Effect of Destabilisation Period and Post Destabilisation Cooling Rate on the Evolution of Microstructure in 8.0 wt% Chromium White Cast Iron

Abstract

To study the effect of destabilisation period and post-destabilisation cooling rate on the as-cast microstructure, continuous annealing involving prolonged austenitisation for 4 h followed by furnace cooling and cyclic annealing using repeated austenitisation, each of 0.66 h duration, followed by forced-air cooling were carried out at 900, 950, 1000, 1050 and 1100 °C on a 8.0 wt% chromium white iron. Destabilised microstructures show precipitation of secondary carbides on a pearlite plus martensite matrix after continuous annealing treatment and on a martensite plus austenite matrix after cyclic annealing treatment. Both the treatments exhibit characteristic role in monitoring the size and distribution of the secondary carbides and also in modifying the eutectic pattern with varying annealing temperature. At higher temperatures of 1050 and 1100 °C, absence of the secondary carbides becomes a common feature for both the heat treatments; while fragmentation of the eutectic carbides happens to be an additional feature after cyclic annealing of the as-cast alloy.