Brief history of nodularizer
In 1943, K.D. Miller (Mils) of the International Nickel Corporation (INCO) discovered that magnesium could precipitate spherical graphite from the solidification structure of cast iron, and applied for a US patent in 1948. In 1948, H. Morrogh of the British Cast Iron Research Institute (BCIRA) pointed out at the American Foundry Society (AFS) meeting held in Philadelphia, USA that cerium was added to the hypereutectic iron liquid and inoculated with silicon manganese zirconium alloy, Cast ductile iron is available. In 1949, Wang Zunming of Tsinghua University in China also successfully prepared nodular cast iron with magnesium. In 1950, nodular cast iron was produced with copper-magnesium alloy as nodulizer, and in 1964, it was developed into rare earth magnesium nodular cast iron with ferrosilicon rare earth alloy as nodulizer. China is rich in rare earth metal resources, and ductile iron has become a widely used structural material.

Organization and Performance of nodularizer
The solidification structure of normal ductile iron is that small and round graphite balls are evenly distributed in the metal matrix. Since graphite balls do not have sharp graphite edges like flake graphite, their damage to the metal matrix is greatly reduced, so that the cast iron metal matrix performance is fully utilized. Therefore, the mechanical properties of ductile iron are much higher than that of gray cast iron, the tensile strength can reach up to 1400 MPa, and the elongation can reach up to 24%. However, the shock absorption performance of ductile iron is worse than that of gray cast iron, and the notch sensitivity is higher than that of gray cast iron.

Classification of nodularizer
Through different heat treatment methods, the matrix structure of ductile iron can be easily controlled, and ductile iron with different properties can be obtained to meet the needs of various working conditions. According to the different types of matrix structure, ferritic ductile iron, pearlitic ductile iron, pearlite-ferritic ductile iron, austenitic-bainite ductile iron, etc. are common in industrial production. In Chinese national standards, ductile iron is divided into QT350-22L, QT350-22R, QT350-22, QT400-18L, QT400-18, QT400-15, QT45010, QT500-7, QT550-5, QT600-3, QT700-2 , QT800-2, QT900-2 and other different grades. The meaning of the grade is: the first two letters QT represent ductile iron (the capital of the first letter of the pinyin of ductile iron), the numbers behind are the tensile strength and elongation, and the letter L in the grade indicates that the grade has a low temperature (-20C or -40C) impact performance requirements, the letter R indicates that the grade has room temperature (23°C) impact performance requirements. Among them, the ductile iron of QT450-10 and below is a ferrite matrix, the ductile iron of QT500.7, QT550-5 and QT600-3 is a pearlite + ferrite matrix, QT700-2 is a pearlite matrix, QT800 -2 is pearlite or sorbite matrix QT900-2 is tempered martensite matrix or troostite + sorbite matrix.

Preparation and application of nodularizer
Add a small amount of nodularizers such as rare earth or magnesium, and then add a small amount of inoculants such as ferrosilicon to the molten cast iron to change the nucleation and growth conditions of graphite during the solidification of cast iron, and obtain fine and uniform spherical graphite in the cast state of high-strength cast iron. Ductile iron has simple production process, excellent performance and low cost, and is widely used in industrial production, especially in automobiles, machine tools, cast pipes, general and engineering machinery and other industries.


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