The influence of heating parameters on the microstructural behaviour of a hypoeutectic high chromium cast iron alloy

Nayak, Ullal Pranav

The applicability of high chromium cast irons (HCCIs) in the mining and mineral industries stems from their improved abrasion resistance. Moreover, subjecting the cast HCCI alloy to destabilization heat treatment (DHT) results in the precipitation of fine secondary carbides (SC) and an associated transformation of the matrix, leading to a further improvement in the wear resistance. In fact, the alloy properties are highly dependent on the amount, distribution, and specifics of the various micro constituents. Furthermore, given the multi-scale nature of the HCCI’s microstructure, it is imperative to understand the precipitation behaviour at each stage of the HT to appropriately design a cycle ensuring a successful microstructural tailoring.

In the present study, an as-cast 26% HCCI alloy was subjected to different DHT by varying the heating rate and temperature. Microstructural characterization was performed on the HT samples using a combination of optical microscope, SEM and EBSD. Corelative microscopy indicated the precipitation of fine SC primarily at the periphery of the matrix for higher heating rates, irrespective of the destabilization temperature. As the heating rate was lowered, extensive precipitation was seen proceeding inwards into the body of the matrix. Furthermore, the SC size and volume fraction showed no significant variation when the destabilization temperature was increased, although slower heated samples showed a higher value compared to its counterpart. The amount of retained austenite reduced with increasing temperature as indicated by EBSD and further quantified using Rietveld refinement. Previous work showed the interdependence between the wear behaviour and microstructural distribution, with increasing destabilization holding time. In this work, the carbide precipitation together with the microstructural evolution at the early stages of heating will be corelated with the associated tribological behaviour to develop a better understanding and tune the HT parameters to tailor the specific microstructure.