Continuous cooling

In industrial heat treating operations, steel is not isothermally transformed at a temperature above the martensite start temperature but is continuously cooled from austenitic temperature to the room temperature. In continuous cooling of a plain carbon steel, austenite to peartite transformation occurs over a range of temperatures rather than at a single isothermal temperature. Figure 36.2 compares transformation during continuous cooling with that at isothermal cooling. Note the following