Features of the carbide phase degradation under heating and deformation

Abstract

The present work reflects the results of comprehensive studies of the carbide phase behavior (cementite) in cast irons, which are widely used as a forming tool in metallurgy. This structural component determines the stable operation of the tool in production. Due to the development of new scientific approaches, special methods of structure variability analysis are being developed. Such methods allow one to have a deep look into the processes that determine the nature of degradation phenomena, including those occurring in the carbide phase. In this work, we use the results of the new techniques, which made it possible to identify degradation processes occurring inside the massive inclusions of the carbide phase of chromium-nickel cast iron during deformations at high temperatures (400 -600°C). Here we report the significant instability of the carbide phase revealed under such processing conditions. Basing on the optical-mathematical analysis of the obtained SEM microstructure images, we show that such a carbide phase degrades under the local deformations. At the first stage of deformation, the creation of local stresses is intensified, while the subgrain boundaries and individual defects are being formed. Such individual defects (dislocations) define the degree of carbon and iron diffusion which determines the formation of a number of new phases: ferrite with various carbon saturation values, bainite, carbides of nonstoichiometric composition (such as FeC and Fe x C y ).We also analyze the paired and triple interactions between these new phases. The influence of localization of the deformations on easy sliding of dislocations is considered. As it occurs, this process is accompanied by a decrease in the dispersion of the formed new ferrite and carbide phases, as well as in their mutual interactions. However, we show that when dislocations slip, the new ones appear. As a result, energy dissipation occurs. The obtained qualitative and quantitative representation of the carbide phase degradation during heating and deformation can be used to develop new technological processes of the production and hardening of such a material with a specific purpose taken into account.