Effect of Chemical Composition on the Microstructure of Carbide Reinforced Indefinite Chilled Rolls

Abstract

In the present work, effects of elements such as V, Nb, Si and Cr on the microstructures of the conventional indefinite chilled rolls made by small vertical centrifugal caster were investigated, using optical microscopy, Scanning Electron Microscopy (SEM, Jeol 6400), Energy Dispersive X-ray Spectroscopy (EDXS, Cu-Kα radiation) to identify the type, morphology, and to measure the volume fraction and the distribution of carbides and graphites formed during solidification. Microstructural analysis indicates that, the amount of graphite is dramatically reduced by adding V element. The volume fraction of the square-like carbides NbC increases with the Nb content increasing. However, if Nb content is over a critical point, large amount of the square-like NbC carbide can be seriously segregated in the out part of the section. The test also shows that, by increasing Si and reducing Cr content, the volume fraction of the graphite increases accordingly, whereas much of its shape turns to be finely flake-like. In addition, it can be found from the microstructures observed by optical microscopy that, the volume percentage of the rod-like NbC carbides increases as the examining position is near the inner portion of the section, and that of the cubic-like NbC carbides decreases contrarily.