Effect of vibration frequency on matrix structure of vermicular graphite cast iron

The figure shows the matrix structure of cast iron prepared under different vibration frequencies. Figures (a) – (d) show the matrix structure of cast iron prepared at vibration frequencies of 0,35,50 and 100Hz respectively.

It can be seen from the figure that the matrix structure of EPC vermicular cast iron without vibration is austenite dendrite + pearlite + vermicular graphite + spheroidal graphite. When vibration is applied to cast iron alloy, the matrix structure is composed of austenite dendrite + pearlite + flake graphite + vermicular rudiments. When the vibration frequency is 35Hz, the primary austenite dendrite arm and secondary dendrite arm are more developed, forming eutectic clusters with smaller size, which are composed of the rudiments of vermicular graphite. When the vibration frequency increases to 50Hz, the primary austenite in the alloy is granulated, and the dendrite structure of austenite is not obvious. When the vibration frequency is further increased to 100Hz, there are a certain number of primary dendrite arms in the alloy, but the secondary dendrites peel off from the primary dendrite arms and disperse in the matrix of cast iron.

Vibration during solidification of vermicular graphite cast iron increases the solidification undercooling of the alloy, reduces the eutectic temperature of the alloy, and prolongs the solidification time of the alloy. On the one hand, the vermicularizing agent in the alloy has a serious failure, which reduces the content of residual magnesium and rare earth in the alloy. In the region of lack of spheroidizing elements, the vermicular graphite rudiments are transformed into flake graphite; On the other hand, when austenite dendrites grow, carbon atoms are discharged to the interface, which enriches carbon atoms at the austenite interface, providing favorable conditions for graphite nucleation, and the vermicular graphite rudiments are precipitated along the shape of austenite perimeter.