The application of rare earth in steel
The application of rare earth in steel
Our country is the world's rare earth resources and production in the first big country, the first steel and steel output power, but it is not power, steel varieties quality compared with foreign advanced level there is a considerable gap, there are still many steel imports.
With the rare earth high-tech materials to strengthen and improve traditional industry, add trace rare earth in low alloy steel, alloy steel, improving steel to enhance international competitiveness, the rare earth resources advantage into steel varieties of advantages and economic advantages, has the extremely significant significance.
There are three main applications of rare earth in steel
1. Purify the steel fluid. Rare earth has deoxygenation and desulfurization, reducing and refining the inclusion in steel.
2. Metamorphic inclusion. Rare earth added generated in steel spherical rare earth sulfide or sulfur oxide, instead of a long strip manganese sulfide inclusions, have complete control of sulfide morphology and toughness of the steel transverse impact toughness, in particular, to improve the anisotropy of steel. The rare earth transforms the high hardness of alumina into spherical sulfur oxide and aluminic acid rare earth, significantly improving the fatigue resistance of steel.
3. Microalloying. Rare earth has a certain amount of solid solution in the steel, it's on the grain boundary of partial poly can inhibit phosphorus, sulfur and low melting point impurity lead, tin, arsenic, antimony and bismuth in grain boundary segregation or with these impurities form high melting point compounds, eliminate the harmful effect of low melting point impurity; The purification of rare earth and the strengthening of grain boundary can hinder the formation and expansion of intergranular crack, which is conducive to the improvement of plasticity, especially the high temperature plasticity. Rare earth can inhibit dynamic recrystallization, refine grain and precipitation phase size and promote Nb (C, N) in ferrite, (Nb, Ti) (C, N) and V (C, N). Dissolved rare earth can change the composition and structure of carburized body and make carbide spherification, refinement and uniform distribution.
Rare earth is a good metamorphic agent and a strong microalloy element. The rare earth has the h ydrogenicity, which can improve the h ydrogen-induced fracture performance of steel. Rare earth can improve the corrosion resistance of weathering steel, stainless steel, heat-resistant steel oxidation resistance and high temperature strength, spring steel, gear steel and bearing steel fatigue resistance performance, hard thermoplastic deformation of high alloy steel rail and the wear resistance of wear resistant material, etc.
After the addition of rare earth in steel, it can improve the transverse impact toughness of steel plate and seamless steel tube by more than 50%, increase the corrosion resistance by 60%, and improve other performance. Every ton of steel plus rare earth 300 grams, but the function is very significant, really is four or two jins.
The rare earth treatment of steel has the characteristics of little investment, no pollution, quick results and high economic benefits. Beijing iron and steel research institute and wuhan iron and steel company do several kinds of common steel of salt fog corrosion experiment results show that the corrosion resistance of rare earth of weathering steel is nearly 2 times of ordinary steel (Q235), more than the international famous brand weathering steel Corten steel level in the United States.
The shenyang institute of metal in the Chinese academy of sciences has developed a hydropower station, a water pump, and a rare earth stainless steel, which has nearly doubled the anti-wear performance of the current 0Cr13Ni4Mo steel. Which made a lot of contrast test, the stainless steel with a moderate amount of rare earth (0.3%) than without greatly improve the performance of rare earth, rare earth alloy corrosion resistance, wear resistance and abrasion resistance than without rare earth alloy respectively increased by 57%, 55% and 55%.
The rare earth treatment steel also has disadvantages:
(1) rare earth inclusions than major, generally between 5.5 ~ 6.5, not easy to rise, especially when excessive amounts of rare earth to join, will increase the inclusion in steel, and even produce brittle intermetallic compounds of rare earths and iron worsen the performance of the steel. By computer simulation, we can determine the optimal rare earth addition and the automation of the rare earth feeding machine, which can realize the accurate control of the quantity of rare earth and achieve the purpose of improving the steel quality.
(2) when the rare earth treated steel is easy to be knotted at the time of pouring, the problem of water nodule can also be found with strong deoxidizer such as A1 and Zr deoxygenation. At present, it is used to feed the rare earth wire in continuous casting crystallizer, which can be used to solve this problem. Du ting, han qiyong, professor wang changzhen pointed out that the use of molten quartz water port and zirconium water port have better effect to prevent the nodules containing rare earth steel.
(3) rare earth metals are more expensive. The price of rare earth wire and rods is 9 ~ 98,000 yuan/ton, which is more expensive than silicon calcium alloy, which affects the expansion of rare earth steel.
The present situation of China's rare earth steel
Through the national science and technology commission of ">" science and technology research, to solve the ordinary drawing speed slab even cast steel and die steel casting method of rare earth to join problem, the role of rare earth in steel mechanism research has also made significant breakthrough.
The metallurgical department specially formulated the standard of rare earth, the standard of rare earth wire and rod of steelmaking and mould casting of mould casting and casting mould. The state planning commission has set up a national rare earth steel collaboration network, and local rare earth offices have also been active in the work. It has vigorously promoted the development of China's rare earth steel, lead to a rare earth steel production by 1985 in 2003 to 900000 tons, 110000 tons of growth in more than 80 species of for countries to create a huge economic and social benefits, only 1996 to 1999, China's production of rare earth steel 2.39 million tons, direct economic benefits for the country increase by RMB 727 million yuan, the indirect benefit of 3.635 billion yuan. The change of output and steel output of rare earth steel in China from 1990 to 2003.
In the development of the rare earth feeding machine, the baotou rare earth research institute and wuhan iron and steel co., LTD. Have made great progress. Rare earth wire, rod and rare earth silicon alloy, rare earth silicon iron core products, also better meet the needs of the steel mills to develop rare earth steel.
The development of new varieties of rare earth steel has made great achievements. Baotou steel (group) company subordinates, iron and steel research institute, Beijing railway academy, joint development of rare earth niobium heavy rail wear life of more than 50% higher than that of U74, U71Mn heavy rail, in 1997 passed the joint identification of metallurgical department and the ministry of railways.
Wisco in container plate three copy foreign steel SS400, SPA - H, SM490A, by adding rare earth can improve the cold bending performance, enhance the competitiveness in the international market, from 1996 to 1999 into 460000 tons, the total exports or produce foreign exchange earning $154 million. Panzhihua iron and steel company's equipment level than the baoshan iron and steel company and the wuhan iron and steel company is poor, but because they have the rare earth and alkaline earth compound processing of liquid steel process, greatly enhancing the competitiveness of the steel plate, their production of pipeline steel and auto joist steel, get the favour of the oil sector and dongfeng automobile company.
Daye special steel has been more than 10 varieties of alloy steel and low alloy steel, rare earth, made significant effect, 0 cr14ni14si4 steel perforated pipe rate increased by 10%, and SN2025, 521, ZF6, ZF7 and steel grade of the physical quality level of similar foreign products. Shanghai iron and steel factory in molten iron sulfide is higher, but they developed 10 pcure weathering steel, rare earth has been successfully used in yangpu bridge pedestrian fence railings, Shanghai stadium and is known as "Asian first" Shanghai O riental television tower sphere peripheral structure. Taiyuan iron and steel company also reap the benefits of the make rare earth steel, in 1996 began trial production, the production of 1997 reached 35600 tons, the main varieties are gas bottle with Hp295 steel, etc.), in 1999 reached 139200 tons, that create economic benefits for the taiyuan iron and steel company 34.8 million yuan. Shanghai baosteel, China's largest steel company, also produced 31,000 tons of rare earth resistant steel in 2000.
Existing problems
The main problems exist, one is that the rare earth joins the technology and the equipment is backward, the second is the rare earth steel varieties and the production is less, the third is rare earth's action mechanism research in various kinds of steel is not deep.
Rare earth application in the steel in our country has made greater achievements, but the addition of rare earth in steel technology and equipment imported from abroad is not satisfy the steelmaking and highly automated equipment, continuous refining outside the furnace. Baotou steel imported from Germany of bloom, great circle billet continuous casting production line, annual production of 1.2 million tons, be badly in need of solving the problem of rare earth to join the process, to produce the ministry of railways is badly in need of rare earths and niobium important steel such as heavy rail;
Baosteel and wuhan steel slab continuous casting production line, the high speed of domestic old rare earth wire feeding machine has not form a complete set, need to research a new generation of automatic feeding machine to solve the problem of high speed slab continuous casting of rare earth to join process; In addition, it is necessary to research and solve the problem of the addition of rare earth in continuous casting, the problem of rare earth treatment and other refining process, and the addition of rare earth to the process.
China's mass production of rare earth steel, with only nine steel Numbers, accounts for less than 1 per cent of the total steel output of rare earth processing steel, compared with 5 per cent in the us.
The research on the mechanism of rare earth in various types of steel is not in-depth, the results are not authoritative, and the shortage of research funds is the main reason.
In our country developed during the process of rare earth steel technology, with the development of steelmaking process and equipment and production progress, gradually lost its novelty, must continue to the depth development of science and technology, to promote the new development. Catching rare earth steel is not a simple application problem. Along with the hot metal pretreatment, the development of the technology of refining outside the furnace, sulfur content in steel has been greatly reduced, to reduce the dependence of rare earth, no rare earth resources of Western Europe and Japan, technology route, use calcium treatment instead of rare earth had a great influence on China's baosteel, has recently started to affect the wisco.
China's production of rare earth steel has been around again, with output in 2000 and 2001 only approaching 800,000 tonnes. At present, China's rare earth steel work has reached a critical juncture, which requires state funding. Take it seriously, you can go up to a new level, enter a wide world, and not grasp the possibility of gradual decline.
Development of foreign rare earth processing steel
Such as the United States, Western Europe, Japan and the Soviet union in the 1970 s, the average sulfur content control of low alloy steel at about 0.015%, they use a lot of rare earth to control the sulfide inclusion shape, 1974 years of rare earth treated steel, reach a climax, when in 6000 metric tons of rare earth in steel consumption (REO), rare earth processing steel output of 16 million tons. Later, with the development of hot metal pretreatment, refining outside the furnace technology, the sulfur content in western countries, the production of low alloy steel has dropped to 10 x 10-6 ~ 50 x 10 - that low, using calcium treatment can control sulfide inclusion shape, so there is no rare earth resources of Western Europe and Japan basic calcium treatment to replace the rare earth processing, is used as a modifier of rare earth, was replaced in the field of low alloy steel.
Yet the west's role in steel is certain. The rare earth, a book by the Japan new metals association, concludes that rare earths have six roles in steel. Japan has no rare earth resources and rare earths in low alloy steel, but rare earths are also used in some of the alloy steel, such as electrothermal alloy special stainless steel. Sweden's development of rare earth heat resistant steel 253 ma, high temperature lasting strength 20% ~ 40% higher than that of without rare earths, developed by the French new carburizing alloy XM,
XTM trace rare earth get excellent performance, make it widely used in petrochemical industry in the world. Rare earth resources are rich in the United States and Russia, not only in high alloy steel but also in low alloy steel.
The United States spent 2000 tons of rare earth (REO) in steel (mainly steel) in 1995. The country's metals magazine published: "using rare earth and calcium to deal with steel is more effective than using calcium alone to control sulphide inclusion." The data also confirms the alloying effect of rare earth in steel.
The significance and prospect of developing rare earth steel in China
1. Rare earth treatment for steel is an easy and easy way to improve steel quality
Rare earth treatment is a kind of furnace external refining technology, rare earth treatment basically does not need the technical transformation input, the feeding machine equipment is only tens of thousands of yuan, the experiment success can be transferred. Rare earth is not only a good metamorphic agent, but also a strong microalloy element, which is not replaced by silicon calcium.
The practice of many steel mills proves that treating steel with rare earth is one of effective measures to improve the quality of steel and develop new varieties.
China's national conditions need to develop rare earth steel
The United States in the annual output of 100 million tons of steel, steel, rare earth rare earth processing steel production has been close to 8 million tons per year, is the first big steel production in China, the steel output will reach 160 million tons in 2005, in the field of such an enormous quantity wide, strengthen the application of rare earth, has the extremely significant significance. China's rare earth annual separation capacity has reached 120,000 tons, with rare earth consumption far less than the production capacity.
As long as the funds granted by the state science and technology support, rare earth steel may very well become bigger and stronger in China, if the annual output reached 5 million tons, rare earth steel will consume every year mixed rare earth metal (with relative surplus element lanthanum, praseodymium, cerium) 2500 tons, to promote the healthy development of rare earth industry in China has important significance.
Rare earth office and the state development planning commission of the state planning commission expert group, the China iron and steel association, the application of rare earth in steel work very seriously, the state ministry of science and technology also has "rare earth steel varieties, new technology research and development", included in "15" national science and technology research project "rare earth application engineering", believe that after a few years, China's rare earth steel work will be a big step, a new look, will create enormous economic benefits for the country, and the process technology of rare earth steel will reach the international advanced level, the role of rare earth in steel mechanism will reach the international leading level.
Hot metal pretreatment about 23% than that of our country, the liquid steel refining ratio is about 21%, the vast majority of large and medium-sized steel mills present situation of low alloy steel sulfur content, sulfur content is approximately 0.01% (except tianjin steel, baosteel and wuhan), in the late 80 s to the early 80 s levels; It is the steel mill because of the poor quality of steel, low alloy steel sulfur content is also this level.
The sulfur content is several times higher than abroad, treated with calcium alone is not enough, rare earth treatment technology is needed to thoroughly control sulfide inclusion shape, can guarantee the production of high quality low alloy steel, alloy steel,
participate in international competition. After joining WTO, China needs to develop low alloy steel and alloy steel with Chinese characteristics.
3. The development prospect of rare earth steel from rare earth in steel
Wisco and northeastern university, test the X65 pipeline steel X65 and rare earth in different sulfur content, the impact toughness of the results showed that even if the sulfur content in steel dropped to 0.005%, rare earth still can greatly improve the steel impact value.
Beijing university of science and technology and cooperation of wisco, the role of rare earth elements in ultra low sulfur steel is studied, the conclusion is that the rare earth in ultra-low sulphur (S < 0.003%), niobium and titanium micro alloyed steel is still in the purification and microalloyed steel, metamorphic inclusions, rare earth solid solution can reach 10-5 ~ 10-4 orders of magnitude, the sulfur content is generally steel 6 ~ 10 times the amount of rare earth solid solution, a significant reduction in grain boundary partial poly (S, P, delay the niobium and titanium nitride precipitation.
The rare earth on the Beijing iron and steel research institute of aviation with 16 ni10co14cr2mo steel with high strength and high toughness properties, the influence of the steel are ultra-low sulphur (0.002% ~ 0.005%), but after mixed rare earth lanthanum and cerium, still make the MnS, CrS inclusion into rare earth sulfur oxide inclusions, so as to improve the fracture toughness of the steel.
Rare earth plays a significant role in alloy steel and special alloy. E.g., material department of southeast university Zhang Zhonghua cerium et al. studied the effect on the properties of high temperature alloy al Fe - 28, in binary Fe - 28 al alloy with 0.15% (atomic fraction) Ce can raise the room temperature plasticity of alloy nearly 1 times, and the yield strength and tensile strength of the alloy are obviously improved.
China's ministry of weapons industry baotou May 2 institute of research and development of rare earth stainless steel, excellent performance. The rare earth heat resistant steel 0Cr23Ni12 produced by Beijing iron and steel research institute has greatly reduced the use of Ni, which reduces the cost by thousands of yuan per ton of steel and has a significant effect. Although the total amount of rare earth alloy steel and special alloy steel is small compared with ordinary steel, the economic benefits of rare earth are very high, and the amount of rare earth is 5 ~ 10 times that of low alloy steel. The field is also promising, potentially reaching tens of thousands of tons. It is estimated that the annual demand for the final year of the tenth five-year plan will be 70,000 tons of rare earth, 128,000 tons of steel and 50,000 tons of steel.
4. The development prospect of rare earth steel from market demand
With the development of national economy construction, besides requiring steel to have high strength and toughness, it also requires good corrosion resistance, which can play a key role in this field. Rare earths also play an important role in improving the toughness, plasticity, heat resistance and abrasion resistance of steel. This is the advantage of rare earth steel and its development prospect is very good.
Weathering steel (atmospheric corrosion steel). Currently, the annual output of rare earth resistant steel is 400,000 tons, mainly used in container steel, train trunk, bridge and the railings of the stadium, and the future application prospect is very broad. Container steel plate in China annual production capacity of 1.5 million tons, used in weather resistance, refractory steel, especially in light steel structure is also a potential market of one million tons, and electrified railway iron tower, is expected to "15" the end of the weathering steel market demand for 800000 tons of rare earth. In the next 10 years, China's construction structure steel will grow from 1.5 million tons to 7 million tons, providing a broad space for the development of rare earth resistant steel.
Heavy rail steel. In the next 10 years, including the development of the western region, China's railway construction will have a great development, and the current annual production capacity of the heavy rail will be 1.37 million tons. Baosteel's rare earth and niobium weight rail has been approved by the ministry of railways. The next step is to realize industrialization. Anshan also gave the shenyang railway bureau and Harbin railway bureau a trial system of tens of thousands of tons of the steel rail, which received favorable comments. It is estimated that the heavy rail production of rare earth in China can reach 30 ~ 400 thousand tons in 2005.
Weld gas cylinders with steel. Taiyuan iron and steel company in welding gas cylinder steel by adding rare earth can improve the performance, a good momentum of development, in recent years, rare earth steel cylinders, panzhihua iron and steel company, benxi iron and steel company's development has made gratifying achievements, "the end of the 15" as "west-east gas" national consumption can reach 50 ~ 600000 tons.
Ship steel, etc. Shipbuilding steel plate is an important variety, with annual steel volume of about 1.2m tons. In the 903 shipboard steel, the rare earth has a good effect on toughness and corrosion resistance and is expected to be popularized in the civil ship plate. In addition, both the offshore oil platform and the tunnel steel need to improve the corrosion resistance, and the rare earth also has a good application prospect. It is estimated that the steel can reach 200,000 tons at the end of the tenth decade.
Production practice proves that rare earth processing steel is one of effective measures to improve the quality of steel and develop new varieties. Rare earth processing requires little investment and no additional processing time is required in steelmaking. It can be purified (deoxidized, desulphurized), metamorphic and microalloying, which can greatly reduce the harmful effects of low melting point impurities, which can not be completely replaced by silicon calcium treatment. So rare earths in steels, general can increase the transverse impact toughness of steel plate and seamless tube 1 times or so, at the same time can improve the flexural performance of steel and corrosion resistance, is conducive to improve the steel hot workability, improve lamellar tearing and h ydrogen induced cracking. Only 300 grams of rare earth metals can be added to each tonne of steel.
Our country USES rare earth processing steel nearly 60 ~ 700 thousand tons each year, net profit nearly 100 million yuan, rare earth treatment steel steel plant already more than 80. By 2000, the annual output of rare earth processing steel was 3 million tons, with a net profit of 336 million yuan. The amount of rare earth used for steel in 2003 was 400 tons, accounting for 7.5% of the total consumption of metallurgical machinery applications.