Signs of Degradation of Carbide Phases in Chromium-Nickel Cast Iron at the Operating Temperatures of Forming Rolls

We study the causes and signs of degradation of cementite in chromium-nickel cast iron used for the production of massive forming rolls and the specific features of structural formation in cementite under the influence of operating temperatures and local strains formed in the rolls in the course of their operation. For this purpose, we use the procedure of high-temperature vacuum etching in order to detect dislocations, scanning electron microscopy, and the method of optical-mathematical description of the phases and their heterogeneity. It is shown that the degradation of cementite is connected with the formation of dislocation structures and diffusion, which promote the formation of new types of carbide phases with nonstoichiometric compositions, quasicrystalline graphite, and also ferrite and bainite. Possible combinations of newly formed phases are identified. They are also responsible for the stability of carbides. By analyzing the results of our studies of the degradation of cementite (regarded as a structural component specifying the level of hardness of the operating cast iron), we give recommendations concerning the possibility of improvement of stability of the cementite structure and decreasing the level of stresses in the rolls.