Why were the ingots mostly round?

PUFF · 5th April 2006, 03:40 AM

Unlike solid state smelting, the wootz smelting turn whole thing to liquid mixture. With slow cooling, liq. slag and liq. metal separated into two distintive phases like water and oil. Most of impurities partitioned into slag phase and floated up to the surface. I don't know about air bubble. Any bubble in the ingot indicates that smelting temperature 's too low and such a low smelting temp could trap some slag either.

Cracks are not "as baked" flaw. They happened when forging stress goes beyond the material elasticity (either forging temp 's too low or hammering 's too hard). Dear Jens, forging would make the blade more homogeneous as slag inclusions were forged out. But flaws like crack (or bubble) could not be closed unless you reach forge welding temperature (~1400 C). Unfortunately, wootz pattern melt down at 900-1000 C and forge welding of cracks or two ingots 's unlikely (possible but very difficult to bring the pattern black

).

Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece. IMO,As a smith, the worst flaw 's quench crack

Jens Nordlunde · 5th April 2006, 09:17 PM

Hi Puff, thank you for the explanation, I had an idea that it may be like you described, but I was not sure. Also I knew about the heat, but it is better to hear it one more time. Also there may still be some of the forumites who have not heard about this before.
So I suppose that the temperature of 900-100C is the cherry colour Hendley writes about.
Nice to have people like Greg, Jeff and you onboard, when it comes to the construction of our collectives.

PUFF · 6th April 2006, 12:40 PM

Quote:

Originally Posted by Jens Nordlunde

Hi Puff, thank you for the explanation, I had an idea that it may be like you described, but I was not sure. Also I knew about the heat, but it is better to hear it one more time. Also there may still be some of the forumites who have not heard about this before.
So I suppose that the temperature of 900-100C is the cherry colour Hendley writes about.
Nice to have people like Greg, Jeff and you onboard, when it comes to the construction of our collectives.

Just a minor correction, 900-1000 C going to be a yellowish cherry, a bit sour for my taste. Nice sweet & sour cherry red 's around 800 C.

Jeff Pringle · 9th April 2006, 05:27 PM

To add a bit to what Puff said, regarding bubbles:
I said 'air', but really it's carbon monoxide or oxygen, and they occur for a variety of reasons - undercooked ingots mostly (the melt has not reached equilibrium), but since liquid steel can hold more gasses in solution than solid steel, you can find porosity occuring during solidification too.
Regarding cracking, it can occur from working at too high or too low a temperature, or pushing the material too fast - the as-solidified grain stucture needs to be coaxed into a finer, more forgeable state. Impurities in the steel (oxygen, sulfur, phosphorus etc.) will precipitate out at grain boundaries during solidification, and can cause cracking too.
Forging temps for wootz are not high enough for cracks to get welded back together, so they don't go away. As Puff said, "Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece", and that's how those one-sword ingots get to be multiple-knife ingots.

I have some ingot slices that demonstrate most of the flaws you can run across, here's one ingot with some probable CO bubbles - cube is 1 cm for scale:

This ingot also suffered from too much intergranular oxygen and proved to be unworkable, after a lot of work!

galvano · 9th April 2006, 09:57 PM

Here two ingots.
One with bubbles.
One with cracks. galvano.

Rivkin · 10th April 2006, 12:05 AM

I don't really know metallurgy, so a stupid question: what if one "on purpose" adds some localized impurity - can it be a seed for the pattern to grow, i.e. the pattern will nicely grow from this point?

Like, for example in the sample above it seems that the pattern "grows" from the sample's surface and is much sparser in the sample's middle; it also nearly absent on the sample's bottom. Could one add something to the sample so it will be an artificial centre of the pattern's growth.

Jeff Pringle · 10th April 2006, 12:38 AM

I think the pattern difference above is a lighting artifact, with different lighting the pattern should look uniform across the surface.
Patterns in wootz come from the fact that when the steel starts to solidify, the first crystals 'want' to be pure iron/carbon - the impurities in the melt become concentrated in the areas of secondary crystalization, in between the networks of already solid metal. So the impurites do get localized to a degree.
Theoretically, you can control the grain orientation, and hence ultimate pattern, by manipulating the shape of the solidifying metal (by casting into a mold of varying thickness), but I don't think anyone is working on this yet.

5th April 2006, 09:17 PM	#2
Jens Nordlunde Member Join Date: Dec 2004 Location: Europe Posts: 2,718	Hi Puff, thank you for the explanation, I had an idea that it may be like you described, but I was not sure. Also I knew about the heat, but it is better to hear it one more time. Also there may still be some of the forumites who have not heard about this before. So I suppose that the temperature of 900-100C is the cherry colour Hendley writes about. Nice to have people like Greg, Jeff and you onboard, when it comes to the construction of our collectives. Last edited by Jens Nordlunde; 5th April 2006 at 09:35 PM.

9th April 2006, 09:57 PM	#5
galvano Member Join Date: Jan 2006 Posts: 178	ingots Here two ingots. One with bubbles. One with cracks. galvano. Attached Images

5th April 2006, 03:40 AM	#1
PUFF Member Join Date: Feb 2006 Location: 30 miles north of Bangkok, 20 miles south of Ayuthaya, Thailand Posts: 224	Unlike solid state smelting, the wootz smelting turn whole thing to liquid mixture. With slow cooling, liq. slag and liq. metal separated into two distintive phases like water and oil. Most of impurities partitioned into slag phase and floated up to the surface. I don't know about air bubble. Any bubble in the ingot indicates that smelting temperature 's too low and such a low smelting temp could trap some slag either. Cracks are not "as baked" flaw. They happened when forging stress goes beyond the material elasticity (either forging temp 's too low or hammering 's too hard). Dear Jens, forging would make the blade more homogeneous as slag inclusions were forged out. But flaws like crack (or bubble) could not be closed unless you reach forge welding temperature (~1400 C). Unfortunately, wootz pattern melt down at 900-1000 C and forge welding of cracks or two ingots 's unlikely (possible but very difficult to bring the pattern black ). Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece. IMO,As a smith, the worst flaw 's quench crack

9th April 2006, 05:27 PM	#4
Jeff Pringle Member Join Date: Nov 2005 Posts: 189	To add a bit to what Puff said, regarding bubbles: I said 'air', but really it's carbon monoxide or oxygen, and they occur for a variety of reasons - undercooked ingots mostly (the melt has not reached equilibrium), but since liquid steel can hold more gasses in solution than solid steel, you can find porosity occuring during solidification too. Regarding cracking, it can occur from working at too high or too low a temperature, or pushing the material too fast - the as-solidified grain stucture needs to be coaxed into a finer, more forgeable state. Impurities in the steel (oxygen, sulfur, phosphorus etc.) will precipitate out at grain boundaries during solidification, and can cause cracking too. Forging temps for wootz are not high enough for cracks to get welded back together, so they don't go away. As Puff said, "Any flaw appear during forging stage can be easily work around by either trimming out or shortening the piece", and that's how those one-sword ingots get to be multiple-knife ingots. I have some ingot slices that demonstrate most of the flaws you can run across, here's one ingot with some probable CO bubbles - cube is 1 cm for scale: This ingot also suffered from too much intergranular oxygen and proved to be unworkable, after a lot of work!

10th April 2006, 12:05 AM	#6
Rivkin Member Join Date: Dec 2004 Posts: 655	I don't really know metallurgy, so a stupid question: what if one "on purpose" adds some localized impurity - can it be a seed for the pattern to grow, i.e. the pattern will nicely grow from this point? Like, for example in the sample above it seems that the pattern "grows" from the sample's surface and is much sparser in the sample's middle; it also nearly absent on the sample's bottom. Could one add something to the sample so it will be an artificial centre of the pattern's growth.

10th April 2006, 12:38 AM	#7
Jeff Pringle Member Join Date: Nov 2005 Posts: 189	I think the pattern difference above is a lighting artifact, with different lighting the pattern should look uniform across the surface. Patterns in wootz come from the fact that when the steel starts to solidify, the first crystals 'want' to be pure iron/carbon - the impurities in the melt become concentrated in the areas of secondary crystalization, in between the networks of already solid metal. So the impurites do get localized to a degree. Theoretically, you can control the grain orientation, and hence ultimate pattern, by manipulating the shape of the solidifying metal (by casting into a mold of varying thickness), but I don't think anyone is working on this yet.