1. Carbon equivalent: The effect of excessively high carbon equivalent of molten iron (especially high silicon content) makes graphite nodularization. Tests have shown that thick-walled heavy-duty universal wheels can produce flowering graphite when the carbon equivalent exceeds the eutectic composition. But the increased carbon content increases the recovery rate of molten iron and magnesium. Therefore, the principle of most high-carbon and low-silicon production is usually to control the silicon content at about 2%. In addition, the carbon equivalent and the choice of the wall thickness of the heavy-duty universal wheel: when the pipe wall thickness is 6.5 to 76 mm, the carbon equivalent is 4.35% to 4.7%; the wall thickness is> 76 mm, the carbon equivalent is 4.3% to 40.35%.
2. Sulfur: When the sulfur content in the molten iron is too high, the sulfur of the seamless steel tube forms magnesium, rare earth and sulfides, which float to the surface of the molten iron due to its low density, and these sulfides react with oxygen in the air Sulfur is generated, and the sulfur returns to the molten iron, and the above process is repeated, thereby reducing the content of magnesium and rare earth. When the sulfur in the molten iron is greater than 0.1%, even if a large amount of spheroidizing agent is added, the graphite cannot be globalized.
3. Rare earth and magnesium: When the content of rare earth and magnesium is too low, poor spheroidization or spheroidization often occurs. General factories require the addition of spheroidizing agent to be 1.8% 2.2% 4 Wall thickness: Heavy-duty universal wheel wall is too thick and it is easy to produce bad spheroidization and recession defects, mainly because the molten iron is in liquid state for a long time in the mold, magnesium The steam floats up, resulting in a decrease in the magnesium content; the latent heat of crystallization that is generated when a large amount of graphite is generated during eutectic remelting the austenite shell, and the graphite extends out of the shell and grows abnormally, forming aspheric graphite.
4. Temperature: If the temperature of the molten iron is too high, the molten iron will be seriously oxidized. Because magnesium and rare earth easily react with oxides, the content of magnesium and rare earth will be reduced. At the same time, high temperature will also increase the burning and evaporation of magnesium; If the temperature is too low, the spheroidizing agent cannot melt and be absorbed by the molten iron, but floats to the molten iron surface to burn or be oxidized.
