Graphitization in high carbon commercial steels

Graphitization kinetics in two commercial high carbon steels, AISI types 1075 and 1095, are studied by conducting a series of isothermal annealing treatments in the temperature range of 560 to 680‡ C for periods of time ranging from 20 to 500 h. The samples selected were collected along the processing route in a commercial production line dedicated to the fabrication of thin strip. The structures studied were those of hot rolling (consisting of fine pearlite), cold rolling (spheroidized carbides within a deformed ferritic matrix), and subcritical annealing (spheroidized carbides in undeformed ferrite). The samples obtained from hot rolled coils do not graphitize, whereas those cold rolled graphitize at a rate that depends on the type of steel and degree of deformation. No graphite was found in samples from the lower carbon steel, which were subcritically annealed, although they were observed in specimens from the other steel, which were cold rolled to a reduction of 50% prior to the subcritical annealing.