Effect of Sub-critical Tempering and Deep Cryogenic Treatment on Slurry Erosion of Cr-Mn-Cu White Cast Irons

The effect of deep cryogenic treatment and air cooling subsequent to sub-critical tempering treatment on the structural evolution and the resulting wear performance of Cr-Mn-Cu white cast iron in sand-water slurry media were studied. The as-cast matrix of Cr-Mn-Cu white cast iron is predominantly austenitic which can be transformed to a martensitic matrix embedded with fine M7C3 carbides, by a sub-critical tempering treatment followed by air cooling. But the retained austenite is not totally converted. Quenching of alloy in liquid nitrogen bath after subcritical tempering enables more amount of transformation of austenite with simultaneous homogeneous precipitation of fine carbides. The phase transformation and corrosion-erosion behavior were characterized by optical and scanning electron microscopy, bulk and micro-hardness measurement and x-ray diffraction analysis, measurement of corrosion rate and slurry erosion test. The slurry erosive wear performance has been found to be much better in the cryotreated alloys compared to those with conventional sub-critically tempered alloys.