The low rare earth nodulizer is smelted in molten iron in a 20Kg or 50Kg non-vacuum induction furnace. Chemical composition of pig iron 3.70% C, 0.51% Si, 1.70% Al, 0.60% Mn, 0.10% P, 0,04% S Spheroidized mixture prepared with 60% metallic magnesium powder, 28% MgO, and 12% phenolic resin mixture, cured and sintered at 300°C. The molten iron is melted and superheated to 1400°C. After removing the surface slag, the pre-prepared low rare earth nodulizer is added to the molten iron using the bell jar method. After the liquid metal has stopped bubbling, the bell jar is removed, deslagged and poured. In order to optimize the composition ratio of the spheroidized mixture, the same pig iron is still used, and its chemical composition is 3.70%C, 0.51%Si, 1.70%Al, 0.60%Mn, 0.10%P, 0.04%S. The weight of molten iron is still 20Kg. The reaction speed of metal magnesium and molten iron is controlled by adjusting the ratio of MgO after calcination.
In order to safely add cast iron nodularizers to molten iron, it must be solidified and sintered at 250-300°C in advance. The spheroidized mixture prepared by sintering below 250°C contacts molten iron during the spheroidizing process and releases a large amount of gas, which greatly slows down the spheroidizing process and reduces the absorption rate of magnesium. When sintering at a higher temperature, a large amount of metal magnesium will be violently oxidized in the air, which will increase the content of metal magnesium and reduce the spheroidizing effect. Cast iron spheroidizing treatment can achieve the best effect in the temperature range of 1350-1450 ℃. Spheroidizing molten iron at lower or higher temperatures will be accompanied by a decrease in the absorption rate of metallic magnesium, which is due to the longer time for metallic magnesium to evaporate or explode at high temperatures.
The low rare earth spheroidizer can ensure that the silicon content of the cast iron remains unchanged during the spheroidizing process of molten iron, which greatly expands the process possibility of the cast iron spheroidizing treatment method, and ensures the obtaining of low-silicon and high-strength aluminum nodular cast iron.
Compared with low-rare-earth nodulizers, pure magnesium nodulizers have the disadvantages of requiring special equipment, taking too long to prepare a tundish, and being unable to nodulize a small amount of molten iron (≤50Kg), resulting in serious waste. However, the use of master alloys as spheroidizers to spheroidize cast iron will increase the silicon content of the treated molten iron, which is not suitable for the production of low-silicon high-strength nodular cast iron. Low rare earth nodulizer contains metal magnesium, no metal splash, nodularization effect is the same as pure magnesium and can guarantee high strength cast iron with different silicon content, especially when dealing with a small amount of molten iron.
Application prospects of low rare earth nodulizers: Ductile iron castings are widely used in the fields of automobile, machinery and equipment manufacturing, and there are many kinds of nodulizers for the production of nodular cast iron. At present, master alloys containing magnesium and rare earth are mainly used as nodulizers in production. Other noduliar exist such as pure magnesium, mechanical mixtures containing magnesium. The selection of spheroidizing agent and spheroidizing treatment method mainly depends on production conditions, casting properties, etc.