SPHEROIDIZING TREATMENT OF LAMELLAR CARBIDE IN EUTECTOID OR HYPOEUTECTOID STEEL

摘要

PURPOSE:To finely spheroidize the pearlite structure of a eutectoid or hypoeutectoid steel in a short time and to improve the toughness and workability by cold working the steel before heat treatment for spheroidizing under specified conditions. CONSTITUTION:A eutectoid or hypoeutectoid steel contg. 0.8wt.% C has a lamellar pearlite structure consisting of lamellar ferrite and cementite (Fe3C). Since this pearlite structure brings inferior workability and causes defective hardening and the deterioration of the toughness at the time of heat treatment, the cementite is spheroidized by heat treatment. Before this heat treatment, the steel is cold worked at =30% working rate to finely divide the lamellar pearlite structure and then the steel is heated to a temp. between the recrystallization temp. and the A1 transformation point and held for 30-600sec. The lamellar cementite (Fe3C) in the pearlite is spheroidized to =1mum grain size and the toughness of the steel is improved.