TRANSFORMATIONS IN ELECTROTEMPERING OF CAST IRON.

Electrotempering at 250-500 degree C is accompanied by structural transformations caused by decomposition of the high C martensite, thus increasing the low C martensite content. The carbide particles, during their nucleation and growth, preserve coherence with the matrix. This coherence ceases to exist only when the particle size reaches a certain critical value. Silicon has no pronounced effect on the rate of coherent growth of the carbide particles. When the coherence disappears, the growth of these particles is limited by bulk diffusion of C whose rate is determined by the Si effect. Electrotempering at 250-500 degree C does not produce martensite with a uniform composition. The high nonuniformity can be the reason for high strength and hardness after quenching followed by electrotempering. This phenomenon suggests that electrotempering can be successfully employed instead of tempering with high-frequency heating.