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Joined: Sep 2012
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I've spent a lot of time considering Adam's photomicrograph of the blown out barrel section and his analysis of the black spots being graphite nodules. I find the same anomalies in micrographs that I have taken of the old damascus barrel in my possession. But too, find them in micrographs of damascus that I have made from modern steels.

While I am NOT an expert in the field of micrograph analization, I have found that there are a number of reasons why black spots can appear in micrographs. They can be caused by the degree of surface prep of the sample, the effects of the type of etchant used and also the size of the material's grain structure. The micrograph posted of the blown out barrel section was taken at 20X magnification. The microscope in my shop is only capable of 20X maximum. I have found it very difficult to determine the exact cause of small anomalies at this magnification level. I hope that Adam will view the blown out section at a higher magnification level, to make certain of his analysis.

Regarding the analysis that the black spots are graphite nodules from the use of ductile iron, or any type of cast iron being used in the manufacture of damascus barrels; I am not yet convinced. I concede that the black spots appear similar to graphite nodules in the 20X image. However, the specific product named "ductile iron" was not invented until 1943. Ductile iron has magnesium added, which inhibits the graphite's growth directions, turning it into nodules. A similar graphite nodule formation can be created in gray cast iron, by heating it to 900C/1650F, and holding it at that temperature for 72 hours. I seriously doubt that damascus barrels were subjected to such a heat treatment process.

Nothing in my research of the historical manufacture of damascus barrels has indicated that cast iron was used. And my experience with making damascus steel causes me to doubt that cast iron could be utilized to weld damascus. Cast irons have a very high carbon content. The high carbon content makes cast iron what blacksmiths call, "hot short". If you heat a piece of cast iron and hit it with a hammer, it will shatter. It cannot be forged. I cannot conceive of trying to incorporate cast iron into a billet of damascus.

Again, I am not an expert and I don't intend to be argumentative. But my message to Adam, is to look closer. The use of cast iron in a damascus barrel seems improbable to me.

My research into damascus barrels has led me to a theory that the barrels were made up of a medium to high carbon steel, laminated with wrought iron. There is ample historical documentation stating that the barrels were made of steel and iron laminations. I base my theory of the iron element being wrought iron, from having read innumerable pages of old documents on iron making and usages, that were written contemporary to the manufacture of damascus barrels. In all cases that I have found, when the word "iron" was used, the material being spoken of was wrought iron. This was simply the common name used at that period of time. If cast iron was being written of, they used the words cast iron, gray iron, pig iron, etc. If they used the word "iron", they meant wrought iron.

Wrought iron was produced from cast iron, by a process of heating the metal to just below the melting point. An air blast was directed at the surface of the iron, to burn off the carbon content and most of the damaging impurities. The iron was maintained in a semi-melted plastic state and constantly stirred to mix in the iron oxides that formed on the surface of the iron from the air blast, and also silica from sand and limestone used as a flux. This admixture being basically an iron oxide bearing glass. This constant stirring of the material is where the name "wrought iron" comes from. Wrought meaning, hand worked. Once the iron was sufficiently decarburized and thoroughly mixed, a ball of the material was removed from the furnace and taken to a power hammer, or press, where the ball was forged into a bar. During forging out the bar, the globs of iron/silica are stretched out into strands, lengthwise of the bar. This first bar was often cut into pieces, restacked and forge welded, then drawn out again. The restacking and welding would reduce the size of the strands of silica and also force out some amount of it. Depending on the intended end use of the material, restacking and welding could continue until the material was nearly pure iron. A common product of the foundries was called merchant bar. Merchant bar was fairly high in silica content. The intention was that the end user could restack and weld the material to suit their needs.

Below are three micrographs that I took of a piece of wrought iron from a anchor chain link. You can see the strands of silica in the side (first) image, running lengthwise of the bar. The micrograph of the end of the bar, shows the black spots created by the ends of the silica strands. Note the image of the entire end of the wrought iron bar. The lighter hued lines are the edges of the restacked bars that were forge welded to make up this single bar.





I have a section of damascus barrel tube, that I purchased from Peter Dyson. This barrel tube is in its as forged condition. It was never finished out. It still has the chemise inside it. I sawed part way through the tube and then broke it off. Below are two micrographs of the end of the broken section. The layers of steel in the damascus are very fine grained and a flat gay color. The layers that I theorize to be wrought iron, are very course grained and include black spots; which I believe to be silica strands. The chemise appears to be of nearly pure iron. No silica strands are evident in the chemise at this magnification.




Below is a micrograph of an etched section of the damascus barrel. This image shows black spots in both the steel layers as well as the wrought iron layers. The above image of the broken barrel section does not indicate the presence silica strands, or graphite nodules in the steel layers. I can only assume that the black spots were created by the effect of the etchant.



Below is a combination of two micrographs of the ends of damascus bars that I made. The steels in this damascus are 1084 and 1018. The left image, is of the damascus after thermal cycling to reduce the size of the steel's grain structure. The right image is of the same material, after heat treating to create a spheoridized grain structure. Spherodized grain, is a very large structure. Notice the differences in how they etched. Also notice in the left image, the thin lines. These are decarburized weld lines, where the damascus billet was restacked and forge welded. This area etched less, because of the lack of carbon. In the right image, the weld lines are nearly invisible. During the heat treatment to spheroidize the material, the extra time at heat allowed carbon to migrate back into the decarb areas.



Steve Culver
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As always, thanks so much Steve. We're all in uncharted territory here, and the more guys thinking, and willing to contribute, the better!

I've previously posted that is someone would please whack off the end of their Damascus demonstration rod (science will thank you smile ) METL can separate the iron and steel strips and tell us exactly what they are.


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In part the silica was coming from the coke used in the smelting furnaces. This was a major concern for the damascus barrel makers.

Pete

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Thanks Guys,

Please understand that it is not my intention to disparage Adam's work. I am trying to learn and I have questions about how to understand what you are viewing in these images. The more that I look at micro photos and realize how many factors can affect what is seen, the more questions I have.

Did some work today to try and find a comparison to the layers that I theorize to be wrought iron in my broken off barrel section. (The image posted earlier) The metal in these layers has a very large crystalline appearance. It's hard to tell in a photograph, but the crystalline structure sparkles, like diamonds. The only comparable sample that I have looked at is etched 1018 steel. Etched 1018 has a very similar sparkly, crystalline structure. However, the broken barrel piece has not been etched. Then, there is the black material, that I believe could be silica. But, it looks like a LOT of silica. I'm surprised.

Image of etched 1018 steel, below.



I broke a piece from the sample of etched 1018 steel and looked at it under the microscope. I did not etch the broken area. It appears to be a fairly small grain structure. Not at all like it looks when etched. Notice in the image, the lines similar to those seen in the blown out barrel section. Perhaps a product of stresses induced during the forceful destruction??



I then broke a piece from the wrought iron anchor chain sample. Again, no etchant applied. VERY different than the barrel piece. It almost looks like it has hair. Notice the rather large inclusion, at about 10 o'clock.



Result at the end of the day…………. More questions.


Steve Culver
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Thanks for all that work Steve.

You're getting a standing ovation here...


"The price of good shotgunnery is constant practice" - Fred Kimble
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Thanks also Steve. Good stuff.

I wonder if the lab did find graphite inclusions in the barrel, that it made for a higher carbon content, but the carbon available to form steel might be closer to that 1018 that you looked at. Possibly not a true medium to high carbon steel component of the damascus.

It seems like the materials used were known to have flaws, so I wonder the repeated drawing, twisting and welding was to minimize the dimension of inclusion and disperse them. In Doc Drew's micrograph, if those are carbon inclusions, they seem to be of a generally small size and separated from each other. There doesn't seem to be any obvious clusters of graphite or even larger inclusions like shown in your wrought picture.

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Sorry, have to do it......

Sooo, what would be the better choke for a furnace?

Upland, not industrial district...over pointers? smile

Seriously though, that is some amazing information and imaging, I hope everyone continues to contribute to this in a factual, open minded way as it has been very enlightening.

Best,
Mark




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Steve, that's a very interesting contribution to the discussion. But I doubt if there is actually more than a trace amount of silica in finished 1018 steel. The amounts in wrought iron would typically also be small, as most of the silicon content of the ores is greatly reduced by the addition of limestone or lime to produce slag. Here's some information I found on silica content in iron:

".... Silica (SiO
2) is almost always present in iron ore. Most of it is slagged off during the smelting process. At temperatures above 1300 °C some will be reduced and form an alloy with the iron. The hotter the furnace, the more silicon will be present in the iron. It is not uncommon to find up to 1.5% Si in European cast iron from the 16th to 18th centuries.

The major effect of silicon is to promote the formation of grey iron. Grey iron is less brittle and easier to finish than white iron. It is preferred for casting purposes for this reason. Turner (1900, pp. 192–197) reported that silicon also reduces shrinkage and the formation of blowholes, lowering the number of bad castings...."

It's interesting to note that silicon promotes the formation of grey iron which is "less brittle and easier to finish than white iron". So the presence of some amount of silica in the wrought iron used in Damascus could be either a curse or a blessing depending upon the percentage of silica content. We probably won't know what's in the amalgam of iron and steel used to produce old Damascus without an actual analysis done by a metallurgical lab. I worked in an integrated steel mill for several years after college and recall sending samples to the met lab during a heat and getting accurate results in short order, down to small fractions of a percent. Then the melter could add ingredients, or alter carbon content by blowing oxygen. They used Infrared spectroscopy then, and I wouldn't be surprised if mills use NMR now. The final analysis followed the product to end finishing and directly to the customer. Looking back, I wish I'd paid more attention and asked more questions, but often, the great object was simply not getting burned alive.


A true sign of mental illness is any gun owner who would vote for an Anti-Gunner like Joe Biden.

775 #361582 03/21/14 09:12 PM
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Originally Posted By: 775
Sooo, what would be the better choke for a furnace?


The introduction of coke to the smelting process was a later development. Initially the Liege makers were up in arms because they felt it introduced silica and the barrels just did not look right to them. A long search ensued. They tried steel from every source they could. Eventually Cockerill, "the" maker of steel in Belgian, bent to their desires and changed. What forces were brought to bear on Cockerill is not clear. He certainly did not 'need' their business.

Pete

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Is choke the same as coke in smelting ?

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