Help me understand this statement.

B . Buxton

B . Buxton

Joined
Jul 8, 2001
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O.k. Heres the deal, I was talking to an older gentleman the other day that has been blacksmithing and bladesmithing for probably 40 yrs. He told me that when forgeing and making damascus, using a coal forge, that the coal actually adds carbon to the steel. Now I just don't understand this statement. If you heat a piece of steel to forging and welding heats, you lose carbon, so how can you be putting carbon in, from a fire that is burning the carbon out.
Even at the low end of the forging heat you lose some carbon, so if you have a piece of steel that is high in carbon, and after each forging heat, say, you lose .05 % carbon and the coal fire is expelling .02% carbon at each heat cycle, why would the carbon expelled from the fire be drawn into the steel that is releasing carbon. According to this gentleman, you can start out with a low carbon steel and end up with a higher carbon content then what you started with, when using coal. Also if your burning out more carbon then the fire in releasing, if the steel will absorb it, how in the heck can you end up with a higher carbon content.
This gentleman has been doing this a long time and makes some beautiful stuff, but this just doesn't make any since to me. I know we all have different ideas for what we are doing, but what am I missing here.
I had another bladesmith tell me almost the same thing at a knife show last summer. Any ideas on this would be nice.

Bill ????
 
How do you think carbon was added to steel long ago? Probably it was heated for extended periods of time in a charcoal furnace. I really don't know but that's what I've always assumed. It's cooking next to large chunks of pure carbon. Some of that must get transferred to the steel.
 
isnt that basically what the japanese swordsmiths do?
put the tamahagane into their tatara's and just let the iron meld with the carbon of the charcoal so create a carboned steel?

i have seen a blacksmith who kept forge welding a piece of iron using crushed charcoal as a flux ... and slowly he increaed the carbon content of the metal ..

but i wouldnt like to say about the specifics of it ... i guess it would come down to the ratio of carbon being burnt out compared to what is being taken in ..

D.
 
It still doesn't sink in that you can take a steel to a heat when it is expelling carbon, and at the same time be absorbing more carbon than its expelling, if its at that point of releasing how can it absorb. Its like taking a sponge and holding it under water and squeezing it at the same time, even though its under water your still squeezing the water out and no water can be absorbed until you let go.You've displaced the water by sqeezing, you displace the carbon by heating and I don't understand how you can put carbon in unless it is cooked at a heat that will cause the steel to absorb not expell. It would have to be heated and left to absorb at temps below forgeing and welding heats. I'm comfused and curious, he said that at forgeing and welding heats it gains carbon from the coal. :confused:

Bill ????
 
I'm not sure how much it picks up but it does get some. I am certain it does not get into the steel as much as it gets on the steel. When I first started gunsmithing, case hardening mixes were hard to come by so we would put the part in a pipe with bone meal or something like that, and cook the he!! out of it with a torch. The skin would be hard as glass. It's the same basic thing for forging over a coal fire.
 
Carbon is carbon. It matters not where it comes from, propane or coal. It is up to the bladesmith to fine tune his forging practices to minimize the loss of carbon. Choose a steel with enough carbon to achieve the potential you seek and nurture it carefully to the fisished product. I have heard about adding carbon in a coal forge, never seen any empirical evidence of it. I do know that carefully forged blades, worked down from a 5 1/2 inch round bar, multiple quenched and tempered demonstrated no measurable carbon loss when compared to the chemistry of the parent steel.
 
...of the fire.

Steel has a tendency to lose carbon in a high oxygen atmosphere. It (the oxygen) combines with carbon and escapes as carbon dioxide. If all of the oxygen is used up, either by being burnt or by the steel being isolated by clay or a container of some sort, it will absorb carbon from a high carbon source in the fire.

Japanese swordsmiths use a process called oroshigane to add or remove carbon in the forge to produce steel with the right amount of carbon. They do it by placing the steel on top of the fire to increase carbon(the oxygen is burned up before it gets to the steel) or at the bottom of the fire next to the air blast to reduce the carbon.

Old style case hardening was done by wrapping the steel up in a sealed container with bone or charcoal to seal out the oxygen and then cooking at high temperature till it absorbed carbon.

....I think that's how it goes anyway, Bill.:)

Brian
 
:eek: :D :D I do , I do !!!!


I do beleive that is my new knife on your web site . Can't wait to see it in person and put her to work .

Sorry to be off topic guys , I'll go away now .



Jerry
 
The ancient japanese smiths picked up sand ore from the banks of the rivers. The ore had no carbon yet. They dug a deep pit and put alternating layers of sand ore and charcoal. They lit the charcoal on fire and covered it back up with dirt. They had a pipe running into the fire and pumped oxygen in to melt the whole mess together. The oxygen was trapped and consumed by the fire and wasnt allowed to escape very fast therefore pressurizing the fire. It is the fumes or gas from the coal that has the carbon. The gas and carbon are absorbed into the ore and steel is the result. If we take graphite and wd40 in a closed container like mosaic damascus is made today, we will add a few points of carbon to our steel. The wd40 is the carrier. graphite is carbon.
 
Wow Greg! My hair is smokin' after looking at that thread. Too technical for me... especially before my coffee this morning.

On the same idea as Bruce Bump,...

When iron ore is smelted in a coke fired blast furnace, the resultant product (pig iron) may have as much as 6.7% C. Then a fellow named Bessemer came along and blew oxygen into a ladle of bubblin', molten pig iron and found that he could reduce the carbon content and his new product was called "steel". Your basic cast iron has so much carbon that you can almost see the free graphite (carbon) segregated in the grain structure when you closely look at a fracture. Note the nodular, bumpy , brittle surface. The Bessemer process effectively reduces the carbon content of the pig iron down into the eutectoid range of the iron-iron carbide phase diagram. So in general, steel is defined as an iron-carbon alloy that contains less than 2.1% carbon.

Hence, to over-simplify the steel making process:
we start with pure iron ore (no carbon)....
melt it in a blast furnace and consequently introduce excess carbon (pig iron)...
then remove some of carbon with free oxygen (Bessemer process)...
and we have "steel"

As far as what's happening in the forge...heck I dunno :confused:.

I certainly have had my share of troubles with De-carb while heat treating tool steel in an electric furnace without atmosphere control. Also, I've used "Kasenite" to carbon enrich.

So...sure! you can definately move the carbon around a bit...for me I just can't control it and it alway seems to go the wrong way at the wrong time. :(

Take care,
Rob
 
Bruce has the start of it right.
After the resultant bloom cooled, it was taken and broken into pieces and sorted by grain texture and color. The peices that were deemed to be good steel were forge welded back into a bar and saved to make the cutting edges, the other stuff was welded into a bar and used to make the rest of the sword. According to a book that I have The core of the blade and the out side of the blade were treated the sqame with the exception of the core being folded and welded a minimum of fourteen times but no more that eighteen times. The steel that was to become the outer part of the blade was folded twelve times. During the welding process the whole billet was covered in amixture of clay and ground charcoal. This was reported to help even the hardness that could be attained in the sword. The author also stated that after eighteen welds the steel could be made no better and further folding and welding often made for a poorer quality sword.
The book that I have, was written in the late ninteen thirties and was published in June, of 1941. The author and his family had been first sword smiths and then sword polishers for over seven hundred years. For what it's worth.

Bill B????
 
Well its all as clear as mud now, and thanks Greg, not only did your post cross my eyes, now I have a spliting headache :D .

I just wanted to know if it was possible, for carbon to be absorbed into a steel when it was heated to a point that it was releasing carbon, not how to mass produce steel. I would say yes it probably does, after all this reading, but it has to be in a deep fire with all the oxygen consumed before it reaches the steel, any trace of oxygen and the carbon will be removed from the steel, I think :confused:, so actually even though it is possible it is unlikely to add carbon to a steel when forging or welding. To add more carbon then you are loosing, anyway.

Ed, thanks for your imput here, I believe you hit it on the head.

Thanks guys

Bill ????
 
I may be wrong in this but from talking to various people and reviewing various books and articles I've read (and as Ed Fowler mentioned earlier)I don't think there really is much total carbon loss in the normal forging and heat treating process except in a thin skin on the surface of the steel and in the thinnest cross sections. Heating into the burning ranges however probably does reduce carbon content quite a lot.
The Neo-Tribal adherents will forge a blade nearly completely to shape and seem to experience no lack of hardening near the edge though I have heard of knives made by blacksmiths that didn't hold an edge well until after being sharpened a few times (possibly the sharpening wore away the minute area of decarbed steel along the micro thin edge.) This could also be explained by the fact that blacksmiths are generally used to working with wrought iron and mild steel at higher temperatures than a bladesmith would use.
When I first started knifemaking I was explaining what I was doing to the father of a friend of mine. He asked me if I was going to "carburize" the steel to make knives. This puzzled me as I couldn't figure out how you could add carbon to steel and I told him I was starting with high carbon steel so more carbon wasn't needed. I later found out that he had worked in the Mobile shipyards as a welder and that they often carburized (added carbon to) steel plating and such using their gas cutting torches.
All coal fires as I understand it have an oxidizing layer (bottom of the fire near the tuyerre), a neutral layer (in the middle of the fire) and a carburizing fuel rich layer (the top of the fire). Propane forges can be adjusted to be oxidizing (oxygen rich), neutral (all gas and oxygen is consumed) and rich (fuel exceeds the amount of oxygen needed to burn it.) I find it unlikely that significant amounts of carbon are added in the relatively short amount of time that steel is in the fire for forging and heat treating operations but at longer times the steel in a carbon rich environment at the right temperature will absorb more carbon by processes already mentioned.
Sorry for being long winded but I was working things out in my head as I wrote to get a better understanding of this myself. If there are any glaring inaccuracies in my reasoning please point them out. I wish I had more practical experience than I have to back all this supposition up.

Guy Thomas
 
Looking way back to my chemistry courses, it seems that the process of the loosing or gaining carbon is much like the process of a drying a piece of wet wood. What matters is the relative concentrations water (carbon) at the wood to air (steel to air) interface.

If the surounding air is dry, it has a low concentration of water vapour, then it can absorb more water from the wood than if the air was saturated with water vapour. Saturation (100% humidity) is defined as the point at which the air can hold no more water vapour. Similarly, the wood has a capacity to hold water. There is constant evaporation of the water from the wood into the air. There is also constant condensation of the water out of the air onto the wood. This last point is not intuitive, at least not for me.

If the wood is wet (high concentration of water) and the surrounding air is dry (low concentration of water), the water that evaporates off the wood is carried off by the surrounding air so that the air reaches a uniform concentration of water vapour. The net effect is that the water moves from the wood to the air and the wood becomes drier. This is what occurs in the Bessemer process.

If the wood is dry and the air is wet, the wood has more capacity to hold water than the air and the water condensing on the wood is absorbed into the bulk of the wood. The net effect is that the water moves from the air to the wood.

If the wood and air are at the same capacity to hold water, then the rates of absorption in both directions at the wood to air interface is balanced. The net effect is that the water content of the wood and the air remain unchanged. Note that there is still an interchange of water between the wood and the air.

I hope that I have remembered it right. Please feel free to post corrections if you have a better understanding of this than I do.

Phil

PS: The process of having the solid absorb a material from the surrounding gas is used in the semiconductor industry to add various elements such as boron, arsenic phoshorus, etc. to the pure silicon wafers to make transisitors.
 
After reading all this, I have to wonder how deep into the metal carbon can migrate or be absorbed?
 
As I said in my post, I think it's almost a surface treatment but I also don't think the burnoff occurs deep in the steel. I think it's a surface action also. I also feel and I'm really opening myself up here...that the problem is small for the most part and we spend way too much time worrying about it.
 
Sorry, didn't mean to cause any headaches. I probably should have been more specific in regards to that article, quoting this paragraph:

"A soft iron bar, inch square, which after heating and quenching in water did not obtain any hardness, was wrought at one end to a point. In charcoal before a blast of air this was allowed to take a good welding heat, strongly sputtering with fine white sparks, without casting any sand on it. At this heat the point was quickly quenched in cold water; whereafter it was found to be completely clean and white. As far as the welding heat had reached it was so hard that no file could bite it. It was especially hard at the point, where it had begun to melt into a little drop. . . ."

Owe you some beers, fellas.

Regards, Greg
 
One of my old handbooks gave the following for case hardening low carbon steel: the practical maximum about 1.1% and after 2 - 3 hours a thickness of 0.5 mm. Theoritical values are those given by the stability diagram at that temp and how long you want to wait.

Apparently what ever mthod of carburizing is used the appearance of CO is necessary, meaning low oxygen conditions.

TLM
 
I'm not very technically minded, mind you, but this is the way I understand it. Put a hot piece in a oxygen rich enviroment and carbon loss occurs. Put it in a carbon rich enviroment and carbon enrichment occurs. In a pure neutral enviroment very little cabon loss or gains occur. This is why case-hardening powders work on low-carbon steel. My .02 worth mw
 
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