Application of rare earth in metallurgical industry

First, the application of rare earth in steel

Application of rare earth in steel has nearly 30 years of history, through the study of rare earth metals in the steel rule and mechanism of action, to figure out the role of rare earth in steel; experimental study of the process for adding, master of rare earth Process conditions, varieties of rare earth metals added, and amount added. By the end of the 1980s, there were no technical obstacles to the application of rare earths in steel. China's rare earth steel production increased from 110,000 tons in 1985 to nearly 600,000 tons in 1997, with more than 80 varieties. Only one WISCO company produced 1.6 million tons of rare earth steel during the “Eighth Five-Year Plan” period, creating economic benefits of 320 million yuan, social benefits of 1.83 billion yuan, and saving foreign exchange of 50 million US dollars.

When rare earth is added into steel, it can play the role of deoxidation, desulfurization, change of inclusions and other purification and metamorphism. In some steels, it can also have microalloying effect. Rare earth can improve the oxidation resistance of steel, high temperature strength and plasticity. Fatigue life, corrosion resistance and crack resistance.

(1) The main role of rare earth in steel

Purification: steel, adding rare earth, sulfur and oxygen may be substituted may be generated in the steel of manganese sulfide, aluminum oxide and aluminosilicate inclusions, formed of rare earth compounds. Some of these compounds float up from the molten steel into the slag, so that the inclusions in the molten steel are reduced and the molten steel is purified. This is the purification effect of rare earth on steel.

Refined structure: Since the rare earth compound formed by the reaction of rare earth in steel with inclusions has a higher melting point and precipitates before the molten steel solidifies, these fine particles can be used as a heterogeneous nucleation center to reduce the degree of subcooling of the crystallization process. Therefore, not only the segregation can be reduced, but also the solidification structure of the steel can be refined.

Morphology control of inclusions: After adding rare earth into the steel, the manganese sulfide will be replaced by rare earth oxides or sulfides with low plastic deformation ability at high temperature. These compounds do not deform along with the steel during the rolling process, and remain spherical. They have less influence on the mechanical properties of steel, so the addition of rare earth in steel can improve the toughness of steel and improve the fatigue resistance of steel.

The rare earth is added to the atmospheric corrosion resistant steel to make the inner rust layer of the steel dense, and the bonding force with the matrix becomes strong, and it is not easy to be detached, which can prevent the diffusion of O2 and H2O in the atmosphere, thereby reducing the corrosion rate, and adding the rare earth steel. The corrosion resistance is increased by 0.3 to 2.4 times than that of the steel without rare earth. The addition of rare earth in MnNb low alloy high strength steel can significantly improve the cold bending properties, impact properties, low temperature impact resistance and wear resistance of steel, greatly improving the processing properties of steel and improving its service life. Adding rare earth rail in the rail, the rail can be significantly improved abrasion resistance, the peeling resistance, after years of use of proven rail life increased 1.5 times.

(2) China's main rare earth steel grades

China's rare earth treated steel has more than 80 grades, with an annual production capacity of 600,000 tons. Application of a large number of steel but only a dozen rare earth, primarily steel comprises copper phosphorus atmospheric corrosion-resistant steel, Mn-Nb series of low alloy high strength steel, X-based steel, niobium, rare earth rail steel, in addition to gear steel, Bearing steel, spring steel, die steel, engineering machinery steel, low carbon microalloy deep drawing steel, stainless steel and heat resistant steel. Corrosion-resistant low-alloy steel, the corrosion resistance of rare earth treatment is improved by nearly 10 times. The service life of the weather-resistant truck made with it is doubled, and the period of overhaul to return to the factory is extended from 6 years to 10 years. In 1988, WISCO produced 180,000 tons of 09CuPTiRE steel, which can produce 20,000 wagons, directly earning 43.83 million yuan, and the profit per ton of steel is 243 yuan, saving the maintenance cost of the wagon of 170 million yuan, while the secondary benefit (user benefit) is 944 yuan / ton of steel.

At present, the development of new varieties of rare earth steel has achieved significant results. The rare earth 铌 heavy rail jointly developed by Baotou Steel, Beijing Iron and Steel Research Institute and the Research Institute of the Ministry of Railways has a wear life of more than 50% compared with U74 and U71Mn heavy rails. In 1997, it passed the joint appraisal of the Ministry of Metallurgy and the Ministry of Railways and became China. Major upgrades for heavy rails. In addition, after two years of track-laying tests, Pangang and WISCO's rare earth-added pipeline steels have been favored by the petroleum sector for their excellent performance. At present, the main uses and manufacturers of rare earth steels in China are shown in Table 1.

Table 1 China's main rare earth steel

(3) The main method of adding rare earth to steel

The rare earth addition method in steel is mainly based on the feeding method, followed by the rare earth metal rod hanging method, the rare earth ferrosilicon alloy method in the package and the rare earth ferrosilicon alloy core wire method in the package. Each plant selects the appropriate method for the steel grade, casting process and equipment.

In the development of rare earth wire feeders, Baotou Steel Rare Earth Research Institute and Wuhan Iron and Steel Second Steelmaking Plant and other units have made great progress. Rare earth wire, rod and rare earth silicide alloy, rare earth silicon iron cored wire products better meet the needs of various steel mills to produce rare earth steel. The equipment for adding rare earth in steel not only has low investment, but also can obtain obvious economic and social benefits. Taking the feeding method as an example, a wire feeding machine is only 50,000 yuan, and the cost of adding rare earth steel is not more than 40 yuan, but the effect is twice the result with half the effort, which can double the lateral impact toughness of the steel and improve the hot working performance. Thereby increasing the yield.

(4) Development trend of rare earth steel

Recently, the State Bureau of Metallurgical Industry has formulated the near-term target and long-term plan for the application of rare earths in steel smelting. It is estimated that the output of rare earth treated steel will reach 3 million tons by the year 2000. It is conservatively estimated that the output of various types of rare earth steels in the country will reach 90-1.5 million in 1999. The application rate of rare earths will reach 500-850 tons, which will exceed 1.3-2.3 times in 1998. The consumption of rare earth in steel from 1991 to 1997 is shown in Table 2.

Table 2 Consumption of rare earths in steel in China (REO, tons) from 1991 to 1997

Second, the application of rare earth in cast iron

Cast iron is a generic term for high-carbon ferrosilicon alloys with a carbon content between 1.8 and 4.5. Cast iron can be classified into gray cast iron, ductile iron, pearlitic cast iron, malleable cast iron and white iron by the distribution of carbon in the alloy. In the mid-1960s, China began to study the action mechanism and treatment process of rare earth and iron, and solved the problems of smelting preparation of rare earth spheroidizing agent, inoculant and rare earth addition method. At present, rare earth-treated cast irons are mainly divided into three categories: ductile iron parts, vermicular iron pieces and high-strength gray iron castings, and rare earth-treated alloy cast iron parts.

(1) The main role of rare earths in cast iron

Metamorphism: It is highlighted by the transformation of flake graphite into spheroidal graphite. Graphite spheroidization can reduce stress concentration, refine the as-cast microstructure, improve the shape and distribution of non-metallic inclusions, and improve the material properties. Therefore, rare earth ductile iron has higher mechanical properties than gray cast iron, and its seismic resistance and resistance. Grindability and machinability are better than steel.

Purification: Iron water often contains harmful impurities such as oxygen and sulfur. These impurities will cause pores and cracks in the castings and form slag inclusions, which will reduce the strength, toughness and plasticity of the material. The rare earth element has strong binding ability to sulfur and oxygen, and forms a refractory compound, which can act as a desulfurization and deoxidation in molten iron. At the same time, rare earth can also eliminate the harmful effects of harmful elements such as Pb, Zn and Bi in molten iron.

Improve casting performance: The addition of rare earth to molten iron can significantly improve the flow of molten iron and reduce casting defects such as segregation and thermal cracking.

(II) Development status of rare earth cast iron

At present, China produces about 1.5 million tons of rare earth iron annually, including 300,000 tons of ductile iron. The consumption of rare earth in cast iron accounts for 25% of the total consumption of rare earths in China. The amount of rare earth in cast iron from 1991 to 1997 is shown in Table 3.

Table 3 Rare Earth in cast iron (REO, tons) from 1991 to 1997

Rare earth cast iron is mainly used in roll and ingot molds of metallurgical industry; crankshaft, cylinder block, gearbox and track in automobile and tractor industry; various gears, camshafts and various bases in machinery industry; various calibers in construction industry Water and gas pipelines and radiators. The output of rare earth cast iron in China has increased by 9% annually since 1993. The output in 1998 was about 1.1 million tons, and the amount of rare earth used was 3,800 tons, accounting for about 1/4 of the total domestic rare earth consumption. Apply the largest field.

Third, the application of rare earth in non-ferrous metals

(1) The main role of rare earth addition to non-ferrous metals

Rare earth has high chemical activity and large atomic radius. It can be added to non-ferrous metals and their alloys to refine grains, prevent segregation, degassing, impurity removal and purification, and improve metallographic structure. Achieve comprehensive objectives such as improved mechanical properties, physical properties and processability.

 Due to the purification and tempering of rare earth metals, these non-ferrous metals can refine grains and increase the recrystallization temperature, which can significantly improve the process performance of cast alloys, and can significantly improve the processing properties of the modified alloys. The nickel- and cobalt -based heat-resistant alloys have improved resistance to oxidation and high-temperature corrosion, and can improve toughness and wear resistance for super-hard alloys. These performance improvements have significantly improved the economics of manufacturing companies and users, and can reduce the consumption of these valuable resources for the country.

(II) Application of rare earth in non-ferrous metals

1. Application of rare earth in aluminum wire and cable

At present, China's rare earth aluminum wire mainly has high-strength rare earth aluminum alloy cable with Al-Mg-Si-RE, which is used for high-voltage transmission lines. Its tensile strength reaches 26kg/mm ² , and the sag performance and bending performance are good. long lasting. The highly conductive aluminum wire is made of Al-RE, and the rare earth is added in an amount of 0.15 to 0.3%. The high-conductivity rare-earth aluminum wire used at a higher temperature (<150 ° C) has a composition of Al-Zr-RE, and its current carrying capacity is 1.6 to 2.0 times that of a pure aluminum wire, and is used as a high-current wire. The rare earth aluminum cables and wires produced each year not only meet the needs of the domestic market, but also export a large amount, with significant economic benefits. The output of rare earth aluminum high-conductivity wires and rare earth aluminum alloy cable lines is expected to reach 500,000 tons in 1999, and the consumption of rare earths is about 1,000 tons.

2, 6063 rare earth aluminum alloy and its application

This is one of the most commonly used deformed alloys, mostly used in industrial and civil constructions. Its composition (%) is Mg 0.67-0.70, Si 0.45-0.48, Fe 0.20-0.21, and the balance is aluminum. In the alloy smelting process, 0.20 to 0.25% of rare earth metal is added, the tensile strength is increased by 24%, the extrusion speed is increased by 0.5 times, the finished product rate is increased by 3%, and the surface quality is improved. Increased corrosion resistance and colorability. In addition, an Al-Si-M (M=Cu, Mg, Mn) alloy to which rare earth is added is used to manufacture a cylinder block and a piston.

3, rare earth zinc aluminum hot-dip alloy

In order to prevent corrosion of steel, Zn-Al hot-dip alloy (Galfan) is generally more form-forming and corrosion-resistant than galvanizing, but zinc consumption is high and corrosion resistance needs to be improved. In recent years, Zn-Al-Mg-RE hot-dip alloy has been successfully developed and put into production. The flowability, corrosion resistance and formation properties of the rare earth hot-dip alloy are superior to those of zinc and Zn-Al alloys.

4, rare earth copper wear-resistant alloy

Generally, the bearing material is tin bronze (ie, babbitt), but the price is relatively expensive. The service life of rare earth wear-resistant lead bronze alloy (RPH) is 1.5 times that of babbitt alloy, and the cost per ton is reduced by 5000-6000 yuan. It is currently used in textile machinery.

5, rare earth hard alloy

Cemented carbide is used for metal cutting, drill bits, molds, etc. It has high hardness and high strength, but it has poor bending resistance and is easy to break. Rare earth additives with a binder and the hard phase WC, TiC milling together titanium carbide raw material powder was prepared, and then the pressure-type carbide produced by sintering process, the bending strength increased by about 15%, hardness increases 0.5RHA, The service life is more than doubled.

6, rare earth magnesium alloy

The high specific strength of rare earth magnesium alloy has broad application prospects for reducing aircraft weight and improving tactical performance. The rare earth magnesium alloy developed by China Aviation Industry Corporation includes about 10 grades of cast magnesium alloy and wrought magnesium alloy. Many grades have been used for production and the quality is stable. The rare earth element has a large solubility in the magnesium alloy, and thus has an obvious heat treatment strengthening effect. Neodymium was added and variations in the casting of magnesium alloys, yttrium significantly improved strength and process performance. At present, the cast magnesium alloys that have been industrially produced have ZM2, ZM4, and ZM6; and the modified rare earth magnesium alloys have BM6 and BM25. In addition, the application of rare earth magnesium alloy in medical engineering is also under study. At present, the material is being used in medical biological experiments. It is expected that rare earth magnesium alloy will be used as artificial bone joint material instead of the current metal fixture to reduce the patient's second removal of the fixture. This will open up a new and vast application of rare earth magnesium alloys.

(III) Development status of rare earths in non-ferrous metals

The development potential of rare earths in non-ferrous metals and alloys is great, but the depth and breadth of development are not enough. In the current application of RE indicated nonferrous metals and alloys, have a significant effect on the addition of rare earth elements of aluminum, copper, magnesium, titanium, molybdenum, nickel, cobalt, tantalum, niobium and other platinum group metals, rare earth metals such colored The amount of addition in the metal and the alloy is usually not less than 0.5%, but the effect is extremely remarkable.

At present, in addition to the application of rare earth in aluminum wire and a small part of aluminum alloy to achieve industrial scale, the application in other non-ferrous metals and alloys has not yet reached the industrial scale. The annual output of rare earth aluminum cables produced in China is about 300,000 tons. The amount of rare earths in non-ferrous metals is increasing year by year. The amount of rare earths in non-ferrous metals in China from 1991 to 1997 is shown in Table 4.

Table 4 The amount of rare earth in China's non-ferrous metals (REO, tons) from 1991 to 1997

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