Adding sulfur to cast iron.

[100model]

In a previous post I touched on adding sulfur to, molten cast iron. It seems that some people did not believe me so here is a link to a paper showing the need to add sulfur when the level is lower than 0.05%. There is a lot of reading so go to section one introduction and scroll to the last paragraph. Read all of that paragraph to get the context and see where they say "it should be enriched with sulfur" If you have time read the whole paper but it is heavy reading. Here is the link to that paper. The Influence of Undercooling ΔT on the Structure and Tensile Strength of Grey Cast Iron

 

[GreenTwin]

Interesting paper.

Unfortunately most of it is over my head.

My understanding of the ductile iron making process is that the sulphur level must be reduced to "X" amount, and I don't know what that level is.

So I think it is no as much about increasing tensile strength, but preventing cracking if the iron is flexed/bent.

I wish I understood it more, but that is the extent of my iron knowledge (ie: it has graphite flakes in it, and it machines well, and works well in high vibration situations, and with the addition of nickle-mag, it can be made into ductile iron, which rivals steel in strength).

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[100model]

Unfortunately most of it is over my head.

The reason why they add sulfur so the ferrosilicon will soften cast iron. It is ironic that too much sulfur much causes chilling and too little causes chilling and also lower tensile strength. In a backyard situation we do not know how much sulfur is in cast iron so in the case of ductile iron we are only guessing.

 

[GreenTwin]

I think when the sulphur content is unkown, then add some calcium carbide just to be on the safe side.

I am told that NickleMag and other similar additives will not work with elevated sulphur levels.

It seems like the guy from Lodge (the cast iron cookware company) said when in doubt, just overdose to lower the sulphur level.

Us backyard casting folks are operating blind, but if one can get consistent and repeatable results, then we don't have to do things as precise as a full sized iron foundry.

I still have not located any nickel-mag, at least not any that anyone is willing to sell in small quantities.

I do have a small amount of nickel-mag that a foundry guy sent me, but once that is gone, I won't have any more to use.

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[awake]

I take it that calcium carbide added to the mix will lower the sulfur content? Does it come out as dross, or ... ?

 

[GreenTwin]

I am not sure how the sulphur comes out.
It seems like trivial amounts of sulphur, but I am told even small amounts will intefere with making ductile iron.

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[100model]

I am not sure how the sulphur comes out.

The sulfur in the iron combines with calcium carbide to form calcium sulfide which floats to the top to be skimmed of and the carbide becomes carbon and floats to the top as well. Calcium carbide has a great affinity for sulfur but so does all other alloys that are used to make ductile iron. So when you add nickelmag or any alloy that makes ductile iron to a high sulfur cast iron it will desulfurise first and what is left may not be enough to make ductile iron.