Pure iron is barely harder and stronger than copper. Impurities are to iron, what paint is to an artist's canvas.
Red Ochre is Iron
The problem with iron at this level of purity is that it is too soft and too ductile for most commercial uses.
This means that the iron products that we know and recognize are relatively and deliberately impure.
Iron also has three allotropes or crystal forms, delta iron (body centered cubic) gamma (face centered cubic) and alpha, body centered cubic. I was originally taught* that delta and alpha iron were the same allotrope, a distinction that now appears to be a charming sign of old age… and the addition of impurities (alloying elements) have different solubilities based on these forms.
It is the addition of carbon and other elemental impurities which alter these allotropic forms that gives commercial iron and steel products their diverse properties.
When we look on the material certs that accompany our steel products , the first element that is reported is carbon. Carbon is ubiquitous, and has the dominant effect on the behavior of the iron based product to which it is part, even in the presence of large amounts of alloying elements.
What is implied by the certs is that after adding up all of the elements reported, the balance of the material is "iron."
In 2009 world Iron and steel production was estimated to be 1,219.7 million metric tonnes.
Physics trivia: Iron is the heaviest atom that can be made by the fusion of stars. Iron is is the 'ash' of stellar nuclear fusion. Iron is abundant- the fifth most abundant element on earth, and sixth most abundant in the universe. Our blood is red because of iron, and since iron is an essential part of our bodies, we can truly claim that we are "Stardust."
The preceeding is written by Miles Free on the Engineer's Blog. More on this topic here...