The hot metal overheats, which is the primary condition for improving the quality of malleable steel pipe casting. Research on the metallurgical properties of molten iron found that cast iron still maintains an inhomogeneous state for a long time after melting. The specific reason is not fully understood for the time being. It is generally believed that molten iron contains a variety of impurities, some of which hinder the dissolution of graphite, so that solid graphite crystals dissolve too slowly in molten iron, resulting in non-uniformity of performance and organization. High temperature and overheating can speed up the dissolution of carbon and the homogenization of molten iron. The molten iron can get a series of benefits after entering high temperature and overheating.
The primary indicator of molten iron quality is the temperature of molten iron. Regarding the influence of molten iron overheating temperature on the quality of malleable steel pipe fittings, there have been different opinions in recent decades. One view is that the higher the molten iron superheat temperature, the better, which can refine the graphite and improve the mechanical properties of the casting; the other view is that the molten iron superheat temperature has a critical temperature. When the value exceeds this value, the quality of the casting decreases with the increase of the overheating temperature.
Although the casting process temperature of malleable steel pipe parts is not high, most of them are between 1260 and 1400 degrees Celsius. But from the point of view of obtaining high-quality molten iron, it should have a higher melting temperature. High temperature smelting ensures high iron tapping temperature, Fe, Si, Mn burns less, furnace conditions are stable, chemical composition fluctuations are small, high temperature smelting, S, Q, H, N and inclusions in the molten iron will be reduced, and the charge Bad heredity will be reduced.
1) At high temperature, the activity of carbon increases, and the activity of silicon decreases. The deoxidation effect of carbon on FO, MnO, SO2 and other oxides is dominant, which promotes the reduction of oxides, thereby effectively clearing the non-metallic inclusions in the molten iron. .
2) The hydrogen and nitrogen molecules in the molten iron are easily concentrated in the CO bubbles formed by deoxidation at high temperatures, and escape from the molten iron with the bubbles, thereby effectively clearing the gas in the molten iron.
3) At high temperature, the kinematic viscosity of molten iron decreases, the mass transfer is accelerated, and it is easy to achieve homogenization in convection and electromagnetic stirring.
Only the molten iron that has undergone high-temperature heat treatment can cast excellent malleable steel pipe fittings. The molten iron is released at high temperature and low temperature casting is the prerequisite to ensure the quality of malleable steel pipe castings.
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