Wire Electric Discharge Machining of P91 Steel: Microstructure and Thermal Modeling Studies

The effect of different cutting parameters used during wire electric discharge machining (WEDM) of P91 steel on the cutting process, microstructure on or under the surface, and the surface finish was examined in this study with a view toward understanding the cutting process fundamentally. The approach used was based on heat transfer modeling and experimental validation of the thermal effects by examining the microstructure and the surface smoothness. The microstructure below the surface was analyzed experimentally in considerable detail using, besides other tools, a high-resolution transmission electron microscope to examine the nature and the morphology of the phases. The different microstructural features were explained from the heat generated and cooling rates estimated in thermal modeling and a good agreement was found. The understanding of the plasma formation and heat transfer during the process provides a means of predicting the surface finish after WEDM in any material provided the thermal properties are known. This aspect was verified in this study by examining the cut surface generated in a variety of materials and by thermal modeling study.