Vortrag (20 Min., 5 Min. Diskussion, 5 Min. Raumwechsel)
High Chromium Cast Irons: Chemical composition and thermal processing effect on secondary carbide precipitation, hardness and wear propertiesMittwoch (18.09.2019) 17:30 - 18:00 Uhr Masing Saal Bestandteil von:
High Chromium Cast Irons (HCCI) have been a material of choice for wear resistant components in the mining and mineral processing industries for a long time, given their outstanding wear and erosion resistance. The main reason for such resistance can be found in the hard MnCm reinforcement carbides embedded within the metallic matrix, being those of hypoeutectic, eutectic or hypereutectic origin. The microstructure and mechanical properties of HCCI are a direct consequence of the eutectic carbide content, matrix microstructure and the presence of secondary carbides embedded within the metallic matrix. Particularly, the presence of secondary carbides has shown to improve the wear resistance behavior of the entire composite.
In this work, a destabilization process is carried out followed by a sub-critical diffusion (SCD+Q) step before quenching to precipitate and grow secondary carbides. The main objectives of the present work are: (a) to compare the effect of two chemical compositions (15% and 26% Cr) in combination with a SCD step in the secondary carbides precipitation and growth and (b) to compare such results with a standard above critical destabilization quenching (Q) and (c) to analyze the effect of such increased carbide precipitation on wear resistance. The destabilization of the austenite at high temperature leads to a final microstructure composed by eutectic and secondary carbides, with an M7C3 nature, embedded in a martensitic matrix. An improved wear resistance was observed in the SCD+ Q samples in comparison to the Q one, which was attributed to the size of secondary carbides. Moreover, higher Cr contents leaded to a sharper change in wear resistance.
Optical Microscopy and SEM characterization was carried out for Phase morphology and distribution. Electron Backscattered Diffraction together with the TSL OIM Data Collection software were used for the carbide type identification. XRD was performed for phase identification.. Macro and micro hardness test were carried out to outline mechanical properties, as well as wear test that were carried out in a CSM macro tribometer in rotational mode.