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2021
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Do you know what ductile iron is?
Ductile iron is a high-strength cast iron material with comprehensive properties close to steel, developed in the 1950s. It has been successfully used to cast parts that are subject to complex stresses and require high strength, toughness, and wear resistance due to its excellent performance. The term 'replacing steel with iron' mainly refers to ductile iron, which has rapidly developed into the most widely used cast iron material after gray cast iron.
Ductile iron is a high-strength cast iron material with comprehensive properties close to those of steel, developed in the 1950s. It is successfully used in casting parts that are subject to complex stresses and require high strength, toughness, and wear resistance due to its excellent performance. The so-called 'replacing steel with iron' mainly refers to ductile iron, which has rapidly developed into the most widely used cast iron material after gray cast iron. Ductile iron obtains spherical graphite through spheroidization and inoculation treatment, which greatly improves the mechanical properties of cast iron, especially the plasticity and toughness, thereby obtaining higher strength than carbon steel.
In high-strength low-alloy ductile iron, nickel and niobium have been studied in addition to copper and molybdenum. Although the performance of medium-manganese ductile iron is not stable enough, years of production application and systematic research have achieved good economic benefits. In addition to medium-silicon ductile iron, in terms of heat-resistant ductile iron, the influence of total silicon-aluminum content on the growth resistance of rare earth magnesium ductile iron has been systematically studied. The RQTAL5Si5 heat-resistant cast iron developed in China, as a heat-resistant furnace grate, has a service life twice that of ordinary heat-resistant cast iron and three times that of gray cast iron, which is comparable to Japanese Cr25Ni13Si2 heat-resistant steel.
Progress has also been made in high-nickel austenitic ductile iron, which has been successfully applied to chemical equipment, petroleum extraction machinery, and industrial furnace installations. As for acid-resistant ductile iron, the rare earth high-silicon ductile iron produced in China is more uniform, finer, and denser than ordinary high-silicon ductile iron. Its mechanical strength is significantly improved, and its corrosion resistance is also improved by 10% to 90%.
Rare earth elements can spheroidize graphite. Since cerium was used to obtain ductile iron, many people have studied the spheroidizing behavior of various rare earth elements and found that cerium is a very useful spheroidizing element, and other elements also have varying degrees of spheroidizing ability. Studies since the 1960s have shown that cerium-containing inoculants can increase the number of spheroids in molten iron throughout the holding period, resulting in more graphite spheroids in the structure. Studies have also shown that rare earth-containing inoculants can improve the inoculation effect of ductile iron and significantly improve the resistance to recession. The reason why adding rare earth elements can increase the number of graphite spheroids can be attributed to: rare earth elements can provide more crystal nuclei, but compared with FeSi inoculation, it provides different crystal nucleus components; rare earth elements can make the original inactive crystal nuclei (existing in molten iron) grow, resulting in an increase in the total number of crystal nuclei in the molten iron.
Due to its pasty solidification characteristics, ductile iron often has defects such as shrinkage cavities and porosity due to poor feeding. In order to predict these defects before casting production, numerical simulations of the casting process have been carried out at home and abroad since the Indian era. Numerical simulation of the casting process is the use of numerical simulation technology to simulate the actual casting process in a computer virtual environment, including the filling process of metal liquid, the cooling and solidification process, and the stress forming process, to determine the influence degree of the main elements in the forming process, predict the structure, performance and possible defects, and provide a basis for optimizing the process and reducing waste products.
Ductile iron
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