Simulation of solidification paths in high chromium white cast irons for wear applications

Thermodynamic calculations of the solidification paths in the Fe-Si-Cr-C system using the CALPHAD approach have been used for the interpretation of the solidification microstructures of high chromium white cast irons containing high silicon contents. The results show a reasonable agreement between experiments and calculations for alloys up to 2 wt% Si. The results suggests that the stability of the cementite phase is underestimated in the thermodynamic database. The calculations predict a change in the topology of the phase diagram, with the cementite primary field disappearing in favour of a new ternary eutectic involving liquid, austenite, graphite and M₇C₃ carbide, this is partially in agreement with the observed microstructures for the alloys containing 4 wt%Si. The calculations predict the existence of a complex invariant peritectic reaction involving liquid, graphite, austenite, cementite and M₇C₃ carbide in the Fe-Si-Cr-C system.