Microstructural examination of service exposed coal mill liner material

This study mainly focuses the microstructural characterisation of the service exposed coal liner. These liners are generally referred to as bull ring segments in the bowl mill of coal pulveriser systems. The failed bull ring segment was collected from a coal-fired power plant of Kolaghat thermal plant, West Bengal, India. The crack that has been observed in the middle of the liner was observed under SEM and detailed microstructural studies are made for the liner material. The hardness measurements are made and XRD is carried out to identify the phases present in the sample. The results suggest that the material confirms to high chromium cast iron and microstructural studies reveal that the cracks are mainly due to the heavy service exposed conditions where lumps of coal and silica sand falling on these liners causing severe impact and abrasion conditions. High abrasive studies on the liner material are carried out and it showed that increasing the abrasive size as well as load is responsible for higher wear loss. The results suggest that prolonged exposure to abrasion conditions results in the progressive removal of the matrix material and due to various phase transformations from austenite to martensite introduces surface volume changes and causes the generation of cracks and further lead to failure of the component.