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2. Hot metal

Graphic and photo of Electric Arc Furnace
Picture 1. An electric arc furnace. The photograph shows how hot it gets!

Heating and cooling
Heating steel
A simple way to heat something up is to put it in contact with something else at a higher temperature. For example, you can heat water in a kettle. The kettle's electric element gets hot and heats up the water.

An electric arc furnace is similar to a kettle. It is used for melting steel. What happens as the steel gets hotter?

You can find out more about the electric arc furnace in the Chemistry of steelmaking e-source, which is aimed at 14 to 16 year olds.
What’s the difference between hot and cold?
The particles of a solid are fixed in a regular arrangement. We call this a lattice. At room temperature, the particles are vibrating. As the steel gets hotter, the particles vibrate more.
Animated graphic of vibrating lattice.
Picture 2. The lattice of steel particles in solid steel

Graph of increasing temperature against time
Picture 3. Graph of temperature against time for a constant rate of heating.

Picture 2 shows the particles in steel at room tempertaure. Heating solid steel makes its temperature rise - the particles vibrate more. When the steel starts to melt (at 1450 ºC), the particles break free of the bonds that hold them in the lattice.

What happens after melting?
Once the steel has melted, the particles are free to move in the liquid. They are still loosely held together and stay in the bottom of their container. The steel is heated up a bit more so that it flows easily. As the temperature goes up, they will move faster.

If it were heated to more than 3000 ºC it might boil. The liquid particles would then break free and form a gas.

Heating the surroundings
The molten steel is at a temperature of 1500 ºC. This is much hotter than the surroundings. Therefore it will transfer energy to the surroundings (a hotter body will always heat up a cooler one). There are three ways in which it will do this:
  1. Conduction
  2. Convection
  3. Radiation

In the next three pages, we will look at what happens in each case.

Question 2-1.

Look at the sentences below. Each one is describing a solid, a liquid or a gas. Decide what the sentence is describing then choose that from the list.

A. The particles are bound in a lattice
B. It fills the space available to it
C. The particles vibrate more as they are heated
D. The particles are loosely bonded but not in a lattice
E. It can flow around but stays in its container
F. The particles move around faster as it is heated (2 possibilities).
Summary                   Close
  • Solid steel is a lattice of bonded particles
  • The hotter the solid, the more the particles vibrate
  • When a solid melts, the strong bonds are broken
  • The atoms in a liquid are free to move around