page 2-1
2. Hot metal

Graphic of furnace
Picture 1. An electric arc furnace. The photograph shows how hot it gets!

Heating and cooling
Electric heating
When we pass an electric current through a piece of wire, it gets hot. We can use the same idea to heat up steel in an Electric Arc Furnace. The carbon electrodes make contact with the steel and pass a current through it. This current will make the steel get hotter directly – there is no need for a heating element because the steel itself acts as the element. What happens to the particles as the steel gets hotter?
You can find out more about the electric arc furnace in the Chemistry of steelmaking e-source.
What’s the difference between hot and cold?
The particles of a solid are fixed in a regular arrangement (a lattice). At room temperature, the particles are vibrating around their normal position. As the steel gets hotter the particles vibrate more vigorously. They have more kinetic energy.
Animation of vibrating particles
Picture 2. The lattice of steel particles in solid steel. These are mostly atoms of iron (with some carbon and other trace elements).

Picture 2 shows how the particles might be moving in steel at room temperature. Heating solid steel makes its temperature rise (the energy is being used to make the particles vibrate more vigorously). When the steel starts to melt (at 1450 ºC), the particles break free of the bonds that hold them in the lattice.

Whilst it is melting, its temperature doesn't go up. All the energy is being used to break the bonds rather than making the particles move faster.

Have a look at The chemistry of steelmaking for more on the make-up of steel.
Interactiv graph of melting etc
Picture 3. Graph of temperature against time for a constant rate of heating.

What happens after melting?
Once the steel has melted, the particles are free to move in the liquid. However, they don't move much more than the hot steel just before it melted. As the temperature goes up, they will move faster. The temperature of the liquid steel is related to the average kinetic energy of its particles.
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.

Fill in the gaps in the paragraph below. Choose the best answer in each case.

The temperature of a liquid is related to the of its particles. When we heat solid steel its temperature will rise until it . When the steel melts, the temperature because the energy is used to the atoms.
Summary                   Close
  • Solid steel is a lattice of bonded particles
  • When a solid melts, the strong bonds are broken
  • Energy is needed to break the bonds
  • The atoms in a liquid are free to move around