Why does the atomic structure of plain carbon steel used for structural work?
A crystalline structure is good for a material that is tough because under stress the atoms in a metallic crystalline structure will easily change places allowing the material to deform or bend under a load without breaking. When carbon atoms are added they get in the way not allowing some of the atoms in the crystalline structure to move. This gives the metal more strength because it will not bend as much under stress due to the carbon atoms getting in the way. This also makes the metal more brittle, so choosing the carbon content to make the metal stronger, but not too brittle is important. Which is why low carbon steel is generally used in structural members (they will have decent strength but will be able to bend some so that when wind or earthquakes hit they will not be too brittle).
