Question

Plain steel that is cooled slowly is made up of pearlite and primary ferrite. The pearlite is a fine layering of ferrite and Cementite (Fe3C). If plain steel has a weight percent of carbon of 0.425, which is between 0.022 and 0.77 weight percent, and is cooled slowly to room temperature, what is the weight % of the pearlite in the resulting structure?

Answer 1

Iron-Carbon phase diagram is assumed to hold good for the case of slow cooling. Thus, Weight % pearlite will be calculated using the Lever rule at Eutectoid temperature.

C = 0.022 weight %

C_eut = 0.77 weight %

For the given composition, C = 0.425 weight %

The fraction of pearlite = (C - C)/(C_eut - C) = (0.425 - 0.022)/(0.77 - 0.022) = 0.53877

Therefor weight % pearlite = fraction x 100 = 0.53877 x 100 = 53.877 %.