Casting technology! Defect Treatment of Ductile Iron. 　　Ductile iron is nearly 40 years to develop China's important casting metal materials. As the spherical graphite caused by the small concentration of stress on the matrix of the split effect is also small, so the ductile iron tensile strength, plasticity and toughness are higher than other cast iron. Compared with the corresponding steel, plasticity is lower than that of steel, and the fatigue strength is close to that of medium carbon steel, and the cost is lower than steel, so its application is becoming more and more extensive.

　　Of course, ductile iron is not perfect, it will produce in addition to the general casting defects, but also produce some unique defects, such as loose loose, slag, subcutaneous stomata, spheroidization and recession. This article will discuss the main common defects of ductile iron: slag.

　　Influencing factors
　　(1) silicon: silicon oxide is also a major component of slag, so as far as possible to reduce the silicon content.
　　(2) sulfur: iron sulfide in the molten iron is the formation of slag defects one of the main reasons. The melting point of the sulfide is lower than the melting point of the molten iron. During the solidification of the molten iron, the sulfide will precipitate from the molten iron and increase the viscosity of the molten iron, so that the slag or the metal oxide in the molten iron can not easily float. So the molten iron sulfur content is too high, the casting is easy to produce slag. Ductile iron cast iron liquid sulfur content should be controlled below 0 06%, when it is 0 09% ~ 0 135%, cast iron slag defects will increase dramatically.
　　(3) rare earth and magnesium: In recent years, research that slag is mainly due to magnesium, rare earth and other elements due to oxidation, so residual magnesium and rare earth should not be too high.
　　(4) pouring temperature: pouring temperature is too low, the metal metal metal oxides and other metal liquid viscosity is too high, easy to float to the surface and remain in the metal liquid; temperature is too high, the molten metal surface slag Become too thin, easy to remove from the liquid surface, often with the metal liquid into the type. The actual production, pouring temperature is too low is caused by slag one of the main reasons.
　　(5) sand: If the sand surface adhesion of excess sand or paint, they can be combined with the metal oxide oxide slag, resulting in slag generation; sand compactness is not uniform, low degree of compact wall The surface is easily eroded by the molten metal and the formation of low melting point of the compound, resulting in casting slag.

　　Preventive measures
　　(1) Minimize sulfur content (<0 06%) in molten iron,
　　Appropriate amount of rare earth alloy (0 1% ~ 0 2%) to purify the molten iron,
　　Minimize the amount of silicon and the amount of residual magnesium
　　(2) smelting process: to maximize the temperature of the molten metal baked, suitable for calm, in order to facilitate the non-metallic inclusions floating, gathered. Grilled clean iron liquid surface of the slag, iron surface should be placed on the cover agent (perlite, ash, etc.), to prevent iron liquid oxidation. Choose the appropriate pouring temperature, preferably not less than 1350 ℃.
　　(3) pouring system to make molten iron flow is smooth, should be set with slag bag and slagging device (such as filter slag network, etc.), to avoid sprinkler sand.
　　(4) mold tightness should be uniform, the strength is sufficient; when the box should be blowing the sand in the mold.