Definitions and history of "Wootz" and such

[Tim Mitchell]

Jan, as you make charcoal, you have different hydrocarbon gasses burned off during the process.  Hydrocarbon... hence you are losing your carbon to the air and fire.  Wood is about 50% carbon per weight, and if you have a roughly sealed crucible, the gasses will be absorbed in the melt to a large degree.  Jan using your calculation of 22% of organic matter being carbon will give you twice as much in the ingot resulting in cast iron, and using a calculation of 50% weight of carbon in organic material will give you good steel, if you seal your crucible.

Edited December 20, 2017 by Tim Mitchell
clarified about percentage of carbon

[Joshua States]

Wait a minute, what?.

Jan, if I understand you correctly (let's make the math easy shall we?) For every kilogram of iron, I'd add 50 grams of charcoal. to get abut 2% carbon steel. Tim if I understand you correctly, I could take that same kilo of iron and add 500 grams of raw organic material and achieve the same result. (you kind of lost me on the 22% gets cast iron and 50% gets good steel. That seems backwards)

[Jan Ysselstein]

Joshua..let's see if I follow.

1000 grams at 2% carbon is 20 Grams of carbon in the iron,,,,,when I added 40 grams of carbon my steel was at about 1.5% ( guessing here).

I do not want to speak for Tim but I think in his case you can add twice the weight of organic material to get a weight of carbon. 

These situations vary in use as oxygen is always ready to screw up the results.  SO 50 grams of dry organic material would yield an equivalent of 25 grams of carbon.

 

[Joshua States]

Right. I messed up. 10% of that kilo is 100 grams of charcoal at 22% carbon gets you 22 grams of carbon per kilo of iron or 2.2% steel. Mas o menos loose some along the way and probably end up at 1.8% or thereabouts.

[Tim Mitchell]

4 hours ago, Joshua States said:

Wait a minute, what?.

Jan, if I understand you correctly (let's make the math easy shall we?) For every kilogram of iron, I'd add 50 grams of charcoal. to get abut 2% carbon steel. Tim if I understand you correctly, I could take that same kilo of iron and add 500 grams of raw organic material and achieve the same result. (you kind of lost me on the 22% gets cast iron and 50% gets good steel. That seems backwards)

Firstly you don't want to have an ingot which is 2.2% carbon or even 1.8% carbon, or you will end up with something that a beginner will have a really hard time working with, they are more prone to cracking and hard to work.

If you add charcoal to a melt, it is 100% carbon per weight, so you add 15 grams of charcoal in order to get 1.5% carbon in a 1kg ingot.  It works the same with graphite.

However if you add organic matter to a melt you need to know how much organic matter is actually going to be released by that wood or bark.  Wood or bark is 50% carbon by weight, so why do you get only 20% approx. of charcoal from burning wood? The other half of the carbon is released as gas and is burned in the process.  So if you add organic matter to a crucible and then seal it, you get the total 50% of the wood raw dry weight being picked up by oxides and by the metal instead of only 20%.

That is the basic theory.  Adding organic matter is far from a precise way of doing things, and oxygen and oxides will mess with any well laid plan as Jan pointed out  The metal won't pick up all the carbon unless the carbon source is finely ground and mixed with finely ground metal, that is why it can be problematic.

I find that adding metals with different carbon contents works well for me and it is very precise..

PS. I modified my slightly confusing previous post to make it more clear.

Edited December 20, 2017 by Tim Mitchell

[Joshua States]

Thanks

[Dan Waddell]

There was a comment, about hydrogen in organic matter lowering the melting point of iron, made by Al Pendray at about 14:30 from the following post.  It seems like a pretty big deal to be able to achieve liquid iron at lower temperatures.  Could this be explained a little further? 

I'm confused why more recipes don't use organic matter.  Even in recipes that use cast iron, having relatively lower temperatures still seems desirable.  Does the inconsistency of carbon content end up outweighing the benefit of lower melting points?

 

[Jan Ysselstein]

Dan,  Hydrogen would maintain a reducing atmosphere by reacting with any oxygen entering or any carbon dioxide formed  ..scrubbing the atmosphere in the crucible, making a more efficient carbonization of the iron.

 

[Vern Wimmer]

I thought that I heard, in the Pendray video, that the green leaves were included in part because they introduced nitrogen in the closed crucible ?

[Dan Waddell]

Thank you Jan,  So if I'm understanding what your saying correctly.  It's not that hydrogen makes the iron melt at a lower temperature.  Just that the iron carbonizes faster.  So comparing 2 other wise identical crucibles, 1 using charcoal and 1 using green leaves,  the temperatures would be the same, but green leaves would possibly lower the soak time required to go full liquid.  I think I may be misunderstanding the context of some of this information.

[Tim Mitchell]

I'm not sure about the actual mechanism, but Al did say that the Hydrogen lowered the melt temperature.  You don't want nitrogen in the ingot as that will make it brittle... very bad . As far as I can see, having more complete carburisation would not lower the actual temperature where the charge became fully molten, it would just help in the absorption, so it would start melting earlier.  The point of full melting of the charge is a factor of the carbon content not how well it is absorbed by the metal as far as I understand.  It is something that I do not fully understand and I should do some digging to find out exactly what is going on in the melt.  It is my guess that just as nitrogen alloys with the iron in the ingot to make it harder and more brittle (not desired), the hydrogen also can alloy with the iron to make it easier to forge and also any alloy lowers the melting temperature.  I am convinced that it is more than just creating a reducing atmosphere.

That is a really good question Dan, the reason that most people don't use organic matter is that it is just harder to control the carbon content in the final ingot.  Most modern smiths use a variation of the Deccani process which in the latter days didn't use organic matter as far as I remember.  You get several benefits from the addition of organic matter rich in tannins, but the precision is what you lose... you get more failed ingots and that is a bit of an issue for most smiths who aren't made of money and time.  The Deccani process allows much more precision and consistency in the final ingot quality.

That is it in a nutshell, I hope that helps a little.

 

[Joshua States]

When I think of tannins I think of making leather, and oak. Particularly, the leaves and acorns. How do tannins positively affect the ingot? 

I am going to assume that Deccani opted for straight charcoal rather than organics. Were there any documented experiments with hybrid mixtures?

Edited December 22, 2017 by Joshua States

[Jan Ysselstein]

Joshua,   All this material is organic material which chars and turns to organic vapors and carbon ( smoke, tars, acids etc) cough cough. I have experimented using tan oak leaves and they work..I have also experimented with Madrone sticks and Bamboo sticks and they work. The material must be somewhat dense  unless the crucible has lots of vacant space left over.

Dan, I think that is correct ( I have a book on carburizing steel and will look it up )..another variable is..during the decomposition of organic material the sealed crucible has an internal positive pressure..that may play a larger role than I have assumed...some of the crucibles in the olden days in Southern India  contained charred rice hulls in the ceramic material ....both the hulls and the decomposing organic material would have contributed to reducing the amount of oxygen entering the crucible. 

In your hypothetical example both crucibles would be equally sealed and equally porous and experience the same furnace pressure and temperature.

Edited December 22, 2017 by Jan Ysselstein

[Tim Mitchell]

5 hours ago, Joshua States said:

When I think of tannins I think of making leather, and oak. Particularly, the leaves and acorns. How do tannins positively affect the ingot? 

I am going to assume that Deccani opted for straight charcoal rather than organics. Were there any documented experiments with hybrid mixtures?

To be completely honest, we have no idea what role tannins play, it is a readily converted form of carbon which will aid in cleansing the steel of impurities, it can act as the building blocks of carbon nanotubes, but the most important thing is that the ancients thought it was important.  Most of the old recipes were rich in tannins.  I guess that time will reveal why...

The process at Deccani / Hyderabad / Trichinopoly (same location different names) did not add carbon at all. They used two different types of metal which they combined in a crucible.  One type was high in carbon and was a type of cast iron, the other type was more of a bloom iron and low in carbon.  I am sure the processes at the Deccan changed over time, but I don't have any accounts of an earlier process which used organic matter or charcoal added to the charge.  If anyone has copies of the early accounts from this location please send me a PM..

 

[Dan Waddell]

I think I get the basics of what's going on.  The relationship between iron and carbon is very intriguing, and I'm looking forward to learning more about how they interact with each other. 

[Charles dP]

47 minutes ago, Dan Waddell said:

I think I get the basics of what's going on.  The relationship between iron and carbon is very intriguing, and I'm looking forward to learning more about how they interact with each other. 

Dan, have you read the Verhoeven book yet?

 

[Tim Mitchell]

That is an awesome book and a real good start if you want to understand how steel behaves, and why.  JD is a great guy and this is a real gem which he was generous enough to share with bladesmiths.  This was made with a few additions into an ASM book called Metallurgy for the Non-metallurgist. Well worth downloading the copy... just don't try to sell it, that caused some smiths some problems in past years. 

 

[Joshua States]

6 hours ago, Tim Mitchell said:

6 hours ago, Tim Mitchell said:

If anyone has copies of the early accounts from this location please send me a PM..

Or, let us all know where to find it!

[Dan Waddell]

Thanks for the link Charles! I haven’t read that yet. 

[Tim Mitchell]

To further the discussion on banding agents, or Carbide Forming Elements which aid the process of banding, I just re-read a paper by JD. Verhoeven entitled "Genuine Damascus Steel: a type of banded microstructure in hypereutectoid steels" http://onlinelibrary.wiley.com/doi/10.1002/srin.200200221/full

I can't find the full text available free online, but the article is well worth a read if you can find a copy. 

In this paper John outlines the attempts that were made to determine the mechanism of banding in crucible steel.  They took pure 1.5%C steel and added specific Carbide Forming Elements to see which elements contributed to banding and which ones did not.  They found that the elements which were most effective in causing the specific type of banding that they were looking for, with very straight sheets of carbides, were Vanadium, Molybdenum and Chromium. Manganese was also found to cause banding, but not as strong as the other elements. They found that the Vanadium and Molybdenum were the most effective at causing strong banding.

Phosphorous by itself did not cause banding, although it does have a role in increasing the intensity of the banding. 

His method of testing was quite good and the results were reliable in the main elements which they tested for.  There are other elements which may also cause good strong banding in crucible steel, but these have yet to be determined.  Also the elements can either be in the raw ore, or in the charcoal which is used to make the bloomery iron that is used in the production of the crucible steel. 

This paper had many little gems in it.  By reading between the lines it was possible to see the process which Al used to create his patterns back in the early days.  He showed how slow solidification of the ingot caused porosity and graphitization of the ingot and how to remove that porosity (with graphite in the porosity) in ingots and render them usable again, among other things.  As I said.. well worth a close read.

 

[Jan Ysselstein]

Thanks Tim, I do not want to use that method for eliminating porosity,  too risky.  I have not seen too much porosity lately. The Pendray methodology may have changed quite a bit over time. Do you have a clear image of any of his steel? I have never seen it, all his blades on the web were not clearly photographed. 

[Tim Mitchell]

I will have to look to see what I have as far as patterns from Al.  The method of closing porosity is to raise the steel to above Agr and then after a bit of a soak, you forge it hard.  This is fine to do once you have established a bit of a bar and the bar is moving sufficiently.  If you have ingots which are too high in carbon or if you have too much sulphur in your ingots it can be an issue though....

If you have an ingot which has porosity and you do a roast at a temperature below Agr, then you will be having troubles with it turning to graphite, so you want to roast above Agr (just a hair above Acm), to avoid graphitization.

[Vern Wimmer]

For the metalurgically challenged could someone explain "Agr" and "Acm" ?

Also for the folks like me, who are slightly behind the curve, a little discussion of "banding" would be nice to help us catch up.

[Tim Mitchell]

Ok Vern, sorry for not going into more detail.  Agr and Acm refer to lines on the Iron Carbon phase diagram, most diagrams show Acm but few show Agr.  

The phase diagram shows the changes of state and crystal structure of iron as the carbon content of the iron increases. When you look at a phase diagram you see a horizontal line across the lower quarter of the diagram.  This is at around 727°C which is called A1, critical temperature, non magnetic and also Curie temperature.  The temperatures change slightly from diagram to diagram, but the line represents the place where these all exist.

Now when you look at the diagram you will see at around 0.7%C there is a V shaped line which joins the A1 horizontal line. On the right hand side of the V section is what we are usually talking about when we mention Acm in conjunction with crucible steel.  This is the A Cementite line and it represents the place where all cementite (iron carbide) dissolves completely in the steel. Slightly above this line, I can't remember exactly how far, it is something like 30 to 50 °C above the Acm line you will find on some diagrams a line called Agr.  This is the A Graphite line where all graphite dissolves in the steel and it mirrors the Acm line exactly.

Now of course if there are other alloying ingredients in the steel these lines will change just a bit, but it is a pretty good guide. Also once a piece of steel raises above this level the carbon doesn't immediately dissolve, if the steel lump is large it can take a few minutes to have it all fully dissolve. 

There is more to these lines and what they signify in the phase diagram, but I will leave that to others at another time to describe. I suggest that you look up a good PowerPoint or YouTube video on the Iron Carbon Phase Diagram and get edumicated . 

 

[Tim Mitchell]

Banding is a phenomenon that occurs as a result of having specific carbide forming elements which become microsegregated only in the regions between the dendrites as the steel ingot solidifies.  The dendrites are basically purer iron (0.7%C) Christmas tree like crystals which grow out into the cooling liquid metal.  As the dendritic crystals grow out into the cooling liquid, they push the impurities into the spaces between them and segregate these impurities into groups of lines going different directions.  This is called microsegregation, and when you look at an ingot you see lines of carbides which outline where the dendrites used to be.  

Now as you forge the ingot down and reduce it's proportional thickness, you see that there is a squashing of these IDR (inter-dendritic-regions) and they begin to form rough lines, which are more angled lines than straight lines.  This is the beginning of the forming of the planar banding or as some call them, cluster sheets.  

When you have Vanadium, Molybdenum, Chromium or Nobium or other unknown Carbide Forming Elements (CFEs) the carbon is specifically attracted to these CFEs and they form in lines of Vanadium Carbides or Molybdenum Carbides etc. in the IDR which create the banding effect which we see in the final crucible steel blade.  

Some CFEs attract carbon in a stronger way than other CFEs.  Those which attract the most carbon cause the highest concentration of carbides in the IDR and therefore they create the strongest banding in the final blade.

The strange thing that no one can explain is how these slightly angled IDR sections come to be lined up in precise straight lines.  It seems that when you forge the steel above Acm these sections of IDR somehow line up individually into larger straight lines.  If it was just the IDR being squashed you would still see shallow angles in the cross section of the blade.  However, when forged at the correct temperature range, these lines straighten out and the angles seem to disappear. Elements of what is going on is understood, but this effect is as yet without explanation. 

Edited December 25, 2017 by Tim Mitchell