Deformation and dissolution of spheroidal cementite in eutectoid steel by heavy cold rolling

Abstract

The microstructural evolution of a spheroidised Fe-0.85C wt- steel during heavy cold rolling and post-aging was studied, with the emphasis on cementite. A new morphology of cementite, wavy thin bands nearly parallel to the rolling plane, was found in the specimens subjected to rolling reductions >90. Slip on 001theta planes was observed in the deformed cementite particles. By X-ray diffraction, it was found that the initial spheroidal cementite particles dissolve partially in a solid solution of ferrite by deformation, in a manner similar to that of the lamellar cementite of pearlite. Greater strain age hardening was observed for the spheroidised steel than for a similarly treated pearlitic Fe-0.85C steel. The strain age hardening peak was observed at 573 K for the spheroidite structure, which is 150 K higher than was observed for the pearlite structure. The activation energy for age hardening was estimated to be 122 kJ mol1, which is attributed to carbon atom diffusion from cementite to dislocations in ferrite.