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

The microstructural evolution of a spheroidised Fe-0.85C (wt-%) steel durin g heavy cold rolling and post-aging was studied, with the emphasis on cemen tite. 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 (001)(0) planes was observed in the deformed cementite parti cles. By X-ray diffraction, it was found that the initial spheroidal cement ite particles dissolve partially in a solid solution of ferrite by deformat ion, in a manner similar to that of the lamellar cementite of pearlite. Gre ater 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 ag e hardening was estimated to be 122 kJ mol(-1), which is attributed to carb on atom diffusion from cementite to dislocations in ferrite.