Cast iron vs steel

Rich_S · Dec 28, 2006

I'm trying to learn a little metallurgy and finding some things confusing. For example, I always thought that it was the presence of carbon that distinguished steel from iron. Then I read this on wikipedia:

Steel is a metal alloy whose major component is iron, with carbon content between 0.02% and 1.7% by weight.

Cast iron contains 2% 4.0% carbon , 1% 6% silicon , and small amounts of manganese.

So then what makes steel different from cast iron? Is it the way that the carbon is structured with the iron molecules?

Is there a good metallurgy resource available on the net with information relevant to knives and knifemaking?

the possum · Dec 28, 2006

Rich-
Verhoeven's paper "Metallurgy of Steel for Bladesmiths and Others Who Heat Treat & Forge Steel" would probably be the best place to go if you want an in depth yet layman's explanation. He starts out discussing iron since steel is mostly iron, and also covers several kinds of cast iron. I haven't read the whole thing myself yet, but you could probably glean something from the parts that interest you.

Rich_S · Dec 28, 2006

Thanks a bunch.

tirod3 · Dec 28, 2006

Just to clarify for some: steel is low carbon iron. Not what I thought at first either. Makes for an interesting juxtapostion: the purer iron is, the more we call it steel. High carbon steel becomes iron.

Go figure.

moontroll · Dec 28, 2006

From what I understand cast iron is just that cast.Steel is rolled usually with a lower carbon content with a higher density.

Rich_S · Dec 28, 2006

From what I read in the metallurgy pdf, the 1.7% limit for steel is because that's the most carbon that will remain in solution in solid iron (considerably more will dissolve in liquid iron) so any more precipitates out when the iron solidifies and that changes the properties of the material.

mete · Dec 28, 2006

Wikipedia is not the best place to get info !!! Looking at the 'Iron-carbon diagram ' you will see the difference and why they refer to 2 % and above as 'cast iron'.

FullerH · Dec 28, 2006

However, some of the Crucible Particle Method steels, such as CPM 440V, have carbon content of over 2%. They are able to accomplish this by means of their special processing.

yoda4561 · Dec 28, 2006

tirod3 said:
Just to clarify for some: steel is low carbon iron. Not what I thought at first either. Makes for an interesting juxtapostion: the purer iron is, the more we call it steel. High carbon steel becomes iron.

Go figure.

Ermm, not quite. Cast iron should NOT be confused with "true" iron, such as wrought iron railings, horseshoes, etc , which has very little to no carbon whatsoever. Cast iron is just a name, and it occurs when there is too much carbon for one of the various steel crystaline structures to form with common smelting techniques.