FYI, a short discussion of cast iron vs steel from the Iron Founder's Society "Iron Castings Handbook".
"The term, cast iron, designates an entire family of metals with a wide variety of properties. It is a generic term like the word, steel, which also designates a family of metals. Steels and cast irons are primarily iron that is alloyed with carbon, but steels always contain less than two percent carbon and usually less than one while all cast irons contain more than two percent of carbon. Cast irons must also contain appreciable silicon, usually from one to three percent. These differences are not arbitrary, buy have a metallurgical basis and effect the differences in the useful properties of these two families of ferrous alloys.
The high carbon content and the silicon in cast irons make them excellent casting alloys. They are easily melted, are very fluid in the liquid state, and do not form difficult surface films when poured. Irons also solidify with nominal shrinkage and contraction problems. But their high carbon content precludes the practicality of forming cast irons in the solid state as is done with wrought steel."