Heat treatment of steel
You will need several 5 cm long steel needles and a pair of pliers.
Annealing is the process of heating a metal and allowing it to cool slowly. Heat the needle until it is glowing red hot. Then slowly take a minute to remove it from the heat.
This produces a soft metal that is easy to bend around a pencil.
Quenching is the process where by a metal is heated and then rapidly cooled. This makes steel harder and non-ferrous metals, such as copper, softer.
Heat a needle until it glows red hot. Remove it from the flame and quickly plunge it into a beaker of water.
This will produce a very brittle needle that is easy to break. Click to see a 400 Kb video..
Tempering of steel is when quenched steel is reheated until a blue tinge appears on the metal surface and allowed to cool slowly.
This makes the steel (needle) durable and hard wearing. Try to bend the needle. You will see it is tough and springy
.