I studied mechanical engineering at UCSD for my sophomore and junior years after transferring in from being a math major at Pomona College (east of LA). One thing I remember is that we talked about the material composition of steel. It has a crystal lattice such that the carbon atoms fill in the spaces in between the iron atoms. This makes the crystal latttice more solid. (Ironically, too many carbon atoms weakens the steel because then the carbon atoms start replacing the iron atoms as well.) Of course, this is not correct unless we state it along the lines of quantum mechanics, but it's on a macroscopic scale on the whole. So is all of this correct? It's been about 10 years since I took the class. My memory is worse than hazy. And can anyone add to it?