Alloy Banding aka steel segregation?

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Corradobrit1

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I'm as guilty as many, falling for the allure of a pretty face in this case the banding that can be seen in many honyaki and mono steel blades. I want to try and rationalize this and wean myself off the marketing flannel.
Reading around the subject on steel segregation I constantly hear that its something to be avoided and that in a worse case scenario can impact negatively on the properties of the blade. That its a product of lower temps during HT and normalization to reduce the risk of failure.
So is the customer being duped if banding is being marketed as a desirable feature?
 
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Kippington

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It's a messy topic, that's for sure.
Alloy banding is present to some degree in most knife steels. The exceptions are the powdered ones, and the low alloy ones that have almost everything go into solution during the quench.
With certain polishing/etching techniques it can look fantastic but at the cost of lower toughness.

Honestly, it's not worth worrying too much about. If you like the look then go for it - Knives with alloy banding still get the job done, and the people on this forum tend to treat their knives quite well. Be wary of laser grinds with alloy banding, really thin edges take the most stress in the kitchen.
 

M1k3

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Unless the banding is in the cladding? :pinkelephant:
 

Luftmensch

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I want to try and rationalize this and wean myself off the marketing flannel.
Why? You like what you like... :)

Honestly, it's not worth worrying too much about. If you like the look then go for it - Knives with alloy banding still get the job done, and the people on this forum tend to treat their knives quite well. Be wary of laser grinds with alloy banding, really thin edges take the most stress in the kitchen.
+1
 

Matus

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Well, alloy banding gave the original damascus steel its pattern that made it so famous l. I think it would take a very detailed testing to see what kind of impact the banding has.

I would be interested to know whether the banding only comes from lot of hot working, or is more determined by the steel production steps.

I think that this would be a great topic for @Larrin to write a nice article about :)
 

Corradobrit1

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I was picking up a lot of useful insight on the Bladesmiths Forum. In particular Richard Furrer. It seems steel producing companies have gone to a lot of effort to minimize the potential for steel segregation. Its just reintroduced inadvertently by the processes adopted by the individual knifesmiths.

But I like Kipps suggestion to get these blades if the effect appeals and not have knives that are ground too thin as the deficiencies could be more evident. I'm just not up with paying a premium based solely on the look.
 

Larrin

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Kippington

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It seems steel producing companies have gone to a lot of effort to minimize the potential for steel segregation. Its just reintroduced inadvertently by the processes adopted by the individual knifesmiths.
This is only semi-true. I'm not sure how much you know about the topic, so I'll do the "explain like I'm 5" version.

So if you took a cup of hot water and mixed a heap of salt into it, you would expect the salt to dissolve - the same way that alloying elements dissolve into hot iron. This is also known as "going into solution".
Importantly, there's a big difference between mixing in fine-grained salt, or a single large crystal of salt of the same weight. Whichever one you choose will influence the time it takes to dissolve - this is the time/kinetics side of the coin.

Keep adding salt to the hot water and it will reach the point where it won't be able to dissolve any more - the water has gone over it's saturation point.
This saturation point is partly determined by the temperature of the solute. As the saturated saltwater solution cools, salt starts to come out of solution and precipitate back into a solid form. Once again, kinetics comes out to play. The slower we cool the solution, the more time the salt molecules have to arrange themselves. They will seek out similar molecules and latch on to them, growing back into crystals - otherwise known as grains. Given time, the molecules will latch on to existing crystals. If we give it no time, the salt will latch onto whatever it can that's nearby - a nucleation point - to come out of solution. If the nucleation points are in the form of a line or a string, you get banding.

So let's apply this to steel coming out of the mill. They obviously create it in huge batches - mixed as a liquid and solidified over time. With all that mass it takes a lot of time to cool it down unless you use a fancy and expensive method to cool it (e.g powdered steel cooled in little drops).
As the steel cools and alloying elements start to come out of solution, the steel is rolled which draws the precipitate out into bands or segmented chains down it's length. Sure, they'll do things to not allow it to run out of control, but practically speaking they need to get the job done at a reasonable cost, not to mention a bit of banding isn't a problem for most steel applications.

Individual smiths that receive the steel will try to stop the problem from becoming worse, but the truth is there's not much we can do to make it any better. The time and temperatures needed to completely dissolve these bands is most often out of our practical reach, and will likely cause other problems if attempted - The loss of carbon in the air and growing huge iron crystals/grains would be two issues that immediately come to mind.
So unless the steel in question has very low levels of alloying, the normal heating and cooling done at the forge will never hit a high enough temperature (and spend enough time there) to fully dissolve the pre-existing bands, and those will always be present up to the end product. We simply try to not allow these bands to get fatter.

I've personally tried to get rid of them by normalising at a much higher temperature then cooling quickly. But alas, no dice.
 

Corradobrit1

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Lets try the 3 year old, just out of nappies version.

Nice explanation that even my 5 yo metallurgic level brain can absorb and comprehend. I'm enjoying that documentary on wootz steel manufacture too.
 
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Kippington

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I meant no offence. :p

I don't like throwing around chemistry terms, but they were important in the explanation of why banding exists and why smiths can often be helpless to remove them.
 

DevinT

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Mostly what we see in knife steels is carbide banding. Coarse spheroidite is caused by certain types of annealing and the carbides will continue to coarsen with low temperature forging.

Alloy banding usually occurs in low carbon steels and leads to mixed microstructure banding like ferrite and pearlite.

Inclusion banding occurs in some steels with added sulfur for easy machining, or dirty steels with high impurity levels.

Industry tries to avoid or minimize banding even though it occurs in most cast wrought steels. Banding can look cool when etched though.

Hoss
 

Corradobrit1

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I meant no offence. :p

I don't like throwing around chemistry terms, but they were important in the explanation of why banding exists and why smiths can often be helpless to remove them.
I'm an organic chemist so I totally get the analogy and nerd out on the details.
 

Luftmensch

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so I'll do the "explain like I'm 5" version.
Really nice explanation!

Individual smiths that receive the steel will try to stop the problem from becoming worse, but the truth is there's not much we can do to make it any better. The time and temperatures needed to completely dissolve these bands is most often out of our practical reach, and will likely cause other problems if attempted
This was my impression? If it is in the stock material then you are stuck with it.... No doubt you are right. You probably could make it worse!

I suppose by your analogy... it is like trying to remove saturated salt by applying different temperature profiles to the water. Even if the salt is soluble at higher temperatures, it has to precipitate out as the water cools... Making temperature is a blunt and ineffective tool.


I've personally tried to get rid of them by normalising at a much higher temperature then cooling quickly. But alas, no dice.
Suits me fine... I find it pretty :)
 

JOSHUA PETERSON

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This is only semi-true. I'm not sure how much you know about the topic, so I'll do the "explain like I'm 5" version.

So if you took a cup of hot water and mixed a heap of salt into it, you would expect the salt to dissolve - the same way that alloying elements dissolve into hot iron. This is also known as "going into solution".
Importantly, there's a big difference between mixing in fine-grained salt, or a single large crystal of salt of the same weight. Whichever one you choose will influence the time it takes to dissolve - this is the time/kinetics side of the coin.

Keep adding salt to the hot water and it will reach the point where it won't be able to dissolve any more - the water has gone over it's saturation point.
This saturation point is partly determined by the temperature of the solute. As the saturated saltwater solution cools, salt starts to come out of solution and precipitate back into a solid form. Once again, kinetics comes out to play. The slower we cool the solution, the more time the salt molecules have to arrange themselves. They will seek out similar molecules and latch on to them, growing back into crystals - otherwise known as grains. Given time, the molecules will latch on to existing crystals. If we give it no time, the salt will latch onto whatever it can that's nearby - a nucleation point - to come out of solution. If the nucleation points are in the form of a line or a string, you get banding.

So let's apply this to steel coming out of the mill. They obviously create it in huge batches - mixed as a liquid and solidified over time. With all that mass it takes a lot of time to cool it down unless you use a fancy and expensive method to cool it (e.g powdered steel cooled in little drops).
As the steel cools and alloying elements start to come out of solution, the steel is rolled which draws the precipitate out into bands or segmented chains down it's length. Sure, they'll do things to not allow it to run out of control, but practically speaking they need to get the job done at a reasonable cost, not to mention a bit of banding isn't a problem for most steel applications.

Individual smiths that receive the steel will try to stop the problem from becoming worse, but the truth is there's not much we can do to make it any better. The time and temperatures needed to completely dissolve these bands is most often out of our practical reach, and will likely cause other problems if attempted - The loss of carbon in the air and growing huge iron crystals/grains would be two issues that immediately come to mind.
So unless the steel in question has very low levels of alloying, the normal heating and cooling done at the forge will never hit a high enough temperature (and spend enough time there) to fully dissolve the pre-existing bands, and those will always be present up to the end product. We simply try to not allow these bands to get fatter.

I've personally tried to get rid of them by normalising at a much higher temperature then cooling quickly. But alas, no dice.
Such respect for anyone that knows their profession like this. Kudos! And thank you for the information!
 

Matus

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I really recommend reading the book that Larrin mentioned - it is actually very readable and - short :)
 

Luftmensch

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interesting YouTube documentary at the end
The crushed glass in the crucible was very interesting - to me at least... Seems like a really elegant low tech solution to a problem
 

andrewsa

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Could this alloy banding/steel segregation be due to the smith folding the steel billet/stock material during the forging process to shape the knife?

I have recently come across this youtube video which had peaked my interest on this subject as I've seen there's been no real definitive answer and some retailers saying its a "mystery"... Turn closed captions on for English subtitles.


With a little more research on the "Jigane" I came across this glossary page on Nihonto. Could this alloy banding/steel segregation be related to the different forms of Hada/Jihada in regards to Nihonto? As these Honyaki's we are speaking of are made in a almost similar/traiditon way of Nihonto.
 

Luftmensch

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Could this alloy banding/steel segregation be related to the different forms of Hada/Jihada in regards to Nihonto? As these Honyaki's we are speaking of are made in a almost similar/traiditon way of Nihonto.
I see you are dipping your toes into the world of Nihonto. 😈

There is probably no other form of craftsmanship that appreciates the aesthetic of steel more. I believe this is evidenced by the large specific-language set used to describe types of hada and hamon.

In answer to your question: no....

The predominant effect you are seeing in nihonto is due to folding the initial steel billet. For all the mythology of tamahagane... it is really just a bloom steel - impure by today's manufacturing standards. It is difficult to ensure the carbon additions (and impurities) are distributed evenly across the smelt. One way of 'homogenising' the end product is to repeatedly fold a billet of the steel. This can help remove impurities and even out the carbon content. When you see the layers in nihonto, you are seeing these weld boundaries (of potentially slightly different steel).

Almost all bladesmiths who make honyaki kitchen knives use modern steels. Pretty much none of them fold their initial steel stock over and over - they dont need to and it is hard work!! As mentioned earlier in the thread, the banding is already present in the original, modern steel stock - the smith can choose to exaggerate it if they wish.
 
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Luftmensch

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I guess I was quite far off from my observations. 😂
Not entirely :)

Hamons are more of a direct transfer between the worlds. But there are differences. Nihonto have more 'organic' hamons. Kitchen knifes have more 'geometric' hamons. Perhaps that has something to do with blade length?? Maybe 'organic' hamons look bad over a short length - not enough space for nice rolling dips and troughs?

But yeah... I think most blacksmiths avoid folding where they can. It is hard work! Clearly it is still done for pattern welded stock material - but you'd be loco to do it on modern monosteels. Why would you?! Perhaps this is a shame. I am not a huge fan of pattern welded steel... I find it too 'busy' and gaudy. I quite like banding and 'clouds' - grain and patterns that are easy to miss at a distance but have some interesting detail on closer inspection.
 
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