Thanks for the appreciation guys,
Perhaps I should explain the purpose of my work with the microphotography. I am searching to find a combination of steels to use for making damascus gun barrels. I am hoping that these steels will also be capable of heat treating to make knife blades. I have chosen 1018 steel as the replacement metal for what I believe is wrought iron in old barrels. I have welded several billets of damascus, having the 1018 layered with a different high carbon steel in each billet. The billets were drawn out into 1/2 inch square rods. I am subjecting the rods to different heat treating processes, which are the same as I will be doing to the material if used for a barrel or knife blade. After each heat treating process, the rods are etched with ferric chloride to see the result. I will also be etching these samples with a couple of different acids, as well as testing how well they are capable of taking browning and bluing. I have a lot of tests yet to do.
To better understand the results from my testing of these materials, I am studying the chemical reaction of different acids and metal salts (like ferric chloride and copper sulfate) on steel. As etchant solutions and bluing/browning chemicals are all types of acids, or metal salts, I feel that it is important to understand how they work, in order to be able to get predictable results in finishing the damascus. Acids and metal salts effect steel in ion exchange reactions. Essentially, like hooking a microscopic battery to the steel. My testing suggests that the "connections" for these electrical exchanges, are the edges of the steel's grains. The size of the steel grain structure appears to affect the number of electrical connections available for the ion exchanges to occur. This can be seen in the image that I posted earlier of the damascus rod of 1084/1018 steels. The finer grained rod etched very uniformly, because of the many connection points. The rod with the larger spherodized grain structure etched very coarsely, because the contact points for the exchange of ions were farther apart.
As there was no specific heat treatment utilized to control the size of grain structure in old damascus gun barrels, this could well be the reason why barrel refinishers sometimes will find a damascus barrel that does not finish well. The acids used for coloring the barrel cannot effect a uniform bite on the steel, because the grain structure was not refined after forge welding.
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.
I am fairly confident that the "steel" component of old damascus barrels was actually high carbon steel. At that period in time, they fully understood what high carbon steel was and were capable of producing it efficiently. I also base my analysis of the material on its reaction to etching with ferric chloride. It etches and colors very similar to the 1084 steel that I use for knife blades. The reaction of steels to etchant solutions, can tell a lot about the alloys in the steel and also help to display the grain structure.
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.
Agreed. I am using analytical 1018 steel. So, I know there is only a trace amount of silica in it. The fact that the etched 1018 sample appeared to have a similar large grain structure as the metal in the old barrel was what caused me to test the 1018 by breaking it. Note that the 1018 sample had undergone the same spheroidizing heat treatment as my high carbon steel samples. I was surprised to see that etching the 1018, caused it to appear as if it had a large grain structure. Breaking the 1018 sample, indicates that it does not have a grain structure as large as suggested by the etching. The crystalline appearance of the etched 1018 was solely a function of the etchant's effects on the steel. Why; I do not yet know. Another reason to get a better understanding of how etchants effect steel.
The introduction of choke 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.
I think most will be more familiar with the spelling as coke, rather than choke. Coke (fuel), a solid carbonaceous residue derived from destructive distillation of coal.
Pete, I think you may be confusing silica with sulfur. Silica is not a major issue in steel. The inclusion of silica in wrought iron actually makes it easier to forge weld, causing it to be somewhat self fluxing. Sulfur is very damaging to steel. Too, sulfur will inhibit forge welding. Blacksmiths who use coal forges always seek out low sulfur coal. High sulfur coal in the forge can prevent forge welding.
Do you know where Cockerill got the iron ore for their steel making? I found an old book on mining, that has the chemical analysis' for ore samples from mines around the world. If we have information on where Cockerill obtained ore, we may be able to find the analysis for it and learn more about the alloys in the steel produced.
Steve, are you accurately using the term "broke" to describe your method of exposing the inside of your sample? If you are actually "breaking" the material then I don't think you can accurately diagnose the exposed edge.
I did actually break the samples. It is an accurate way of exposing the grain structure in hardened steel. I have examined hundreds of broken knife blades, to see if the material was properly heat treated to reduce the grain size after forging the blade to shape. It is not an easy method to employ with soft steel. Hardened steel will snap off cleanly, leaving a surface that is easy to analyze. Breaking soft steel can leave so much structural damage, that there is often only a small place on the sample surface to analyze. Takes some experience to know the difference between grain boundaries and structural damage.
