Effect of intermediate cooling after hot-deformation on the proeutectoid cementite evolution at the grain boundary in hyper-eutectoid steel rods

摘要

Grain boundary cementite in hyper-eutectoid steels has been considered to cause brittle fracture during drawing and nonuniform cementite during spheroidizing. Suppression of carbon segregation in the center of bloom or billet and annealing for the homogenizing the segregated carbon have been examined to retard a proeutectoid cementite evolution(1). Si(2) and Co(3) having low solubility in the cementite are effective to suppress the cementite precipitation. However, Si is harmful to the drawability and Co is very expensive to add. It is well known that fast cooling retards proeutectoid cementite evolution. However, cooling rate immediately after hot-deformation has not been considered to retard the cementite evolution. Intermediate cooling rate and method after hot-rolling were considered to retard proentectoid cementite in hyper-eutectoid steels.