the quench. Either way, I will probably work with A2 to begin learning the furnace (when it get here) It and O-1 are the only steels used for knife making that I have experience with. And I love A2....one of the most stable tool steels to work with.

In regard your forum experiences:I have quit giving how to advise on a machining forum for some of the same reasons you state above. I now just go there to share chuckles and homespun philosophy. I'm 53, went into a private trade school at 15, was making stuff in dad's shop at 12, did an informal apprenticeship in a tool and gage making shop at age 19, worked as a journeyman toolmaker for 6 yrs, went to night school to learn CNC programming, Worked in a production job shop as a working foreman in first the mill dept and later the lathe dept. got tired of production machining and went to work as a model maker for a product development firm and eventually became supervisor of the design studio while concurrently opening my own prototype shop which I've now run for 13 yrs. So having guys with a whopping three years experience "shout me down" on a forum concerning methods I'm already making a living with......sheesh. And it always seems to be the "threebies" as I call them. They have enthusiasm, some genuine skill, a little knowledge, very little experience, and lot o' opinions.....:20:

I certainly do not know everything. I have also come to realize that in any shop environment (I'm betting knife shops are no different....) that there are a myriad of variables which are difficult to identify that goes into each persons methodology. Often what works for one guy cannot seemingly be duplicated by another. Human nature being what it is, always seems to contest the advise not the implementation of the advise.....

I think this is why guys like to visit shops. There is a lot of subtle cues you get by watching someone do something that they themselves have long ago tucked away in the ol' memory banks and aren't even consciously aware of anymore......anyone that doesn't think this is so, let a 15yr old come watch you work for a while. questions, questions....and more questions.:biggrin:

In defense of some of the guys I have "crossed blades with" on forums over the years.....an old boss of mine told me many moons ago (this is a paraphrase) that to work with metal you have to be stubborn, and opinionated, and strong willed because metal doesn't give it up easy.....he then went on to say he thought I would become a good machinist. I was never sure if he was trying to complement me or just calling me a young idiot.....(which I was back then...a bonafide threebie)

Sorry for the filibuster......I'm rested up and on my second cupa joe...and you all are just the unlucky recipients of the morning caffeine rush.....:eek:
 
Normalize: Heat to 1600 or so for 5 to 10 minutes and air cool. This may or may not be necessary, depending on what condition your steel is in before hardening (as forged, hot rolled, annealed, already hardened, etc.)

Heat to 1525 or so and cool in air. Again, this may not be required. You'll have to check and see if it helps.

Heat to 1525 or so and quench in medium speed oil. The little bit of Cr in 5160 allows a medium speed oil to get the job done. If you have access to a hardness tester, check a coupon (flat and polished) here. Ideally you get between 62 and 63, but may be lower, depending what the exact carbon % is in your steel. Should be above 61 in any case.

Temper to desired hardness. I'd recommend avoiding tempering temperatures between 450 and 650. This range can lead to embrittlement. Temper twice for 0.5 to 1 hour each time, water quench between and after final.

Handle, sharpen, and enjoy. Straighten with various methods of your choice between tempers, or add a 3rd or 4th if needed.
 
Mr. Caffrey, after rereading the thread I have a couple of question. What is the mechanism that is involved with grain refinement during the cooling in the quench? Those grain sizes are extremely fine, even finer than those claimed by Ed Fowler and are in fact right off the ASTM scale, which stops at 15. Last I saw Mr. Fowler's blades were around a 13 or 14.

Also, what type of spectrograph did youhave done? Did it also provide chemical analysis? I occasionally have need of both types of information, and a single test that will provide them would be handy.
 
EdCaffreyMS;289656 Yes said:
So Ed what you are saying," is that that to work with metal you have to be stubborn, and opinionated, and strong willed because metal doesn't give it up easy....."
...AND
You must form YOUR OWN OPINIONS!! Do YOUR OWN Testing, try to find what works better, best, and Bestest!!! And have the data to back it up? Is that what you're saying Ed, is that Steel is a Cold hearted B! And that she does not care if you make the very first thing! Much less a knife, it's her job to sit there and tell you, " you can't" and she is very happy as long as everyone either believes her or thinks they have to follow the crowd all the time! And never learn anything new earth shocking, because that may just be her next secret that she is forced to release and by force, I mean to say, "we merely asked the right question".
Rex
Btw Ed, I finally understand why you want everyone to do their own testing, their own discoveries, Thank You for that , Rex
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me2 said:
What is the mechanism that is involved with grain refinement during the cooling in the quench?
Click to expand...

If the blade is allowed to cool then the heat in the oil could be auto tempering it vs letting it cool more rapidly if you take it out of the hot oil. The very low temperature tempering for martensite produces transitional carbides, this is stage I tempering. If this is happening then these carbides will cause a refinement of the austenite grain size in the next quench. This will keep happening each successive quench. It is possible that it could be increased further by a other carbide manipulations. This is of extreme importance now because it is how ultra-high carbon steels are being processed to provide very high ductility and compressive strength with literally nano-scale austenite by using martensite as a preparatory stage for the final hardening due to the fact that cycling from martensite to austenite has such a strong refinement on grain size. It can also be done through mechanical processing at elevated temperatures (near the recrystallization point) but that is much harder to do obviously than cycling.
 
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Ed: After following your posts for a number of years, let me just say that if you told me it was raining, I'd grab my umbrella.

Thanks for all your help and advice.

Bob

"Sometimes I wonder whether the world is being run by smart people who are putting us on or by imbeciles who really mean it."
-Mark Twain
 
"If the blade is allowed to cool then the heat in the oil could be auto tempering it vs letting it cool more rapidly if you take it out of the hot oil." It it to my understanding that this is backwards. I'm not expert, so I had to ask around of this very issue of leaving a knife to cool in the oil vs taking it out. "If left to cool in the oil, 100% alpha martensite will be formed. If taken out of the oil once the PN has been reached and Ms, and allowed to air cool, then as much as 30% of the martensite will be forming at temperatures within the tempering range, causing some auto tempering." A reading of both samples would give the same Rc number, tho.

I could definitely agree, tho, if the volume of the oil was not sufficient to actually cool the blade all the way thru Mf.
 
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samuraistuart said:
It it to my understanding that this is backwards.
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To clarify, this is the procedure I was responding to based on the question that me2 raised :

"As a base line I also sent a blade of 5160 that had been single quenched, and then immediatly tempered (not allowed to cool in the oil)"

Now a few things need to be understand, I am simplifying some things of course but these are generally true. Martensite transformation doesn't keep happening at a given temperature, if you hold the steel at a temperature under the Ms point you don't get increased martensite transformation, you have to keep cooling it and as you cool it the further you get to Mf the more martensite forms. Tempering is different as it (again generally) takes place by diffusion based processes and thus it continues at a given temperature if the time is increased.

Now we have two cases :

a) The blade is quenched in oil and left to cool in oil over night and then tempered

b) The blade is quenched in oil, removed once the oil stops cooling it and then tempered

Now if you stop both process at the same point and look at the blades right before the second one is taken out then they are both the same micro-structure wise, the question then becomes what happens in these two cases :

a) the blade slowly decreases from the oil quench temperature to room temperature

b) the blade is subjected to a tempering temperature

Now the second one (b) is straightforward. The tempering temperature of 350 F is in the first stage of tempering where carbon diffuses out from martensite and forms vs fine transition carbides. The other tempering reactions (transformation of austenite, cementite formation, loss of tetragonality of martensite) start to take place above 200 C.

Now what happens in the first case (a) ? The blade is still hot and this heat has gone into the oil, that heat keeps the temperature of the oil elevated which is why Ed noted it takes over night for the blade to cool. The blade is then subjected to two processes which happen at the same time :

-the temperature is decreasing from the Ms point to room temperature which means the formation of martensite increases, how much martensite forms depends on the composition of the austenite and the resulting Mf temperature, it is however extremely unlikely it will have zero retained austenite for a number of reasons

-auto-tempering will start because the steel is also at the temperature at which the diffusion processes take place and the carbon starts coming out of the steel and forming transition carbides. This is also being allowed to happen for an extremely long time (at least 8-12 hours as it notes over night) and thus there is a very long time and thus the diffusion is likely maximized or at least very high

Thus, in short, the original statement that the slow cooling through the first state of tempering is likely creating a significantly volume of transition carbides and this is known, through quench cycling to produce ultra-fine grain. It is used for example to promote hyper toughness in UHC steels through this mechanism.
 
EdCaffreyMS said:
I've actually stopped visiting a couple of online knife forums for that very reason.....because I got so tired of being "called to the carpet" by people who I know have zero experience, but yet are willing to tell me that I'm "dead wrong" in how I do things. Even now I get a bit riled when I think about it......and without trying to be a pompus butthead, I have both a JS and an MS stamp, with 30 years of experience to lend validity to may claims.
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With all due respect Ed, do you really want people to accept anything you say regardless of its content?

Would you not want people to actually think about what you say and see if it makes sense? Do you not want people to not only question what you say but demand that you have justification for any claims you make based on both direct empirical data and/or inference from known materials behavior?

This questioning, this demand for justification, this necessity for evidence and the refusal to accept claims based on authority - these are the fundamental aspects of science.

Now does it get annoying when someone with very little knowledge says you are wrong and it is obvious they are making this conclusion without sufficient rationalization? Well to me it is amusing as they are making the very mistake they are accusing you of making (lack of justification)?

The problem is that they don't know they don't have proper justification, from their perspective they do so should they ignore it? Should they ignore what they deem rational and just have faith and accept irrational conclusions? Of course not, they should point out what they see are false statements that is how we learn, by an open dialog and criticism of irrational claims.
 
CliffStamp said:
If the blade is allowed to cool then the heat in the oil could be auto tempering it vs letting it cool more rapidly if you take it out of the hot oil. The very low temperature tempering for martensite produces transitional carbides, this is stage I tempering. If this is happening then these carbides will cause a refinement of the austenite grain size in the next quench. This will keep happening each successive quench. It is possible that it could be increased further by a other carbide manipulations. This is of extreme importance now because it is how ultra-high carbon steels are being processed to provide very high ductility and compressive strength with literally nano-scale austenite by using martensite as a preparatory stage for the final hardening due to the fact that cycling from martensite to austenite has such a strong refinement on grain size. It can also be done through mechanical processing at elevated temperatures (near the recrystallization point) but that is much harder to do obviously than cycling.
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You are completely off base here. It is IMPOSSIBLE for quench oil temps., (130 or less) to have any tempering effect on a blade. You don't get any actual tempering effect until you get to at least 250, more like 300. Stuart is correct, if you're shooting for auto-tempering, you must remove it from the oil in the 300-400 degree range.
 
The way Darren explained it is kinda how I see it in my head. I understand what Cliff is saying, tho. The oil is 130F to start with. But place a blade in there at 1500F or whatever, and the oil is going to warm up. My thought tho was, that especially with commercially produced quenchants, and proper movement/agitation/volume, the blade could be in contact with relatively cool oil throughout the quench process, from aust temp to ambient.
 
Darrin Sanders said:
You are completely off base here. It is IMPOSSIBLE for quench oil temps., (130 or less) to have any tempering effect on a blade.
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Darrin,

Please read what I wrote specifically, I was not saying that tempering, as in reduction of hardness was happening. The softening happens in the second and third stage of tempering which becomes significant above 200C. Above that temperature the transition carbide is replaced by cementire which coarsens by Oswald ripening, the martensite loses tegragonality and gradually becomes ferrite and the austenite is replaced by various phases (depending on temperature and alloy content).

What I was talking about was the formation of transition carbide which happens at much lower temperatures and is most significant in the range of 100-200C. Again this range won't soften the steel, but it has a dramatic change on the micro-structure even though there is little no to HRC change and in fact it will even increase in hardness in some steels. It does in 1095 for example. This by the way is why some makers like Roman Landes quench after tempering as they want to minimize precipitation which will happen as the blade cools from the tempering temperature.

Now is it the case as to why it happens, I don't know. However the experiments that Ed noted don't provide strong evidence that it is even the causal effect as there are multiple things which changed between the control and reference group so it can't be said what is causing the observed effect. It is however well known that carbide precipitation in UHC steels and quench cycling does cause grain refinement though this is usually achieved by something similar to :

-quench and then temper hot to precipiate carbides strongly
-quench and temper low to produce the working micro-structure

In the second stage the fine array of carbides will both pin the austenite and serve as nucleation sites and the higher the number of nucleation sites the finer the austenite. This can easily be done to achieve ASTM 15 and above grain sizes. It is well documented in the literature.

However, I noted it was only a possibility because I have not seen anyone look at quench cycling from low tempering temperatures, or quench cycling from some kind of long scale room temperature hold. These are usually argued against because untempered martensite can autocrack. But again we have to realize that in knives the local strains we are talking about are fairly reduced compared to complicated and very large parts which can be subjected to severe strains because of uneven hardening.
 
Stuart, you are correct, with proper agitation the oil should stay about the same temp. during the whole process. If one blade causes your oil temp. to rise more than 5 degrees you aren't using enough oil.

Cliff, you stated, and I quote, "If the blade is allowed to cool then the heat of the oil could be auto tempering vs letting it cool more rapidly if you take it out of the hot oil". 130 degrees will not have a tempering effect on a knife blade. Long winded posts and scientific names will not change this fact. Steel will cool to the oil temp a lot quicker in the oil than it will in air. The statement you made is untrue and as long as I am a mod here I will correct mistakes when I see them.
As far as "transitional carbides", I don't know anything about them and don't really care. As a knifemaker, I know what works and what doesn't. This forum is for education not confusion so please stop posting false info..
 
Darrin Sanders said:
As far as "transitional carbides", I don't know anything about them and don't really care.
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They are part of tempering and they form at very low temperatures as they are diffusion based. The diffusion of carbon is one of the reasons why austenite stabilizes for example at room temperature and why if you want minimum retained austenite you have to do a continuous quench. Diffusion of carbon will pin the dislocations at the martensite/austenite interface and stabilize the austenite and prevent it forming martensite even at sub-zero temperatures.

What is your reason for saying that tempering doesn't happen? I assume it is something similar to the fact that you don't see any change in hardness (or possibly toughness)? As I said, that is because there are many stages of tempering which is a complex process in which there are many phase transformations happening at the same time. The ones which soften steels do indeed take much higher temperatures. Tempering is simply the process of holding a steel (in this case) below the critical temperature.

As noted there is more to tempering than softening steel, there are four general stages of tempering all of which have varied effects on steels and they happen over a very wide range of temperatures and the one that I referenced happens at the lowest temperatures as it is based on diffusion of carbon to a meta-stable carbide form.
 
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me2 said:
What is the mechanism that is involved with grain refinement during the cooling in the quench?
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Chris,

I knew I had read this before, very low tempering but it took awhile to track it down. I got the temperatures a bit mixed up, what Ed is sering is most likely not transition carbide but something else. I blame the fact I mixed it up as the original citation used the Kelvin's scale. It was Nagajura's work. He has look at the tempering reactions in steel at very low temperatures and identified two stages which take place below the classic first stage of tempering (100 to 200C). They are :

-tempering between 0 and 90C, carbon atom clustering on the 102 martensite planes

-tempering between 60 and 80 C, formation of Fe4C orthorhombic structures

I could not turn up what happens if you cycle quench after forming these structures, however the diffusion of carbon at those temperatures does form distinct structures and it is likely they will effect the nucleation of austenite in repeated quenches.

Thus from a metallurgical perspective there is a physical basis for long period low tempers doing something, as to if it refines the grain, again, nothing on that I can see in the literature but other work points to it as plausible. In short, it doesn't look like what Ed is saying opposes what is known in metallurgy.
 
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CliffStamp said:
They are part of tempering and they form at very low temperatures as they are diffusion based. The diffusion of carbon is one of the reasons why austenite stabilizes for example at room temperature and why if you want minimum retained austenite you have to do a continuous quench. Diffusion of carbon will pin the dislocations at the martensite/austenite interface and stabilize the austenite and prevent it forming martensite even at sub-zero temperatures.

What is your reason for saying that tempering doesn't happen? I assume it is something similar to the fact that you don't see any change in hardness (or possibly toughness)? As I said, that is because there are many stages of tempering which is a complex process in which there are many phase transformations happening at the same time. The ones which soften steels do indeed take much higher temperatures. Tempering is simply the process of holding a steel (in this case) below the critical temperature.

As noted there is more to tempering than softening steel, there are four general stages of tempering all of which have varied effects on steels and they happen over a very wide range of temperatures and the one that I referenced happens at the lowest temperatures as it is based on diffusion of carbon to a meta-stable carbide form.
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You're trying to twist this around to justify incorrect information and I WILL NOT allow it. Show me a data sheet (any data sheet) that quotes a tempering temp. of 130 or less. There are definitely things happening at those temps. but (for knifemakers) that temp. range is NOT considered part of the tempering process. When a knifemaker talks about tempering he is talking about temps. of 300 or higher.
 
Darrin Sanders said:
You're trying to twist this around to justify incorrect information and I WILL NOT allow it.
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Darrin,

There is no twisting, you simple seem to not be able to understand that tempering of steel happens even at room temperature, I noted not only the exact temperatures but the actual materials reference to the published data which is in a peer reviewed materials journal. There are carbon structures formed during the tempering of steel which happen even at room temperature.

As for your warning in PM not to post false information, there is no need for a warning. As a moderator you represent this form and you have clearly shown that actual materials data isn't desired so no issue for me, lots of places want actual discussion of materials data, no need to talk to people who don't want it.
 
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