Medium frequency furnace is used to melt molten iron. See Table 1 for chemical composition. After the composition in front of the furnace is qualified, the molten iron will be transferred to the spheroidizing ladle, and the spheroidizing treatment and primary inoculation will be carried out during the ladle process, and then the molten iron will be injected into the quantitative casting box from the spheroidizing ladle, and the secondary inoculation of the molten iron will be realized during the ladle process. The molten iron shall be placed in the pouring box for 2 min, and the pouring shall be started after the oxide slag floats to the surface. The pouring temperature shall be controlled between 1 340~1 360 ℃, the pouring time shall be controlled between 120~300 s, and the surface of ductile iron castings with a pouring time of more than 300 s are prone to cold shut casting defects.
| Ingredients | C | Si | Mn | S | P | Mg |
| Before spheroidization | 3.5~3.7 | 1.4~1.8 | ≤ 0.2 | ≤ 0.02 | ≤ 0.04 | \ |
| After spheroidization | 3.6~3.8 | 2.2~2.4 | ≤ 0.2 | ≤ 0.02 | ≤ 0.04 | 0.035~0.050 |
When the ductile iron castings are cooled to below 300 ℃, they are unpacked. After rough cleaning, the billets are sent to the kiln for low-temperature annealing treatment. The purpose is to eliminate the residual stress of the ductile iron castings, so as to prevent local small deformation of the ductile iron castings in the finishing stage, which affects the assembly and sealing.