Composition of the silver decarb line.

[Quintin66]

Hello Gentlemen, My name is Quintin Kittle, from Southeast Indiana. I have just recently begun forging with my cousin at his shop, The DogHouse Forge, in Moores Hill. While studying some of his recent blades I noticed a very small silver line of steel inbedded in the layers, where two layers of file steel have been welded together mostly. I enquired about the line, but my cousin doesn't know exactly what it's made of. After exhaustive searches of forging and blade sites, I basically learned that carbon migration towards the weld has a contribution, and that it may be iron carbide, but I'm not positive. Then I ran across an article written by Mr. Fogg were he talks about using carbon black in his flux sometimes to lessen the silver decarb line. At our shop the damascus we're making is not from exact metals, just a few files and bandsaw pieces thrown in with a banding strap or two to make some layers. But knowing just exactly what we're looking at may help when we get brave enough to do projects like feathered W's and the like. So I'm trying to learn all I can about the composition of the metals we use. There may come a time when, as Mr. Fogg stated in the article, that a pattern welded steel may benefit from the removal of this line for asthetic reasons. That's why I'd like to know exactly what it is, and even what temp it forms at if someone knows. Thanks,..........Quintin

[GEzell]

Welcome to the forum!

I'm guessing it would be the 'skin' of the steel loosing carbon while it is brought up to and held at welding temperature, the difference in carbon causing the steel to etch whiter than the higher carbon areas. It's the same phenomena that causes welded steel cable to show a pattern...

 

My second guess is that the flux is alloying with the steel, again forming a skin of material that etches differently. What type of flux did he use?

[KPeacock]

although my experience is certainly limited, I agree with the above post. I recently hammered out a couple of cable knives after my father and his hunting buddy saw some pictures of what I'm doing. They requested a couple of knives so I'm making them and I was a bit cutious as to what causes the pattern to develop. The cable strands are presumably all of the same construction...so why the lines at the interface of strands? I chalked it up to lost carbon from high temp forging to weld the strands. I'm not sure of this is correct, but it sure seem to be a likely cause. You may want to give the cable a try. it's free/cheap to obtain and very easy to work with. I get my cable from a local elevator repair company. it can be purchased pretty cheap from a chain/cable company. I bought a 4' section of 1" diameter cable for under $20. there is enough mass that you get a decend knife out of it, and the strands are large enough that you don't lose all of the carbon. thats the idea anyways...we'll see how it works when I get it finished.

 

My next project is to use a timing chain out of a small block chevy engine. It's good steel, and a spark test indicates a fair bit of carbon in it. perhaps a neat pattern will develop. I'm using these projects to improve my finishing skills and to gain practice at forge welding before I attempt a more elaborate pattern. You can get timing chains and ATV chains from local motorsports shops and engine machine shops. At some point I'd like to make a knife entire of small block engine components. easy enough to do, but i think it'll be hard to make it look good.

[Quintin66]

The flux was 20 Mule Team, that was spread in the oven on a sheetcake pan and heated until molten, left to cool, then crunched back to powder. It doesn't seem to blow up a blizzard when applied to hot metal after that treatment.

 

The process both of you describe is what I believe also. What makes me curious is that carbon migration also happens on the outside of the billet as it is forged but there's no evidence of a build-up of this shiny metal, only scale. I was reading the other day a progression of crystalline structures that develop during cooling from martensite down through austinite and then pearlite. If I read correctly, iron carbide crystals can be trapped during the beginning stages of pearlite metastisization where high carbon contents exist. Maybe there's not enough with a single plane of migration, but with two planes back-to-back, it may form the iron carbide crystals. I don't know the make-up of iron carbide, but when someone says carbide, I think some damned hard stuff, as in carbide tipped blades. If it's the same, it would account for why it turns out so shiny and un-etchable. I may be waaayy off base with this theory, but it's only based on what I've been able to dig up.

Edited December 9, 2008 by Quintin66

[DFogg]

I don't know what the silver line is, but if you don't use borax for flux and/or weld at high temperatures, above 2400F, you don't get it.

[Howard Clark]

The debate goes on...

 

I think it is boron pickup from the flux, combined with decarburization. I do not believe that anyone really knows for sure, except maybe Hephaestus himself.

[Quintin66]

Ahhhh... Clash of the Titans, ...his starring role. A man who can make a solid gold owl fly certainly would have the answer!

I absolutely love that movie.

I guess I'll research some new flux recipes, any takers?

[Steve King]

Dog House Forge, I have been there. Nice shop, hammer, and Jon is a good fella as well.

 

I live a little farther Southwest of Jon. If you can catch a ride with Jon the last Saturday in Janurary to my place. We have a hammerin here the last Sat of each month. There are a few of us that have the Pattern Weld Disease.

 

Anyone else in or around the area is invited. I am 1 hour from Louisville, KY, 1 hour South of Bloomington IN.

 

Jon was telling me about your research Sat.

 

Steve

[Mike Krall]

I don't know anything about this... If a person puts a piece of clean cable in a "can" that just fits it and a couple of layers of SS foil, no paper, no flux, no kerosene, no powdered metal... and welds at 2000F -2100F, it etches the same as a piece done "the regular way", except with no weld flaws.

 

Mike