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Time from quench to temper?
- Thread starter AA Forge
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If forging and hardening was done right you can put your blade in the freezer overnight with out having any problems before tempering and usually gain a couple of points on the RC scale. When blades need to be tempered immediately you are probably doing something wrong, usually overheating them.
This is my experience working with 52100 and quality 5160..
This is my experience working with 52100 and quality 5160..
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Ive set blades aside for weeks before tempering, Havent had a problem yet, If its gonna break or crack its probably already happened while quenching
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Something to consider in high alloy steels (stainles and complex tool steels) is a second purpose of the temper. In those steels, not only are you tempering the newly formed martensite and thus relieving stress within the steel, but you are also creating new martensite which is converted from retained austenite (RA). That is why many higher alloy steels require 2-3 tempers. You stress relieve and create new martensite with the first temper, and then you stress relieve the newly formed martensite with the subsequent temper.
In those situations, if you wait too long before tempering, the retained austenite will stabilize, and you will be unable to convert it to martensite with a temper. For those blades, I try to get them in the oven as soon as possible after quenching. As to exactly how long you have? I couldn't say, but I'd do the first temper within a couple of hours.
The reason Ed suggested putting them in the freezer right after quenching is because cooling the blade significantly below room temperature after quench will also convert RA. I use liquid nitrogen for that purpose, but others use a dry ice slurry with good success. If you don't have access to a decent form of cryo, the freezer as Ed suggested may help some, though I don't know that it's cold enough to create significant conversion.
--nathan
In those situations, if you wait too long before tempering, the retained austenite will stabilize, and you will be unable to convert it to martensite with a temper. For those blades, I try to get them in the oven as soon as possible after quenching. As to exactly how long you have? I couldn't say, but I'd do the first temper within a couple of hours.
The reason Ed suggested putting them in the freezer right after quenching is because cooling the blade significantly below room temperature after quench will also convert RA. I use liquid nitrogen for that purpose, but others use a dry ice slurry with good success. If you don't have access to a decent form of cryo, the freezer as Ed suggested may help some, though I don't know that it's cold enough to create significant conversion.
--nathan
Mr Fowler, can you expand a bit on the specific circumstances of this process and the results you've seen in your lab testing? I'm specifically interested in the results of the metallography of samples treated in this manner. Have you seen a significant reduction in retained austenite by cooling to the standard 0F range of a home freezer? It has always been my understanding that cryogenic conversion of retained austenite didn't begin until approximately -100F. I know my freezer isn't that cold
As for a response to the OP. If you're working with hypereutectoid steels (1095, W-1, etc) I believe you're more likely to experience issues here. Of course it also depends on your quench medium to a great extent as well. The more violent the quench, the more stress you generate, the quicker you have to temper. An engineered fast quenching oil will provide the speed you need to properly quench your steel, while reducing much of the stress created by a quenching medium such as water or brine. I'd recommend you go take a look at the working the three steel types sticky for a little more clarity on the differences in the three major types of simple carbon steels.
-d
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Ed, let me start by giving you an apology for all the times I have had to counter your advice, but it will be hard to understand what it is I am apologizing for because I firmly believe that giving a counter is entirely the right thing to do. What I want to you know is how unpleasant it really is for me to be in opposition to you, and I mean that with all sincerity, as I have expressed in private communication in the past. You have often said how important it is to allow your critics to be a positive motivator, I am perhaps one of your bigger critics, but find no pleasure in it at all and would take great comfort in your finding positives in my opposing positions. So know that having to post the following will probably ruin the rest of my day but my integrity and passion for correct information in our business will allow me to do no less. Please believe me that I only oppose the information and not the man.
AA Forge came here looking for and answer to a basic question and I see him as being sent away with information that could lead to a lot of heartache in his future if he follows it. I believe anybody knowing better and reading this thread should have the conscience to speak up and give another perspective rather than letting him, and all the other guys seeking that answer, leave with just the one perspective given thus far.
From no other source, except a portion of bladesmiths, will one get the advice to leave parts for any extended period without a temper in a high carbon steel. One thing that may need to be addressed is whether AA Forge will be edge quenching or through hardening, and then weigh it heavily against the knowledge that Ed edge quenches, a possible misunderstanding there.
Extraordinary claims require extraordinary evidence, and the claim that the heat treater is doing something wrong if they need to temper immediately, is a very extraordinary one that takes virtually every other heat treater, and almost 200 years of ferrous metallurgy, to task. The very nature of steel, and all the mechanisms that go into hardening it, counter the statement that freezing an untempered blade overnight is without risk. Adding to the problematic nature of the claim is that if one gains any points in Rockwell from such a treatment there is but one expalination for it, and that is retained austenite (nothing else converts to martensite to give a gain in Rockwell). Ironically this is a clear indicator that something was certainly done wrong in the heat treatment, and the main contributing factor for retained austenite in high carbon steels is overheating and putting too much carbon in solution. Even those who treat steels with alloying that makes RA unavoidable will utilize a very slight temper to stabilize the blade before cryo.
AA Forge, you have one side of the issue, now I offer all of my experience, observations and study, I also offer the findings and experience of scores of other knifemakers who I do not believe are doing their heat treatment incorrectly. To that let me add Bain, Grossman, Palmer, Luerssen, Verhoeven, Moniz, Smith, Siebert, Doane, Brandt Etc and all the other guys who wrote the books on the shelves behind me as I write this, as well as ASM. I could go on, but the point is that I concur with virtually every other industry working with high carbon steel in saying that a properly hardened piece of high carbon steel needs to be tempered to some degree as soon as possible if it was hardened correctly.
AA Forge, you do not have to get ulcers if you dont have your tempering oven right next to your quench tank but properly hardened steel has its very atomic stacking unnaturally distorted and strained, it should go without saying that the longer you leave it like that the greater the risk that something has to give. Get the blade to room temperature and then temper it. You may let 100 knives set overnight, depending on the level of hardness you achieved, without a problem, but that 101st blade never has to happen if you just follow almost universal standard of tempering as soon as possible.
I would be more than happy to explain why this is in detail but I have already given up much valuable Blade show prep time but felt that not responding would have been an injustice. I am also willing to take the heat myself, but I would encourage every maker who has seen the consequences of not getting on the temper, after a proper heat treatment, to share their experience.
Ed, let me once again express my displeasure in having to correct you. You have said that you and I suffer from a lack of communication. I sincerely hope that your post was just that, totally misunderstood due to poor wording, I would really like to believe that. If I am to be despised for standing for what I see as right, then so be it.
AA Forge came here looking for and answer to a basic question and I see him as being sent away with information that could lead to a lot of heartache in his future if he follows it. I believe anybody knowing better and reading this thread should have the conscience to speak up and give another perspective rather than letting him, and all the other guys seeking that answer, leave with just the one perspective given thus far.
From no other source, except a portion of bladesmiths, will one get the advice to leave parts for any extended period without a temper in a high carbon steel. One thing that may need to be addressed is whether AA Forge will be edge quenching or through hardening, and then weigh it heavily against the knowledge that Ed edge quenches, a possible misunderstanding there.
Extraordinary claims require extraordinary evidence, and the claim that the heat treater is doing something wrong if they need to temper immediately, is a very extraordinary one that takes virtually every other heat treater, and almost 200 years of ferrous metallurgy, to task. The very nature of steel, and all the mechanisms that go into hardening it, counter the statement that freezing an untempered blade overnight is without risk. Adding to the problematic nature of the claim is that if one gains any points in Rockwell from such a treatment there is but one expalination for it, and that is retained austenite (nothing else converts to martensite to give a gain in Rockwell). Ironically this is a clear indicator that something was certainly done wrong in the heat treatment, and the main contributing factor for retained austenite in high carbon steels is overheating and putting too much carbon in solution. Even those who treat steels with alloying that makes RA unavoidable will utilize a very slight temper to stabilize the blade before cryo.
AA Forge, you have one side of the issue, now I offer all of my experience, observations and study, I also offer the findings and experience of scores of other knifemakers who I do not believe are doing their heat treatment incorrectly. To that let me add Bain, Grossman, Palmer, Luerssen, Verhoeven, Moniz, Smith, Siebert, Doane, Brandt Etc and all the other guys who wrote the books on the shelves behind me as I write this, as well as ASM. I could go on, but the point is that I concur with virtually every other industry working with high carbon steel in saying that a properly hardened piece of high carbon steel needs to be tempered to some degree as soon as possible if it was hardened correctly.
AA Forge, you do not have to get ulcers if you dont have your tempering oven right next to your quench tank but properly hardened steel has its very atomic stacking unnaturally distorted and strained, it should go without saying that the longer you leave it like that the greater the risk that something has to give. Get the blade to room temperature and then temper it. You may let 100 knives set overnight, depending on the level of hardness you achieved, without a problem, but that 101st blade never has to happen if you just follow almost universal standard of tempering as soon as possible.
I would be more than happy to explain why this is in detail but I have already given up much valuable Blade show prep time but felt that not responding would have been an injustice. I am also willing to take the heat myself, but I would encourage every maker who has seen the consequences of not getting on the temper, after a proper heat treatment, to share their experience.
Ed, let me once again express my displeasure in having to correct you. You have said that you and I suffer from a lack of communication. I sincerely hope that your post was just that, totally misunderstood due to poor wording, I would really like to believe that. If I am to be despised for standing for what I see as right, then so be it.
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Kevin: you can disagree all you wish, but I suggest that you don't call me wrong and I won't call you wrong, we differ and this is good. I rely on complete and thorough destructive performance testing of my blades for answers and not the dictates of traditional science. We still have a lot to learn and will not progress if we rely on accepted text book practice. It is easy to stand on the safety net of tradition when you have volumes of material to fortify your stand. It is another matter entirely to explore and share your results for others to criticize. I am reminded of a quote that first came to me during the Kennedy administration:
"Behold the turtle, he makes no progress unless he sticks his neck out."
I don't mind sticking my neck out and will continue to do so. We continue to learn, that is easy - sharing what we learn is more difficult but there are some who will listen, some who will understand and some who will benefit. Naturally there are many who will seek to discredit what we share.
Please remember when I talk about heat treat I only speak to 52100 and 5160 that we work with. It is up to each individual to do their own testing and prove what works for them and their clients.
During our last seminar we tested what is claimed to be the #1 combat blade, without warning it catastrophically failed, shattered into three pieces, at 15 foot pounds of torque at about a 15 degree flex, one of these fractures was in the handle which would have left the man using it with a handle and no blade to complete his work. My heart goes out to those who chose to depend on that blade, but they made their choice.
Our blades of similar size require over 70 foot pounds of torque, will make 10 180 degree flexes and incidentally out cut the factory blade tested.
The house hold freezer:
Rex's lab was doing some hardening experiments on a batch of 52100, the batch failed to reach the required RC by a couple of points. Rex took a sample of the steel, placed it in the lab refrigerators freezer and 4 hours later it had gained the required RC with a little to spare, thus saving an entire pour of steel from a re-melt. The increased hardness remained in the sample weeks later. Rex and I (and others who have worked with us in the past) knew it would work.
At first the other men in the lab laughed at Rex, they became pretty quiet when they shot subsequent RCs. and noted the increased hardness. I don't try to explain it, that is for the folks who worship accepted and traditional science, some will seek to know why, others will deny the results. I just know it happens through personal experience.
I would much rather have what I consider an inferior blade fail in my freezer than in the hands of a client who absolutely needs to use that knife in a survival situation.
"Behold the turtle, he makes no progress unless he sticks his neck out."
I don't mind sticking my neck out and will continue to do so. We continue to learn, that is easy - sharing what we learn is more difficult but there are some who will listen, some who will understand and some who will benefit. Naturally there are many who will seek to discredit what we share.
Please remember when I talk about heat treat I only speak to 52100 and 5160 that we work with. It is up to each individual to do their own testing and prove what works for them and their clients.
During our last seminar we tested what is claimed to be the #1 combat blade, without warning it catastrophically failed, shattered into three pieces, at 15 foot pounds of torque at about a 15 degree flex, one of these fractures was in the handle which would have left the man using it with a handle and no blade to complete his work. My heart goes out to those who chose to depend on that blade, but they made their choice.
Our blades of similar size require over 70 foot pounds of torque, will make 10 180 degree flexes and incidentally out cut the factory blade tested.
The house hold freezer:
Rex's lab was doing some hardening experiments on a batch of 52100, the batch failed to reach the required RC by a couple of points. Rex took a sample of the steel, placed it in the lab refrigerators freezer and 4 hours later it had gained the required RC with a little to spare, thus saving an entire pour of steel from a re-melt. The increased hardness remained in the sample weeks later. Rex and I (and others who have worked with us in the past) knew it would work.
At first the other men in the lab laughed at Rex, they became pretty quiet when they shot subsequent RCs. and noted the increased hardness. I don't try to explain it, that is for the folks who worship accepted and traditional science, some will seek to know why, others will deny the results. I just know it happens through personal experience.
I would much rather have what I consider an inferior blade fail in my freezer than in the hands of a client who absolutely needs to use that knife in a survival situation.
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I'm gonna chime in with my two cents, cause that's about all it's worth. I have read many books on heat treating and all say temper tool steels right out of the quench.
There are many steels that benefit from the cryo and 52100 is one of those. Not all steels benefit from a cryo. Its been a while and my memory fades with all the numbers and stats but I believe the 10xx series steels do not benefit from the cryo. I know the stainless steels benefit as well as the 52100, is it because of the chromium?
I don't know about the other forumites out there, but I really enjoy it when the two ends of the spectrum ( Ed and Kevin ) have discussions like this.
Thanks guys
There are many steels that benefit from the cryo and 52100 is one of those. Not all steels benefit from a cryo. Its been a while and my memory fades with all the numbers and stats but I believe the 10xx series steels do not benefit from the cryo. I know the stainless steels benefit as well as the 52100, is it because of the chromium?
I don't know about the other forumites out there, but I really enjoy it when the two ends of the spectrum ( Ed and Kevin ) have discussions like this.
Thanks guys
Mr. Fowler -
Just a minor point that, as a scientist myself, I would like to clarify on. You say that Mr. Cashen is relying on 'traditional science' and you are not. In fact, you are both relying on traditional science: Mr. Cashen is calling on theoretical foundations that are backed by experimentation in related areas, whereas you are relying on your own research in the area at hand. As frequently happens in all areas of science, the two do not agree. As always, the answer to this is more experimentation.
Fortunately, this scientific debate has two advantages over others that I have been party to: (1) it is far more civil than many similar debates I've seen in the world of science, and (2) the answer is easily obtainable using methods that the two of you are both familiar with. If the outcome is not what is expected based on the theory, then the theory must be modified.
Happy scienceing!
- Chris
Just a minor point that, as a scientist myself, I would like to clarify on. You say that Mr. Cashen is relying on 'traditional science' and you are not. In fact, you are both relying on traditional science: Mr. Cashen is calling on theoretical foundations that are backed by experimentation in related areas, whereas you are relying on your own research in the area at hand. As frequently happens in all areas of science, the two do not agree. As always, the answer to this is more experimentation.
Fortunately, this scientific debate has two advantages over others that I have been party to: (1) it is far more civil than many similar debates I've seen in the world of science, and (2) the answer is easily obtainable using methods that the two of you are both familiar with. If the outcome is not what is expected based on the theory, then the theory must be modified.
Happy scienceing!
- Chris
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But Ed, with the following statement you did indeed say that anybody not following your approach is wrong-
despite the overwhelming majority of very successful heat treaters from all fields who would disagree with you, and to be honest it was that more than anything which I felt necessitated a rebuttal.
You have not had problems without tempering with your method of doing things, but by your own admission your methods are very different than what many would choose. So to make a blanket statement of results different than your own being the result of doing something wrong, is well into the penalty area you yourself have defined here.
I do not at all dispute that you found a gain in Rockwell from cold treatment in your steel, I am more than happy to hear about your findings along those lines. Just for the life of me I cannot understand why you would include that admission in the same paragraph in which you inferred that others could be doing something wrong in the hardening operation. A gain of a couple points of Rockwell with cold treatment of a low alloy steel such as 52100 is nothing to sneeze at, it is a serious problem, and the most common cause of that problem in this case is putting too much carbon into solution by over-austenitizing before the quench.
I will not bother with all your input about Ft. Lbs. of torque in blade tests not only does none of it make any sense, I cant even see how it relates to our conversation.
You see Ed here is where I feel a little less guilty, I tried to stay with the cold facts I have available and present them in the humblest and most conciliatory manner I could. You decided to go with condemning me or anybody who does not share your assumptions, and lets be clear that drawing conclusions without even a desire to explain something or know why it happened is nothing more than assumption or opinion. An opinion is a far greater safety net than actually taking a chance on getting an explanation wrong. I dont see lobbing your opinions like grenades and then ducking for cover when it comes time to explain them as risk taking. Really taking a risk involves the possibility of getting the explanations wrong.
If we were to follow your rules of conduct, the most appropriate way of answering Mr. AA Forge would to be to simply say that since you have never had an issue with it, in your opinion it is not a problem. But with not even caring to explain why it was the declaration that
"When blades need to be tempered immediately you are probably doing something wrong, usually overheating them." Which could not go unchallenged.
I am not a brave man, but I do have a strong moral compass that always pushes me toward doing the right thing even when it will bring me endless stress. So I feel I am a risk taker in my willingness to be the bad guy with the nerve to disagree with Ed Fowler. Dont get me wrong, I will get my usual PMs, e-mails and face to face ata boys, for taking the stand that none of them wanted the negative PR from, but that is not how I do things Ed. I will take the risks of publicly disagreeing with you just as I would in private, and you will know where I stand. I feel I owe that to the knifemaking community, and I feel I owe it to you Ed.
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Hesperus, thank you for recognizing the experimentation efforts on my part. If I may, I would like to also point out that too often others are portrayed as relying on their own empirical evidence while I am believed to represent pure theory. I have been practicing my craft my entire life and draw mostly from personal experience. I have just found that when you structure your testing and observation carefully to accurately measure the properties in question your findings, not surprisingly, also coincide with all of the texts written by people who were just as careful with their methods.
This morning when I wrote my reply I was in an office surrounded by those textbooks, now I write from the research and testing area of my shop where I am surrounded by metallurgical analysis equipment that few, if any other, bladesmiths have went to the lengths I have to obtain and use. Please understand that I do not say this as a boast but to suggest that on more careful consideration the roles of empirical study and that of a more theoretical approach can easily be inverted to where I feel they more often are. The only thing I do not have is a running column in a knife magazine to disseminate my theories, but that really would have little bearing on the accuracy of my observations. I so often refer to textbooks to give people other sources of information to which to turn, but most of my writing is based on direct practical application of the very sound and proven principles folks can find in those texts. And I do try to be consistent, if science is good for lending credence to my views in one instance; it is not to be ignored by me or anyone else as soon as it says something I do not like.
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I find this back and forth banter entertaining to say the least. when i first started (attempted) to make knives i would jump from one camp to the other on ht. The best advice i personally (which isn't worth allot) could give anyone, in particular a newer maker is to test, test, test and use every method out there and draw your own conclusions from the results of your tests. Don't take what somebody tells you or shows you in a book, do it yourself. that is how we learn and also watch others if you have the opportunity to see if you are doing it right according to their method.
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Kevin: I ask one simple question when someone tells me they have superior methods I simply ask "How do you personally test the performance qualities of your blades?"
That either ends the conversation or we enter into interesting discussion.
I am a part of a team that works together, each individual contributing from his experience.
My laboratory consists of materials and tools to test many variables as they influence actual knife performance in venues we feel are important. Aspects of performance that you state make no sense to you.
I could say a lot more, but this pretty much sums up our positions.
I will quote myself: "Some hang onto the science of steels like a drunk hangs onto a lamp post for support, rather than using the illumination provided to explore where none have gone before." me July 10, 2008
I thank all who have contributed to this discussion.
That either ends the conversation or we enter into interesting discussion.
I am a part of a team that works together, each individual contributing from his experience.
My laboratory consists of materials and tools to test many variables as they influence actual knife performance in venues we feel are important. Aspects of performance that you state make no sense to you.
I could say a lot more, but this pretty much sums up our positions.
I will quote myself: "Some hang onto the science of steels like a drunk hangs onto a lamp post for support, rather than using the illumination provided to explore where none have gone before." me July 10, 2008
I thank all who have contributed to this discussion.
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We are in agreement, anybody with the hubris of making claims of superior methods or performance must to be called to task to verify and explain those claims.
I said your activities with the torque wrench makes no sense, I am not part of that equation at all as they would mean nothing to anybody who is aware of the physics of flexing any material. I have tried before to explain the basic principles of elasticity that our entire civilization uses every day to construct things from steel, I will not trouble you with it again. But since you are a student and scholar of steel studies, I am really trying to do you a favor when I ask that you research with an open mind the topics of Youngs modulus, stress v.s. strain and area moment of inertia, and then reexamine your torque wrench efforts. A scholar would not dismiss such information out of hand just because Kevin suggested it but would want to know more.
I am disappointed that you now choose to sidestep the topic of saying people are wrong when their findings do not match our own. That seems like a good rule and I am very willing to abide by it if you like. A simple comparison of information that details and explains the hows and whys of our differing positions should be more than enough without any judgments of right or wrong . I will even go one step more and offer to say I was wrong for any occasion in the past, that you can find, where I may have said you were wrong instead of attempting to discuss the details. However with this agreement I also promise to ask questions that anybody devoting years to these studies should have no problem answering, and you are more than welcome to do the same.
I have read your quote so many times now that I have considered one of my own-
In the light the drunk clings to a lamp post and watches with amusement as others crawl around in a dark, blind alley proclaiming they have found the way home. As the bus pulls up, he smiles knowing that tomorrow he at least will be sober.
I will once again tell you how much it pains me that life did not bring us together as good friends, as I get no pleasure at all from disagreeing with you. But the approaches of those needing to know the details before drawing conclusions and those who only need personal experience without trying to explain it are so irreconcilably different as to find little common ground. While I cannot support many of your conclusions, believe me that I wish you yourself nothing but the best and hope your knives will always find happy owners.
I said your activities with the torque wrench makes no sense, I am not part of that equation at all as they would mean nothing to anybody who is aware of the physics of flexing any material. I have tried before to explain the basic principles of elasticity that our entire civilization uses every day to construct things from steel, I will not trouble you with it again. But since you are a student and scholar of steel studies, I am really trying to do you a favor when I ask that you research with an open mind the topics of Youngs modulus, stress v.s. strain and area moment of inertia, and then reexamine your torque wrench efforts. A scholar would not dismiss such information out of hand just because Kevin suggested it but would want to know more.
I am disappointed that you now choose to sidestep the topic of saying people are wrong when their findings do not match our own. That seems like a good rule and I am very willing to abide by it if you like. A simple comparison of information that details and explains the hows and whys of our differing positions should be more than enough without any judgments of right or wrong . I will even go one step more and offer to say I was wrong for any occasion in the past, that you can find, where I may have said you were wrong instead of attempting to discuss the details. However with this agreement I also promise to ask questions that anybody devoting years to these studies should have no problem answering, and you are more than welcome to do the same.
I have read your quote so many times now that I have considered one of my own-
In the light the drunk clings to a lamp post and watches with amusement as others crawl around in a dark, blind alley proclaiming they have found the way home. As the bus pulls up, he smiles knowing that tomorrow he at least will be sober.
I will once again tell you how much it pains me that life did not bring us together as good friends, as I get no pleasure at all from disagreeing with you. But the approaches of those needing to know the details before drawing conclusions and those who only need personal experience without trying to explain it are so irreconcilably different as to find little common ground. While I cannot support many of your conclusions, believe me that I wish you yourself nothing but the best and hope your knives will always find happy owners.
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I temper as soon as the blade is comfortable to hold in my bare hand. I do this based on what I know of RA and the induced stresses of hardening a blade.
Testing is good.
Knowing how to vary the results is useful.
Achieving consistent results is needed.
Having the capability to predict the outcome is valuable.
Being able to manipulate the process to attain a desired outcome is rich.
Having the knowledge to explain the "how and why" behind all the above... PRICELESS.
Testing is good.
Knowing how to vary the results is useful.
Achieving consistent results is needed.
Having the capability to predict the outcome is valuable.
Being able to manipulate the process to attain a desired outcome is rich.
Having the knowledge to explain the "how and why" behind all the above... PRICELESS.
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Mr. Fowler, I've read several similar statements from you in the past and never once seen you go into more detail. I for one, would be very interested to hear some further information about your laboratory, the equipment used, the tests run, and some of the results you've observed.
Please, tell those of us who are interested some more. We'd love to hear it. If you feel this isn't the appropriate thread, I encourage you to start a separate thread to share your experience with us.
Thanks,
-d
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Thank you Deker for reminding us of some very key factors that I for one forgot in my less focused pursuits in this thread. You are very correct in pointing out the differences between lathe and plate martensite. Steels with less than .6% carbon will form martensite at high enough temperatures for it to take on the lathe type morphology. Lathe martensite is in very stable packets what will not experience the same embrittlement issues that plate martensite will. Those working with hypoeutectoid steels will get a natural helping hand in avoiding catastrophy from not tempering that those using hypereutectoid steels will not benefit from.
Above .6% carbon steels begin to form plate type martensite which has some quirks in its arrangement and orientation that cause the plates to impinge on each other with a lot of stressful issues.
Here is an image of 1095 I have posted before that shows the shocking amount of microfracturing that will occur in this stuff if conditions of grain size, too much dissolved carbon and cooling get out of control. These are not cracks that are visible to the naked eye but are inside the steel at 500X magnification or more. These cracks span a vast amount of the martensite plates and contribute to the brittleness. Do not let this image scare you out of good high carbon steel, these issues can be controlled with how much carbon you put into solution, and is why you need to treat high carbon steel a little differently.
Also without exception, every metallography sample I have prepared from high carbon alloys, that did not see a temper, has macro type facturing. The fully hardened steel was merely sectioned with water cooling and encased in a polyester mount and polished. Within hours to days each one develops microfracturing that eventually is easy to see with the naked eye. This happens even with the best of heat treated steels- how do I know, because I have to look around the cracks to see the very fine homogenous condition.
So there are two mitigating factors for how fast you need to temper fully hardened steel- how much carbon the steel has, and anything above .6% is asking for trouble, and how fast you quenched it. Water will increase the strain of the hardening and will need immediate attention if the cracking does not occur before the quench is done, oil will be more gentle and may even allow a smidge of autotempering, salts will virtually get a start on the tempering process before the hardening is even done, so while I know very well the hazards of a traditional quench I too can get away with a some delay because I martemper almost all my stuff. The safest bet with any steel is to get it hardened and then get it right into the temper. No harm is done by tempering sooner, even if it is a snap temper before cold treatment.
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Darn it Kevin, why did you open a new ball game?
I do not make knives solely to make my customers happy, I make knives for myself. If I am not satisfied with a knife it becomes a test blade. If I only sought to make my customers happy there would be thousands of my knives out there, including 3 collaborations.
I make knives to make myself happy, each one is a statement of its own, no two have been or ever will be alike, each a learning opportunity for me and those who understand.
Don't get me wrong, I am overjoyed when a client likes my knives and grateful for those who have supported our quest, I consider each client a partner in the future development of the high endurance performance knife.
Decker: I thank you for your interest. If you want to read about and see photos of our testing, there are detailed explanations and photos on my form. You will find it easy reading and hopefully understandable, I invite you to visit. It is not that I do not want to explain them here, and now, but I am getting ready for Blade Show and still have a lot to do.
I do not make knives solely to make my customers happy, I make knives for myself. If I am not satisfied with a knife it becomes a test blade. If I only sought to make my customers happy there would be thousands of my knives out there, including 3 collaborations.
I make knives to make myself happy, each one is a statement of its own, no two have been or ever will be alike, each a learning opportunity for me and those who understand.
Don't get me wrong, I am overjoyed when a client likes my knives and grateful for those who have supported our quest, I consider each client a partner in the future development of the high endurance performance knife.
Decker: I thank you for your interest. If you want to read about and see photos of our testing, there are detailed explanations and photos on my form. You will find it easy reading and hopefully understandable, I invite you to visit. It is not that I do not want to explain them here, and now, but I am getting ready for Blade Show and still have a lot to do.
Nathan the Machinist
KnifeMaker / Machinist / Evil Genius
Moderator
Knifemaker / Craftsman / Service Provider
- Joined
- Feb 13, 2007
- Messages
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Small side note, largely unrelated:
A commonly recognized Mf for D2 that I have seen is frequently listed as -100F. Obviously that value would depend a lot on the way it was treated, but for arguments sake, lets say you gotta get it -100 to complete your quench. Is that a fair statement?
It is also commonly recognized that a significant delay during your quench can cause the austenite to stabilize or form into a more stable structure that is not martensite. I'm not a metallurgy expert, is that an accurate statement?
In a steel like D2 that already has a tendency to retain significant amounts of RA (I have seen larger values in recent literature suggesting it may be understated in older texts) it seems logical to me that going directly into sub zero before a temper will maximize martensite conversion, at the risk of causing cracks. risk -> reward. Someone please tell me what I'm missing here.
I'm not a metallurgy expert, but it was a subject in my materials classes at NCSU (RIP Armand Cook) and, being an interest of mine I took full advantage to discuss it with my professors, and I spent plenty of hours reading about it in the library (5th floor - M, I still remember). So, while I don't know nearly as much about the subject as some of the people here, I have seen it from the industrial and academic points of view and practiced it later in my tool and die work and something I have learned from all of this is that in industry a steel designed for a ball bearing or stamping die will have more research focused on things like predictable dimensional changes and reduced risk of cracking than fine edge stability.
This leads me back to the point I was making about freezing before temper, which generally goes against most accepted industry practice. My own HT experiments showed that D2 works better if you go all the way to Mf before fiddling around with any kind of snap temper. Perhaps I was doing something wrong? But then the results were duplicated when I got Bos to skip his snap temper (which goes against his standard HT for reasons already listed). Did he also do something wrong?
So, based on both my (admittedly weak) understanding of metallurgy and empirical observations, it is my opinion that some steels should be frozen before tempering when used as a knife rather than a stamping or forming tool because cracking is less likely in a thin object like a blade and issues like toughness in impact and predictable dimensional changes may be less important.
So based on this, I don't think it can be said that all knives should receive a temper immediately. I think it depends on their Mf and their intended use.
For reasons that I do not understand, transformation at Mf that occurs at very low temperatures appears to be less than instantaneous. Perhaps someone could shed light on that for me. Why is cryo a multi hour prospect?
I'm not trying to argue with anybody, I have a lot of respect for everyone here. My eyes and ears are wide open. Please explain what I'm missing here.
A commonly recognized Mf for D2 that I have seen is frequently listed as -100F. Obviously that value would depend a lot on the way it was treated, but for arguments sake, lets say you gotta get it -100 to complete your quench. Is that a fair statement?
It is also commonly recognized that a significant delay during your quench can cause the austenite to stabilize or form into a more stable structure that is not martensite. I'm not a metallurgy expert, is that an accurate statement?
In a steel like D2 that already has a tendency to retain significant amounts of RA (I have seen larger values in recent literature suggesting it may be understated in older texts) it seems logical to me that going directly into sub zero before a temper will maximize martensite conversion, at the risk of causing cracks. risk -> reward. Someone please tell me what I'm missing here.
I'm not a metallurgy expert, but it was a subject in my materials classes at NCSU (RIP Armand Cook) and, being an interest of mine I took full advantage to discuss it with my professors, and I spent plenty of hours reading about it in the library (5th floor - M, I still remember). So, while I don't know nearly as much about the subject as some of the people here, I have seen it from the industrial and academic points of view and practiced it later in my tool and die work and something I have learned from all of this is that in industry a steel designed for a ball bearing or stamping die will have more research focused on things like predictable dimensional changes and reduced risk of cracking than fine edge stability.
This leads me back to the point I was making about freezing before temper, which generally goes against most accepted industry practice. My own HT experiments showed that D2 works better if you go all the way to Mf before fiddling around with any kind of snap temper. Perhaps I was doing something wrong? But then the results were duplicated when I got Bos to skip his snap temper (which goes against his standard HT for reasons already listed). Did he also do something wrong?
So, based on both my (admittedly weak) understanding of metallurgy and empirical observations, it is my opinion that some steels should be frozen before tempering when used as a knife rather than a stamping or forming tool because cracking is less likely in a thin object like a blade and issues like toughness in impact and predictable dimensional changes may be less important.
So based on this, I don't think it can be said that all knives should receive a temper immediately. I think it depends on their Mf and their intended use.
For reasons that I do not understand, transformation at Mf that occurs at very low temperatures appears to be less than instantaneous. Perhaps someone could shed light on that for me. Why is cryo a multi hour prospect?
I'm not trying to argue with anybody, I have a lot of respect for everyone here. My eyes and ears are wide open. Please explain what I'm missing here.
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