For a eutectoid steel, describe isothermal heat treatments that would be required to yield specimens having the following Rockwell hardnesses: (a) \(93 \mathrm{HRB}\) (b) \(40 \mathrm{HRC}\) (c) \(27 \mathrm{HRC}\)

Answer: To achieve a hardness of 93 HRB, eutectoid steel can be annealed, a process which involves heating the steel above the eutectoid temperature, cooling it slowly, and allowing it to reach room temperature. For a hardness of 40 HRC, the steel must be hardened by forming tempered martensite. This involves heating the steel above the eutectoid temperature, quenching it rapidly, and tempering the martensite by reheating and cooling down the steel to room temperature. To achieve a hardness of 27 HRC, the heat treatment should promote a higher proportion of pearlite in the microstructure by heating the steel above the eutectoid temperature, cooling it to a temperature below the eutectoid range, and allowing the steel to reach room temperature.