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The application of rare earth in cast iron

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Update time : 2017-12-29 10:12:14

The application of rare earth in cast iron

Cast iron is one of the main fields of rare earth application and is the largest user of rare earth use. Since the 1970s, rare earths have been widely used in ductile iron, vermicular cast iron and gray cast iron. After more than 30 years of research and development, the application process technology of rare earth in cast iron has matured and its use has been the first in China and has made great technological progress.

The application of rare earth elements in casting alloys begins in ductile cast iron (1948). Although it began in the age of obscurantist, it was widely used in the industry in various fields of casting alloy in the 1950s and 1960s, in the enlightenment era. After entering the 70 s, the application of rare earth in cast alloy, in both quantity and quality of an unprecedented level, that is to say, in the 70 s, the application in the field of rare earth alloy casting and other fields into the golden age.

1. Research and application of rare earth in various cast iron
1. nodular cast iron
In 1947, h. Morrogh discovered that graphite was spherical when additional cerium was added to the eutectic cast iron in the amount of 0.02wt %. In 1948, A study by a.p. Ganganebin et al. found that the addition of magnesium to cast iron was subsequently incubated with ferrosilicon, and the spherical graphite was obtained when residual magnesium was greater than 0.04wt %. From then on, ductile iron began large-scale industrial production.

The development speed of ductile iron as a new engineering material is amazing. In 1949, the production of world ductile iron was only 50,000 tons, from 535 million tons in 1960 to 5 million tons in 1970, 7.6 million tons in 1980 and 9.15 million tons in 1990. It reached 15 million tons in 2000. The production and development speed of ductile iron is particularly fast in developed countries. 75 percent of the world's ductile iron production is produced by the United States, Japan, Germany, Italy, Britain and France.

The production of ductile iron in China started very early. In 1950, it was successfully developed and put into production. The annual output of ductile iron in China is 2.3 million tons, which is the third place in the world after the United States and Japan. Rare earth magnesium nodulizing agent suitable for China's national conditions, the successful development of as-cast nodular cast iron and austenite bainite ductile cast iron and other fields of production technology and research work have reached a very high technical level.

(1) casting of the cast pearlite ductile iron crankshaft and cast iron plain ductile iron chassis parts were put into production at the second automobile plant, nanjing automobile plant and the first automobile plant respectively in China. This indicates that the production of cast ductile iron in China has reached a high level. Corresponding outside the package of desulfurization, duplex melting, instantaneous inoculation, inoculation technology and audio test and thermal analysis quick analysis techniques such as the adoption of the marked the our country a lot of water in the production of automobile castings technology with the international advanced level of the gap is narrowing.

(2) the metallurgical factors of nodular cast iron and corresponding production process measures were studied. Using the right amount of yttrium base heavy rare earth compound nodulizing agent, forced cooling, directional solidification, delay the inoculation, when it is necessary to add trace antimony and bismuth, can prevent nodular cast iron center pieces of graphite distortion and loose organization, etc., has been successfully made 38 tons of large complicated structure, 17.5 tons of d iesel oil body, cross section is 805 mm of nodular cast iron roll, etc.

(3) study and application of austenite - bainite ductile iron. In the early 1970 s, China almost at the same time, the United States, Finland three countries announced research success has high strength, high toughness of austenite to bainite ductile iron (ADI) general in the world, as well as the material of the tensile strength of 1000 mpa, so it is widely used in gear and a variety of structures, compared with the alloy steel, Mr - Mr Nodular cast iron has a remarkable economic benefit and social benefit.

(4) ductile iron pipes and horizontal continuous casting ductile iron profiles. Several ductile iron pipe works have been built successively in China, and several ductile iron pipe plants will be built in recent years. In 2000, China's annual production of centrifugal casting ductile iron pipe reached 900,000 tons. In addition, China's self-developed continuous casting ductile iron profile production line has been approved by the state and has been put into production by many enterprises. Combined with the introduction of a production line in China, in 2002, the capacity of China's annual production of ductile iron profiles reached tens of thousands of tons.

(5) the mechanical properties and other properties of rare earth magnesium ductile iron were determined systematically, and the data was provided for the designers. The influence of graphite and matrix on the properties of nodular cast iron was studied by using the metallographic standard. The properties of ferritic ductile iron in normal temperature, low temperature, static and dynamic conditions were determined systematically. In addition, the stress and strain properties of rare earth magnesia nodular cast iron, the resistance of small energy and fracture toughness were studied, and they were used to guide the production. Combined with the application of nodular cast iron gear, the bending fatigue strength and contact fatigue strength of ductile iron are systematically studied, and the pitting and peeling mechanism of ductile iron gears are studied.

(6) rare earth magnesium nodular cast iron. In addition to copper and molybdenum, the study of nickel and niobium was studied in the field of high strength and low alloy ductile iron. In this paper, the production of vanadium titanium alloy ductile iron by natural vanadium titanium pig iron is used in a large number of domestic units. Although it is not stable in performance, the system research and production application has achieved remarkable economic benefits.

In the field of heat-resistant nodular cast iron, in addition to silicon ductile iron, the system studied the influence of Si+Al total on the resistance of rare earth magnesium nodular cast iron. The RQTAL5Si5 heat resistant cast iron developed in China is three times as long as gray cast iron and is twice as long as the normal heat resistant cast iron, and is equivalent to the life of the Japanese Cr25Ni13Si2 heat resistant steel.

In the field of high nickel austenitic ductile cast iron, it has been successfully applied in petroleum mining machinery, chemical equipment and industrial furnace devices.

In acid nodular cast iron, the production of rare earth high silicon ductile iron than ordinary high silicon cast iron of small, uniform, dense, as a result, the corrosion resistance increased by 10% ~ 90%, and its mechanical strength has improved significantly.

(7) the role of rare earth in ductile iron. Rare earth can make graphite spherification. Since h. Morrogh nodular cast iron using cerium, first has many people research the spheroidizing behaviors of various rare earth elements cerium found is the most effective element of spheroidizing, other elements also have varying degrees of spheroidizing ability.

Combined with national conditions, the spheroidizing effect of rare earth in China a lot of research work, found that rare earth elements on the commonly used nodular cast iron component (C3.6 ~ 3.8 wt %, Si2.0 ~ 2.5 wt %), it is difficult to obtain with magnesium nodular cast iron as a complete uniform spherical graphite; And, when the amount of rare earths, there will be various kinds of abnormal shape of the graphite, chilling tendency also increases, but, if it is high carbon eutectic composition (C > 4.0 wt %), rare earth residue was 0.12 ~ 0.15 wt %, can obtain good spheroidal graphite.

It is necessary to add rare earth according to the conditions of low iron quality, high sulfur content (blast furnace melting) and low iron temperature. Magnesium is the dominant element in the spheroidizer, which can promote the spherification. On the other hand, it is necessary to overcome the influence of sulfur and impurity elements to ensure spherification.

The rare earth prevents interference from the spherification. The study showed that when the total amount of interference element Pb, Bi, Sb, Te and Ti was 0.05wt %, the rare earth with 0.01wt% (residual quantity) was added, which could neutralize the interference and inhibit the production of abnormal graphite. Most of the pig iron containing titanium in our country, some of titanium in pig iron is as high as 0.2 ~ 0.3 wt %, but the rare earth magnesium nodulizing agent because of rare earth residue in the can make the iron up to 0.02 ~ 0.03 wt %, so still can guarantee the graphite spheroidizing is good. If you add 0.02 ~ 0.03wt%Bi in ductile iron, you almost completely destroy the spheroidal graphite. If you add 0.01 to 0.05wt% Ce, then the original spherification is restored, which is because Bi and Ce form stable compounds.

The nucleation of rare earth. Studies since the 1960s suggest that the inoculant of cerium can increase the number of pellets throughout the entire period, making the final tissues more graphite and less white. The research also shows that the incubating agent containing rare earth can improve the inoculation effect of ductile iron and improve the ability of anti-recession. The reason for the increase in the number of graphite spheres can be attributed to the fact that rare earth can provide more nucleation, but it is different from the nucleation component provided by FeSi. The rare earth can cause the unactivated nucleation of the original (existing in iron liquor) to grow up, resulting in the increase of the total crystal nucleus in the iron solution.


2. vermicular cast iron
As a new type of cast iron, vermicular cast iron appeared in the 1960s. China is one of the earliest countries to study the vermicular cast iron. In 1966, shandong institute of mechanical design published the rare earth high strength grey cast iron paper, which marked the successful development of Chinese vermicular iron production technology.

So far, domestic and international studies have agreed that rare earth is the dominant element in the production of vermicular cast iron. China is rich in rare earth resources and provides extremely favorable conditions and material basis for the development of Chinese vermicular cast iron.

Due to the performance of the vermicular cast iron and nodular cast iron and grey cast iron, therefore, it has a unique purpose, in the ingot mould, automobile engine, exhaust pipe, glass mold, the application of d iesel engine cylinder head, brake parts, etc are all achieved good effect. In particular, the production of vermicular cast iron in the second automobile plant of China has reached a high level.

So far, the output of the world's vermicular cast iron has been hard to count, because vermicular cast iron is often counted in the production of gray cast iron, rather than from individual project statistics. The annual output of vermicular cast iron in China is inexact, about tens of thousands of tons.

The creep agents used in the production of vermicular iron in China contain rare earth elements, such as rare earth ferrosilicon alloys, rare earth silicon ferroalloys, rare earth silicon calcium alloys, rare earth zinc and magnesium alloys, etc. Thus, a series of vermicular agents suitable for the situation are formed.

The research on the formation mechanism of vermicular cast iron is the leading position. In addition, extensive and in-depth studies have been carried out on the treatment process of vermicular iron, the smelting of iron liquid and the quality control of the furnace, the normal temperature of the vermicular cast iron and the high temperature performance. It is important to point out that, under the conditions of China's cupola, many factories can produce the vermicular cast iron steadily, and have achieved remarkable economic benefits.

Can be expected, the use of vermicular cast iron has good comprehensive performance, high mechanical properties, has high strength at high temperature, the oxidation growth small, compact structure, high thermal conductivity and small section sensitivity etc, replace part of cast iron, nodular cast iron and malleable cast iron, therefore, will obtain good technical and economic effect.


3. gray cast iron
In the 1960s, the use of rare earth inoculants in gray cast iron has been widely used in production. Inoculants with rare earth has stronger recession-proof, reduce white, improve section uniformity and casting mechanical properties, wear resistance, density and pressure resistance and other functions, therefore, someone called the inoculants containing rare-earth ferrosilicon high - effective inoculant.

The study of the behavior of rare earth in grey cast iron shows that the rare earth has good influence on the structure and properties of eutectic, eutectic and eutectic cast iron, which can obviously increase the total number of eutectic groups. There is a double peak effect between the addition of rare earth and the tensile strength, and the rare earth has a strong ability to eliminate the white mouth, but the excessive amount of it can promote the generation of white mouth. In addition, rare earth can improve the shape of the sensitivity and inclusions.

The application of rare earth in the radiator has been a great success. Due to add rare earth can increase the tensile strength of radiator material 20 ~ 50 mpa, compression performance can be improved 1 ~ 2 kg/cm2, and improve casting yield, thus has obtained the remarkable economic and social benefits.

About 80 percent of the 10 million tons of cast iron in our country is gray cast iron, so it has great potential to increase the performance of rare earth in gray cast iron, especially in low-grade gray cast iron.

The development prospect of rare earth application in cast iron

The application proportion and annual production of rare earth magnesium ductile iron will continue to increase. The most notable change is that the ratio and yield of centrifugal ductile iron pipes will increase at a faster rate. To solve the shortage of water in arid region of the north, the country will start the south-to-north water transfer project, the region will soon build long distance water diversion project, the towns will accelerate the reform of water supply network, the project will need a lot of all kinds of centrifugal ductile iron pipe diameter. In the next few years, our country the use of centrifugal ductile iron pipe proportion will reach level of France, Japan and other developed countries (95% ~ 98%), ductile iron castings in production in our country will be more than 3 million tons (including nodular cast iron pipes is about 180-2 million tons/year), should be rare earth oxides can be more than 1800 tons.

Mr - Mr Nodular cast iron as a new type of material, in spite of the total accounted for the proportion of ductile cast iron is not big, but it is still increasing at an annual rate of 15%, and widely used in the crankshaft, gears, camshafts, hook, traction frame of an important security, such as grinding balls and wear-resistant parts. Ductile iron crankshaft and auto, internal combustion engine, tractor and other mechanical security ductile iron castings will also increase with the increase of host production.

Rare earth application in grey cast iron and vermicular cast iron will increase stability, also should be noted is that with the development of China's automobile industry, engine cylinder block, cylinder head will be heavily used vermicular cast iron, gray cast iron to replace the current widely used. This will be a new field for the use of rare earths in cast iron.

According to the above analysis of application prospects, the use of rare earth oxides in cast iron alloys will reach 1800 ~ 2000 tons/year in 2005.

In the mid-1960s, China began to study the mechanism and treatment process of rare earth and iron, and solved the problems such as the preparation of rare earth pellet, the preparation of the inoculation and the addition of rare earth. The cast iron parts currently used in rare earth processing are mainly: nodular cast iron parts, vermicular cast iron parts, high-strength gray cast iron parts and alloy cast iron parts. The role of rare earth in cast iron is very obvious, the macrostructure and microstructure of rare earth can make the iron elaboration and homogenization, graphite morphology by long flake in the iron ball direction development, so as to improve the performance of cast iron, increase its strength, toughness and corrosion resistance, create considerable economic and social benefits.

At present, China produces 150 million tons of rare earth cast iron and 10,000 tons of rare earth alloy, which is a major domestic market. In 2003, the rare earth consumption of cast iron was 4,000 tons, accounting for 73 percent of the total consumption of metallurgical machinery, accounting for about a quarter of the total amount of rare earth in China.​​​​​​​