Abstract: Hadfield manganese steel specimens containing 1.46 wt% C and 12.54 wt% Mn were studied in as received condition, after annealing normalizing, quenching, tempering and cold working. The microstructure, phase transformation and Rockwell hardness (HRC) were measured after each heat treatment. It was found that normalizing and quenching had no effect on microstructure and the hardness but annealing, tempering and cold working cause a change in the microstructure and increase the hardness. The increase in hardness on tempering was due to fine distribution of carbides while on annealing, precipitation of carbides at austentic grain boundaries and within the grains causes hardness to increase. Cold working may cause the formation of twin boundaries / martensites which increase the hardness of specimen.