Electron microscopy study of carbides precipitated during destabilization and tempering heat treatments of 25 wt.%Cr-0.7 wt.%Mo high chromium cast irons

Abstract

The effect of a 0.7 wt.%Mo addition on the microstructure and hardness of a heat treated 25 wt.%Cr–2.4 wt.%C cast iron has been studied via comparison with a Mo free reference 25 wt.%Cr–2.4 wt.%C iron. Destabilization led to precipitation of M7C3 and M23C6 secondary carbides in the reference iron, whereas M23C6 secondary carbide was found in the iron with 0.7 wt.%Mo. Tempering resulted in additional secondary carbide precipitation and formation of ferrite. Secondary hardening was found in the iron with 0.7 wt.%Mo. For the destabilized + tempered condition the macro-hardness of the iron with 0.7 wt.%Mo addition was higher than the reference iron due to a finer and denser distribution of secondary-carbides.