Grain Refinement of α-iron by Repeated Carburizing and Decarburizing Reactions

The grain refinement of alpha-Fe using repeated carburizing and decarburizing at 1 073 K are investigated. It is found that the grain sizes are decreased by carburizing reaction but are increased by decarburizing reaction. Repeated alpha <-> gamma phase transformations make grain size smaller. However, without pinning elements, the reduction of the grain size has limitation. Sulfur does not have enough effects on the grain growth with the grain size of less than 30 mu m. To improve the grain refinement process, Fe(3)C was introduced by annealing at 873 K along with the carburizing and decarburizing processing. Formed Fe(3)C can supply a lot of nucleation site for austenite nuclei during the reaustenitizing and retards ferrite grain growth during gamma -> alpha transformation by the decarburization reaction. The fine uniform grains of less than 10 mu m have been produced by the carburizing and decarburizing processing at 1 073 K along with adjusting the cementite size and the whole volume during the heat treatment at 873 K.