In 1947, British H.Morrogh found that when cerium was added to hypereutectic gray cast iron, so that the content of cerium was above 0.02wt%, the graphite was spherical. In 1948, A.P.Ganganebin et al. of the United States pointed out that adding magnesium to cast iron, followed by inoculation with ferrosilicon, when the residual magnesium content was greater than 0.04wt%, spheroidal graphite was obtained. Since then, ductile iron has started large-scale industrial production. The development speed of ductile iron as a new engineering material is amazing. In 1949, the world output of ductile iron was only 50,000 tons, in 1960 it was 535,000 tons, in 1970 it increased to 5 million tons, in 1980 it was 7.6 million tons, and in 1990 it reached 9.15 million tons. In 2000 it reached 15 million tons. The development speed of ductile iron production is particularly fast in industrialized countries. 75% of the world’s ductile iron production is produced by the United States, Japan, Germany, Italy, the United Kingdom, and France. The production of ductile iron in China started very early. It was successfully developed and put into production in 1950. The annual output of ductile iron in China reached 2.3 million tons, ranking third in the world after the United States and Japan. The rare earth magnesium nodularizing agent suitable for China’s national conditions has been successfully developed, and the production technology and research work in various fields such as as-cast ductile iron and austenitic-bainitic ductile iron have reached a high technical level.
(1) As-cast pearlitic ductile iron crankshaft and as-cast ferritic ductile iron automobile chassis parts have been put into production in my country’s No. 2 Automobile Plant, Nanjing Automobile Plant and No. 1 Automobile Plant. This marks that China’s as-cast ductile iron production has reached a higher level. The adoption of suitable out-of-package desulfurization, duplex smelting, instantaneous inoculation, inoculation block technology, audio detection and rapid analysis of thermal analysis and other technologies indicates that the technical level of China’s mass production of automobile castings is comparable to the international advanced level. The gap is narrowing.
(2) The metallurgical factors and corresponding production process measures of ductile iron with large section (wall thickness greater than 120mm) were studied experimentally. The use of an appropriate amount of yttrium-based heavy rare earth composite nodularizer, forced cooling, sequential solidification, delayed inoculation, and the addition of trace amounts of antimony and bismuth when necessary can prevent graphite distortion and loose organization in the center of ductile iron castings. Large and complex structural parts weighing 38 tons, diesel engine blocks weighing 17.5 tons, ductile iron rolls with a cross-section of 805mm, etc.
(3) Research and application of austenitic-bainitic ductile iron. In the early 1970s, almost at the same time, China, the United States, and Finland announced that they had successfully researched austenitic-bainitic ductile iron (collectively referred to as ADI) with high strength and high toughness. It is widely used in gears and various structural parts. Compared with alloy steel, austenitic ductile iron has significant economic and social benefits.
(4) Ductile iron pipes and horizontal continuous casting ductile iron profiles. Several ductile iron pipe factories have been built in China one after another, and several ductile iron pipe factories will be built in recent years. In 2000, China’s annual output of centrifugally cast ductile iron pipes reached 900,000 tons. In addition, China’s self-developed horizontal continuous casting ductile iron profile production line has passed the national appraisal, and many enterprises have put it into production. Coupled with a production line introduced in China, by 2002, China’s annual production capacity of ductile iron profiles reached tens of thousands of tons.
(5) The mechanical properties and other properties of rare earth magnesium ductile iron were systematically measured, and relevant data were provided for designers. The specific gravity, thermal conductivity, electromagnetic properties and other physical properties of rare earth magnesium ductile iron were measured, and the influence of graphite and matrix structure on the properties of ductile iron was studied in combination with metallographic standards. Various properties of ferritic ductile iron under normal temperature, low temperature, static and dynamic conditions were systematically determined. In addition, the stress-strain properties, low-energy multi-impact resistance and fracture toughness of rare-earth magnesium ductile iron were also studied, and began to be used to guide production. Combined with the application of ductile iron gears, the bending fatigue strength and contact fatigue strength of ductile iron, as well as the pitting corrosion and spalling mechanism of ductile iron gears are also systematically studied. (6) Rare earth magnesium ductile iron. In terms of high-strength low-alloy ductile iron, in addition to copper and molybdenum, nickel and niobium have also been studied. In the production of vanadium-titanium alloy ductile iron using natural vanadium-titanium pig iron, some units in China have carried out a lot of systematic work. Although medium manganese ductile iron is not stable enough in performance, it has achieved significant economic benefits in systematic research and production applications.
Post time: May-10-2022