The figure shows the hardness change curve of vermicular graphite cast iron prepared under different vibration frequencies. It can be seen from the figure that with the increase of vibration frequency, the hardness value of cast iron alloy first decreases, then increases and then decreases, showing a broken line change law. Because the vermicular graphite cast iron without vibration is vermicular graphite cast iron, and there is more austenite in the matrix structure, pearlite structure is formed after its transformation, which increases the hardness of the matrix.
When the vibration is applied in the lost foam casting process of cast iron, the graphite type in the alloy prepared according to the composition of vermicular cast iron changes from vermicular and spherical mixed graphite to flake and vermicular graphite rudiments. Therefore, the hardness value of cast iron decreases. When the vibration frequency is, the length of flake graphite in the alloy is large, which increases the microcracks in the alloy, and the hardness of the alloy is low. When the vibration frequency is, the hardness of the alloy will increase because the size of flake graphite in the alloy is small and there are more vermicular graphite crystals. When the vibration frequency is further increased to 100Hz, the length of flake graphite in the alloy increases and the hardness value of the alloy decreases.