Here goes nothing (photo heavy)

[Joshua States]

6 hours ago, Aiden CC said:

Is this stuff something like a mixture of ore that got reduced and some which was just melted? I can imagine that if there wasn't a clear slag layer, this material may be a challenge as would be a good deal of non-metallic material that needs to be separated.

In my crucible I am using crushed green glass for a slag/sealant/flux. This floats to the top in a melt, and this melt was no different. I had to break through the glass/slag layer before getting to this stuff at the bottom of the crucible.

 

6 hours ago, Aiden CC said:

I'm not sure if wootz intends to use columnar (same orientaion, from) or equiaxed (random orientation) dendritic growth, or some mix, but I would imagine that also has subtle influence on the pattern. If I had to guess, I would say many of the dendrites in the etched photo grew "into the page", and what we see is like looking up at a tree from underneath it.

I am no expert on this by any means, and I certainly don't have the metallurgical savvy, but....

From what I have been able to learn from guys who have done this a lot, is the dendritic pattern type is largely dependent upon two things:

1. The amount of carbon

2. The amount and type of carbide forming elements (CFE) that are added to the melt.

 

The patterning is really just excess carbon that hasn't been absorbed by the iron and is now locked in the cementite. Get enough carbon in the mix and get the temperature control just right, you can create a dendritic pattern. The CFE controls whether that pattern is linear (like in the second puck above) or more watery, like most wootz patterns we think of. CFE are things like Vanadium, Nobium, Titanium, etc. They combine with the Carbon and form carbides in the steel. The CFE molecules provide an anchor point for carbide formation and if you get the heat control just right, you can get that classic watery patterning in the steel.

 

Now watch as Jerrod Miller corrects me on everything I got wrong....

 

The first puck has some CFE content. I threw in some of the cast iron buttons I made here.

The second puck is just iron and charcoal.

Edited March 1 by Joshua States

[Jerrod Miller]

To say that things get complicated in this type of thing would be an understatement.  Carbides can be a bit tricky, as the formation of them depends not just on whether there are the proper atoms present, but what other atoms are there, too.  For example, in the high chrome white irons (HCWI) my foundry produces we can develop Cr2Fe5C3 to Cr5Fe2C3 carbides based on the ratio of Cr:C (not just total quantity of one or the other).  Add onto that that V or Ti (or any of several other elements) will form carbides before the Cr or Fe can even begin to form carbides and you have now just changed the overall chemistry (and as such the ratios of elements in it) for the still liquid metal.  We use this and add FeTi just before pouring to get TiC carbides spread throughout the material to act as nucleation sites for the Cr carbides to grow on.  We do this to prevent larger dendritic carbides to form because large carbides and dendrites are bad for mechanical properties.  This is why I personally dislike wootz; because the "cool structure" is a sign of less than ideal structure.  It can still be significantly better than really bad alloy or processing choices, though.  Trading off a little performance for style is a valid choice, just not one I prefer to do in this case.  

 

So, in broad strokes, the types/quantities of CFEs you have will vary what types of carbides form and when they form (temperature dependency).  Pile onto that the cooling rate and you can really start seeing big effects on the structure.  Once you start forming nucleation sites (i.e. carbides in this case) things will want to start growing on them.  The longer your melt is in the temperature range where only that carbide forms, the larger those carbides will form.  Then, once you get enough dendrites (carbides or otherwise) you start getting pockets of liquid that start to get cut off from the rest of the material.  This can lead to segregation (which is also happening with the carbide formation) as well as porosity.  

[Joshua States]

2 hours ago, Jerrod Miller said:

Pile onto that the cooling rate and you can really start seeing big effects on the structure. 

This was something I hadn't realized until I got done with these first two melts. The first one was allowed to cool for an excessively long time, which I think led to the lack of visible carbide formations.

 

Thanks for the science Jerrod!

[Joshua States]

The experiments continued yesterday after I got a new T-couple and ran a calibration melt. This puck recipe:

960g pure(?) iron, 24g W-2, 20g charcoal and 16g of magnetite sand. Target is 1kg puck with 1.5-1.6% C content.

 This one came out pretty nice and so close to target mass.

 

 

 

I ground a window in the side to check solidification and patterning. There is some watering in there, but the pattern is very tight.

 

 

[Alan Longmire]

Nice!  The ingot itself looks great, but I suspect the carbon content may end up lower than you were looking for, based on the pattern in that window.  I could of course be completely wrong, but I'd expect more dendrites on the surface for the desired carbon content.  But there's nothing wrong with a 1%C ingot in the grand scheme of things.  

[Joël Mercier]

That's cool! I'll be following.

 

May I ask why the W2? My uneducated guess would be for the traces of vanadium that helps with the formation of dendrites?

[Joshua States]

7 hours ago, Alan Longmire said:

I suspect the carbon content may end up lower than you were looking for,

You may be correct, but we will see. I plan on sending 3 or 4 of these out for testing so I can compare what I put in with what I get out. These are open-top crucible melts, so there is a bit of charcoal loss in the burn. The placement of the charcoal in the crucible is supposed to help mitigate that loss. There is a certain mass in the charcoal that isn't carbon, but other organic matter that burns away. Hence the prescence of ash after a charcoal fire. The puck also uptakes some carbon out of the graphite crucible. So there is a bit of give and take going on.

Simple math says I lost 21g of something along the way, but what? Could be carbon, organic material, stuff in the sand.....

From what I understand, the amount of dendritic grain in the original puck has more to do with the cooling rate than anything else. It's supposedly a matter of capturing the carbides in the cementite phase (please don't ask me what that means). Anyway, see what Jerrod said above about carbide formation being largely temperature dependent.

 

5 hours ago, Joël Mercier said:

My uneducated guess would be for the traces of vanadium that helps with the formation of dendrites?

Winner winner chicken dinner. In this puck I am mixing the W2 and the magnetite to see what happens with more than one CFE (carbide forming element). I will do a test with iron, charcoal and a bigger chunk of W2. That will take some math to figure out what the vanadium content needs to be to end up with the prescribed amount of V in the final 1kg puck.

 

Today I did another melt just using the magnetite sand as CFE donor.

976g iron, 11g sand, 25g charcoal. I hit the 1 kilo mark.

 

 

Same tight grain in the grind

 

 

For those of you who are interested, here is a link to the videos of the furnace running and the window grinding.

https://drive.google.com/drive/folders/1W5vsyGAhWEFPgDtTd37bowz6ff58pbmc?usp=share_link

 

 

Edited April 2 by Joshua States

[Joshua States]

Now I have to find that post where @Jerrod Miller told sombody about testing labs we could use.....

 

[Jerrod Miller]

On 4/1/2023 at 8:39 PM, Joshua States said:

Now I have to find that post where @Jerrod Miller told sombody about testing labs we could use.....

 

Here is the comment with that info: