Toughness and Abrasion Resistance of High Alloy Cast Iron

Abstract

High chromium cast irons have been recognised as a hard, wear resistant alloy for use in crushing, grinding and material handling applications. The successful operation of these wear resistant components has been limited by their inherent brittleness and failure to withstand impact conditions. Laboratory work has shown that the fracture toughness of a molybdenum alloyed high chromium cast iron can be significantly increased by carrying out a specialised high temperature heat treatment which modifies the eutectic carbide morphology. Trial swing hammer castings have been produced and treated to attain a suitably modified carbide morphology. Microstructural examination of the alloy together with fracture toughness evaluation at specific specimen locations have been carried out. A matrix leeching technique has been used to observe the changes in carbide morphology. After 16months service a returned casting was examined as described and in addition the wear damage was analysed and micro mechanisms suggested. Conventionally heat treated material was also examined in the unused condition and the results compared with the specially processed alloy. High temperature heat treatments have been observed to have a significant effect in modifying eutectic carbide morphology and a less angular, more spheroidised carbide has been produced. The short bar fracture toughness specimen has been found to be capable of discriminating between austenitic and martensitic matrix alloys, the austenitic material having the higher toughness. Two distinctly different wear regimes have been identified as operating during service. The characteristics of these regimes have been related to the mechanics of the particular size reduction process studied.