1 Equipment selection
1.1principle of high efficiency and low consumption, on the premise of meeting production needs. The advantages of the induction furnace are: the heating speed is fast, the furnace has high thermal efficiency, the oxidation loss is light, and the absorption gas is less. Therefore, the smelting in the intermediate frequency electric furnace can avoid the problem of increasing sulfur and phosphorus, so that the P in the molten iron is not more than 0.07% and the S is not more than 0.05%.
1.2 Determination of the spheroidizing package In order to improve the absorption rate of the spheroidizing agent and increase the spheroidizing effect, the spheroidizing treatment package should be deeper than the general iron liquid package. The height to diameter ratio of the spheroidized bag is determined to be 2:1.
2 Raw material selection
2.1 The choice of the choice of the charge of the ball iron spheroidizing agent is: high carbon, low silicon, large fertility. In order to stabilize the chemical composition and effectively control the promotion of white-mouthing elements and anti-spheroidizing elements, and to ensure the quality of molten iron, Zhanggang Z14 pig iron is selected, its chemical composition: C>3.3%, Si 1.25%～1.60%, P≤0.06 %, S ≤ 0.04%.
2.2 Selection of spheroidizing agent The spheroidizing agent should be selected according to the different smelting equipment, ie the temperature of the tapping iron and the purity of the molten iron (such as sulfur content, oxidation degree, etc.). The most commonly used rare earth magnesium ferrosilicon spheroidizing agent in China is that when the spheroidizing agent is used, the high silicon content in the alloy can significantly reduce the severity of the reaction during magnesium treatment. At the same time, it can also have some gestation effects due to silicon. When the electric furnace is produced, the spheroidizing agent FeSiMg8Re7 is used because of the relatively high temperature.
3 furnace control
3.1 Chemical composition selection of ductile iron should be high carbon, low silicon, low sulfur, low phosphorus. Controlling the sulfur content is an important condition for the production of ductile iron.
3.2 Spheroidization and inoculation treatment The addition amount of spheroidizing agent should be determined and determined according to the factors such as the composition of molten iron, the wall thickness of the casting, the composition of the spheroidizing agent and the absorption rate of the spheroidizing treatment. Generally, it is 1.6% to 2.0%. If the spheroidizing agent is placed for a long time, it should be added in an appropriate amount. The key to the control of spheroidization reaction is the absorption rate of magnesium, high temperature, intense reaction, short time, high magnesium burning loss, poor spheroidization effect, low temperature, stable reaction, long time, magnesium absorption rate.
High, good spheroidization effect. Therefore, under the premise of ensuring sufficient pouring temperature, it is desirable to reduce the spheroidizing treatment temperature as much as possible, and control it at 1420 to 1450 °C. The spheroidizing agent should be smashed into small pieces, and the particle size is generally 5 to 25 mm, which is added to the bottom of the bag, and then ferrosilicon and iron filings are added thereon.
Inoculation is an important part of the production process of ductile iron. It not only promotes graphitization, prevents the appearance of free cementite and white mouth, but also helps to spheroidize and make graphite smaller, more round and evenly distributed. , thereby improving the mechanical properties of ductile iron. The inoculant generally uses FeSi75, and the amount thereof is generally 0.8% to 1.0% according to the mechanical properties of the casting. The particle size of the inoculant is generally divided into small pieces of 5 to 25 mm depending on the amount of molten iron. Inoculants should be kept clean and dry.
The spheroidizing agent and the inoculant should be added to the bag before the iron is discharged. In the continuous production, after the first furnace iron is finished, the package is very hot. If it is added too early, it will stick to the bottom of the package and weaken the spheroidization and gestation. effect. In order to delay the spheroidization reaction time and enhance the spheroidization and inoculation effect, a layer of iron filings is applied to the spheroidizing agent and the inoculant. There are many methods for spheroidizing treatment, and the spheroidal iron is generally treated by a simple operation.
3.3 Spheroidizing effect The pre-furnace inspection of the furnace is carried out to test the gestation and spheroidization effect. Generally, a triangular specimen is used. The triangle sample was poured, cooled to dark red, quenched and cooled, and the fracture was observed after breaking. The fracture is silvery white, the tip is white, the center is loose, and both sides are concave. At the same time, there is a calcium carbide smell when the hammer is broken. The knocking sound is similar to steel, and the spheroidization is good, otherwise the spheroidization is bad.
3.4 Pouring Because the spherical iron liquid is prone to spheroidal decline, the molten iron should be poured as soon as possible after spheroidizing treatment. Generally, the pouring is completed within 15 minutes after the treatment, and there will be no spheroidization deterioration.