Abstract
Electron-microscopic examinations were carried out on cementite isolated from annealed, cold-rolled and subsequently annealed 0.65% carbon steels, and the behaviours of cementite during these treatments were studies with the following results: (1) During cold deformation of steel, a cementite crystal in the steel curves elastically, and then splits along its cleavage into many laminar fragments. The width of the split laminae lies in the range from 1500 to 3000 Å, and these laminae themselves show a fibrous substructure, having a width of about 300 Å. In the case of spheroidal pearlite, however, the cementite globules suffer no change in the process of cold-rolling. (2) Due to annealing after cold-rolling, a crystalline cementite is spheroidized through three stages, that is, incubation, nucleation, and growth stages. The spheroidization of cementite is regarded as a “intra-cementitic” recrystallization phenomenon. (3) During prolonged annealing of normalized steel at a subcritical temperature, a crystalline cementite in it undergoes local thickening and local thinning, and finally separates into several cementite globules. The spheroidization of cementite in this case may be caused by surface tension and lattice imperfection inherent in the cementite.
