Currently widely used rare earth magnesium silicon nodular agent, which contains elements of magnesium, rare earth, calcium, there are certain iron, silicon, and a small amount of manganese, aluminum, titanium and so on. The composition of the nodular agent is related to the ballistic treatment, iron liquid condition and so on. In this paper, the use of the most common rare earth ferrosilicon nodular as an example for analysis.
1. The content of spheroidal elements
The spheroidizing element is the element that converts the flaky graphite in the molten iron into spherical graphite. The conversion capacity of almost all elements in the chemical cycle table has been studied. Finally, magnesium is the most important spheroidizing element, and in some cases cerium, lanthanum, calcium and yttrium can also be used as auxiliary spherulites.
The amount of spheroidized elements in nodular cast iron is related to the size of castings, the thickness of the walls and the sulfur content of the molten iron. To ensure the stability of graphite and spheroidization, the effective residual magnesium content should be 0.030%. In order to ensure the necessary recovery of magnesium, magnesium alloy nodular agent magnesium content is often less than 10%. In the choice of nodular magnesium content, the general high-temperature ball molten iron (1500 ~ 1550 ℃) use Mg slightly lower point of the nodulation agent (magnesium 5% ~ 6%), low temperature ball molten iron (1400 ~ 1450 ℃) selected Mg slightly higher point of the nodularizer (magnesium 6% ~ 8%), which can control the smoothness of the ball reaction to obtain the appropriate amount of residual magnesium. In the actual production, the temperature difference is not very large, the workshop in order to facilitate the operation, often not so strict distinction, the general use of reasonable coverage of the ball agent, control the amount of the way to control the stability of the ball outbreak to To obtain the appropriate amount of residual magnesium.
(7% ~ 9%), the amount (4% ~ 6%) and low (1% ~ 3%) of the rare earth content of the rare earth files. In contrast to the large-scale use of foreign ductile iron furnace smelting, the use of desulfurization process, so the main use of low Mg (2.5% to 6.0%) low RE (<2.0%) of the ball agent. So the ball reaction is smooth, ductile roundness is higher.
Rare earth has light rare earth and heavy rare earth, the domestic production of ordinary ductile iron mainly cerium (Ce), lanthanum (La) mainly light rare earth spheroidal agent, but with the heavy rare earth continuous research, its thick section Ductile iron has been used, and the use of good results, can effectively overcome the large section of large ductile iron pieces prone to ballistic recession, cross-section sensitivity, cross-section of the central part of the mechanical properties of low problems.
Calcium is generally a limiting element in the nodularizing agent. Appropriate amount (2% ~ 3% Ca in the furnace) can control the absorption and reaction rate of the nodularizer in the molten iron. But should pay attention to excessive calcium, not only the melting agent slow, but also lead to the development of graphite to the worm-like, especially the large ductile ductile iron, so in the production of large ducts nodular iron must be noted that the control of calcium in the nodularizer, Calcium in the nodularizer There is also an intuitive reflection of the spaghetti in the ladle.
Barium in the nodularizer is to play a rare earth, magnesium, calcium coordination role, reduce the content of rare earth and magnesium, the ball better. Barium as a graphitizing element together with magnesium can reduce the vapor pressure of magnesium at high temperature, increase the absorption rate of magnesium, increase the number of graphite ball per unit volume of ductile iron, strengthen the effect of inoculation, inhibit the formation of carbides.
2. Iron and silicon content
Silicon and iron are the baSiC components of the nodularizer, are melted alloy with the ingredients, change their content can adjust the density and melting point of nodularizing agent. Rare earth magnesium silicon nodularizing agent in the silicon generally 40% to 50%, the melting point of 1220 ℃, Si low, Fe high melting point increases, the density increases. Si is too low (Fe will be high), the ball agent is difficult to melt, and this nodularizer in the melting, the end of the high temperature, Mg burned larger, the amount of MgO may be more. When it is necessary to use ductile iron back to the charge, it is appropriate to use the pressed low Si or "no Si" ball agent.