Correction re. cast iron 

I want to tell you personally (just in case you missed looking at the ref desk) that I was WRONG re. the point where a binary iron-carbon system goes from iron-cementite to iron-graphite  I said the transition point is at about 2% carbon, but in fact it NEVER transitions to iron-graphite unless silicon is added as an alloying element.  My apologies, 24.5.122.13