How wootz blades were forged?

kai · 20th September 2019, 07:47 PM

Hello Ariel,

My condolences!

Thanks for the pic - could you try to get a macro shot, please? It seems to show 2 rather than a single cold shut from forging; I don’t think I’ve seen that before...

The folded structure of many wootz blades has been discussed here before. I agree with your general assumption that the wootz often got folded upon itself (despite having a tough time to imagine the forging work needed to end up with a neat elongated blade with intact internal configuration).

From what I’ seen of ingots, they seem to be clean steel also at the top. The dendrites seem to be better developed towards the lower part though. The folding may well be intended to expose this structure rather than hiding any impurities.

Since wootz needs to be forged at “low” temperatures, any cold shut after folding the ingot upon itself may well be from working at too low a temperature to achieve proper welding. It’s a thin line...

Regards,
Kai

ariel · 21st September 2019, 12:16 AM

The break area on my example was not polished and etched.
There is a similar example ( polished and etched) in a Russian book by Kamil Khaidakov: much better resolution of the junky area.
Folding was not intended to hide anything: it just assured that the important parts of the blade used the best part of the ingot.
Quite possible the junky part was squeezed out through the crack in the spine. Just a thought.

RobT · 21st September 2019, 03:28 AM

Ariel,
According to Föll, all true crucible steel has a high carbon content because the alloy must be at least eutectoid in order to become liquid at the furnace temperatures of the time. If it had no affect on the function of the blade, the SI content is irrelevant. Remember, the people that made this steel and forged these blades had no concept of modern metallurgy. If the SI didn't break it, they weren't about to fix it.
Ian,
In her doctoral desertation (Crucible Steel in Central Asia: Production, Use and Origins), Dr Anna Feuerbach mentions a ring of glassious material inside the crucibles. If I recall correctly, Nonikashvili says that finding was the reason for his experiment. I wonder, however, about the possibility of any glassious material sticking to the steel of the ingot and being incorporated into the blade during forging. Even under low forging temperatures, that material should become liquid and run off the steel right away, no? I think that any SI content in the steel would be in the form of an alloy precipitate as the crucible charge cools. I am more than a bit unclear about this but, it appears from what I have read of Föll's monograph, it is the way in which the precipitates (C, SI, P, etc) are manipulated during forging that governs the strength/durability of the blade.

Sincerely,
RobT

Ian · 21st September 2019, 05:11 AM

Quote:

Originally Posted by RobT

... Ian,
In her doctoral desertation (Crucible Steel in Central Asia: Production, Use and Origins), Dr Anna Feuerbach mentions a ring of glassious material inside the crucibles. If I recall correctly, Nonikashvili says that finding was the reason for his experiment. I wonder, however, about the possibility of any glassious material sticking to the steel of the ingot and being incorporated into the blade during forging. Even under low forging temperatures, that material should become liquid and run off the steel right away, no? I think that any SI content in the steel would be in the form of an alloy precipitate as the crucible charge cools. I am more than a bit unclear about this but, it appears from what I have read of Föll's monograph, it is the way in which the precipitates (C, SI, P, etc) are manipulated during forging that governs the strength/durability of the blade.

Sincerely,
RobT

Rob,

Thank you for the feedback. Interesting to know that glass featured in the manufacture of crucible steel. It is a while since I read Ann's thesis and I had forgotten that point.

I'm no expert on the history or properties of glass, although I think the old masters of wootz-making would have had silica glass available. In its finished state this is mainly an amorphous (i.e., non-crystalline) form of silica (SiO2). Thermal decomposition of silica glass can occur at sufficiently high temperatures and I don't know whether that happened during the making of wootz. According to Schwind (2002), depending on it's composition, some glass will melt at temperatures as low as 500 °C (900 °F), others melt at 1650 °C (3180 °F). As far as glass particles getting incorporated into the wootz, that seems at least a possibility, especially if these are sub-micron in size.

When discussing the Si content of wootz, I think Ariel was likely talking about an elemental analysis for silicon (Si). We don't know if the form of silicon present is elemental silicon, amorphous silica, one or more silicates, or some other chemical form.

Ian

Bob A · 21st September 2019, 06:10 PM

I thought this information on production of silicon carbide was of interest.

The simplest process to manufacture silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F). Fine SiO2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material.*

Sand would obviously melt into a glass at the temperatures involved in the wootz process.

In light of above posts, I may be merely belaboring the obvious here. Nonetheless, the reference to plant material in the Wikipedia entry discussing silicon carbide was interesting.

*https://en.wikipedia.org/wiki/Silicon_carbide

Richard Furrer · 21st September 2019, 09:42 PM

Ariel, No need to notch the ingot...it folds at the top on its own during forging...for two reasons. One being that unless high forces are delivered it is the natural tendency for metals to move more at the surface that the middle and they "fish mouth" or "duck bill". After more light forging the edges of the steel touch and you get a folded appearance. The second is that the poorest part of the ingot is the top and it almost always had gas pockets from the cooling process and as such is less dense and moves differently under the hammer. Often collapsing onto its center as forging progresses.

I have yet to see a "sound surface" at the top of an ingot. All ingots have some surface irregularities in them in the form of pockets or bulges and if the porosity is not visible it exists in micro form with the most porous at the top.

Often the top of the ingot becomes the spine of the blade. I would call the folded over bit a seam and I have seen several where the seam wanders from the spine onto the flat of the blade. In one case it fell off and was cold riveted back into place.

Ariel...if that broken blade is for sale I would like to purchase it and do chemical, hardness and microscopic analysis on it to add to my database.
That goes for anyone else who has broken crucible steel blades or bits and pieces.

Edit: It is a simple matter to add silicon to the steel when it is liquid (very hard to stop if glass is present actually) and I have yet to see any glass survive in the bar once forged out to a blade. It all goes away when the ingot is being forged into bars. This is due to its liquid nature at temperatures used for forging and also that if allowed to cool on the anvil it is untempered glass which is very brittle and simply falls away when left to its own devices after a day of forging.

Edit Edit: I would guess that large grain size (and shipping abuse) was the cause of the fracture. If the break is at all black on the edges then it could also have been a flaw from the quench which waited for the stress of shipping to finally break. Cracks caused in forging or the quench or almost always black color due to high temperature oxidation. In modern blades if the crack is yellow or blue then the crack was in the tempering stage of manufacture...the color is again due to oxides, but lower temperature oxidation.

Ric

ariel · 22nd September 2019, 04:04 AM

Richard,
What sale are you talking about? :-)
Send me your address and you will get it for free. I shall only be delighted to contribute something useful to the community of wootz-smiths.
One condition: after you polish and etch the break, could you send me a pic of it, please?
And if something interesting comes up from the measurement you will be taking, please let me know. OK?

Ariel

21st September 2019, 03:28 AM	#3
RobT Member Join Date: Mar 2005 Posts: 533	Glass in the Crucible Ariel, According to Föll, all true crucible steel has a high carbon content because the alloy must be at least eutectoid in order to become liquid at the furnace temperatures of the time. If it had no affect on the function of the blade, the SI content is irrelevant. Remember, the people that made this steel and forged these blades had no concept of modern metallurgy. If the SI didn't break it, they weren't about to fix it. Ian, In her doctoral desertation (Crucible Steel in Central Asia: Production, Use and Origins), Dr Anna Feuerbach mentions a ring of glassious material inside the crucibles. If I recall correctly, Nonikashvili says that finding was the reason for his experiment. I wonder, however, about the possibility of any glassious material sticking to the steel of the ingot and being incorporated into the blade during forging. Even under low forging temperatures, that material should become liquid and run off the steel right away, no? I think that any SI content in the steel would be in the form of an alloy precipitate as the crucible charge cools. I am more than a bit unclear about this but, it appears from what I have read of Föll's monograph, it is the way in which the precipitates (C, SI, P, etc) are manipulated during forging that governs the strength/durability of the blade. Sincerely, RobT

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20th September 2019, 07:47 PM	#1
kai Member Join Date: Apr 2005 Posts: 3,255	Hello Ariel, My condolences! Thanks for the pic - could you try to get a macro shot, please? It seems to show 2 rather than a single cold shut from forging; I don’t think I’ve seen that before... The folded structure of many wootz blades has been discussed here before. I agree with your general assumption that the wootz often got folded upon itself (despite having a tough time to imagine the forging work needed to end up with a neat elongated blade with intact internal configuration). From what I’ seen of ingots, they seem to be clean steel also at the top. The dendrites seem to be better developed towards the lower part though. The folding may well be intended to expose this structure rather than hiding any impurities. Since wootz needs to be forged at “low” temperatures, any cold shut after folding the ingot upon itself may well be from working at too low a temperature to achieve proper welding. It’s a thin line... Regards, Kai

21st September 2019, 12:16 AM	#2
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	The break area on my example was not polished and etched. There is a similar example ( polished and etched) in a Russian book by Kamil Khaidakov: much better resolution of the junky area. Folding was not intended to hide anything: it just assured that the important parts of the blade used the best part of the ingot. Quite possible the junky part was squeezed out through the crack in the spine. Just a thought.

21st September 2019, 06:10 PM	#5
Bob A Member Join Date: Feb 2014 Posts: 435	I thought this information on production of silicon carbide was of interest. The simplest process to manufacture silicon carbide is to combine silica sand and carbon in an Acheson graphite electric resistance furnace at a high temperature, between 1,600 °C (2,910 °F) and 2,500 °C (4,530 °F). Fine SiO2 particles in plant material (e.g. rice husks) can be converted to SiC by heating in the excess carbon from the organic material.* Sand would obviously melt into a glass at the temperatures involved in the wootz process. In light of above posts, I may be merely belaboring the obvious here. Nonetheless, the reference to plant material in the Wikipedia entry discussing silicon carbide was interesting. *https://en.wikipedia.org/wiki/Silicon_carbide

21st September 2019, 09:42 PM	#6
Richard Furrer Member Join Date: Mar 2006 Location: Sturgeon Bay, Wisconsin Posts: 163	Ariel, No need to notch the ingot...it folds at the top on its own during forging...for two reasons. One being that unless high forces are delivered it is the natural tendency for metals to move more at the surface that the middle and they "fish mouth" or "duck bill". After more light forging the edges of the steel touch and you get a folded appearance. The second is that the poorest part of the ingot is the top and it almost always had gas pockets from the cooling process and as such is less dense and moves differently under the hammer. Often collapsing onto its center as forging progresses. I have yet to see a "sound surface" at the top of an ingot. All ingots have some surface irregularities in them in the form of pockets or bulges and if the porosity is not visible it exists in micro form with the most porous at the top. Often the top of the ingot becomes the spine of the blade. I would call the folded over bit a seam and I have seen several where the seam wanders from the spine onto the flat of the blade. In one case it fell off and was cold riveted back into place. Ariel...if that broken blade is for sale I would like to purchase it and do chemical, hardness and microscopic analysis on it to add to my database. That goes for anyone else who has broken crucible steel blades or bits and pieces. Edit: It is a simple matter to add silicon to the steel when it is liquid (very hard to stop if glass is present actually) and I have yet to see any glass survive in the bar once forged out to a blade. It all goes away when the ingot is being forged into bars. This is due to its liquid nature at temperatures used for forging and also that if allowed to cool on the anvil it is untempered glass which is very brittle and simply falls away when left to its own devices after a day of forging. Edit Edit: I would guess that large grain size (and shipping abuse) was the cause of the fracture. If the break is at all black on the edges then it could also have been a flaw from the quench which waited for the stress of shipping to finally break. Cracks caused in forging or the quench or almost always black color due to high temperature oxidation. In modern blades if the crack is yellow or blue then the crack was in the tempering stage of manufacture...the color is again due to oxides, but lower temperature oxidation. Ric

22nd September 2019, 04:04 AM	#7
ariel Member Join Date: Dec 2004 Location: Ann Arbor, MI Posts: 5,503	Richard, What sale are you talking about? :-) Send me your address and you will get it for free. I shall only be delighted to contribute something useful to the community of wootz-smiths. One condition: after you polish and etch the break, could you send me a pic of it, please? And if something interesting comes up from the measurement you will be taking, please let me know. OK? Ariel