Simulation of the Evolutions in Real Microstructure of Material under Thermal Cycle with High Thermal Gradients

Simulation research on the thermal phase transition of EDM and the formation mechanism of remelted layer in single pulse spark discharge crater

“…The microstructure of the remelted layer and the heat affected zone depends on the temperature distribution around the discharge pit, i.e., as the temperature applied by the heat source changes, there is a complex metallurgical phase transformation during EDM, and the microstructure of the discharge pit surface changes, and the metallurgical phase transformation process is split into two stages: the first stage is the heating stage, and when the temperature is higher than 995 K the microstructure undergoes a significant change, i.e., the two types of organizations constituting the parent material Between the percentage content will change, and when the temperature is higher than 1253 K, the phase becomes α + β → β; the second stage for the cooling phase, that is, after the disappearance of the heat source, when the temperature is lower than 1073, the phase becomes β → α ', that is, transformed into martensite process [28] . At a temperature gradient of > 80 K/s [29] , a fully martensitic organization is obtained. Therefore the remelted layer produced during EDM is mainly composed of residual austenite and martensitic columnar structure [30].…”