Iron is a pure element. Every atom in a chunk of iron is an iron atom. Iron is nice, but it's not very strong.
Steel is even better. To make steel, they melt down iron and mix in
small amounts of other elements. There are different types of steel
based on what they mix in and how much. Each type of steel has
different advantages, such as stength, durability, chemical reactivity,
and many other qualities. Typical elements that are added to iron to
make steel include Carbon, Manganese, Silicon, Chromium, and
Molybdenum. But most of the atoms of steel are still iron, because they
only usually add in a few percent of other elements.
Now comes rust. Many elements like to go through chemical reactions
with other elements. Iron likes to react with oxygen to for
iron-oxide...or rust. We can't keep oxygen away from the iron in our
cars since much of the atmosphere is oxygen. Rust weakens the iron and
can make parts break. Steel has the same problem, but some of those
elements that are added during the steel production can help prevent
rust or at least slow it down. For example, "stainless steel" is
designed so that it will not rust, but it is more expensive that other
types of steel.
(republished on 07/18/06)