The characteristics of microcrack initiation process in cast iron materials under thermal shock test

The thermal microcrack initiation process of two cast iron materials is investigated. The thermal shock load is applied to the material specimen periodically by induction heating and water quenching. The entire process of microcrack initiation is observed and recorded by the metallographic microscope. It is found that the thermal microcracks initiate rapidly at graphite phases and gradually develop into stable microcrack networks. The microcrack networks are analyzed with the quantitative statistic method and the fractal method for further study. The results show that the average length of the microcracks in microcrack networks is about 0.1 mm for both but the fractal dimension which reflects the thermal fatigue resistance is different for the two materials. Finally a fractal model characterizing the microcrack initiation process is proposed.