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 carbon are more useful materials (C) KEY WORDS: Alloy Layers Slide Brittle Outcomes: You should be able to... Explain why pure iron has limited uses but alloys of iron are useful materials To understand the hardness of steels

An alloy is a mixture of a metal with at least one other element. 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. What is an alloy?

What types of alloys are there? Alloys have been used for thousands of years. Bronze, an alloy of copper and tin, was commonly used by civilizations before iron extraction methods were developed. Other well-known alloys are: brass – an alloy of copper and zinc. It does not tarnish and is used for door knobs, buttons and musical instruments. solder – an alloy of zinc and lead. It is used in electronics to fix components to circuit boards. amalgam – an alloy of mercury with silver or tin. It is used for dental fillings because it can be shaped when warm and resists corrosion.

When is a copper coin not a copper coin? When it is a copper-coated alloy! Since 1992, UK copper coins have been made from copper-plated steel and are magnetic. A magnet can be used to separate copper coins by age. Copper coins used to be made from pure copper but most ‘copper’ coins used around the world are now made from copper alloys. Previously, as the value of copper increased, the metal used to make the coin became worth more than the actual coins. A melted-down, pure copper coin could have been sold for more than the face value of the coin!

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.

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 carbon are more useful materials (C) KEY WORDS: Alloy Layers Slide Brittle Outcomes: You should be able to... Explain why pure iron has limited uses but alloys of iron are useful materials To understand the hardness of steels

Steel can contain up to 2% carbon. Varying the amount of carbon gives steel different properties. For example, increasing the carbon content, increases the hardness of the steel. Different types of steel are classified by how much carbon they contain: low carbon steel contains less than 0.25% carbon. high carbon steel contains more than 0.5% carbon. Two other important types of steel are: What types of steel are there? stainless steel – an alloy of iron that contains at least 11% chromium and smaller amounts of nickel and carbon. titanium steel – an alloy of iron and titanium.

Using different types of steel

Using different types of steel – activity