TITLE: How do the structures of steels affect their hardness? Objectives (We are learning that): Pure iron is a soft metal and does not have many uses. (C) Alloys of iron are more useful materials (C) KEY WORDS: Alloy Layers Slide Distort Brittle Thermal conductor Malleable Ductile Outcomes: You should be able to... Explain why pure iron has limited uses but alloys of iron are useful materials

Steel is a common example of an alloy. It contains iron mixed with carbon and other elements. Adding other elements to a metal changes its structure and so changes its properties. The final alloy may have very different properties to the original metal. By changing the amount of each element in an alloy, material scientists can custom- make alloys to fit a given job.

Steel is an alloy of iron and other elements, including carbon, nickel and chromium. Steel is stronger than pure iron and can be used for everything from sauce pans… …to suspension bridges! What is steel?

The atoms of other elements are different sizes. When other elements are added to iron, their atoms distort the regular structure of the iron atoms. The atoms in pure iron are arranged in densely packed layers. These layers can slide over each other. This makes pure iron a very soft material. Why is steel stronger than iron? It is more difficult for the layers of iron atoms in steel to slide over each other and so this alloy is stronger than pure iron.

Using different types of steel

Key words and meanings Thermal Malleable Ductile