The effect of ductile iron structure on impact toughness In actual production applications, with a certain carbon content, the spheroidization rate and the number of graphite balls have a significant impact on impact performance. The relationship is shown in Figure 2 and Figure 3. At the same time, the rounded graphite balls can improve the impact toughness of ductile cast iron, and the increase in the volume fraction of graphite or the number of graphite balls can reduce the brittle transition temperature and increase the upper impact absorption energy. Therefore, in actual production, the spheroidization and inoculation process must be strictly controlled, and the content of trace elements in raw materials (pig iron, scrap, reheating materials, etc.) must be controlled, especially the content of de-spheroidization and interference elements must be restricted. Figure 4 shows that the matrix structure of ductile iron has a significant impact on its impact properties. It can be seen from Figure 4 that as the volume fraction of pearlite increases, the impact performance decreases. Therefore, it is necessary to ensure that the low-temperature and high-toughness ductile iron is an all-ferrite matrix.
(2) The influence of the chemical composition of ductile iron on impact toughness. Under certain process conditions, the chemical composition of ductile iron has a decisive effect on the structure and determines its performance. The effect of C on the impact performance of the V-notch of ductile cast iron is mainly reflected in the impact on the upper impact absorption energy. The upper limit impact absorption energy decreases with the increase of the carbon content of ductile iron. The reason is that the fracture of ductile iron is caused by the vacancy formed on the graphite ball. The high carbon content will increase the number of balls and the size of the aggregate growth, so the plastic deformation during the vacancy growth and aggregation process will decrease, resulting in a decrease in the plastic deformation energy during the fracture process, which is manifested as a decrease in the upper impact absorption energy. . However, if the carbon content is too low, the plastic-brittle transition temperature range will move to the high temperature direction, which will affect the low-temperature impact energy absorption.