CEMENTITE PARTICLE COARSENING DURING SPHEROIDIZATION OF BEARING STEEL SAE-52100

A of the spheroidisation process was carried out on bearing steel SAE 52100 utilising two different heat treatment cycles. For transformation temperatures of 700 and 740 degrees C a cubic power law dependence of the Lifshitz-Wagner-Greenwood type was found to apply to the coarsening of cementite particles in both an austenitic and a ferritic matrix. The rate of coarsening was highest above the critical A(1) temperature. The process was found to be diffusion controlled and values for the operative diffusion coefficients were determined both above and below the critical temperature. The spheroidisation process was found to involve only the precipitation and coarsening of carbide after austenitising, with retained carbide particles serving as nuclei for the reprecipitation process.