Hmmm… where to begin? Well first off don’t sweat being confused, an awful lot of this is about as clear as mud even in the text books, and even they don’t always agree.

A week with Ric Furrer will drive you to many things, with me it was drinking, but Ric sort put the glass in front of me and poured <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//biggrin.gi f' class='bbc_emoticon' alt=':D' />. I probably missed you by a few days since I had just left from being Mr. Furrer’s acting coach and makeup person (and the guy who has to bang on his trailer door when he won’t come out because the water provided was not “Perrier”).

I am a bit confused as what thermal treatment we are discussing here. Normalizing is much higher and for different goals than hardening. I am not really comfortable with using 100 degrees above Currie as a rule by any means. I would think of it as any steel with more than .84% C should not be heated above 1475F for hardening operations. For normalizing high heats are often utilized to fully dissolve and break up carbide, in which case the rate of cooling is almost more critical than the maximum temperature.

Normalizing often involves temps in excess of Acm in order to homogenize, which for wootz is counter- productive in pattern development, but very beneficial for modern alloys. Proper normalizing involves temperature in excess of 1600F to accomplish this. What bladesmiths often lump together into normalizing are subsequent thermal cycles for the purpose of grain refinement . These are the lower temperature heats you describe, and while they are effective in nucleation of new sub-grains, they don’t do too much at all for moving carbides around. And for what it’s worth I never saw a butt in the Fe-Fe3C diagram either, at least not a J-Lo or Kim Kardashian eutectoid.

1314F would indeed be less than the ideal point of 1333F of A1, yet another reason not to get too hung up on the Currie point. We must however be careful with the dreaded “M” word when discussing ferrous metallurgy. The only molecules present are in the chemically bonded carbides while the entire rest of the surrounding matrix is metallically bonded crystals instead of proper molecules. Below Ac1 proper what you get is enlarged tempering/spheroidal carbides and some of the sub-grain nucleation I mentioned previously.

Lamellar structures are the result of slower cooling from above Ac1 or Acm as the Fe3C and ferrite segregate out in a diffusive process permitted by that rate of cooling. If the cooling is slow enough proeutectoid cementite will precipitate first followed by a more eutectoid lamellar arrangement of Fe and Fe3C (pearlite) until you get below 900F when you enter into the upper bainite range.

Spheroidal carbide is, for the most part, a result of heating as opposed to cooling like lamellar structures. Keeping things below Ac1 in heating will allow diffusion of carbide into spheroidal clusters until you pass Ac1, and then the higher you go the more the spheroids dissolve back into solution. The exception to this is when Ac1 is exceeded and then a rate of cooling is employed to engage the divorced eutectoid reaction resulting on very coarse spheroidal carbide.

When discussing the time to beat the pearlite nose, we are now working with the I-T or TTT curve and not the Fe-Fe3C diagram. The Fe-Fe3C is based upon equilibrium conditions and thus is of little use in determining active cooling reactions while the I-T (Isothermal Transformation) or TTT deals with different points of equilibrium at varying temperatures on the way down. Of Course, the most accurate for quenching are CCT or continuous cooling diagrams which are tougher to find and even harder to read so most of us just sort of extrapolate from the I-T/TTT curves.

Yes, with 1080 you have around .75 seconds once cooling begins, according to the TTT curve. But do not confuse the differences in diffusion based transformations and athermal ones. 1095 has perhaps .25 seconds less to beat the pearlite nose due to its lack of manganese when compared to 1080. However, Ms designates an entirely new transformation type. The martensite transformation is based upon shear type deformation driven by cooling and not diffusion. So here the carbon content makes a larger difference in the Ms point by depressing it. .55% Carbon or less will put Ms around 500F while .9 %C or greater will bring Ms to 350F or lower. Here time plays no factor, only continuous cooling to maintain the shear type transformation of the austenite to martensite interface. More alloying and more carbon reinforces the austenite and suppresses that deformation. It is here that many make the mistake of just looking at the chemistry of the steel and not considering the soak time and temperatures. If the carbon is left locked up in the chemical bonds of the carbides then Ms will be higher, but if the austenitizing heat is sufficient to break those bonds and free up more carbon Ms is suppressed quite a bit. Thus, one can take a fairly simple steel, like wootz, and fill it with retained austenite by overheating, and also sacrifice some of the patterning in the process.

Grain size is affected by rate of heating, rate of cooling and the amount of points of energy present during recrystallization. Very fine carbides everywhere will be points of new grain nucleation, the more grains present, the smaller they will be. Fine carbides also act as inhibitors to grain growth by stabilization of the grain boundaries.

I have cracked Pandora’s ferrous metallurgical box open just enough in this discussion to give you an idea of the whole new universe that awaits you on the other side. I think I do this so I can share the misery of the addiction and not feel so alone in realizing how much more I have to learn and explore.

Mr. Cashen - thank you for another excellent post on the metallurgy of heat treatment. Every time I read one of your descriptions the fog that surrounds states & stages of steel clears just a little more in my old brain.

Hi Kevin. I heard you had been there. Ric didn't drive me to drink: I went there with that bad habit. However, the look in metallurgy's Pandora's box is dang near about to drive me to knitting. Nice, well behaved, well studied strands of keratins.... it's tempting. This study really isn't science, is it?

First of all, thanks for the explanation and your time.

"I am a bit confused as what thermal treatment we are discussing here." I wasn't. I was trying to relate the heat treatment methods I am learning to the theory, particularly the solubility and IT/TTT diagrams, as I use both in my day job (along with CCT ones you mentions and some TIT ones)for polymeric materials.

"Normalizing is much higher and for different goals than hardening. I am not really comfortable with using 100 degrees above Currie as a rule by any means. I would think of it as any steel with more than .84% C should not be heated above 1475F for hardening operations. For normalizing high heats are often utilized to fully dissolve and break up carbide, in which case the rate of cooling is almost more critical than the maximum temperature. Normalizing often involves temps in excess of Acm in order to homogenize, which for wootz is counter- productive in pattern development, but very beneficial for modern alloys. Proper normalizing involves temperature in excess of 1600F to accomplish this. What bladesmiths often lump together into normalizing are subsequent thermal cycles for the purpose of grain refinement . These are the lower temperature heats you describe, and while they are effective in nucleation of new sub-grains, they don’t do too much at all for moving carbides around."

Thank you. That was what I was asking and apparently missed. In practice, we blend two operations into one sequence to both distribute carbides and reduce grain size.

"And for what it’s worth I never saw a butt in the Fe-Fe3C diagram either, at least not a J-Lo or Kim Kardashian eutectoid."

Good. Y'all were worrying me for a bit there.

"1314F would indeed be less than the ideal point of 1333F of A1, yet another reason not to get too hung up on the Currie point. We must however be careful with the dreaded “M” word when discussing ferrous metallurgy. The only molecules present are in the chemically bonded carbides while the entire rest of the surrounding matrix is metallically bonded crystals instead of proper molecules. Below Ac1 proper what you get is enlarged tempering/spheroidal carbides and some of the sub-grain nucleation I mentioned previously."

Okay. I admit I have a fondness for curie points as they are used for calibration standard. This solid state stuff... well, Updike's Dance of Solids comes to mind.

"Lamellar structures are the result of slower cooling from above Ac1 or Acm as the Fe3C and ferrite segregate out in a diffusive process permitted by that rate of cooling. If the cooling is slow enough proeutectoid cementite will precipitate first followed by a more eutectoid lamellar arrangement of Fe and Fe3C (pearlite) until you get below 900F when you enter into the upper bainite range. Spheroidal carbide is, for the most part, a result of heating as opposed to cooling like lamellar structures. Keeping things below Ac1 in heating will allow diffusion of carbide into spheroidal clusters until you pass Ac1, and then the higher you go the more the spheroids dissolve back into solution. The exception to this is when Ac1 is exceeded and then a rate of cooling is employed to engage the divorced eutectoid reaction resulting on very coarse spheroidal carbide."

So basically overheating the metal gives me the tool dulling lamellar forms unless I do something to avoid it on cooling?

"Of Course, the most accurate for quenching are CCT or continuous cooling diagrams which are tougher to find and even harder to read so most of us just sort of extrapolate from the I-T/TTT curves."

Interesting. I am kinda surprised that someone like Netsche doesn't have them. Then again, I've had students develop them for polymers and its slow work.

"Yes, with 1080 you have around .75 seconds once cooling begins, according to the TTT curve. But do not confuse the differences in diffusion based transformations and athermal ones. 1095 has perhaps .25 seconds less to beat the pearlite nose due to its lack of manganese when compared to 1080. However, Ms designates an entirely new transformation type.

And again why I hate solid state behavior. Yes, I forgot all about that Ms.

"The martensite transformation is based upon shear type deformation driven by cooling and not diffusion. So here the carbon content makes a larger difference in the Ms point by depressing it. .55% Carbon or less will put Ms around 500F while .9 %C or greater will bring Ms to 350F or lower. Here time plays no factor, only continuous cooling to maintain the shear type transformation of the austenite to martensite interface. More alloying and more carbon reinforces the austenite and suppresses that deformation. It is here that many make the mistake of just looking at the chemistry of the steel and not considering the soak time and temperatures. If the carbon is left locked up in the chemical bonds of the carbides then Ms will be higher, but if the austenitizing heat is sufficient to break those bonds and free up more carbon Ms is suppressed quite a bit. Thus, one can take a fairly simple steel, like wootz, and fill it with retained austenite by overheating, and also sacrifice some of the patterning in the process."

I would rather not discuss my first blade from the stuff as I think I screwed it up both ways. I need to chew on that a bit more. Thanks.

"Grain size is affected by rate of heating, rate of cooling and the amount of points of energy present during recrystallization. Very fine carbides everywhere will be points of new grain nucleation, the more grains present, the smaller they will be. Fine carbides also act as inhibitors to grain growth by stabilization of the grain boundaries."

Which leads to the question, how do I make sure my grains are fine? Back to the books...

"I think I do this so I can share the misery of the addiction and not feel so alone in realizing how much more I have to learn and explore."

Oh you do. Like I said, knitting looks better and better <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />

Thanks again. I really appreciate your time. So much to learn...

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This solid state stuff... well, Updike's Dance of Solids comes to mind .

Obviously anybody can get it with a little patience, the funny thing about that is it seems to be a matter of how the individual mind is geared, the solid state stuff is so simple and elegant to me that it just all makes sense, while your field of very complex compounds and interactions loses me in very short order. I squeaked out a passing grade in basic chemistry I think only because the teacher felt sorry for me. Numbers are my undoing. Newton created a physical universe forever out of my reach, described in a language I could never speak, Einstein gave me beautiful thought experiment concepts and allowed me to see it clearly in something as simple as curved space.

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So basically overheating the metal gives me the tool dulling lamellar forms unless I do something to avoid it on cooling?

Not so much overheating, as the rate of cooling from the overheating. From full solution in overheating one can make increasingly fine pearlite simply by the rate of cooling through Ar1. From Arcm to Ar1 you will get proeuetctoid carbide precipitation on slow cooling, if it is very slow you will get heavy sheeting and very embrittling grain boundary cementite. If cooling through Ar1 is slow you will get coarse lamellar pearlite, but the shorter the time, the finer the lamellar spacing. Either form of pearlite will affect edge holding but the finer stuff will not be as apparent. Grain enlargement with grain boundary cementite and large blocky carbides will actually affect how sharp the edge can get due to stability and also how long the edge will last for the same reason.

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Which leads to the question, how do I make sure my grains are fine? Back to the books...

Temperature control, it is that simple. The most effective way to refine grain is by quick heating to a recrystallization temperature well below the grain coarsening temperature, followed by quick cooling. The points of nucleation for new grain formation will be at points of higher energy in the prior grain boundaries, so it is a natural that with carefully controlled heating the grain will multiply with duplexing like effects. Carbides are also little islands of high energy that can stimulate grain refinement. Some folks quench in normalizing to increase the points of nucleation and speed up grain refinement. All of this is done within the narrow range between recrystallization and grain growth.

But most bladesmiths miss the ball by focusing so much on grain size while ignoring carbide size, which is much more critical to the edge. Carbide refinement cannot be accomplished in the same ranges as grain refinement since it is the stable carbides that keep the grains from growing. To bust up carbides and redistribute them you obviously need to totally recrystallize. So do the real hot stuff and get your carbides all in order and then move on to getting you grain size where you want it and the fine carbides will help our instead of being a problem. Bladesmiths are so afraid of the grain growth Bogey man that, I fear, carbide refining benefits are never realized. In fact moving on to low temp cycling without refining carbide can lead to further segregation, and why we see so much alloy banding in so many bladesmiths blades. This of course is not so much a problem with wootz where, for aesthetics, it can be desired for that pattern to be enhanced.

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Oh you do. Like I said, knitting looks better and better <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//wink.gi f' class='bbc_emoticon' alt=';)' />

Some folks develop a method of simple heating and cooling that they settle with for good and then expand on blade designs, damascus patterns etc. for new areas to challenge themselves. To them a look at the deeper metallurgical aspects of the process would unnecessarily complicate things and the infinite universe of things to explore within the steel is discouraging. I felt a moment of discouragement when I first opened that door, but then I saw endless possibilities to explore in this whole new world, and I knew I would never want for challenges for the rest of my life. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

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Obviously anybody can get it with a little patience, the funny thing about that is it seems to be a matter of how the individual mind is geared, the solid state stuff is so simple and elegant to me that it just all makes sense, while your field of very complex compounds and interactions loses me in very short order.

It's all electrons, sir, but they normally don't tell you that until grad school. The difference is carbon, like a good upright molecular, only shares its electrons discretely, while metals dump that into the orgy of electron bands. The mindset is interesting - I see it in thermal analysis all the time. Some people see it immediately: others have to work at it. I'll make sure I bring a "God speaks Math" tee shirt to a Hammer in for you.

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Not so much overheating, as the rate of cooling from the overheating. <snip> In fact moving on to low temp cycling without refining carbide can lead to further segregation, and why we see so much alloy banding in so many bladesmiths blades. This of course is not so much a problem with wootz where, for aesthetics, it can be desired for that pattern to be enhanced.

I'm not even going to ask about alloy banding yet. Happily (well for me), I had the opprotunity to visit Mr. Tomberlin yesterday and he was kind enough to demostrate some of this practically. Thanks so much for answering these. I feel very much like a new graduate student. I have a pile of partially learned skills, a similar pile of non-fully grasped theory, and no clue how to match them up.

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Some folks develop a method of simple heating and cooling that they settle with for good and then expand on blade designs, damascus patterns etc. for new areas to challenge themselves. To them a look at the deeper metallurgical aspects of the process would unnecessarily complicate things and the infinite universe of things to explore within the steel is discouraging. I felt a moment of discouragement when I first opened that door, but then I saw endless possibilities to explore in this whole new world, and I knew I would never want for challenges for the rest of my life. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//smile.gi f' class='bbc_emoticon' alt=':)' />

I can see that. Which leads me to some more questions from working with Mr. Furrer and Mr. Tomberlin, when I take the normalizing blade out of the forge and hold it pointing due north so the magnetic field of the earth aligns the atoms, how many degrees off can I be? Would an NMR do the same thing? And for the tempering to work, the sacrificial chicken - should it be a black or a white hen? <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//laugh.gi f' class='bbc_emoticon' alt=':lol:' />

More seriously, thanks again. You've been most kind

Kevin

Hello Kevin, I am glad I could help. Sorry I forgot about the true north part. And calling me Mr. is like painting a pigs toenails, it just don't fit. You can call me Brion or Too Tall. Just let me know when you want to get together again.

Brion

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But most bladesmiths miss the ball by focusing so much on grain size while ignoring carbide size, which is much more critical to the edge. Carbide refinement cannot be accomplished in the same ranges as grain refinement since it is the stable carbides that keep the grains from growing. To bust up carbides and redistribute them you obviously need to totally recrystallize. So do the real hot stuff and get your carbides all in order and then move on to getting you grain size where you want it and the fine carbides will help out instead of being a problem. Bladesmiths are so afraid of the grain growth Bogey man that, I fear, carbide refining benefits are never realized. In fact moving on to low temp cycling without refining carbide can lead to further segregation, and why we see so much alloy banding in so many bladesmiths blades.

Kevin, I need to check... normalizing is equalizing and refining grain size. Grain growth temps are 1695F. - 1795F.

I've picked up recently (over last year) from you, pointing at 1600F. for normalizing. And, it seems, as a one step process.

With W2 (modern chemistry... 1% +/- C) and quench at 1450F., I have been "normalizing" three steps (fast heat to stabilized temp., cool to room temp. in still air), 75F./50F./25F. higher than quench... stepping down from the highest. That is not 1600F. and now I'm wondering if I've refined carbides, as I thought I had.

Mike

Hello Mike, normalizing, as traditionally defined by industry, is heating to above the upper critical (Ac3 or Accm). This is obviously a range based upon carbon content, and when viewed as such the temp can be from below 1500F for the simplest carbon steels around .8%C to above 1,700F for extremes above and below that carbon level. And, of course, steels with more alloying will push it even higher until you get into alloys that can't even technically be normalized since they will just air harden.

The idea behind actual normalizing is to put things into full solution and homogenize the inside of the steel. This is of great benefit for steel with segregated carbide conditions or carbides that are too coarse. It obviously is not good for making fine grains. What keeps the grains the size they are is the undissolved carbide material, so if you exceed the upper critical by that much you obviously have to exceed the grain coarsening temperature as well. So yes, actual "normalizing" will grow grain but grain size is very easy to adjust, and by much lower temperatures than are necessary for dissolving carbides. But of equal importance to actual grain size in grain refinement, is uniform grain size. So another homogenizing effect of these high temperatures is uniformity of grain size so that subsequent heat can reduce the overall grain size evenly.

Subsequent heats at lower temperatures will then involve finer and more evenly distributed carbides which will be less affected while the grains are then refined in size. So if I feel a full normalization is necessary I get it hot enough for full solution and then follow that with descending heats more in line with familiar bladesmithing heat treating practices. These follow up operation often get grouped under the “normalizing” moniker but are probably more accurately described simply as thermal cycles.

I hope that helps with what you are asking.

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Hello Mike, normalizing, as traditionally defined by industry, is heating to above the upper critical (Ac3 or Accm). This is obviously a range based upon carbon content, and when viewed as such the temp can be from below 1500F for the simplest carbon steels around .8%C to above 1,700F for extremes above and below that carbon level. And, of course, steels with more alloying will push it even higher until you get into alloys that can't even technically be normalized since they will just air harden.

The idea behind actual normalizing is to put things into full solution and homogenize the inside of the steel. This is of great benefit for steel with segregated carbide conditions or carbides that are too coarse. It obviously is not good for making fine grains. What keeps the grains the size they are is the undissolved carbide material, so if you exceed the upper critical by that much you obviously have to exceed the grain coarsening temperature as well. So yes, actual "normalizing" will grow grain but grain size is very easy to adjust, and by much lower temperatures than are necessary for dissolving carbides. But of equal importance to actual grain size in grain refinement, is uniform grain size. So another homogenizing effect of these high temperatures is uniformity of grain size so that subsequent heat can reduce the overall grain size evenly.

Subsequent heats at lower temperatures will then involve finer and more evenly distributed carbides which will be less affected while the grains are then refined in size. So if I feel a full normalization is necessary I get it hot enough for full solution and then follow that with descending heats more in line with familiar bladesmithing heat treating practices. These follow up operation often get grouped under the “normalizing” moniker but are probably more accurately described simply as thermal cycles.

I hope that helps with what you are asking.

Yes it does... I've rearranged the brain cells. Thank you.

Mike