Making Ductile Iron in the Home Foundry

There really is no exact formula...every foundry has a different chemistry of their base iron..to a degree...some may be more controlled than others but even the highly controlled and monitored iron has to be tested because of human error and or mechanical breakdowns..etc. They make adjustments as they go based off of the readings they get from each batch. From what I have seen...and I am no expert and have only messed with it in limited amounts over the past ten years or so...you can either not add enough and not get ductile or get ductile. You really cant over innoculate it...only so much will go into solution. The rest will float on top of the pour basin. We had high sulfur once and tried to go about ten times the calculated amount and made the casting but the sprue was full of undissolved chunks and the casting still was not ductile because of the high sulfur. The sulfur is the key. Get it down low enough and very little alloy addition is needed. I would start with one gram a pound of total pour weight and see what you get. I guarantee if you have sulfur low enough you will see a huge difference in tensile strength and less metal fatigue. You dont even have to do anything special...pour the alloy in the pour cup and then pour the mold. The first iron/casting will be ductile but your gating system might be grey iron. That is the key for industry...the entire melt needs to be consistent for return melt calculations. They also usually are in automotive industry and have to have extra special red tape to generate lots of useless information no one will ever look at unless there is some disaster associated with their product.

 

I came across a very interesting magazine article, the title is " A review of the formation of spheroidal graphite in cast iron by S. Banerjee. It was in the British foundryman magazine September 1965 Page 344-352. It was written about twenty years after the discovery of ductile iron. In that time everyone was hoping to discover if any other additive could could make ductile iron and it turns out that there are plenty of others. Here is the list they provided, Mg, Ce,Li,Ba, Sr,K,Na,Zn,Se,Te,S. There was no mention on how much was added to make ductile iron. It did open my eyes as I thought only Mg was the only additive that will produce ductile iron. There were so many methods showing how ductile iron was made. Some additives were added to molten cast iron making it solidify as white cast iron and then heat treated to get ductile iron. I found it in a private collection that has no facilities to copy it. There should be a copy online somewhere.

 

Yes, I have come across perhaps 4 different metals commonly used as inoculants with Calcium being the first patented to make Meehanite. The fundamental problem is not so much identifying metals that can cause ductile or malleable iron to form, but rather finding a “recipe” that could be used in the small foundry. That has proven illusive to date.

Denis

 

The Wikipedia article on ductile iron mentions Meehanite was made with calcium silicide which I suspect would be less spectacular than magnesium and more like adding ferrosilicon. Also I wonder if magnesium silicide would work the same: it can be made by making a silica sand and magnesium thermite with excess magnesium, again according to Wikipedia. Another interesting thermite would be excess magnesium and Plaster of Paris (calcium sulphate) which would give an alloy of magnesium and calcium metal.

https://en.wikipedia.org/wiki/Magnesium_silicide