Effect of Prior Microstructures on Cementite Dissolution Behavior During Subcritical Annealing of High Carbon Steels

The variation of the morphology and distribution of cementite particles in different prior structures with spheroidizing annealing process has been proceeded in this paper. It is found that the dissolution and coarsening progresses of various initial structures in spheroidizing annealing process are quite asynchronous due to the different interlamellar spacing. The dissolution rate of degenerated pearlite (D-P) with finer interlamellar spacing is faster. The granular cementite in the spheroidized microstructure is fine, uniform and dense. The mean diameter of spherical cementite is refined to 233 nm. However, the initial structure of degenerated pearlite (D-P) is highly sensitive to the austenitization temperature. The cementite is easy to be coarsened under high austenitizing temperature. The coarsening is accompanied by the gradual increase of the Cr content in the cementite, which increases the stability of the cementite. Therefore, the optimal austenitizing temperature for degenerated pearlite (D-P) is suggested to be 770 °C. The dissolution rates of cementite in spheroidized structures are related to the initial pearlite interlamellar spacing and the austenitizing temperature. A detailed experimental research and analysis are needed on the evolution of different initial structures during spheroidizing annealing treatment.