With the rapid development of China's economy and the introduction and absorption of foreign high-end castings, the quality requirements of high-performance, high-efficiency and high-reliability equipment in various fields are increasing day by day. Low temperature and high toughness ductile iron materials are widely used in wind power generation, high-speed railway and other fields due to their high impact toughness at low temperatures. Then, let's learn about the production factors of cast low temperature and high toughness ductile iron!

The toughness of high toughness ductile iron in low temperature environment is affected by many factors, such as chemical composition, casting technology, melting, spheroidizing, inoculation treatment technology and heat treatment system, which determine the final microstructure and mechanical properties of castings.

1) The effect of high toughness ductile iron structure on impact toughness In practical production application, when the carbon content is constant, the influence of the spheroidization rate and the number of graphite balls on the impact performance is obvious, at the same time round graphite balls can improve the impact toughness of ductile iron, the increase of graphite volume fraction or the increase of the number of graphite balls will reduce the brittle transition temperature, thus reducing the hardness of graphite balls, in actual production, the spheroidizing treatment and cultivation process must be strictly controlled, and the content of trace elements in raw materials (pig iron, scrap steel, furnace material, etc.) must be controlled, especially the content of anti-spheroidizing and interference elements must be limited. It is shown that the matrix structure of ductile iron has a significant effect on its impact properties. As can be seen from Figure 4, as the volume fraction of pearlite increases, the impact performance decreases, so it is necessary to ensure that the low-temperature high-toughness ductile iron is all ferrite base.

2) The influence of the chemical composition of high toughness ductile iron on the impact toughness. Under certain process conditions, the chemical composition of ductile iron will have an organizational and decisive effect, and determine its performance. The effect of c on the impact performance of the V-groove of ductile iron is mainly manifested in the upper limit impact absorption energy, which decreases with the increase of the carbon content of ductile iron. This is because the destruction of ductile iron is caused by the formation of pores on the graphite ball and its condensation growth. When the carbon content is high, due to the increase of the number of balls and the increase of size, the plastic deformation energy in the process of pore growth and its condensation is reduced, which is manifested as the reduction of the upper limit impact absorption energy. However, when the carbon content is too low, the plasticity-embrittlement transition temperature range will move to the high temperature direction, which will affect the low temperature impact absorption energy. Considering the carbon content, it is appropriate to determine wC = 3.70-3.80%.

The effect of Si on the impact properties of high toughness ductile iron is twofold. Since Si will strongly change the plastic-brittle transition temperature, in order to obtain excellent low-temperature toughness, it is necessary to reduce the amount of Si in ductile iron as much as possible, but when the amount of Si decreases, the tensile strength and yield strength of ferritic ductile iron will decrease. Considering comprehensively, it is determined that wSi terminal = 1.80~2.00%.

Mn will increase the tendency of segregation, promote the formation of carbide and pearlite in the matrix, which is very unfavorable to toughness, especially the impact absorption of low-temperature ductile iron can be seriously damaged, in addition, the high amount of Mn will also increase the difficulty of annealing heat treatment of ductile iron. Therefore, it is necessary to limit the amount of Mn, and generally, the upper limit is wMn 0.2%. Both s and p are harmful elements, and p not only significantly increases the plastic-brittle transition temperature, but also strongly reduces the upper limit impact energy of ductile iron. Therefore, reducing the amount of P is one of the important factors in the production of low temperature and high toughness ductile iron. It is necessary to limit the amount of wS and wP, and the general upper limit is 0.02.

Ni can be used as a ferrite strengthening element for high-toughness ductile iron, and wNi = 0.4 to 0.6% is suitable.

The above introduction is the production factors of cast low temperature and high toughness ductile iron. If you need to know more, please feel free to contact us!