C P S for ductile cast iron
In order to produce qualified ductile cast iron, except the suitable casting process, the different kinds of elements in molten steel are important to ductile cast iron.
Manganese has the opposite effect to silicon in ductile cast iron. Manganese is an element that prevents graphitization. Manganese can increase the solubility of carbon in molten iron, promote the formation of white mouth and pearlite, and increase the strength and hardness of castings. With the increase of manganese content, the tendency of castings to shrinkage and porosity increases.
Phosphorus enters ductile cast iron with metal charge, such as steelmaking pig iron and recycle charge. Although phosphorus does not affect the spheroidization rate, it is indeed a harmful element. Phosphorus has a certain solubility in iron, but when the content of phosphorus in the metal material reaches a certain amount, it is easy to form phosphorus eutectic in cast iron. The more phosphorus content, the greater the number of phosphorus eutectic. In addition, because the phosphorus eutectic is sharp The angle has a certain cutting effect on the metal matrix, so the strength, flexibility and toughness of the material are reduced, and the casting is easy to brittle. The lower the phosphorus content of ductile cast iron, the better. We control the phosphorus content ≤0.07%.
S has a strong affinity with Mg and Re. The high sulfur content consumes a large amount of spheroidization, which makes the casting material spheroidization poor and spheroidization decline, and the generated sulfide is one of the main reasons for the formation of inclusion (slag) defects in ductile cast iron, so sulfur is the anti-ball in ductile cast iron Chemical elements are harmful impurities. The sulfur content of the raw molten iron should be controlled as much as possible below 0.025%.
Magnesium is the main spheroidizing element, and its functions are as follows:
(1)Spheroidized graphite: A small amount of magnesium remaining in the molten iron can make the graphite spherical when crystallized; at the same time, it increases the supercooling degree of the molten iron, and strongly prevents the graphitization of the primary crystallization, so that the carbide is stabilized, so nodular cast iron has a larger White mouth tendency.
(2)Desulfurization: Magnesium is very easy to combine with the sulfide in the molten iron. The specific gravity of MgS is smaller than that of molten iron and the melting point is higher than that of molten iron, so it can float and enter the slag to be removed;
(3)Deoxidation: The chemical nature of magnesium is very active, and the specific gravity of magnesium oxide, which is easily generated by the interaction with oxygen, is lighter than that of molten iron. It can float up into the slag and be removed, which significantly reduces the oxygen content in the molten iron and makes the surface of ductile cast iron easy to form oxidation membrane.
(4)Degassing and removing inclusions: Magnesium has a low melting point. After being added to the molten iron, the gasification, boiling and vigorous stirring of the magnesium occur, which reduces the gases such as hydrogen and nitrogen in the molten iron and reduces the inclusions.
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