zig zag pattern?

soundmind

KNIFE MAKER
Sanded aggressively with 320.
001.jpg

This is what it looks like lightly sanded 320:
002.jpg

I could faintly see it appearing as I was moving up in grits. I etched for another reason. And I think the bare spot by the plunges are just a bad etch from not cleaning well enough.

I haven't decided if I like it or not and if I want to etch it again and keep the pattern or sand it back to bare steel. There is enough steel to sand the etching out and still have a knife.

Also, I think saw a thread similar to this when I first got into reading on the internet about knives, but I can't remember which forum or any key words.

Thanks for any help.
Luke
 

Mark Knapp

Dealer - Purveyor
It looks like the grain in the steel to me, I think I see a hamon too, up near the spine going through the plunge line. Normally those show up in etching but sometimes in sanding. I would keep it
 

Kevin R. Cashen

Super Moderator
It is alloy banding, and wow! It is a really heavy case of it! You can get rid of it with careful normalizing. I would be very curious to know what steel it is and exactly how you heat treated it, every heat from the time you received the steel. When traditionally poured steel is cooled in the mill production process the iron tends to solidify at a different rate than the alloying elements present. This creates the formation of crystalline structures that look like ferns or trees, kind of like frost crystals on glass in the winter, these metallic crystal formations are known as "dendrites." Left as is, the steel ingot would be a inhomogeneous and unpredictable mess, due to this segregation. There is no way to actually undo this issue entirely but what they can do it make the issue anisotropic (single directional) rather that isotropic (a problem in all directions). This is accomplished by heavy reduction by rolling, thus drawing the dendrites lengthwise through the bar of steel, giving steel its directional properties.

However the segregation effects are still there and when we heat the steel, the carbide will want to bunch up in these inhomogeneous areas. Normally we don't see this too much on the macroscopic level, but if we get too "creative" with our heating and cooling rates, we can gather the carbide up so heavily that it becomes a visible pattern in those alloy bands. The answer is to normalize on a level to totally redistribute the carbide more evenly in the steel. You will often see it on blades with hamons and the edge will not have the banding. This is because the edge is martensitic, thus all of the carbon is in a more homogenous solution but the spine is pearlitic which, by definition, is separated carbide. The habuchi area at the top of the hardened zone will often have the most pronounced banding due to the pro-eutectoid phases that are precipitated there before the pearlite forms.

Now for the question that I know is coming as it is always the question number two, after "what is it"- will this effect the blade? Not really, unless it is too pronounced, particularly at the edge. If you tested the blade to destruction you would find some inconsistencies in tensile and impact properties, but nothing that would bother blade use that much. But if the segregation is heavy at the edge you will be limited on what type of applications the edge can be used for. The ragged edge that could result will make the blade cut more aggressively in a draw cut, but will kind of suck for fine push cuts. Such a blade would probably do alright for a hunting knife, but would be like taking a blender to your face for a on a straight razor, and I personally wouldn't like it for fine cutting kitchen knives.
 
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soundmind

KNIFE MAKER
What kind of steel is it, and where’d you get it?
Edited

It looks like the grain in the steel to me, I think I see a hamon too, up near the spine going through the plunge line. Normally those show up in etching but sometimes in sanding.
Hi Mark. Maybe that is a hamon up there and not due to dirt/grease before the etch. So, maybe I hardened it too high. I edge quenched it.
I etched yesterday to see how much edge I had left since I redesigned the profile as I ground it. I can't believe it hardened that high. I think I'll check all my knives in this batch.
Actually, I did check the whole batch after they were tempered (a few months ago). I wanted to see how much edge I ended up with from my heat treat. But the first time I etched with white vinegar. This time with strong solution of ferric/white vinegar which was a lot faster.


It is alloy banding, and wow! It is a really heavy case of it! You can get rid of it with careful normalizing. I would be very curious to know what steel it is and exactly how you heat treated it, every heat from the time you received the steel.
Thanks, Kevin. I was going to call Admiral, but I figured it was better to start here. I printed up your full response and will take it pieces.

On the heat treat. I didn't normalize before I shaped the knife. But on the HT, I normalized three times with descending heats, heated again to austenite, (all slow and low), couldn't see decalescence due to the coals, so I used a magnet to judge colors, and climbed "a little higher," edge quenched in 1 gal of warm canola (this time). Snapped tips on each knife to see if they hardened. Drew at 385 3x. Double checked(?)with etching in white vinegar. I kept the ones that showed a hardening line.

It was meant to be a hunting knife, but is getting pretty thin. Maybe still good for boning/filleting.
 
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Kevin R. Cashen

Super Moderator
As you have probably already discovered, you can't sand, or even grind, it away, as it is integral to the makeup of the steel, and goes all the way through.

If you want to lessen the effect, focus on those first three heats and avoid over-cycling in the lower ranges, which is what makes it worse. To be that pronounced, the steel probably has a little more alloy zone segregation than normal. If it is 1075 there is a segregated Mn network pulling the carbide around. I will assume that you didn't forge the blade, so if you are going to normalize make sure it is HOT, that is what normalizing is all about. For proper normalizing, you want at least 1550°F, and I wouldn't have a problem going to 1600°F to dissolve that banding. If you follow this with descending heat cycles, limit it to only one or two and keep it above 1450°F with the final hardening heat, above 1460°F. The magnet lets go at 1414°F and that is the top of a temperature range that will make banding worse.

Tempering will have little effect on the banding except, perhaps, to increase the etched contrast a little.
 

soundmind

KNIFE MAKER
so if you are going to normalize make sure it is HOT, that is what normalizing is all about. For proper normalizing, you want at least 1550°F, and I wouldn't have a problem going to 1600°F to dissolve that banding.
Great! This afternoon I wondered just that: if my normalization and hardening temps might have just been too low.
 

jaxxas

Well-Known Member
As you have probably already discovered, you can't sand, or even grind, it away, as it is integral to the makeup of the steel, and goes all the way through.

If you want to lessen the effect, focus on those first three heats and avoid over-cycling in the lower ranges, which is what makes it worse. To be that pronounced, the steel probably has a little more alloy zone segregation than normal. If it is 1075 there is a segregated Mn network pulling the carbide around. I will assume that you didn't forge the blade, so if you are going to normalize make sure it is HOT, that is what normalizing is all about. For proper normalizing, you want at least 1550°F, and I wouldn't have a problem going to 1600°F to dissolve that banding. If you follow this with descending heat cycles, limit it to only one or two and keep it above 1450°F with the final hardening heat, above 1460°F. The magnet lets go at 1414°F and that is the top of a temperature range that will make banding worse.

Tempering will have little effect on the banding except, perhaps, to increase the etched contrast a little.

Invaluable the things I learn here!

:)
 

Mark Knapp

Dealer - Purveyor
It is alloy banding, and wow! It is a really heavy case of it! You can get rid of it with careful normalizing. I would be very curious to know what steel it is and exactly how you heat treated it, every heat from the time you received the steel. When traditionally poured steel is cooled in the mill production process the iron tends to solidify at a different rate than the alloying elements present. This creates the formation of crystalline structures that look like ferns or trees, kind of like frost crystals on glass in the winter, these metallic crystal formations are known as "dendrites." Left as is, the steel ingot would be a inhomogeneous and unpredictable mess, due to this segregation. There is no way to actually undo this issue entirely but what they can do it make the issue anisotropic (single directional) rather that isotropic (a problem in all directions). This is accomplished by heavy reduction by rolling, thus drawing the dendrites lengthwise through the bar of steel, giving steel its directional properties.

However the segregation effects are still there and when we heat the steel, the carbide will want to bunch up in these inhomogeneous areas. Normally we don't see this too much on the macroscopic level, but if we get too "creative" with our heating and cooling rates, we can gather the carbide up so heavily that it becomes a visible pattern in those alloy bands. The answer is to normalize on a level to totally redistribute the carbide more evenly in the steel. You will often see it on blades with hamons and the edge will not have the banding. This is because the edge is martensitic, thus all of the carbon is in a more homogenous solution but the spine is pearlitic which, by definition, is separated carbide. The habuchi area at the top of the hardened zone will often have the most pronounced banding due to the pro-eutectoid phases that are precipitated there before the pearlite forms.

Now for the question that I know is coming as it is always the question number two, after "what is it"- will this effect the blade? Not really, unless it is too pronounced, particularly at the edge. If you tested the blade to destruction you would find some inconsistencies in tensile and impact properties, but nothing that would bother blade use that much. But if the segregation is heavy at the edge you will be limited on what type of applications the edge can be used for. The ragged edge that could result will make the blade cut more aggressively in a draw cut, but will kind of suck for fine push cuts. Such a blade would probably do alright for a hunting knife, but would be like taking a blender to your face for a on a straight razor, and I personally wouldn't like it for fine cutting kitchen knives.
What he said :) :D
 

soundmind

KNIFE MAKER
I did nine and so far seven show it. I don't need to etch anything in order to tell it's there. It's something I learned to look for.
 

soundmind

KNIFE MAKER
If you want to lessen the effect, focus on those first three heats and avoid over-cycling in the lower ranges, which is what makes it worse. To be that pronounced, the steel probably has a little more alloy zone segregation than normal.
If the alloying ingredients are separated, and the effect can only be lessened and not fixed, then is it possible to have "homogenous" steel phase at all. You said it would test different at different parts - I think you meant along the edge. Anyway, is that the right question?

Thanks again Kevin,
Luke
 

Kevin R. Cashen

Super Moderator
It would come down to how one defines "homogenous", as technically none of the phases, aside from very high temp austenite, is homogenous. When casually observed under the microscope martensite looks like a very uniform structure, but on higher magnification one sees the individual lathe packets it is comprised of; a supersaturated solid solution with stuff in between. And with even greater magnification the other precipitates, between the lathes, will be apparent. Pearlite, by definition, must be quite inhomogenous, and it would be impossible to have completely homogenous ferrite and still call it steel.

Alloy banding could be dealt with more aggressively with high temperature forging, but how high, and how long? Under normal heating operations the element in motion the most is carbon. Carbon is know as an "interstitial" alloy because it is a small atom that easily moves between the iron atoms. But these other alloying elements are "substitutional" in nature, in that they do not rest between iron atoms, they are so large that they must replace an iron atom by taking its position. For these atoms to move there must be an adjacent vacancy in the atomic matrix to occupy, like one of the little tile slide puzzles you had when you were a kid. Thus, substitutional diffusion, takes much more time or temperature than interstitial diffusion. This is why staking 15N20 in Damascus allows you to share the carbon readily and still maintain the high contrast nickel in those layers. However... have you ever seen "fuzzy" Damascus? That uglier damascus where the silver layers are not cleanly defined but have boundaries that are rather fuzzy looking? This is a Damascus that the maker took too much time at too high a temperature are began to get substitutional diffusion.

So yes, one could cook the steel to death and have a more profound effect on the segregation, but would it be worth it? For something like a knife blade, banding is really not much more than a cosmetic problem, until it gets very pronounced. If you really want a more homogenous steel, the easiest route would be to use one of the CPM steels, their method of manufacture side steps the issues that leads the ingot segregation. Just be aware that an unskilled smith can even mess up CPM products and get you right back to square one.
 

soundmind

KNIFE MAKER
So yes, one could cook the steel to death and have a more profound effect on the segregation, but would it be worth it? For something like a knife blade, banding is really not much more than a cosmetic problem, until it gets very pronounced.
Ok, if it's only cosmetic I can see why you'd say it would still work for a knife.

I thought the light grey was iron and the darker grey was Mn and that the carbon must be separated from everything else too. I didn't understand that the carbon could still be "homogenous" throughout the edge while the other alloys weren't.

Way back before I started finish grinding, I sharpened and tested the edge by cutting mechanics wire. The edge didn't set or chip. I thought I was good to go. However I only checked in one place because I saw how the whole edge of the blade looked going into the oil and watched it cool. I thought I could expect the whole edge to be the same wherever I did that test.

So if I sharpened it, tested the whole length of the edge (the same way and a brass rod this time), and don't see any chipping or deformation, I'm good to go?

(Bear with me on not having my equipment set back up yet to just get out there and normalize again. They're also pretty thin I don't think I could do it anyway without warping them. But if my forge was on I probably would at least try for the experience- but if it'll work for a knife, should I?
 

Kevin R. Cashen

Super Moderator
A lot will depend on what you do to test the edge. I am not a fan of the brass rod test, as it actually doesn't even tell people anything about what they think it does. What a heavily banded edge will do is sharpen, and wear, differentially giving it a micro-serrated effect. This will make it a more aggressive cutter in in draw cuts on soft fibrous materials, but will make it miserable in push cuts where a fine polished edge is desired.
 
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