Texture and microtexture studies in different types of cast irons

Abstract

Drum and disk brake for trucks are important applications for cast irons. In the design of these components the low cycle fatigue strength is a critical attribute for material selection. It is known that fatigue strength is closely related to microtexture and grain boundary structure. In the present study, these two significant microstructure factors were evaluated for three types of cast irons with the aid of a scanning electron microscope equipped with of electron back scattered diffraction (EBSD) patterns technique. Samples of grey cast iron, compacted graphite cast iron and nodular cast iron were extensively studied, and the microstructure, microtexture and grain boundary misorientation evaluated. Complementarily macrotexture measurements were performed in X-ray diffractometer with texture goniometer to determine the orientation texture of the nodular and compacted graphite cast iron. Differences in the morphologies of pearlite found in those three types of cast irons are also discussed. The microtexture was evaluated by means of EBSD. The analysis of texture suggests random distribution of the orientations of ferrite grains, as a consequence of the process of production, which includes solidification followed by phase transformation. The absence of preferential texture is attributed to the inoculation process, where random nuclei are introduced in the melt. Phase transformations also favors randomization and this occurs in cast irons because solidification first gives origin to austenite with subsequent transformation of austenite into ferrite, after cooling.