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I saw this term in another thread and have seen it before, but am relatively clueless on what exactly it means. I looked in the glossary posted on the website and didn't see it, but maybe I'm not looking in the right spot... Is it something to do with different alloys banding together during the heat treating process that remains visible? Does it always occur, is good or bad, are there particular ways to keep it from occuring or ways to induce it? Sorry if this is one of those no-brainers, I just tend to be a bit slow <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//blink.gi f' class='bbc_emoticon' alt=':blink:' /> . As always, thanks for the help.

Jeremy

When the steel is poured at the mill the different elements in it will want to solidify at different rates. Since metals are crystalline in nature they will do this in just such a fashion making fern or tree like structures within the steel of higher concentrations of different elements, these are called dendrites due to their tree like appearance. Dendritic, or ingotized steel is very problematic to many steel properties and workability in a consistent manner so industry does all it can to counteract the problem. The first thing they do is subject the steel to heavy reduction by rolling, this breaks up the dendrites and rearranges them in an elongated form, stretched along the length of the steel in the direction of rolling. This gives steel a directional property so that instead of the segregation and other issues weakening the steel in all directions (isotropic), it makes the steel stronger along one access and not quite as so much along another (anisotropic). If you impact test steel perpendicular to this flow it is quite strong but if you impact it parallel to it is significantly weaker. After the rolling the steel is then subjected to various heat cycles to break any chemical compounds that want to hang out in the segregated areas and mix them evenly throughout, but the atoms that caused the segregation are much slower to move than things like carbon and there will still be zones in the steel prone to this concentration if the steel is not heat treated properly to avoid it.

Things like heavy thermal cycling and slow cooling from high temperatures will allow carbon to gather in places like this and accentuate the alloy banding. For the most part it is nothing to lose too much sleep over, but if it gets heavy enough to be really visible it can affect the steels consistency in its properties. For instance, in the case of higher carbon steels you will get bands and heavy sheeting of carbides that can have odd effects on the edge. Some people like the way such an edge cuts because they think it is sharper but it is actually less stable and sharpens in a rough and toothy manner and then as it cuts it wears in a very ragged way that allows it to tear through soft fibrous materials like rope and paper, but it does not handle other cuts and materials nearly as well. Another thing to beware of is how much carbon is trapped in the banding and if there is any leftover to fully harden the steel around it. Some steels are much more prone to it than others due to alloying. O-1 is one that will really band out if not heated just right and I often see subtle banding in the habuchi area of 10XX blades that have a hamon. If you see it before the final heat treatment it is easily erased by heating well above critical, holding for a bit followed by a quick air cool. This puts the segregation into solution and then robs it of the time required for going back into the concentrated areas when it comes out of solution. Heavily banded steel can be very ductile in its annealed form, (as was found in the research of Wadsworth and Sherby) since the material between the bands is almost pure iron but ductile is the opposite of strength and not necessarily synonymous with toughness.

In virtually every modern application steel reaches its highest levels of performance by homogeneity, the more even and smooth the internal structure, the more evenly it will respond to our heat treatments and handle forces applied to it, this is why industry and bladesmiths pay such close attention to things like normalizing, since heavily segregated materials are much less predictable than homogenous materials.

Some find banding interesting but its effects are purely aesthetic at best and somewhat detrimental at its worst.

Mr. Cashen-

Thanks for the explanation and putting it in a way that's understandable.

Jeremy

Thank you Kevin. I was hoping that you would answer this one. At least I now have some understanding of what is going on in our steel.

Brion