THE MORPHOLOGY AND COARSENING KINETICS OF SPHEROIDIZED FE-C BINARY-ALLOYS

The tempering and spheroidization of martensitic Fe-C binary alloys ra nging in carbon content from 0.2% to 1.4% in 0.2% increments have been investigated. The tempering was conducted at 690 degrees C for up to 3 weeks. Quantitative metallography techniques were used to determine average carbide diameter and ferrite grain aspect ratio. Recrystalliza tion was not found to occur during tempering, and the ferrite grain as pect ratio was shown to be dependent on the prior austenite grain size , carbon content, and temper time. Carbides were found to reside almos t exclusively in the grain boundaries and the carbide coarsening kinet ics were governed by a power law relationship, d = kt(n), where n is d etermined by the diffusion mechanism. The coarsening kinetic time cons tant, n, fell between 0.2 and 0.23 for the entire range of Fe-C alloys studied, indicating that the coarsening process during tempering is c ontrolled by carbon diffusion in grain boundaries and dislocation.