Effect of Cu Addition on Microstructure and Hardness of As-Cast and Heat-Treated High-Cr Cast Iron

The objective of the present study is to investigate the effect of Cu addition on microstructure and hardness of hypoeutectic high-Cr cast irons (26 wt% Cr) in as-cast and heat-treated conditions. As-cast specimens with varying amount of copper (Cu) addition were produced using an industrial grade high-frequency induction furnace. As-cast specimens were heat-treated in a box furnace using a typical reversed heat treatment sequence where subcritical heat treatment was followed by destabilization heat treatment. Microstructural analysis of the as-cast and heat-treated specimens was carried out using an optical microscope and Feritscope to understand the effect of Cu addition on the microstructure. The bulk hardness of all the specimens was measured using a Brinell hardness tester. The obtained result shows that the microstructures of the as-cast specimens mostly consist of austenitic dendrite matrix with γ+ M7C3 eutectic colony morphology. The eutectic colony consists of fine carbides in the central region and coarse carbides at the boundary region. High Cu containing specimen has a higher amount of thin rod-like M7C3 carbides, whereas low Cu containing specimen has a higher fraction of massive carbide morphology. Heat-treated specimens with various Cu content show mixed microstructure mostly consisting of retained austenite, transformed martensite, eutectic carbides, and secondary carbides. However, their relative volume fraction changes with the change in Cu content. Hardness result shows that higher Cu containing specimen has a lower hardness than the lower Cu contain specimens for both as-cast and heat-treated conditions. Although heat-treated specimens, in general, have higher hardness values than the as-cast specimens.