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DGentile

Understanding alloy banding...

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Thank you so much for your input, Ric!

 

Brian

23134[/snapback]

 

Brian,

My input is worth what you paid for it. My opinion on alloy banding as a technique is from reading and testing, but in the end it is just that....my opinion. Othr have a different opinion to be sure.You will have to form your own and I urge you to do so.

And yes it has been used to sell blade in the past by some. Most say what it is, some do not. It is the latter I have issues with.

 

As to pattern-welding:

If you have a forge that can get hot enough you can do the PW yourself. The most difficult part for you will be forging the billets out, but folk have done this by hand for thousands of years and you can to...just work small at first.

Try welding an old file to a piece of mild steel or between two pieces. You want the fire to produce as little scale as possible on the steel and add a bit of borax flux. Wen the borax bubbles like water when making noodles then pull it out and give it a blow like driving a nail. Then repeat.

Watch to see where the hot flux goes and keep the fire in the forge.

 

Ric

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Just got some new old info on this topic, so I thought I'd put it out there:

In the “Transactions of the American Society for Metals,” Volume 48, 1956, there is an article “On Banding in Steel”, by Jatczak, Girardi and Rowland.

It says that banded structures arise from carbon segregation. They can be created by giving the steel an isothermal treatment, which seems to consist of taking it up to 1550 to austenitize, then dropping to a temp corresponding to the nose of the TTT curve and holding for about a half hour, then cooling to room temp.

Getting rid of the banding consists of holding it at 2200 for 25 or 100 hours.

Tests were done on homogenized versus banded steels, and it was found that longitudinal properties were unaffected, but transverse ductility and impact were “somewhat improved by homogenizing, though the degree of improvement is not of commercial significance”

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ery interesting .Those three are Timken people that I knew when I worked there .As you see it's not very convenient to remove it considering the long times !

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Just got some new old info on this topic, so I thought I'd put it out there:

In the “Transactions of the American Society for Metals,” Volume 48, 1956, there is an article “On Banding in Steel”, by Jatczak, Girardi and Rowland.

It says that banded structures arise from carbon segregation. They can be created by giving the steel an isothermal treatment, which seems to consist of taking it up to 1550 to austenitize, then dropping to a temp corresponding to the nose of the TTT curve and holding for about a half hour, then cooling to room temp.

Getting rid of the banding consists of holding it at 2200 for 25 or 100 hours.

Tests were done on homogenized versus banded steels, and it was found that longitudinal properties were unaffected, but transverse ductility and impact were “somewhat improved by homogenizing, though the degree of improvement is not of commercial significance”

33173[/snapback]

Carbon is but one alloy that can segregate out......there are many others as any alloy in the steel can do so given the right conditions. The banding is simple to do, but as the paper apparently says........difficult to reverse.

"not of commercial significance" .... I read this to be not cost effective.

 

Ric

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"not of commercial significance" .... I read this to be not cost effective.

Ha! I think you nailed it, Ric.

They have a table of the details on 4340, banded vs. homogenized.

Transverse Charpy "V" Impact goes from 31.4 to 39.0 Ft-Lbs, Longitudinal goes from 82 to 86.

Transverse seems to be a significant improvement, even if it did take a hundred hour soak and multiple normalizings...

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One thing that was glossed over was the OTHER elements that tend to segregate along with the carbon: Chromium, Molybdenum and Manganese are significant. These elements can, and do, create a segregate band that could be up to 10 times the nominal concentration. When you temper it, the segregate band might be MUCH harder than the parent metal. That is where you loose performance. You end up with a band of high hardness surrounded by an volume of metal that has been depleted of essential alloys, leaving it soft. I do not find this effect to be so beautiful that I am willing to lose any performance because of it.

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I hope I'm not dredging up too old a thread, but I remember this thread from when it was first posted, and found these new comments, plus things I've read elsewhere, to be very interesting.

 

I've been told that complex banding of carbide-rich sections with carbide-poor sections in a blade actually results in superior performance, since the carbide poor sections act as "shock absorbing" regions, and the complex patterns make this even more effective, since the forces travel longer paths, or somesuch.

I was further told that this was superior to a finely dispersed, even distribution of carbides, like you might find in one of the modern powder metallurgy steels.

 

I found these claims...curious. Can anyone please shed some light on what truth there might be behind these claims? I've been trying to learn what I can about carbides in wootz, and carbides in non-wootz steels, and I seem to often come back to this alloy banding phenomenon.

 

Thanks. :)

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Those are some of the assumptions about damascus [folded] steel also .The softer regions are said to make it tougher .But it hasn't been shown.As far as carbides I'll take finer ,evenly dispersed carbides any day and for many reasons. Remember that what may sound intuitive and logical may be just the opposite.

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.Sorry about the double post .

Edited by mete

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I agree with mete (no surprise there, eh?). Any significant variation in the structure of the material can constitute a metallurgical "notch" which may create a stress riser under even nominal loading. In other words, it can start a crack at stress levels below what would normally cause failure. So how well does Pattern Welded Damascus perform under impulse loading? I dunno....how about one of the swordsmiths telling us if you ever snapped a blade while whacking something... :blink:

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I've only broken sword-blades intentionally in testing.

 

How bout you guys?

 

:)

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I've only broken sword-blades intentionally in testing.

 

How bout you guys?

 

I chop thru stuff (2x4s, automobiles, thick wall cardboard tubes, rope, etc.) with my swords (always damascus) after heat treating (to see if it'll bend or break) and after handle assembly (to make sure nothing's going to loosen up, I don't usually use epoxy), and nothing's snapped....yet :o

Edited by Jeff Pringle

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Been a while since this subject came up originally. I am real interested in this phenomenon and originally wanted to make blades of 5160 and then deliberately make the steel segregate its alloys to some degree for visual effect. Not to fool people into thinking it was pattern welded steel but just to exploit the possibilities of some more visual appeal on some tactical tanto I am cooking up.

 

Never have made a blade and done this but I did thermally cycle some 5160 "sticks" in slowly descending heats to get banding and segregation. The sticks were about 9" long and maybe 1/4" square bars.

 

Then I quenched segregated and non segregated steel samples in the same quenchant and busted them to get a feel for how they reacted and did a lot of subjective bend and file/hardness tests to see how badly the steel was degraded by deliberately segregating the alloys.

 

It was probably my subjective testing being inaccurate or not precise enough but my impression (now don't get mad) was that the stuff that had been thermally cycled 9 times in decreasing heats (and had really cool patterns of banding evident) was every bit as tough and hard and viable as the same stock that had been normalized 3X, quenched and tempered at 450f. Actually, I could not tell the difference and if you put my feet in the fire I have to say that I thought that the banded steel actually outperformed the "good" stuff in bending/breaking tests...seemed actually a little tougher (very little) than the "good" steel.

 

But I gave up on exploiting the possibilities months ago 'cause I have too much on my plate already. It's curious though. I figured I'd ruin it by deliberately causing banding but the steel didn't seem to mind at all...

 

Subjectively speaking that is. :)

 

Brian

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Brian, very interesting. I really did not expect it was possible to CAUSE banding by thermal cycling. I thought the basic laws of thermodynamics would lead us to expect that with repeated heating, Entropy would drive the alloy elements apart, not closer together. Nature abhors a vaccum and alloy concentrations in solid solutions. :261:

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I believe the effect is calling pinning. I am too tired to look it up, but basically carbides will be attracted to previous carbide formations and pin themselves to them as they form. Everything into solution, then subsequent cycles lowering the temps and you will get it every time. Some steels are better than others for forming it.

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5160 seems to want to form this banding very easily. It never occurred to me that this phenomenon is contrary to the basic law of thermodynamics...this *is* interesting R.K. I have no idea of what steels do it easily and which one are more resistant to the phenomenon.

 

Next time I play with it I'll have to get some pictures and maybe that will lend more information about how it happens and why and the conditions that create it.

 

Maybe we are not creating the banding so much as accenting it and making it more visible...maybe the steel is segregated as it comes from the mill. I know that the 1018 and A36 steel I use for fittings show banding when heavily etched and I don't thermally cycle them at all. :mellow:

 

Brian

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Well, kind of expanding on what Don said;

 

What if banding is one thing, and what we are seeing sometimes, as a result of specific thermal cycling, something else?

I think it might have something to do with carbide formation myself, although I'm not sure I have a grasp on it completely. I know I often see this effect as a visible artifact in hamon on some blades, particularly 1086M, especially when heat-treating to create carbides specifically.

It certainly doesn't seem to have a detriment on performance, quite the contrary actually, as I think Brian can attest to, or any poor schmuck who's had to hand polish the miserable stuff.

 

I may be totally off base, but what if there is Banding in the context of what Ric, Mete and RK talked about, and maybe something else?

 

Think that might be a possibility?

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Don, I learn something everyday! :D I looked up "pinning" in my Big Book of Big Metallurgical Words and it was not listed. However, your description sounds like multiple subcritical annealing. Carbide growth is exactly what happens when you subcritical anneal steel. I don't know if the diffusion of the carbon in any way affects the other alloy elements like manganese, chromium, moly, etc. If the carbides are already distributed in alloy bands from the mill, I can see how they can be encouraged to further segregate. This would imply a fairly short time austentize for final hardening or the carbides would just diffuse apart as my comment about Entropy implied.

Edited by RKNichols

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Pinning is commonly referred to in terms of grain refinement, but I couldn't find the reference either, buried somewhere in the library.

 

I did come across and interesting paper that refers to an older discussion of ours.

______________________________

J. Phys. IV France 112 (2003) 275

DOI: 10.1051/jp4:2003882

Transformation of retained austenite during tempering of high carbon steel

D.E. Kaputkin, L.M. Kaputkina and S.D. Prokoshkin

 

Moscow Institute for Steel and Alloys, Leninskii Prospect 4, Moscow 119991, Russia

 

 

Abstract

Dilatometric, electron microscopic, and X-ray diffraction techniques have been employed to analyze transformations of the retained austenite in a 1.85 wt % C steel during tempering. The quenched steel contained 82% of retained austenite. Depending on the tempering temperature, transformations of the retained austenite in the highcarbon steel manifest themselves as the formation of bainite "fringes" around the martensite crystals, new lenticular and thin-plate crystals of isothermal martensite also surrounded with the bainite "fringes" as well as the thin-plate pearlite.

 

Granted it is referring to excess retained austenite, but it was the first reference I found to tempering tripping retained austenite.

____________________

As to the current discussion, I think the way to visualize it is to see the established carbides as seeds. As long as they aren't put into solution the subsequent formations will seed on the existing structure. Do it enough and you will create laminar carbide structures. This is a Pendray discovery while working with wootz and they have a paper out on it somewhere.

 

Anyway enough brain work for today.

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Don, very interesting. When I was in college, we all thought we were learning the most advanced methods and theories and that the science was virtually complete. HO HO HO! I am constantly amazed at what is just now being learned about BASIC METALLURGY! I have been buying one or two new books per year just to try to stay current. It is very difficult and expensive. Some of this is being driven by incredible advances in electron microscopy and even more sophisticated methods that allow us to actually see individual atoms. Yup. They look like rows of ball bearings...... :wacko:

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They are -- nano ball bearings. :D ... As far as new things, is the term nano dispersoids something new or a new name for precipitaion particles ??

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Have you guys been following the research on heating metal with microwaves? Some interesting discoveries: powdered metals won't arc in a microwave; if you raise metal above nonmagnetic it won't arc; they are using microwaves to heat a plasma for focused high temp heating.

 

I have tried the first two in experiments, but am really interested in the plasma concept. If I only knew what gas they were using, feed mechanism and containment requirements. The oven pictures I found on the internet was created by guys in lab coats and I need the redneck version. There are lots of interesting things that could be done with a rig like that.

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i seem to recal a web site that was using a regular microwave bypasing the over load and using a little cruchible serounded bye kaowool to melt steel and or brass i cant remember witch

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