Heat treatment – as applied to steel – can be defined as the application of heat to change a characteristic or condition of the steel.

The amount of heat can be measured by the temperature of the steel being treated.
Temperature can be either cold or hot to the touch, therefore the process treatment temperatures can range from extremely cold to extremely hot. Or, in terms of temperature, the range can be from a cold negative temperature to a hot plus temperature.
Heat treatment is the process of heating up to temperature, soaking at that temperature and then cooling down from the temperature.