Spheroidized elements generally have the following common properties:
(1) There are one or two valence electrons in the outermost electron shell of an element, and 8 electrons in the innermost shell. This electronic structure enables the element to have a strong affinity with sulfur, oxygen and carbon, which reflects the stability of the product and can significantly reduce the sulfur and oxygen in the discount.
(2) The solubility of elements in molten iron is low and there is a significant tendency to segregate during the solidification process.
(3) Although it has a certain affinity with carbon, its solubility in the graphite lattice is low. Based on the above characteristics, Mg, Ce, Y, and Ca are effective spheroidizing elements.
First, the vapor pressure in the molten iron is high, making the molten iron effervescent. The atomic weight and density of magnesium are smaller than that of molten iron, with a melting point of 650 degrees and a boiling point of 1108 degrees. At the processing temperature of molten iron, the vapor pressure generated by magnesium is very high (more than 1Mpa). The heat of fusion of magnesium is 21J/g and the latent heat of evaporation is 406J/ g. Therefore, when magnesium is added to molten iron, it will vaporize and cause the molten iron to churn.
Second, it has a strong affinity with sulfur and oxygen. The generated MgO and MgS have a high melting point and a density much smaller than iron, making them easy to separate from molten iron. Therefore, the contents of sulfur and sheep in molten iron after magnesium treatment are very low;
Third, there is a tendency to segregate in graphite during the solidification process of molten iron. When its residual amount in the molten iron exceeds 0.035%, the powder can be spheroidized. However, when the residual amount of magnesium exceeds 0.07%, part of the magnesium segregates at the grain boundaries. , and an exothermic reaction occurs with carbon, phosphorus, etc. in the grain boundaries to generate MgC2, Mg2C3, Mg3P2, etc. When the amount of residual magnesium is larger, the intergranular carbides increase.
