I hesitated in responding for a while but this seems the proper place to pose the question:

I do a fair amount of mosaics with the majority being tile cut. Often I have noticed after an initial etch a lighter area at the weld of the various tiles. Often this will grind out but not always. I'm assuming that this is the result of carbon loss at the weld but this is only a guess.

The symptom seems to appear whether I use a flux (borax) or not when welding. (I'm reasonably confident that I have a reducing atmosphere in the forge.)

I often will cut the tiles with a chop saw. Could this be the culprit?

Any thoughts as to the cause of the lighter color at the sight of the tile welds?

Gary

Forge welding is metallic bonding.

In metals, the electrons are shared in rows or layers between the atomic nuclei. This helps form a matrix, and it is also why metals conduct electricity. An electron in automatically bumps and electron out the other end in a wave, like pushing grapes into a straw.

A Summary of Bond Types

Previous Page: Comparing Bond Types

This brings to a conclusion the description of bonding. Three types of bonds - metallic, ionic and covalent - each have their own characteristics.

• Metallic bonds are formed by pooled valence electrons of metallic atoms providing the negative charges to hold positively charged metallic ions together. This bonding structure provides for relatively low melting points and easy reshaping (bending, flattening). The delocalised electrons provide high electrical conductivity.

• Ionic bonds are formed when metallic atoms donate valence electrons to non-metallic atoms. The resulting ions have opposite charges and attract each other into rigid lattices. This bonding structure gives high bond strength that provides brittle substances with high melting points and low conductivity. If the lattice is disrupted by being heated or dissolved in water, the ions break apart and find movement easier. Conductivity of molten or aqueous ions is much higher than that of solids.

• Covalent bonds are formed when two non-metallic atoms approach and share valence electrons. These are the strongest of all bonds. Covalent networks form when atoms bond each to several others, making an interlocking web of atoms. Covalent networks are very hard to disrupt, giving these substances very high melting points and low conductivity in any state. Molecules form when a few covalent bonds form between a countable number of molecules, as in CO2 or H2O. While the bonds within the molecule are very strong, the molecules are so small that we commonly deal with a very large number of them. One molecule requires little energy to separate from another, so these substances have very low melting points, often below room temperature. Most liquids and gases that we are familiar with are molecular. Because molecules hold their electrons so tightly, molecules also tend to be poor conductors.

Enjoy

Gary

I am familiar with the light areas about the welds that you describe. While I cannot say what is the cause of this, I will tell you that I am fairly confident that it is not your chop saw. I say this because I used to have these as well and I use a band saw to cut my tiles.

I will tell you that I no longer experience this light area and I attribute it to the method that I use to prepare and weld my tiles. In preparation for tile cutting, I forge my bar to a very even thickness using stop blocks in my press. I then use a surface grinder to get both sides flat and parallel. When I cut my tiles, I do not measure the tiles, but rather use a stop on my band saw so every tile is exactly the same. I then clamp the tiles to a heavy piece of angle iron and so they are tightly touching each other. The surface grinding and the tiles being exactly the same allows me to have nearly 100% contact from tile to tile. I then TIG weld the tiles together using low amperage and just fusing the seams together with no filler rod. I weld around the entire seam.

It may be overkill, but by the time I am cutting the tiles, I have already invested a lot of time into the billet and I want to remove as many possibilities as I can for something to go wrong. Since using this method, I have no light areas, and no failed welds on the tiles.

Brian

Just to bring some more discussion to the table without adding anything to it personally, what about the anatomy of a forge weld with flux vs. the anatomy of a forge weld without flux. It is my understanding through much reading that both seem to have their positives and negatives. Kevin Cashen has published some of his findings which were a very interesting read. I wonder, how big of a deal is the further oxidation of the metal on a dry forge weld? Is the benefit of lack of flux micro-inclusions great enough to overcome the downside of the extra oxidation? I would enjoy hearing everyone's thoughts on the matter. For me, simply not having a layer of flux in the bottom of the forge is reason enough, haha. But the stronger welds was a major selling point as well.

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Gary

I am familiar with the light areas about the welds that you describe. While I cannot say what is the cause of this, I will tell you that I am fairly confident that it is not your chop saw. I say this because I used to have these as well and I use a band saw to cut my tiles.

I will tell you that I no longer experience this light area and I attribute it to the method that I use to prepare and weld my tiles. In preparation for tile cutting, I forge my bar to a very even thickness using stop blocks in my press. I then use a surface grinder to get both sides flat and parallel. When I cut my tiles, I do not measure the tiles, but rather use a stop on my band saw so every tile is exactly the same. I then clamp the tiles to a heavy piece of angle iron and so they are tightly touching each other. The surface grinding and the tiles being exactly the same allows me to have nearly 100% contact from tile to tile. I then TIG weld the tiles together using low amperage and just fusing the seams together with no filler rod. I weld around the entire seam.

It may be overkill, but by the time I am cutting the tiles, I have already invested a lot of time into the billet and I want to remove as many possibilities as I can for something to go wrong. Since using this method, I have no light areas, and no failed welds on the tiles.

Brian

Thanks, Brian. I have been surface grinding the billet before tile cutting and this has helped. I think that you're right in that the tighter the fit between the tiles prior to forge welding, the less the chance of the light area.

I appreciate the response.

Gary

Often I have noticed after an initial etch a lighter area at the weld of the various tiles.

Gary,

I share your confusion over the differential etch of the forge weld lines. I have been asked on a firearms forum, to answer why forge weld lines etch and color differently. The question on this forum has to do with old damascus gun barrels. The guys who refinish these old barrels have found that the weld lines in nearly all of the old gun barrel damascus patterns finish out “white”, except for one particular damascus pattern. I’ve been asked why this one pattern, out of the dozens of gun barrel damascus patterns, is the only one that has black weld lines. I hesitate to answer them, until I have a better understanding of what can cause this effect.

Kevin offered a logical explanation for “white” weld lines; that of the effect being caused by decarb, oxides and boron infiltration. Yet, there are a few things that I have not been able to resolve in my thinking.

Once metallic bonding is achieved, diffusion of interstitial atoms (like carbon) will readily occur between the two parts

To the left is the carbon rich W-1 that becomes carbon depleted white ferrite adjacent to the weld

Decarb, oxides and boron infiltration account for the different effects in the weld zones.

We know that once metallic bonding has been achieved and carbon migration can occur, it takes very little time at heat for the carbon to reach a virtual equilibrium of content between the two bonded metals. If a significant amount of carbon atoms has to pass through the weld line to migrate to the lower carbon content metal, then why is there still a carbon depleted area next to the forge weld? Shouldn’t the decarbed area be the first to repopulate with carbon atoms? Do the iron oxides adjacent to the weld line inhibit the carbon in some way?

I’ve also wondered what the ferrous grain structure looks like on either side of a weld line, and whether the grain structure reforms across the weld line during heat treatment. If the two metals were similar enough in grain structure modifying alloy content to form the same structure, would the grain structure then reform across the weld line?

A photo from the document that Mike Krall shared, shows a weld line at high magnification. This is a sample of annealed 256 layer damascus steel. It is very interesting that the pearlite next to the weld line is oriented perpendicular to the direction of the weld line. But, what does this indicate? I wonder what the grain structure would look like in different states of heat treatment.

Interface in 256 layer annealed sample.

Coarse pearlite is observed to be oriented perpendicular to the interface between the layers.

I question all this grain structure near the weld line stuff, because grain structure has a significant effect on the etching process. It seems possible that the reason weld lines etch differently than the adjacent steel, is because the grain structure near welds lines is different.

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Gary,

I share your confusion over the differential etch of the forge weld lines. I have been asked on a firearms forum, to answer why forge weld lines etch and color differently. The question on this forum has to do with old damascus gun barrels. The guys who refinish these old barrels have found that the weld lines in nearly all of the old gun barrel damascus patterns finish out “white”, except for one particular damascus pattern. I’ve been asked why this one pattern, out of the dozens of gun barrel damascus patterns, is the only one that has black weld lines. I hesitate to answer them, until I have a better understanding of what can cause this effect.

Kevin offered a logical explanation for “white” weld lines; that of the effect being caused by decarb, oxides and boron infiltration. Yet, there are a few things that I have not been able to resolve in my thinking.

We know that once metallic bonding has been achieved and carbon migration can occur, it takes very little time at heat for the carbon to reach a virtual equilibrium of content between the two bonded metals. If a significant amount of carbon atoms has to pass through the weld line to migrate to the lower carbon content metal, then why is there still a carbon depleted area next to the forge weld? Shouldn’t the decarbed area be the first to repopulate with carbon atoms? Do the iron oxides adjacent to the weld line inhibit the carbon in some way?

I’ve also wondered what the ferrous grain structure looks like on either side of a weld line, and whether the grain structure reforms across the weld line during heat treatment. If the two metals were similar enough in grain structure modifying alloy content to form the same structure, would the grain structure then reform across the weld line?

A photo from the document that Mike Krall shared, shows a weld line at high magnification. This is a sample of annealed 256 layer damascus steel. It is very interesting that the pearlite next to the weld line is oriented perpendicular to the direction of the weld line. But, what does this indicate? I wonder what the grain structure would look like in different states of heat treatment.

Interface in 256 layer annealed sample.

Coarse pearlite is observed to be oriented perpendicular to the interface between the layers.

I question all this grain structure near the weld line stuff, because grain structure has a significant effect on the etching process. It seems possible that the reason weld lines etch differently than the adjacent steel, is because the grain structure near welds lines is different.

Steve,

Boy do I wish I thought as critically as you do here!

I've got no answers but I do have a question... about the damascus barrel patterns. I guess not a question, really, but a quandary. It is my understanding damascus barrels are made from a long, thin, patterned billet hot-wrapped around a mandrel, then heated to weld temp. and jump welded. If there is no other making method (I've never come across another, but ???), how in the world can one particular pattern not finish out "white"?

Steve, do you happen to have a link to the damascus barrel thread you would be willing to give me?

Mike

Boy do I wish I thought as critically as you do here!

LOL!!! Some folks tell me that I think too much!!

Regarding the construction method of damascus gun barrels, your description is accurate concerning the method of making spiral welded barrels. Pre-patterned damascus rods are welded together to make a flat strip of damascus material. This strip is wound on a mandrel to create a hollow tube. The appearance of which resembles a compressed coil spring. This coil is then jump welded to create a solid tube. The other method used to make gun barrels, is to use a flat strip of material and scarf the long sides. This strip is then formed longitudinally around a long mandrel and the scarfed edges are forge welded along the length of the barrel. Spiral welding is the method used to make virtually all damascus gun barrels. Longitudinal welding of barrels was/is the most common method for welding wrought iron barrels.

Any consideration of why a particular area of ferrous material colors “black” or “white”, must take into account the grain structure of that area of material. Our etching of damascus, as well as coloring of steel by rust bluing, utilizes electro chemical corrosion. The depth of the etch and/or coloration of the steel, is related to the reactiveness of the material to the corrosive solution. This is vividly demonstrated in blades that are clay hardened to create a hamon. The blade is a mono-steel, yet takes a differential etch. It is the differential reactiveness of the varying grain structure that causes this effect.

Electro chemical corrosion of steel is a known science. Corrosion propagates at the grain boundaries. The finer the grain structure, the more places for corrosion to begin. Hardened and tempered steel has a finer grain structure than unhardened steel; thus more places for corrosion to start. Any consideration of the reaction of an area of material to the corrosive solution, without taking into account its grain structure, is ignoring a key component of the equation. This is why I am interested in the grain structure on either side of and also through the forge weld.

How in the world can one particular pattern not finish out "white"?

We have very few contemporary documents about the making of damascus gun barrels. Nearly all of the old documentation was lost, or destroyed, during WWI. However, it is largely agreed that gun barrel damascus was made of laminations of wrought iron and steel. In early gun barrel damascus, the steel was very low in carbon content. After smokeless gun powder was developed, barrel manufacturers started increasing the carbon content of the steel laminations, to make the barrels stronger. The damascus pattern noted for the black weld lines, was common to this later production of stronger barrels. So it is possible that the higher carbon content steel used, had an effect on the color of the welds. But my perception is that this would only happen if the higher carbon steel managed to repopulate the decarb weld line with carbon. Thus my question; “Why wouldn’t it?”

Damascus gun barrels were not heat treated, though there is old documentation that suggests that many of them were thermal cycled. Just what the resulting grain structure is in these old barrels, can be speculated. But, metallography would be required to know for certain. Once the grain structure was understood, an assessment of the corrosion process results could be made. Dr. Drew Hause has been having metallography done on some old damascus gun barrels. An article that he has written on this topic, is in the current issue of “Double Gun Journal”. Doc Drew is going to send me a copy of this issue.

Below is a link to the thread I mentioned earlier. This is from Doublegunshop Forum. It is a forum that belongs to “Double Gun Journal”. This thread was started, because there is a great deal of confusion about whether it is the wrought iron, or the steel laminations that color "black".

Doublegunshop Thread

Thanks, Steve. That's an interesting observation on the grain structure. I've been trying to relate that to Brian's (as well as my own findings) in that the less the surface of the welds are exposed to air while hot but before getting welded, the less the white line effect.

Any thoughts?

Gary

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LOL!!! Some folks tell me that I think too much!!

So, now I've got another quandary. How could a person ever think too much, especially if thinking is a thing a person likes to do?

Yup, different crystal structures etch differently, and steels of different chemistry etch differently.

Flux use or no flux use should produce a sameness at weld point. Crystalline structure at weld point should be consistent. Heating after welding just about has to be normalizing... grain size equalizing and grain size reduction. Carbon diffusion equal.

After I saw the picture you posted from the paper I posted for the first time, I thought the perpendicular-to-weld-face area ought to be an artifact of the welding type... "things" jumping around under heat then moving across open area to connect... that that caused a permanent crystal form different than the non-weld-zone crystal form. After a while I thought there was an illogic in that. Shouldn't a thorough normalizing make all crystals the same? Even if a stack of identical steel is "pattern welded" I believe the weld area would show the perpendicular lines but I'll be darned if I can make them stay that way though normalizing cycles... and carbon diffusion should make equal chemistry every where unless there are elements lost at the weld interface that do not diffuse as the carbon does. But can that make different crystal structure? I'm not betting my nickle on it.

I can see how a spiral jump weld and a lap weld might be different... one type "white" and the other "not white'. I don't see how a pattern welded spiral or lap (or butt) can be either "white" or "not white" differing by pattern only.

Mike

|quoted:

Below is a link to the thread I mentioned earlier. This is from Doublegunshop Forum. It is a forum that belongs to “Double Gun Journal”. This thread was started, because there is a great deal of confusion about whether it is the wrought iron, or the steel laminations that color "black".

Doublegunshop Thread

I spent the evening with the Double Gun Journal link you put up. Followed some of the thread's links to a great photo gallery of damascus barrel steel patterns, etc. Boy am I glad I asked for the link, Steve... what a wonderful tour. Thank you very much.

Mike

You must be looking at damascusknowledge.com. That site belongs to Dr. Drew House; the guy who is having testing done on old damascus barrel tubes. Doc Drew has become a good friend of mine. He is a very serious researcher of damascus barrels and he has sent me dozens of photographs of old damascus barrel patterns. Damascusknowledge.com

Even if a stack of identical steel is "pattern welded" I believe the weld area would show the perpendicular lines

Welding identical pieces of steel together is one of the things that got me started on this grain structure question. I made very large a mosaic billet of 1084 and 15N20. There were several areas where I needed the 15N20 to be 1/4" thick. I only had 1/8" stock, so I double stacked it. This billet was 3 inches square. ALL of the steel pieces in this billet were surface ground on all four sides. The fit-up between them was perfect. The double stacked pieces were deep inside of the billet. In preparation for welding, the billet was sealed in a sheetmetal "can", which was partly filled with kerosene. The billet was welded and then drawn out into 7/16" square rods. The rods were twisted 3 1/2 turns per inch. Six of the twisted rods were welded together to make a blade. The blade was heat treated, just as I do all damascus blades. It was after etching the blade to reveal the pattern, that I found something that I did not expect.

At every forge weld between the double stacked pieces of 15N20, the weld line etched less than the surrounding steel. There was a small ridge of steel, running right down all of the forge welds. Light sanding on the blade caused all of these small lines to make the blade appear to have spider webs all over it. It took a lot of sanding to flatten these small ridges down to the tops of the 15N20 pieces.

How can surface ground pieces of the same steel, buried deep inside a billet, welded in a can with kerosene, heated dozens of times to draw out and then twist, welded into a blade and then heat treated..... wind up having the weld lines be less reactive to the etchant solution??? I expected that the stacked pieces of 15N20 would essentially become a mono-steel. I thought the weld lines would be lost. But instead, they became a problem during etching.

I was looking at what must be Drew's picture holding site. Now you have linked me into what looks to be quite a few evenings of damascus barrel education. Thank you for that, Steve.

-----------------------------------------

I've been sitting here for over an hour thinking about the 15n20 weld line etch. Chasing my tail is more like it, really. I'm starting to wonder if I'm going to be able to get any where with it at all.

One of the things I've been chasing... kerosene is carbon at the weld face, but I don't know if the steel takes the carbon. If yes, instead of diffusing it creates a local chemistry change... maybe hardness change... then differential etching. Why wouldn't it diffuse, though. I know it wants to. Nickle sheet stops diffusion. Do higher amounts of nickle slow diffusion? Is there enough carbon there anyhow?

Like I said... tail chasing.

Mike

|quoted:

How can surface ground pieces of the same steel, buried deep inside a billet, welded in a can with kerosene, heated dozens of times to draw out and then twist, welded into a blade and then heat treated..... wind up having the weld lines be less reactive to the etchant solution??? I expected that the stacked pieces of 15N20 would essentially become a mono-steel. I thought the weld lines would be lost. But instead, they became a problem during etching.

This may be a wild assumption on my part, and it may not. However, we tend to think that forge welding is somehow the same as making homogeneous steel and it isn't, even when you forge weld two identical pieces of steel to one another. They are still simply bonded to one another. That isn't the same as melting them together in a homogeneous manner. (this is the point in the post where the terminology escapes me, so please allow me some slack)

You have bonded the steels together and the physical/chemical/atomic (whatever) properties at that junction are not identical to those in the rest of the steel pieces, although they may be similar. Evidently, that similarity, and subsequent differences, act differently in a chemical reaction such as acid etching. Different metals react differently to the same chemical process because their physical properties differ. Apply the same rules to the weld area and you will realize that it will not react the same as the base metal does. Why would it?

I still ain't done with this topic....

Apply the same rules to the weld area and you will realize that it will not react the same as the base metal does. Why would it?

Given that the method of joining the pieces of steel is metallic bonding, rather than melting them together, causes me to think that there should be even less of an effect at the weld lines. Melting offers significant chances for analytical changes in the materials. Bonding only involves the valence electrons. Why would there be an automatic assumption that electron attractions would cause a change in the grain structure and consequent etch of the affected area?

My real question is; what causes the weld line grain structure to be different? What is the metallurgical explanation of this phenomenon?

Evidence from my testing, as well as seen in the micrograph from the document that Mike Krall shared, suggests that the grain structure along a metallic bond is incapable of creating the same crystalline lattice as adjacent material that is not involved in the metallic bond. WHY?? What causes this differential grain structure? Is it because the valance electrons are tied up in the effort of creating the metallic bond and therefore are unavailable to participate in grain structure formation? Is differential grain structure along a forge weld (metallic bond) to be expected all of the time and along every forge weld? Does the structure along a metallic bond change with different heat treatments, but always remain a different structure than the adjacent material?

This calls into question whether forge welding methodology actually has any effect on whether the weld line shows in the pattern. If pieces of the same steel, buried deep in a can welded billet with kerosene show the weld line, what chance is there that a change in methodology will change the results of etching? Obviously, there many damascus patterns welded up with little evidence of the weld lines. Possibly this is a visual obscurance of the weld line, due to the complexity of the damascus pattern. Ya’ just can’t see it. After etching, it becomes part of the resulting damscus pattern.

I was indeed praying that there would be a very minimal effect created at the weld lines in the earlier mentioned pattern. My surprise was that they became a significant problem. These problems cause me to wonder if there is anything that can be done to minimize it. Could the differential etch be minimized by a change in heat treatment? Not that the two different grain structures can be changed to a similar state, but perhaps they can be made to have a similar corrosion reactivity. Perhaps a small change in heat treatment would minimize the difference in the corrosion reaction between the two different grain structures.

I suspect the answers to these questions can only come from lengthy testing and SEM observation.

One of the things I've been chasing... kerosene is carbon at the weld face, but I don't know if the steel takes the carbon.

Brian,

I’m certainly not a chemist, but I believe I can give a plausible answer to your question. The carbon from the kerosene is intended to mitigate oxygen from the forge weld, whether in the form of iron oxide, or atmospheric oxygen. It does this in a combustion reaction, combining with the oxygen to create CO2. Any carbon that is not consumed in a combustion reaction is certainly available to migrate into the steel.