# Knife alloy Banding / Steel Segregation



## Customfan (Jul 1, 2017)

Heard a lot lately.... on alloy banding? Steel segregation?

Need a non google crash course from those in the know!

Care to weigh in with explanations and thoughts on this?

Examples, pictures, etc. Please if you can! Thanks....

:biggrin:


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## brooksie967 (Jul 5, 2017)

I'll put up some pics today. Got a couple good ones of my ashi lately.


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## Dan P. (Jul 5, 2017)

I think the upshot on alloy banding is that it is does not not effect steel properties very badly, which is good because it is fairly common and is irreversible.
It's also not uncommon to see it in steel as it comes from the mill, so while it is a technical "flaw", it's not always (or perhaps not even often) the fault of the smith.
In my experience it is particularly common in tungsten steels such as aogami.
Or, you can pay extra for it and call it "TechnoWootz". Lol.
A picture of alloy banding in 1.2519 (WCrV carbon steel);

https://www.instagram.com/p/BHe2w4-DKyc/?taken-by=danprendergastknives


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## OliverNuther (Jul 7, 2017)

I think it looks kinda cool. Gives it a light Damascus look and I'm not usually a fan of Damascus.


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## brooksie967 (Jul 7, 2017)

You can see it in my ashi here: https://www.instagram.com/p/BV8Xr7PjlI2/


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## OliverNuther (Jul 7, 2017)

brooksie967 said:


> You can see it in my ashi here: https://www.instagram.com/p/BV8Xr7PjlI2/



Yup, saw that the other day on Newest knife thread. 

Beautiful knife. Love the way the wavy alloy banding complements/mirrors/accentuates the wavy hamon.


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## BloodrootLS (Jul 7, 2017)

Alloy banding, while it can be pretty, is generally avoided by most industries and knifemakers. When steel is initially cast it is not particularly uniform in composition and through heating and through mechanical means (rolling) they try to make it more homogeneous. Alloy banding is essentially, the incomplete mixing of all of the materials and is a residual effect of the steel manufacturing process. The more homogeneous the steel, the better the properties in terms of toughness and consistency. The more advanced steel manufacturing processes, such as the particle metallurgy (PM or CPM) in large part aim at increasing the homogeneous nature of the material. That said, most steel out there is not completely homogeneous and has alloying elements unevenly distributed. These elements suck carbon to them aggressively and the carbon clumping up is often what makes these bands visible in the steel. A process called normalization, where you heat the steel up quite high (to the degree that all of the carbon is in solution and moving around in the steel) and let it air cool, is what breaks the carbon out of the clumping and spreads it out more evenly throughout the material. This is an essential step and what makes alloy banding disappear (unless you clump it back up again). 

Visible alloy banding in a knife is easily acheived, especially in steels with a lot of carbon and some amount of other alloys in them like most knife steels. To make them visible the blade simply needs to be thermal cycled at relatively low temperatures before hardening to collect carbon around the alloying elements- this cycling is typically done to refine grain size, which may be happening, but the knifemaker is increasing carbide size significantly in the process. In some steels it is hard to avoid having some alloy banding, but in general it is not a good thing and is something to be avoided. Ideally in kitchen knives in particular we want tiny carbides very evenly and finely distributed throughout a homogeneous steel matrix. This is also how the steel industries suggest that most knife steels be heat treated. 

If you search the web on this I suggest that you be careful to what you read as there is unfortunately a lot of misinformation out there. Kevin Cashen and the League of Metallurgical Bladesmiths (sounds like nerdy superheroes!) are names you can trust and if you really want to geek out read John D. Verhoeven's book which is available in many places online for free. 

~Luke


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## Nemo (Jul 7, 2017)

Does this mean that in highly alloyed steels there is a tradeoff between fine grain size and small carbide size?


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## brooksie967 (Jul 8, 2017)

Yoshikazu Ikeda shows banding in his honyaki, so does Watanabe, etc etc.


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## Dan P. (Jul 8, 2017)

BloodrootLS said:


> A process called normalization, where you heat the steel up quite high (to the degree that all of the carbon is in solution and moving around in the steel) and let it air cool, is what breaks the carbon out of the clumping and spreads it out more evenly throughout the material. This is an essential step and what makes alloy banding disappear (unless you clump it back up again).



The only thing I've read on the subject were bone dry industry papers, but they all suggested that the only way that banding/segregation was reversible was by extremely long soaks (tens of hours) at pretty high temperatures (ca. 1000c). Perhaps things can work differently at the thicknesses we use, but in my experience taking a steel like 1.2519 up to austenitizing temperature and letting it air cool will not reduce banding (but may make it air harden, ha ha).


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## BloodrootLS (Jul 9, 2017)

brooksie967 said:


> Yoshikazu Ikeda shows banding in his honyaki, so does Watanabe, etc etc.



Water quenching steels with large amounts of carbon in them requires keeping temperatures low to avoid breakage and if the steel has been cycled at low temperatures before hand it is not surprising that they do have visible alloy banding. Like I said, in some steels it is hard to avoid and their steels are among them, particularly when one of the main goals is getting a bold hamon line and avoiding cracking during the quench. What is happening is that you are concentrating the hard stuff (cementite and other carbides) in zones and reducing it in other zones. If this is not severe you are fine and it's just visible and who knows, you may even get a damascus-like situation where you may get uneven wear along the edge over time at a very fine scale that may generate a toothy edge- not that most of us let knives get dull enough for this to happen. This is hypothetical of course and I have no evidence either way. If you concentrate the carbon into zones too much you may starve the steel in the other zones and make it weaker, this could be a definite problem I would imagine. Also, and the main issue I see, is that carbide sizes in this situation are likely to be quite large.


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## Nemo (Jul 9, 2017)

By large carbides, do you mean cementite or alloyed carbides or both?


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## BloodrootLS (Jul 9, 2017)

Dan P. said:


> The only thing I've read on the subject were bone dry industry papers, but they all suggested that the only way that banding/segregation was reversible was by extremely long soaks (tens of hours) at pretty high temperatures (ca. 1000c). Perhaps things can work differently at the thicknesses we use, but in my experience taking a steel like 1.2519 up to austenitizing temperature and letting it air cool will not reduce banding (but may make it air harden, ha ha).



Yes, I'm not saying that the banding is possible to erase, though it can be reduced some from what I've read by forging at high temperatures. The smith is continuing the same methodologies that industry uses to break up the banding with both high temperature and mechanical means. Kind of like kneading dough to mix it, plus getting the molecules dancing a bit to get them moving around some on their own locally within the crystal lattice. Some alloying elements, like vanadium, require very high temperatures indead to get them to "dance around", others less so. Austenitizing temperatures on most knife steels (above AC1 but below ACM) do virtually nothing for breaking up alloy banding if it's present, and most bought stock is heavily spheroidized (the carbon is as collected as possible into big round clumps to make the steel soft). A trip above ACM is required to break up these carbides and get everything more evenly distributed and this is a true normalization. After this has been done, if you were to austenitize and quench the alloy banding would not be visible. If it still was, then the normalization was not high enough or the soak time (time held at that temperature) was insufficient to acheive a good normalization. 

So alloy banding can't be removed completely, but it can be made invisible and its effect minimized by spreading the carbon out into small carbides more evenly distributed throughout the steel by high-temperature normalization.


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## BloodrootLS (Jul 9, 2017)

Nemo said:


> Does this mean that in highly alloyed steels there is a tradeoff between fine grain size and small carbide size?



You hit the nail on the head (except highly alloyed is very relative, I'm mostly talking about relatively low alloy high carbon steels like W1, W2, 52100, White and Blue steels, etc.). What the heat treater is trying to acheive is fine grain size for toughness and edge stability and fine, well-distributed carbide arrangement for wear resistance without carbide tearout. If you concentrate on getting super fine grain size too much you typically are increasing carbide size by keeping the temperatures low and allowing the carbon to clump up. If you concentrate on carbide size and distribution (the more difficult of the two to get right), you will likely grow grain in the process. It is a balancing act. What the best approach is in my opinion is to concentrate on getting carbides right first, then reduce grain as quickly and efficiently as you can doing the least carbide growth as possible, then quench the blade. What complicates this is that each steel balances these things differently and that is why you really want your smith to know their particular type(s) of steel intimately. 

Most modern steels have alloying elements in them that pin grain boundaries and keep grain growth in check so that the smith can focus on getting the carbides right without causing damage to the grain size and then can get the grains tiny quickly. Vanadium is one of the elements used specifically for this (though it also makes really hard carbides- a secondary benefit). The relationship between increasing temperature and increasing grain size is not linear with these steels. Having alloying elements that pin grain boundaries is even more powerful in high alloy steels like the semi-stainless and stainless steels or air hardening carbon steels that can be heat treated at a very high temperature (like 1900 F) without having huge grain. Old steels or some very simple modern steels do not have these helpful additions in even tiny amounts and grain grows more linearly and quite quickly, making the balancing act of optimizing carbide size and grain size more difficult.


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## BloodrootLS (Jul 9, 2017)

Nemo said:


> By large carbides, do you mean cementite or alloyed carbides or both?



Both, and it depends on the composition of the steel used.


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## Nemo (Jul 9, 2017)

Thanks for that explanation. To paraphrase, getting the carbide distribution correct is more important, especially in V (and I assume Mn?) containing steels because these elements limit the grain growth thst is associated with the high temp soak required to distribute the carbides?

My understanding is that cementite forms in the grain boundaries (in high C martensitic steels). Where fo the carbides of the alloyed elements form, between the grains or within?


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## malexthekid (Jul 9, 2017)

I struggle to understand what you are saying... 

I feel like you are contradicting yourself by saying it happens especially in simple steels treated in ways like honyaki but then saying if done right it can be made "invisible"... because you are talking about steel normalisation and high forging temps which are totally unrelated to the heat treatment stage to make Honyaki.

Are you suggesting that those blades which have visible alloy banding are inferior? Or the smith didn't know what they were doing?

Sorry but just really confused by your making "invisible" comments etc. Seems to contradict the previous statement about difficult to avoid in the previous one.


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## BloodrootLS (Jul 9, 2017)

malexthekid said:


> I struggle to understand what you are saying...
> 
> I feel like you are contradicting yourself by saying it happens especially in simple steels treated in ways like honyaki but then saying if done right it can be made "invisible"... because you are talking about steel normalisation and high forging temps which are totally unrelated to the heat treatment stage to make Honyaki.
> 
> ...



I appologize if I've been unclear or insensitive. I don't want to make statements insulting other maker's methods and am simply trying to explain the mechanisms and why you don't see alloy banding more often, since it can be quite lovely. Part of what makes this confusing is that I am trying to simplify the concepts across steels and knifemakers' different goals. There is a lot of variation there and I don't want to say that there is only one way to do things. Everything in knifemaking is a balancing act and there are few places where there is a clear black and white answer to anything. However, I didn't want to leave the thread going in the direction that alloy banding creates no issues and is just an aesthetic option. 

So, those of you with collections will likely notice that honyaki blades often show alloy banding, while others only rarely do. I would say that it is hard to avoid having visible alloy banding when making knives using a honyaki process. From a knifemaker's perspective I know why that is. I don't know how it effects performance and I don't know how one alloy, hardened with a honyaki process compares against other alloys or even the same alloy hardened under a different process. What I do know is that obvious alloy banding is avoided by the vast majority of industry, scientists/metallurgists and metallurically minded bladesmiths- the "establishment" for what that is worth. 

In our own process we occasionally see alloy banding, and its acceptability in my eyes depends on the alloy I'm using. Like I said, in some it is hard to avoid and still arrive at the balance of carbide and grain size we're looking for. In some ways I use it as a way to visually see if my normalization and thermal cycling processes are acheiving what I think they are acheiving and if it is too strongly defined over what I expect from that heat treatment I start over. 

In terms of it being invisible I would say that almost all steel has it to some degree, but when heat treated by typical methods (including a normalization process) it is impossible or nearly impossible to see. The alloy banding is effectively caused by some parts of the steel having more atoms that attract carbon to them than others. When carbon can move around in the steel a little bit they are attracted to these areas more than others and tend to collect there. When you heat the steel up in a high-temperature normalization it's like you are shaking a snow globe violently, spreading everything out. What you can't change much is the fact that some areas in the steel have more atoms that attract carbon to them than others (except you can change this some with high temperature forging). What you can change is how much carbon you let collect in those areas. If you don't let carbon collect there (keep shaking the snow globe, then freezing it solid before the "snow" can settle), you won't be able to see the alloy banding at all, or hardly at all. It's the carbon collecting back into those areas that makes the alloy banding visible. 

Also, the more "snow" (carbon) you have in the snowglobe, the harder it is to keep it from piling up in those places where the highly attractive atoms are. One of the reasons that honyaki knives tend to show it pretty often is their very high carbon content. The other is that relatively low temperatures are necessary to keep the knives from cracking during heat treatment and this allows some carbon "settling" because you're not shaking the snow globe as vigorously.


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## BloodrootLS (Jul 9, 2017)

Nemo said:


> Thanks for that explanation. To paraphrase, getting the carbide distribution correct is more important, especially in V (and I assume Mn?) containing steels because these elements limit the grain growth thst is associated with the high temp soak required to distribute the carbides?
> 
> My understanding is that cementite forms in the grain boundaries (in high C martensitic steels). Where fo the carbides of the alloyed elements form, between the grains or within?



Nemo, 

Most alloying elements that form carbides pin grain boundaries and help keep grain size small. Vanadium, tungsten, Cromium, etc. and I believe even aluminum as a trace element, but I'm not positive on that one. These simply retard grain growth, which makes grain growth less of a problem during heat treatment and lets you do what you need to do to get the carbides right. 

There are so many types of carbides I don't know enough to speak to where they all form, but I can say that cementite doesn't only form on the grain boundaries and if it blankets grain boundaries the steel has been overheated and too much carbon was brought into solution in the heat before the quench. The result of this cementite accumulation on the grain boundaries is a problem and makes the steel unnecessarily brittle. Ideally cementite and carbides are spread within and among grains in spheroids which maintains great toughness while simultaneously boosting wear resistance over a steel that did not have the carbides or extra carbon to make cementite with.


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## Dan P. (Jul 9, 2017)

BloodrootLS said:


> In terms of it being invisible I would say that almost all steel has it to some degree, but when heat treated by typical methods (including a normalization process) it is impossible or nearly impossible to see. The alloy banding is effectively caused by some parts of the steel having more atoms that attract carbon to them than others. When carbon can move around in the steel a little bit they are attracted to these areas more than others and tend to collect there. When you heat the steel up in a high-temperature normalization it's like you are shaking a snow globe violently, spreading everything out. What you can't change much is the fact that some areas in the steel have more atoms that attract carbon to them than others (except you can change this some with high temperature forging). What you can change is how much carbon you let collect in those areas. If you don't let carbon collect there (keep shaking the snow globe, then freezing it solid before the "snow" can settle), you won't be able to see the alloy banding at all, or hardly at all. It's the carbon collecting back into those areas that makes the alloy banding visible.
> 
> Also, the more "snow" (carbon) you have in the snowglobe, the harder it is to keep it from piling up in those places where the highly attractive atoms are. One of the reasons that honyaki knives tend to show it pretty often is their very high carbon content. The other is that relatively low temperatures are necessary to keep the knives from cracking during heat treatment and this allows some carbon "settling" because you're not shaking the snow globe as vigorously.



So by somehow inhibiting the carbon content from forming carbides with the segregated alloys, you won't be able to see it? What then the use of using hypereutectic steel at all? I don't want to expose myself as being a metallurgical ignoramus (especially given my chosen profession), but I would have thought that the elimination of alloy segregation would rely on the re-distribution of the alloys and/or their carbides (or whatever), which I understand is very difficult.


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## Kippington (Jul 9, 2017)

That's the idea behind normalizing. The great averaging - designed to dissolve everything into the iron and redistribute it more evenly (although it doesn't quite work out so straightforward in practice).
You can surely see why its a bit silly to refer to the subsequent grain-refining heats as 'normalizing cycles' as, much like resetting your PC, there is almost zero reason to normalize twice in a row.

I might be mistaken, but I believe traditional Japanese bladesmithing culture doesn't include normalization in its methods.


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## malexthekid (Jul 9, 2017)

BloodrootLS said:


> I appologize if I've been unclear or insensitive. I don't want to make statements insulting other maker's methods and am simply trying to explain the mechanisms and why you don't see alloy banding more often, since it can be quite lovely. Part of what makes this confusing is that I am trying to simplify the concepts across steels and knifemakers' different goals. There is a lot of variation there and I don't want to say that there is only one way to do things. Everything in knifemaking is a balancing act and there are few places where there is a clear black and white answer to anything. However, I didn't want to leave the thread going in the direction that alloy banding creates no issues and is just an aesthetic option.
> 
> So, those of you with collections will likely notice that honyaki blades often show alloy banding, while others only rarely do. I would say that it is hard to avoid having visible alloy banding when making knives using a honyaki process. From a knifemaker's perspective I know why that is. I don't know how it effects performance and I don't know how one alloy, hardened with a honyaki process compares against other alloys or even the same alloy hardened under a different process. What I do know is that obvious alloy banding is avoided by the vast majority of industry, scientists/metallurgists and metallurically minded bladesmiths- the "establishment" for what that is worth.
> 
> ...



Thanks for the reply. Will reread and digest and sorry my reply was a lot more abrupt and accusatory than intended.... 3am message while helping feed a newborn... should have waited til the morning.


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## malexthekid (Jul 9, 2017)

BloodrootLS said:


> I appologize if I've been unclear or insensitive. I don't want to make statements insulting other maker's methods and am simply trying to explain the mechanisms and why you don't see alloy banding more often, since it can be quite lovely. Part of what makes this confusing is that I am trying to simplify the concepts across steels and knifemakers' different goals. There is a lot of variation there and I don't want to say that there is only one way to do things. Everything in knifemaking is a balancing act and there are few places where there is a clear black and white answer to anything. However, I didn't want to leave the thread going in the direction that alloy banding creates no issues and is just an aesthetic option.
> 
> So, those of you with collections will likely notice that honyaki blades often show alloy banding, while others only rarely do. I would say that it is hard to avoid having visible alloy banding when making knives using a honyaki process. From a knifemaker's perspective I know why that is. I don't know how it effects performance and I don't know how one alloy, hardened with a honyaki process compares against other alloys or even the same alloy hardened under a different process. What I do know is that obvious alloy banding is avoided by the vast majority of industry, scientists/metallurgists and metallurically minded bladesmiths- the "establishment" for what that is worth.
> 
> ...



Ahh I think I get what you were getting at...

As in when HT Honyaki you can do all the work beforehand to attempt to minimise but during the HT, due to the low temp, you will, or are likely, to get deformation of the alloy bands because of the pull factor of the alloying elements (i take it that is what you mean be atoms attracting carbon) at low temp?

On the right path for a massive over simplification?


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## Nemo (Jul 9, 2017)

BloodrootLS said:


> Nemo,
> 
> Most alloying elements that form carbides pin grain boundaries and help keep grain size small. Vanadium, tungsten, Cromium, etc. and I believe even aluminum as a trace element, but I'm not positive on that one. These simply retard grain growth, which makes grain growth less of a problem during heat treatment and lets you do what you need to do to get the carbides right.
> 
> There are so many types of carbides I don't know enough to speak to where they all form, but I can say that cementite doesn't only form on the grain boundaries and if it blankets grain boundaries the steel has been overheated and too much carbon was brought into solution in the heat before the quench. The result of this cementite accumulation on the grain boundaries is a problem and makes the steel unnecessarily brittle. Ideally cementite and carbides are spread within and among grains in spheroids which maintains great toughness while simultaneously boosting wear resistance over a steel that did not have the carbides or extra carbon to make cementite with.



These are similar to the speroids in the steel as supplied from the factory? (obviously there will be fewer of the if some of the carbon is taken up in martensite)


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## Kippington (Jul 9, 2017)

Yep, it's the same thing. The factories will heat-treat and shape the steels into very convenient forms for us.
It doesn't always work out so well though. There was one recent case where the spheroids in a certain batch of steel were too large and robbed the martensite of its carbon. Many bladesmiths struggled to HT their work to high hardness using their normal routine on this batch. To remedy the problem a longer soak time at high heat was needed to dissolve the carbon out of its carbide form.

You can imagine the same thing in the popular experiment of growing a crystal in a jar.
All you need to do to dissolve the crystal in the jar is to raise the temp of the solute, and the crystal will slowly dissolve back into solution with time and temperature. The larger the crystal, the longer time and/or higher temperature needed. This is one of the reasons why we want small (read: fine) spheroid shaped carbides.


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## BloodrootLS (Jul 9, 2017)

Dan P. said:


> So by somehow inhibiting the carbon content from forming carbides with the segregated alloys, you won't be able to see it? What then the use of using hypereutectic steel at all? I don't want to expose myself as being a metallurgical ignoramus (especially given my chosen profession), but I would have thought that the elimination of alloy segregation would rely on the re-distribution of the alloys and/or their carbides (or whatever), which I understand is very difficult.



Dan, 

Many alloying elements can move and each one does so at a different temperature, however it's not necessary for a knifemaker to move them typically, though they can if they want to with high temperatures like is used in forging. If you take steel from the mill and austenitize it according to the suggested recipe you likely aren't moving them around much and are relying on the distribution that the mill put in place, which is more than adequate as the mill engineers know what they are doing. The carbide forming elements are very well mixed the vast majority of modern steels, just not perfectly mixed. Also, the carbon doesn't go anywhere outside the steel and will get used to make carbide, either cementite or other kinds (I know I'm oversimplifying this and that carbon does leave (decarburization) and in some atmospheres and types of forges come in to the steel (carburization), but for the purposes of this discussion let's say it doesn't in any significant way). What matters is where those carbides form, how big they are, etc. Because there is a fixed amount, you can either have many smaller ones, or fewer big ones, and this is in a continuum. 

Lets say the alloying elements (cromium, tungsten, whatever) are like hors d'oeuvres tables in a big conference room and they're pretty evenly spread out, but there's an area where they're closer together in one corner and over time a lot of people (carbon atoms) have tended to congregate in that area and are chatting away and snacking. When the time comes for everyone to sit down (the quench), most people will sit down nearest to where they were standing. Around the room there are lots of perfectly good tables loaded with great food, but there are lots of empty chairs around them, while the area everyone had congregated in has almost no extra chairs. A normalization is like a director making people get in groups of about the same size around each table so that when they sit down the food is shared more evenly and there's no crowding. The area that had more tables that were closer together still have more people than the rest of the room, but the effect is much less pronounced than if the director had not spread people out.


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## BloodrootLS (Jul 9, 2017)

malexthekid said:


> Ahh I think I get what you were getting at...
> 
> As in when HT Honyaki you can do all the work beforehand to attempt to minimise but during the HT, due to the low temp, you will, or are likely, to get deformation of the alloy bands because of the pull factor of the alloying elements (i take it that is what you mean be atoms attracting carbon) at low temp?
> 
> On the right path for a massive over simplification?



Having three young kids myself I know exactly what you mean and no problem, I realized in my first post I came off a little abrupt. Yes I think you're definitely on the right track. Kippington may be right as well. Japanese knifemaking is a continuum of methods from modern scientific approaches to very traditional approaches and I'm not sure how prevalent normalization practices are or what types of cycling is done after normalization, if it was utilized, or who uses what approaches.


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## BloodrootLS (Jul 9, 2017)

Kippington said:


> Yep, it's the same thing. The factories will heat-treat and shape the steels into very convenient forms for us.
> It doesn't always work out so well though. There was one recent case where the spheroids in a certain batch of steel were too large and robbed the martensite of its carbon. Many bladesmiths struggled to HT their work to high hardness using their normal routine on this batch. To remedy the problem a longer soak time at high heat was needed to dissolve the carbon out of its carbide form.
> 
> You can imagine the same thing in the popular experiment of growing a crystal in a jar.
> All you need to do to dissolve the crystal in the jar is to raise the temp of the solute, and the crystal will slowly dissolve back into solution with time and temperature. The larger the crystal, the longer time and/or higher temperature needed. This is one of the reasons why we want small (read: fine) spheroid shaped carbides.



I love your crystal/solute example, its excellent! The spheroids of cementite are the same general shape when they come from the mill, just WAY too big. They make the steel soft by starving the steel around the spherical clumps of cementite so that the metal cutting tools can get around the hard stuff without having to cut through them. While the fine spheroids are the same shape, they are hundreds of times smaller and very widely distributed, AND much of the carbon made the "matrix" around the spheroids hard martensite, so it's more like rocks embeded in concrete where before it was large boulders buried in un-hardened cement dust (portland cement). When you heat the steel up for the first time, the carbon melts off the outside of the bolders like ice melting to water and the water flows around getting into all kinds of good mischief with the cement dust. Like Kippington said, if the boulders are too big and your heat is insufficient, or your time at heat isn't long enough, the boulders may not melt enough and you don't get enough water to turn the cement dust into maximum strength concrete, not to mention you have big boulders that can tear out easily. Many makers have had problems with 52100 with this. The answer is, wait for it--- normalization!  (or you can get around it by a higher quench temp and longer soak time).


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## Kippington (Jul 10, 2017)

Yeah I love to use examples that are similar to this complicated metallurgy/crystallography stuff, only they're the same scientific phenomena happening at more relatable temperatures, sizes and time-frames.

This is a little off topic, but one of my favorite examples is grain growth.






I can go on till I'm blue in the face with dry words such as:
* - "Grains begin growing at the nucleus points and grow until they meet their neighbors, forming grain boundaries"*

Or I can show a picture that makes it easier to understand:






But the best by far is to show a clip of a bubble freezing in the icy weather:






Much more relatable! :biggrin:


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## Nemo (Jul 10, 2017)

Is normalising essentially a prolonged, high temp austenisation step (presumably followed by a quench aiming to form martensite) or is it a seperate step?

I assume that the "normalisation cycles" that aim to reduce grain size must be a different process to this (high temp) "normalisation"? If so, are they done before or after (high temp) normalisation?


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## Kippington (Jul 10, 2017)

Normalizing happens at different temps for different steels. 1084 steel, for example, has few alloying elements in it and has the right amount of carbon in it (roughly 0.8%) where it all goes into solution as the steel turns to austenite (allowing sufficient time for the carbides to dissolve). Keep in mind though that this is ignoring grain size, which is relevant but not quite on topic with this thread.

Normalizing is the first thing to happen during heat-treating. It should go in this order, with grinding/drilling happening at any stage you want, but mostly done after annealing:
1) Forge to shape (you can normalize at any stage during forging)
2) Normalize
3) Grain refinement
4) Anneal/stress relieve
5) Quench
6) Temper

At each step in the HT the temperature used goes down. The only exception to this is the quench.


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## Nemo (Jul 10, 2017)

Good point, this is a little off topic... sorry.

Might start a thread on forging and HTing when I get a chance.


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## Kippington (Jul 10, 2017)

Kippington said:


> Normalizing is the first thing to happen during heat-treating. It should go in this order, with grinding/drilling happening at any stage you want, but mostly done after annealing:
> 1) Forge to shape (you can normalize at any stage during forging)
> 2) Normalize
> 3) Grain refinement
> ...



Actually, I should also post what I've come to understand the Japanese do:
1) Forge to rough shape, using lower temps for each consecutive heat
2) Anneal/stress relieve
3) Cut/stamp/grind to shape
4) Cold forge (at room temp)
5) Quench
6) Temper

Let me know if anyone knows otherwise.


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## DevinT (Jul 11, 2017)

Alloy banding happens when there developes bands of areas that have high and low concentrations of an alloy like manganese or sulfur. This in turn causes bands that have different micro structures, like ferrite and pearlite. This originates during solidification where alloys segregate between dendrites. Hot working and sufficient reduction usually eliminate banding. 

With knives we usually see carbide banding. Carbides will grow and line up if forging temperatures are low enough and time is sufficient. Carbides in simple carbon steels will all dissolve at ~1650-1700f, depending on cooling rates, pearlite, martensite, or spheroidite developes. Long soaks at low temperatures causes fine spheroidite to grow into course spheroidite. Spheroides = carbides. These carbides can grow large enough to become visible when they form bands. (Wootz)

Steels containing tungsten are prone to this because alloy carbides dissolve at higher temperatures.

Hoss


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