In the production of thick section ductile iron parts, in order to improve the anti-recession ability, a certain proportion of heavy rare earth is added to the spheroidizing agent, which can ensure the spheroidizing Mg content and increase the anti-recession ability. Heavy rare earth elements such as lanthanum. According to the test and production practice of many factories in China, it is very desirable to use the composite spheroidizing agent of Re-Mg and yttrium-based rare earth as a spheroidizing agent for the production of thick-section ductile iron parts. The use of this spheroidizing agent in our company is very good. The actual production and application process has also achieved good results. According to the relevant data, the spheroidizing ability of bismuth is second only to that of magnesium, but its anti-recession ability is much stronger than that of magnesium, and it does not return sulfur. It can be added excessively. When high carbon is well bred, no cementite will appear. In addition, bismuth and phosphorus can form high melting point inclusions, which reduce and diffuse the phosphorus eutectic, thereby further increasing the ductile iron elongation. In the spheroidization treatment, in order to increase the absorption rate of magnesium, control the reaction rate and improve the spheroidization effect, a unique spheroidization process is employed. The control of the spheroidization treatment is mainly controlled at the reaction rate, and the spheroidization reaction time is controlled to about 2 minutes.
For this purpose, a composite spheroidizing agent of medium-low Mg, Re spheroidizing agent and cerium-based heavy rare earth is used, and the amount of the spheroidizing agent added is determined according to the amount of residual Mg.
Spheroidization decline prevention: The reason for the spheroidization decline is related to the decrease of the escape of Mg and RE elements in the molten iron. On the other hand, it is also related to the continuous decline of the gestational effect. In order to prevent the spheroidization from declining, the following measures are taken: A, molten iron There should be sufficient spheroidal content in the medium; C, reduce the sulfur content of the original iron liquid, and prevent the oxidation of the molten iron; C, shorten the residence time of the molten iron after spheroidization; D, the spheroidal treatment of the molten iron After the slag is slag, in order to prevent the escape of Mg and RE elements, the surface of the molten iron can be covered with a covering agent to isolate the air to reduce the escape of the elements.