can any one please give me the answer for addition of carbon to cast iron beyond 6.67%..
The iron compound with most carbon by weight, 6.67%, is cementite, Fe3C.
Any carbon added beyond that will form flakes of graphite. Those flakes reduce the useful properties of cast iron by making it softer and more brittle.
It is also quite difficult to make cast iron with higher carbon than cementite because it burns. If there were not much better and lower cost materials, it could be formed using powder metallurgy techniques.
There is no advantage in making cast iron with more than 6.67% carbon.
That depends what you want to use it for. I used to pass an iron foundry every day on the way to work, where that was their speciality product.
Malleable cast iron has only about 2.5% carbon by weight.
You failed to quote the first line of my post.
I know of no useful cast iron that is composed of only iron carbide with graphite.
Maybe you should examine the phase diagram for Fe – C near the top of the page you link to.
Do you know of any cast iron with greater than 6.67% carbon?
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