Ductile iron has been published for 52 years, the rapid development of its surprisingly fast, even in the economic downturn, some development still ductile iron, ductile iron as inappropriate retreat have called the winner, said: Ductile iron still occupies an important position in the material market due to its high strength, high toughness and low price. Although the total output of steel casting has declined in recent years, the production of ductile iron has not decreased. The emergence of enhanced competitive position of ductile iron. Aluminum Alloy Die Casting,Aluminum Die Casting Products,Aluminum Casting Die,Aluminium Casting Design Dongguan Yurun Hardware Products Co., Ltd , https://www.yurunhwfty.com
1. Production and research status of ductile iron
1.1 Conventional ductile iron The current conventional ductile iron—that is, ductile iron based on ferrite and pearlite still accounts for the majority of the proportion of ductile iron. Therefore, pay attention to improving the performance and quality of conventional ductile iron. The competitive position plays an important role.
1.1.1 Strengthening the control of the quality of ductile iron The structure and properties of the spheroidal iron depend on the composition and crystallization conditions of the cast iron and the quality of the spheroidizing agent used. It is believed that in order to ensure the mechanical properties of the ductile iron, it must be specific to the casting. wall thickness, the casting temperature, the, ball handling process parameters to optimize the cooling and effective measures ball slagging agent strictly controlled appropriately reduced carbon equivalent, alloy and heat treatment are effective measures to improve ductile iron.
1.1.2 Effective control of the production of ferrite ductile iron and spheroidal ductile iron [2]
The main factors controlling the ductile iron matrix are the composition of the cast iron, the type of spheroidizing agent used, the type of inoculant, the method of addition, and the cooling conditions.
The composition of the as-cast ferrite ductile iron controls the micro-eutectic composition, wherein the carbon is slightly higher, but the graphite does not float, the silicon content is slightly lower, the inoculant silicon should be less than 3%, and the manganese is as low as possible. Should be Mn <0.04%, sulfur, phosphorus should be low, so that S ≤ 0.02%, P ≤ 0.02%, because silicon can improve the ductile iron structure and the corresponding plasticity, Si = 3.0 ~ 3.5% can get all iron Body organization. Studies have shown that cast iron has the highest elongation and impact toughness when Si = 2.6 ~ 2.8%, but the microsegregation of silicon in iron increases with the increase of phosphorus content, the more serious this segregation, and the mechanical The performance has adverse effects, especially when the temperature is lower than zero, and the low sulfur content can be spheroidized with low- magnesium and low-fraction spheroidizing agent, and reduce the occurrence of "black spot" defects, while "black spot" is mainly Aggregates of magnesium, barium sulfide and oxides, in addition to low silicon spheroidizing agents, to ensure multiple incubations.
ç For pearlite ductile iron, manganese can be increased to 0.8-1.0% in the cast iron composition during production. If some castings are used as wear-resistant crankshafts, manganese can be increased to 1.2~1. .35%, producing as-cast pearlite elemental copper . When the amount is more than 1.8%, it hinders the spheroidization of the graphite, but promotes the complete pearlization of the matrix. Generally, the copper content in the ductile iron should be less than 1.5%. Tin is a strong pearlescent element, and its effect on hardness is greater than that of copper and manganese. However, when Sn ≥ 1.0%, the graphite is distorted, so the content should be limited to 0.08% or less.
1.1.3 The role of rare earths in ductile iron Rare earth can promote the spheroidization effect of magnesium alloy (spheroidization rate and roundness of the ball), which has paid attention to the effect of preventing spherical graphite distortion in wall-thickness ductile iron parts. It is also one of the main reasons for the inclusion of rare earths in spheroidizing agents at home and abroad.
Some elements in the casting can destroy and hinder the spheroidization of graphite. These elements are so-called spheroidal interference elements. The interference elements are divided into two categories. One is the consumption of spheroidal elements, which are combined with magnesium and rare earth to form MgS. MgO, MgSe, RE 2 O 3 , RE 2 S 3 , RE 2 Te 3 , etc., reduce the spheroidal element and destroy the formation of spheroidal graphite; the other is intergranular segregation-type interfering elements, including tin, antimony , arsenic , When eutectic crystallization is carried out in copper, titanium , aluminum, etc., these elements are enriched in the grain boundary, which promotes the formation of malformed dendritic graphite in the late eutectic phase. The larger the atomic mass of spheroidizing interference elements, the stronger the interference effect. Many studies have found a critical content of interfering elements in cast iron. When these elements are less than the critical content, they do not form distorted graphite. [next]
î¶î¶In the cast iron with interference elements, the addition of rare earth can eliminate the interference effect. Some research reports indicate that the sum of the interfering elements in cast iron should be less than 0.10%, ie z=Ti+Cr+Sb+V+As+Pb+Zn+... <0.10%
î¶î¶ Some studies have pointed out that Al, Sb, TI, Pb, Bi, etc. in neutralized molten iron should be added with 0.005 to 0.04% Ce respectively. For example, neutralizing Ti, Pb, Sb, Al, etc. 0.005~0.007%, 0.014%, 0.15% and 0.008% of Ce can be used.
The î¶î¶ interference element has a greater destructive effect in the case of the wall thickness of the casting and the slow cooling rate.
î¶î¶ Interfering elements also have an effect on the ductile iron matrix. Te and B strongly promote the formation of white mouth, Cr, As, Sn, Sb, Pb, Bi stabilize pearlite, and Al and Zr promote ferrite.
It is worth noting that some spheroidizing elements and interfering element composite spheroidizing agents are being developed to improve the treatment effect of large-section ductile iron and the roundness of graphite balls.
1.1. 4 Ball iron detection Strengthening the detection of spheroidal iron is an important measure to ensure its quality. Currently, the development line analysis is being carried out, that is, the product is analyzed in the production process to determine its quality. Many units have been mass-produced. The quality of the casting was analyzed using ultrasonic waves under conditions.
î¶î¶When measuring the cast iron structure with ultrasonic waves, the sound velocity of flake graphite is 4500m/s, the vermicular graphite cast iron is 5400m/s, and the ductile iron is 5600m/s. In addition, the change of high frequency decay rate in cast iron can also judge the type of cast iron. The iron center frequency is 5MHz and the sheet cast iron is only 1.5MHz. At present, there are still units that are using ultrasonic for the spheroidization level. It has been able to measure qualified spheroidization grades and unqualified products (between grades 3 and 4), but it is not possible to perform further subdivision determination. Perfect in the middle.
1.2 Austria - Beiqiu Tielu In the 1970s, the Netherlands, China, and the United States independently of each other, almost simultaneously announced their success in the development of bainite ductile iron, the Chinese research succeeded in the lower bainite, the United States for the next Bainite + martensite, the Netherlands is upper bainite + austenite, the Netherlands is the most representative of the results, which is now known as the Austrian - shell iron. In 1977, M.Jokason announced that the karkkila foundry of the Kgmi Kgmmene company in the Netherlands had developed a new type of cast iron with excellent properties, namely Austrian-Bei ductile iron, and read the paper at the 45th International Convention in 1978. This invention has applied for patents in 13 countries including the United States, Britain, France and Canada (US Patent No.: 3860457, Dutch Patent 1996/72, and former West German Patent 2852870), which has attracted the attention of all countries and has been praised as several dozens. One of the major achievements in cast iron metallurgy over the years.
î¶î¶å¥¥â€”—Bei ball iron has high strength, high toughness and high wear resistance. For example, the British standards are NE-GJS-800-8, EN-GJS-1000-5, and EN-GJS-1400-1.
î¶î¶å¥¥â€”—Beet ball iron composition is the same as conventional spheroidal iron composition, spheroidizing agent and treatment process are the same, the difference is that austempering treatment must be carried out, and upper bainite + austenite can be obtained separately when the austempering temperature is different , Lower Babe + austenite, lower Babe + martensite and other different substrates. This kind of cast iron has high cost and is difficult to produce. Although the application surface is expanding continuously, its total amount is not large, and it is called 21st century material.
2. The status quo of spheroidizing agent is one of the main means of obtaining spheroidal iron. When the rare earth first plant of Zhibao Steel completed the national research project “Rare Earth Three-Drug Serializationâ€, our school team will be 100 in the world. A number of spheroidizing agent production plants, domestic major alloy production research, and obtained product samples from more than 50 alloy production plants in more than 10 countries including Britain, the United States, France, Germany, Japan, the former Soviet Union, India, and domestic major spheroidization The product samples of the agent production plant provide a basis for comparing the performance of spheroidizing agents at home and abroad and the improvement of spheroidizing agent production in the future. [next]
2.1 Types of spheroidizing agents The following types are produced according to the production methods. (1) Types of spheroidizing agents include magnesium-silicon alloys, rare earth magnesium-silicon alloys, calcium-based alloys (more used in Japan), nickel- magnesium Alloy, pure magnesium alloy, rare earth alloy.
Among the above alloys, the most widely used ones in the world are rare earth magnesium ferrosilicon alloys, but the ratio of RE/Mg in Chinese alloys is large (0.5 to 2.2), and the ratio of RE/Mg in foreign alloys is small (0.1 to 0.3). Among the Chinese alloys, the rare earth content of magnesium is greater than or equal to the magnesium content, and the content of rare earth is less than the magnesium content. However, the rare earth content of the spheroidizer alloy in foreign countries (except some alloys of the former Soviet Union) is almost less than the magnesium content. The group recommends that in addition to retaining FeSlMg8E18 (this alloy is an effective creeper), RE/Mg ≤ 1 in all other spheroidizing agents, which was adopted in the revised national standard.
Calcium and magnesium spheroidizing agents are mainly produced and applied in Japan. For example, the calcium content of NC5, NCl0, NCl5, NC20 and NC25 produced by Shin-Etsu (SHIN-ETSU) in Japan varies from 4 to 28%, but the calcium content changes little. The range of variation is 20~31%; the white-mouth tendency of such alloys is small, but the processing temperature is required to be high, and the amount of slag after treatment is large.
Nickel-magnesium alloys are used in the Americas and Europe. Nickel-magnesium alloys produced by American International Nickel Company are up to 82~85%, of which Mg and Ca are 13~16, respectively, and 20%, and nickel is the lowest 57~61% (Mg4) .0~4.5%, Ca<2.5, Fe32~36). In the nickel-magnesium alloy produced by German Metal Chemical Company, Ni47~51%, Mgl5~17%, C1.0%Si28~32%, RE1.0% residual Fe. The advantages of these alloys are that they are more important and reflect a smoother state. Nickel can be alloyed. It is characterized by its high price. This alloy is basically not used in China.
Nickel-silicon alloys are currently largely unused in China. When pure magnesium alloy is treated, special pressure and magnesium package are used, and the absorption rate of magnesium is high, but the treatment safety measures are extremely strict, and the application ratio in production is small.
Rare earth is a spheroidizing agent used in the invention of ductile iron, and its discovery has advanced the process of application of the ductile iron industry. However, the price is high, the white mouth tends to be large, and the excess will make the graphite metamorphosis. Now it is not used as a spheroidizing agent alone, only as an auxiliary spheroidizing element.
(2) The briquetting spheroidizing agent is directly formed by using magnesium powder and iron powder and the designed silicon content. The spheroidizing agent has a low silicon content and is generally called a low silicon briquetting spheroidizing agent. It provides a large room for the subsequent breeding, which is conducive to the production of as-cast ductile iron, but the alloy is easy to float, the treatment effect fluctuates greatly, and it is better to mix with the block-shaped spheroidizing agent during processing.
(3) The core-type spheroidizing agent coats the magnesium powder and the iron powder in the steel plate or the steel plate, and quickly feeds it into the molten iron to achieve the purpose of spheroidization. The spheroidizing agent is relatively expensive, and the equipment investment is large. However, the alloy has a high absorption rate during the treatment, so the total cost of processing the ductile iron is hardly increased.
(4) Powder spheroidizing agent This spheroidizing agent is a patent of Russia. When used, the magnesium powder and the inhibitor are mixed into the bag, and the molten iron flows through the surface of the alloy, and the layering and the alloy are reflected to achieve spheroidization. The effect, this special process is called MC.
2.2 Application of spheroidizing agent î¶î¶ At present, the alloys used in pyrometallurgy are mainly used in the production of ductile iron at home and abroad. The application of briquetting spheroidizing agent, core spheroidizing agent and powder spheroidizing agent is rare. The spheroidizing agent used in the smelting process accounts for more than 90% of the production. Currently, such alloys are added with Ba, Ca, Cu, Ni, etc. to achieve the purpose of controlling the matrix, and the magnesium oxide content in the alloy has a limited amount. A comparative analysis of the production of ductile iron plants in 33 typical factories in China and 77 factories in the United States. [next]
The basic situation of 33 factories in China is: 33 factories have a total of 36 furnaces, of which 9 are 25% of electric furnaces (medium frequency, power frequency, electric arc furnace), 22 are cups of cupola, 61%, cupola furnace and electric furnace are double melting. 4 of the factory accounted for 11%, blast furnace 1 accounted for 3%, ductile iron treatment temperature was greater than 1500 ° C, 4 accounted for 11%, 1450 ~ 1500 ° C, 20 accounted for 56%, 1350 ~ 1400 ° C, 6 accounted for 16.7 %, 1300~1350 °C, two accounted for 5.6%; more than 1270 °C, one accounted for 2.7%; hot metal sulphur content was less than or equal to 0.03%, accounting for 20%; in the treatment method, the flushing method accounted for 94%, and the injection method accounted for 94%. 3%, pressure plus magnesium 3%, the largest amount of 6# alloy Mg8RE8 accounted for 46%, followed by Mg8RE5 accounted for 37%, Mg9RE5 accounted for 11%.
The basic situation of 77 US factories is:
î¶î¶ melting equipment cupola accounted for 30%, induction furnace accounted for 63%, spheroidization temperature 1482~1538 °C accounted for 75%; original iron water before spheroidization treatment 50% of the factory used pre-desulfurization process, 90% of factory S Less than 0.025%, the spheroidization treatment method accounts for 36% of the large-scale plants in the United States, while the small-factory (less than 200 tons/week) rushing method accounts for only 22%, press-in method, porous plug method, type The internal treatment method, the Tundish cover method, and the pressure plus magnesium method account for the majority of the proportion. The spheroidizing agent used contains 8.2% of Mg and 4% of 6% of the spheroidizing agent, accounting for 63.3, and containing less than 4% of magnesium. 16.4% pure magnesium accounts for 5%, and other magnesium alloys account for 8.2%.
î¶î¶The data indicates that there is still a big gap in the production of ductile iron in China. The electric furnace produced in the United States can guarantee the high temperature required for spheroidization treatment. Generally, it is pre-desulfurized, with low sulfur content, and the quality is better than that of China. Therefore, the treatment of ductile iron can be used with low-magnesium, low-rare-spheroidizing agents, and quality control is also strict, including the use of decay time controllers.
î¶î¶In China, the spheroidizing agent production has changed a lot since 1990. The national standard of rare earth magnesium alloy has been revised, and the RE in the alloy has been greatly adjusted. Except for retaining Mg8RE18, the Mg/Re in other alloys is greater than 1. The amount of rare earth in the alloy used in the factory has decreased. The application of Mg8RE5-7 has increased a lot, and the electric furnace has also increased a lot. However, the sulfur content in the original molten iron has not changed much, and the pre-desulfurization process has not been effectively promoted. The spheroidizing agent in China is still at a relatively high level, and the new spheroidizing treatment process is not widely promoted in China. For example, the Tundish cover method which accounts for a large proportion in the United States has not been applied in China. It is a problem to be solved in China's ductile iron production plant.
2.3 problems in the use of spheroidizing agents and quality factors control indicators î¶î¶ factors affecting the quality of spheroidizing agents are: composition, particle size, shape, density, MgO content and so on.
î¶î¶There is only analysis of spheroidizing agents produced by pyrometallurgical smelting, and some of the problems reflected in the use of factories:
(1) The composition of the spheroidizing agent is not accurate.
(2) The particle size of the spheroidizing agent powdered alloy is not satisfactory.
(3) The spheroidizing agent has a large fluctuation in density, some spheroidizing agents float up quickly, the reaction is too intense, and safety is not guaranteed.
(4) The MgO content is too high, the spheroidization treatment is poor, and the spheroidizing agent is added in an excessive amount.
(5) The decline is fast after spheroidization.
(6) The white mouth tends to be large after spheroidization.
In order to solve the above problems, we should start from two aspects:
First, the alloy manufacturer provides quality products. First of all, we must improve the analysis of magnesium oxide, secondly strictly control raw materials, control the elements and interference elements that promote alloy powdering, strengthen management, and thirdly, strictly implement accurate smelting processes, and control the main indicators affecting the quality of spheroidizing agents. Is to provide the granularity required by the user. [next]
On the other hand, the production workers are trained to understand the alloy properties and the exact method of use. The problems in production are directly related to the quality of production workers. Some workers only teach what to do and cannot do the same thing. This is not acceptable. It is necessary to cooperate with the alloy manufacturer and the manufacturer to popularize the understanding of the ductile iron and the level of production technology, so that the production of ductile iron in China can maintain a good development momentum.
3. The application of computer in the production of ductile iron Because of its paste-like solidification characteristics, the cast iron produced by the cast iron often produces defects such as shrinkage and shrinkage due to poor shrinkage. In order to predict these defects before casting production, it is early. In the printing era, the numerical simulation of the casting process was carried out at home and abroad. The numerical simulation of the casting process uses numerical simulation technology to simulate the actual casting formation process in the virtual environment of the computer, including the filling process of the metal liquid, the cooling solidification process, the stress formation process, the influence degree of the main factors in the molding process, and the prediction organization. , performance and possible defects provide a basis for optimizing the process to reduce waste.
î¶î¶ In 1962, Forsund in Denmark first used electronic computers to simulate the solidification process of castings. Since then, the United States, Britain, Germany, Japan, France, etc. have carried out research in this area. In the late 1970s, Dalian University of Technology and Shenyang Foundry Research Institute took the lead in conducting research on this technology in China, and published research reports in 1980 (Guo Keren et al., Digital Simulation of Solidification Process of Large Castings, Dalian Institute of Technology Journal, 1980 (2) 1-16; Shenyang Foundry Research Institute, Electronic Simulation of Casting Solidification Thermal Field, Foundry, 1980 (1) 14-22, after which a large amount of manpower was invested in China's colleges and universities to carry out this research, During the "Sixth Five-Year Plan" and "Seventh Five-Year Plan" period, there are research projects in the middle of the national key project. The "sixth five-year" project is "large-scale steel casting solidification control" and the "seven-five" project is "large steel castings". "Crafting Process CAD", which organizes joint research on production, learning and research, has greatly promoted the development of this technology in China. At present, Tsinghua University and Huazhong University of Science and Technology have been able to provide FT-Star and Huazhu CAE-Inte CAST4.0 commodity chemistry respectively. The software has been applied in units such as Sanming Heavy Machinery Co., Ltd. and has achieved good results.
î¶î¶Computer numerical simulation consists of three parts: pre-processing, intermediate calculation and post-processing, including the establishment of geometric model, grid division, determination of solution conditions (initial conditions and boundary conditions), numerical calculation, processing of calculation results and graphical display. . The basic methods of numerical simulation used are mainly finite difference method, finite element method and boundary element method. The current areas of application in casting are:
î¶î¶ 1) Numerical simulation of solidification process, mainly for heat transfer analysis in the casting process. Including the selection of numerical calculation methods, latent heat treatment, shrinkage and shrinkage prediction, and heat transfer problems in castings and molds.
î¶î¶ 2) Numerical simulation of flow field, involving momentum, energy and mass transfer, which is more difficult. The numerical solution techniques used are MAC method, SAMC method, SOLA-AOF method and SOLA-MAC method.
î¶î¶ 3) Casting stress simulation, this research is carried out later, mainly in the elastoplastic state stress division, currently there are Heyn model, elastoplastic model, Perzyna model, unified internal variable model.
î¶î¶ 4) Organizational simulation, currently in its infancy. Divided into macro, meso and micro simulations. It can calculate the number of nucleation, analyze the type of primary crystal, the growth rate of dendrites, simulate the transformation of the structure, and predict the mechanical properties. There are deterministic models, such as Monte, Cellular, Automaton and other statistical methods, phase field models.
Computers and their applications are currently rapidly developing technology fields. Casting, as one of the important industrial fields, should be strengthened. Research and development of computer applications in the field of foundry research and production, completely change the past "blinking shape, closed eye pouring" state, computer applications will also promote the application and development of ductile iron.