CEMENTITE PARTICLE COARSENING DURING SPHEROIDIZATION OF BEARING STEELSAE-52100

A of the spheroidisation process was carried out on bearing steel SAE 52100 utilising two different heat treatment cycles. For transformatio n temperatures of 700 and 740 degrees C a cubic power law dependence o f the Lifshitz-Wagner-Greenwood type was found to apply to the coarsen ing of cementite particles in both an austenitic and a ferritic matrix . The rate of coarsening was highest above the critical A(1) temperatu re. The process was found to be diffusion controlled and values for th e operative diffusion coefficients were determined both above and belo w the critical temperature. The spheroidisation process was found to i nvolve only the precipitation and coarsening of carbide after austenit ising, with retained carbide particles serving as nuclei for the repre cipitation process.