Retrospect and Prospect of China's Cast Iron Casting Technology
2022-09-05 01:03:47
1 Cast iron smelting technology 1.1 Cupola technology Cupola is still the first in the cast iron smelting equipment, and still bears the smelting task of 80% or more of the weight of cast iron. In the past 50 years since the founding of the People's Republic of China, China's cupola technology has developed rapidly. In the early days, China's foundry industry used the straight-tube three-row large-window cold-air cupola of the former Soviet Union. After years of production practice, combined with China's specific conditions, it has improved and created a variety of cupola furnace types, such as curved furnaces and multiple rows of small air outlets. Hot air cupola, inverted large row two-row ventilating cupola, central air supply cupola row cross-winding cupola, rotating wind cupola, card waist cupola, no furnace lining water cold cupola and so on. Other special furnaces and coal-fired iron furnaces, natural gas iron furnaces, have been researched and applied in China, but their use is not widespread. Especially after the 1970s, the furnace type and smelting technology that conformed to China's characteristics have gradually improved and matured, forming a series of multi-row small vents and two rows of large-pitch cupolas with unique characteristics in China. In terms of operation technology, from the pursuit of low coke consumption to the emphasis on hot metal quality, and then to improve the comprehensive indicators of technical economy, labor hygiene and environmental protection, and gradually develop and apply from the charge treatment, repair furnace, oven to the feeding, Operating techniques for the entire process of blasting, furnace control, and iron inspection. In the production of foreign iron castings, casting coke is commonly used in smelting. The application of hot air cupola and double smelting is common. The oxygen-enriched air supply and dehumidification supply of cupola have been applied, and the temperature of molten iron is higher than 1500 degrees. In the production of domestic cast iron parts, the proportion of casting coke used in smelting is less than 1%. The application of hot blast stove and double smelting is rare. The oxygen enrichment and dehumidification supply have been studied. The temperature of the molten iron is mostly about 1400 degrees. In a relatively short process, we are in the theoretical study of cupola, furnace structure, furnace material, air supply system, heat energy utilization, enhanced bottom coke combustion, furnace atmosphere adjustment control, hot metal furnace pre-test, smoke elimination and dust removal, non-coke The iron, the ingredients and the computer optimization control of the smelting process have achieved gratifying results. The advancement of cupola technology is an important aspect of the modernization of China's foundry industry. For more than 50 years, we have embarked on a successful road to the development of unique cupola technology, and developed the theory and production practice of cupola under the specific conditions of our country. The quality and efficiency of cupola smelting are closely related to the scale of production and the capacity of the furnace. From the perspective of industrial structure, China's related enterprises pursue a small, comprehensive, large and comprehensive production structure, resulting in the country's soaring furnaces, of which small cupolas below 3t / h account for the majority, resulting in waste of resources and Environmental pollution is a problem that cannot be ignored. With the development of joint-stock system and grouping of Chinese enterprises, it will provide the necessary conditions for the development of specialized foundries. However, from the perspective of the long-term economic structure of multiple ownership systems in China, the long-term coexistence of large, medium and small scales of foundries is also certain. Small and medium-sized cupolas below 5t/h will also occupy most of the long-term proportion. Therefore, to improve the operation technology, the development and promotion of low-energy, less pollution cupola and its smelting process is the general trend of the development of cupola in China. The development of cupolas is centered around improving performance, increasing productivity, reducing consumption, improving operations, and reducing pollution. The performance of the cupola is mainly reflected in the three aspects of carbon combustion, furnace heating and metallurgical process. As the production volume of cast iron expands and the casting productivity and casting quality requirements increase, the capacity of the cupola continues to increase. The large-capacity cupola smelting condition is more stable, and it is superior in technology and economy to the small furnace. Therefore, it is reasonable to replace multiple small furnaces with one large-capacity furnace in a single-variety mass production. In the international arena, the latest developments of cupola are mainly plasma cupola, non-coke cupola, new rotary smelting furnace. The layout of China's cast iron industry is scattered, the scale of enterprises is small, the level of socialization of production is low, the level of technology is different, and the production of technological achievements Conversion rate is low. As the basic process facilities, cupola is a concentrated expression of these characteristics. The environmental pollution, waste of resources and low-quality castings caused by a large number of low-level operation of small cupolas are self-evident. In terms of operational technology, manual operation technology has been developed in depth due to the low degree of automation for a long time. The smelting state of the furnace is very dependent on the operator, which causes the smelting level of the cupola to vary greatly. Even the same furnace will fluctuate in the smelting level due to changes in the state of the operator and replacement of the operator. The intelligent and automatic operation of the cupola operation can fundamentally avoid the random adverse effects of the operator and make the cupola operate stably in the best condition. Although the research on the automation of cupola in China started late, it has made rapid progress. It has achieved some practical results in the automatic optimization of batching, feeding and smelting process optimization control, which has greatly improved the automation operation level of China's cupola. The gap in the world's advanced level. Joining the WTO will present a competitive world casting market in front of us. We must not only maintain the status of a large country in the production of cast iron, but also become a strong country in the production of cast iron parts. Therefore, the development of cupola smelting will focus on strengthening management, promoting technological transformation, and improving scale efficiency. The development direction of cupola technology in China mainly has the following aspects:
(1) Take specialized production roads, increase the operating rate of cupola, and develop in the direction of large-scale, intelligent and long-term operation;
(2) Specialization and scale of charge supply;
(3) Vigorously develop the supporting technology of the cupola, and at the same time strengthen the control and detection of the cushioning furnace;
(4) Development of cupola furnace. Electric furnace double smelting technology;
(5) Obtaining high-temperature and high-quality molten iron is the fundamental task of cupola melting.
1.2 Electric Furnace Technology Induction furnaces are used to smelt cast iron. Since it has the advantages of high temperature, stable composition, less pollution and easy adjustment of molten iron composition, it has been popularized in some industrialized countries since the early 1960s. In recent years, the rapid development of medium frequency induction melting furnaces has injected new vitality into cast iron production. The development and application of induction melting furnaces has brought cast iron production to a new stage. Despite some shortcomings of the power frequency induction melting furnace, it is still widely used in metal melting, iron composition adjustment, metal liquid heating and heat preservation, especially as a double furnace for other melting furnaces. The medium frequency induction melting furnace is suitable for melting cast iron, especially alloy cast iron, ductile iron and compacted graphite iron. Its rapid development and superiority have made it a new trend in cast iron production in recent years. It has energy saving, high productivity, and great production flexibility. It is very advantageous for industrial metal repair shops such as iron and steel metallurgical enterprises and other small-volume production. It is highly automated and equipped with dual power supply and control system. At the same time, it has the dual functions of smelting and heat preservation. It is very suitable for continuous operation such as automobile casting and cast iron pipe production; it is suitable for both cold smelting and double smelting furnaces, and has broad application prospects.
2 Cast iron alloy 2.1 Overview of cast iron alloy At present, the production status and trend of the world's cast iron parts is that the proportion of gray iron castings is significantly reduced, but still dominates. The output of ductile iron castings continues to grow, and the creeping iron and special cast iron have also developed considerably. The global production of gray cast iron tends to decline year by year, but the proportion of high-strength cast iron in gray cast iron is increasing, and it is widely used in the manufacture of automobiles, tractors, agricultural machinery, machine tools and general machinery. China's gray cast iron accounts for more than 80% of the total output of cast iron parts, while the high-strength gray cast iron has a small proportion. For example, domestic diesel engine block castings are more than 30% heavier than foreign countries, and the tensile strength is 1-2 lower than foreign countries under the same carbon equivalent. Under the same carbon equivalent conditions, the tensile properties of gray cast iron produced in China are 1-2 grades lower than those in developed countries. In the future, the experimental research on strengthening high-strength gray cast iron should undoubtedly be the development direction of China's gray cast iron. China's total output of malleable cast iron is among the best in the world. Although the output of malleable cast iron in China is large, the demand in the future will increase. Therefore, in the future, China's malleable cast iron will have a big development.
At present, the production of malleable cast iron in China is mainly compared with that of foreign countries. a small variety, only black heart malleable cast iron. Foreign pearlite malleable cast iron is produced in a lot, and has good whitening malleable cast iron. b is of poor quality. Most of the foreign countries mainly use electric furnace or cupola* electric furnace double smelting, and have advanced furnace control and testing technology. The domestic small-scale cupola is the mainstay, and the inspection and control of raw materials is not strict. The experience in front of the furnace and the lack of advanced testing equipment are all important reasons for the unstable quality of the products. c galvanizing process is backward. d lacks an ideal annealing furnace with low energy consumption, good heat preservation and low pollution. The above gaps have to be caught up so that China's malleable cast iron can develop to a higher level. In the case of reduced cast iron production, the proportion of ductile iron in cast iron parts is still increasing. In the 1950s, the world's ductile iron production was still very small. In 1960, it was only 500,000 tons. In 1970, it increased to 5 million tons. By 1980, it had reached 7.6 million tons. In western developed countries, some gray iron castings and malleable casting balls are usually replaced by ductile iron. The output of ductile iron castings in China is relatively low, and the proportion of cast iron parts is much smaller than that of developed countries. In addition, the gap between the quality and production stability of ductile iron castings in China is also large. At present, the problem of the production of ductile iron in China is that the material has poor toughness and many defects. The reason is that in addition to the charge, spheroidization treatment method and spheroidizing agent, the sulphur content of the molten iron is too loose before the spheroidization treatment. In the production of ductile iron in developed countries, when double-smelting with cupola or electric furnace and cupola is used, desulfurization outside the furnace is indispensable, so that the sulfur content of the original iron liquid reaches ≤0.001%, which greatly reduces the level of sulfur. The spheroidizing agent consumption during spheroidization and the content of sulfide inclusions in the cast iron. In order to enable China's ductile iron production to grow substantially, it is necessary to vigorously promote the implementation of supporting technologies that can stably provide high quality ductile iron parts with reliable quality. At home and abroad, the research on the creeping process and the humectant has reached a very high level, and the variety of osmotic agents developed has reached a variety of up to nearly one hundred. China's rare earth resources are abundant. Nowadays, the creeping agents used in production are mainly rare earth silicon iron magnesium alloys, rare earth silicon calcium alloys and rare earth magnesium titanium alloys. The existing creep treatment processes at home and abroad mainly include the punching method, the flow method, the pneumatic method, and the internal method. Vermicular graphite iron has been used in mass production, and a production line (melted by induction furnace) has been built, and the quality is basically stable. China has also gained some experience in the stable production of creep iron, especially in the cylinder head and exhaust pipe. Domestically, it is usually melted in a cupola furnace. The quality of the original molten iron is poor. Although the rare earth magnesium spheroidizing agent is used to ensure the quality of the casting, the dynamic mechanical properties and elongation of the material are lower than the foreign level. At present, the key issue affecting the development of domestic writhing iron is still the problem of production stability, which is mainly reflected in the technical level and production management level of smelting and processing. With the development of modern industry, the demand for materials with special properties is increasing, while the development speed of special cast iron (anti-wear, corrosion-resistant and heat-resistant cast iron) in China is slow, and the technical level is far from the foreign countries. In order to meet the needs of national economic development under the new situation, the research of special cast iron will become an important direction for the development of cast iron in China.
2.2 Development of cast iron alloy 2.2.1 High strengthening and thin walling is the development direction of China's gray cast iron.
Compared with foreign countries, the main gap between high-strength gray iron castings in China is low strength, poor wear resistance, low life, large section sensitivity and poor processability. High intensity gray cast iron to improve the focus of carbon equivalent, to obtain a high strength to ensure good castability simultaneously. However, in order to obtain iron castings with high strength, stable performance and uniform quality, the carbon equivalent must be strictly controlled and guaranteed from the aspects of melting and testing. At present, the production of high-strength gray cast iron in foreign countries, in addition to routine testing, also proposed ten new test indicators, namely molten iron temperature, molten iron purity, eutectic group number, eutectic degree, relative hardness, relative strength, quality Factor, modulus of elasticity, degree of undercooling, ratio of undercooling. Among them, the eutecticity is generally about 0.8-1.0; the relative strength is 1.15-1.20, the performance of cast iron is the most ideal; the relative hardness is 0.8-1.0, the cutting performance is good. The higher the quality factor, the better the material. The degree of subcooling is generally controlled between 6-8 degrees, at which time the best effect is produced; the degree of supercooling is usually controlled between 1.5 and 2.5; the greater the value of the elastic modulus, the greater the tensile strength of cast iron; The finer the crystallites, the higher the strength of the cast iron. Stable quality can be achieved through strict control of the above indicators. The research focus of high-strength gray cast iron in China is: a increase the temperature of molten iron, improve the metallurgical quality of cast iron, adopt synthetic cast iron smelting process; b strengthen the inoculation treatment technology, especially strengthen the research and promotion of cast iron; c research and promote low alloying Inoculate cast iron; d adjust chemical composition, control the Si/C ratio of cast iron to obtain high-strength low-stress cast iron. Domestic practice shows that if the Si/c ratio is 0.5-0.9, and then properly inoculated and alloyed, high-strength gray cast iron with good comprehensive mechanical properties can be obtained. Further, by adjusting the Mn and Si contents so that the Mn content is 0.2% to 1.3% or more higher than the Si content, another high strength low stress cast iron can be obtained. At present, most of the factories in China do not have the instrument to quickly measure the C and Si content before the furnace, so the C and Si changes cannot be grasped in time. The Si content fluctuates greatly, which makes the casting quality difficult to stabilize. This is an urgent problem to be solved in the future. . The thinning, lightweight, and toughening of cast iron is to meet the requirements of the engineering community for energy conservation and reusability of engineering materials, and to meet the needs of the "human sustainable development strategy." For the automotive industry, reducing the weight of the entire vehicle is critical to energy conservation and emission reduction. The “thin wall high strength†of castings is becoming a trend in the engineering field, and its technical application will be increasingly mature and rapidly expanded. In the foreseeable future, 3-5mm high-strength thin-walled ductile iron parts will appear in a large number of general mechanical and electrical products. . The so-called "thin wall high strength", that is, the wall thickness referred to in production is 4-6mm (3.0-3.5mm abroad), and the tensile strength is greater than 250MPa. At present, most of the factory engines in China still use the HT200 grade material standard. As far as materials are concerned, the main reason is that most factories use cupola smelting, and the iron liquid index does not meet the requirements. In particular, the low temperature of the molten iron and the fluctuation of chemical composition make the castings of such products difficult to control, resulting in high scrap rate. . Among them, the material is mainly due to the fact that the performance does not meet the requirements of high grades, the uniformity of the section is poor, the leakage is serious, and the thermal fatigue performance is poor. During the period from the "Sixth Five-Year Plan" to the "Eighth Five-Year Plan" period, China's research on high-strength thin-walled iron castings has made great progress through the joint research of research institutes, universities and manufacturers, and shortened the gap with advanced foreign countries. . Compared with similar foreign products, there is still a big gap in the performance and quality stability of castings. For example, in terms of material wear resistance, foreign vehicles generally have the first major overhaul mileage, with gasoline engines of 300,000 km and diesel engines of more than 500,000 km. The domestic is 10-15 thousand km and 250,000 km respectively. The service life of the cylinder liner can reach 6000-8000h abroad, while the domestic only has 3000-5000h. Since the wear resistance is closely related to the comprehensive performance of the material, it has become the current to meet the ever-increasing requirements of the engine, improve the structure and performance of the cylinder, research new materials and processes of the cylinder, and improve the wear resistance and service life of the cylinder. One of the focuses of research by domestic and foreign scholars and engineers.
2.2.2 Develop new ductile iron varieties and adopt new ductile iron production process (1) Strengthen the development and application of thin-walled and large-section as-cast ductile iron technology. It is necessary to ensure that the mechanical strength and cutting properties of the casting are not reduced by the reduction of the wall thickness. The basic way is to improve the mechanical properties of the ductile iron. The two most important aspects are the reduction and suppression of the tendency of white mouth and the improvement of graphite structure. The rational selection of spheroidizing agents and the addition of rare earth (RE) elements are the key to achieving high strength thin-walled ductile iron casting. The core of the technology is to ensure RE/S = 2-2.5 in the casting (melting) process. The spheroidizing agent should use Fe-Si-Mg-RE-Ca-based materials. The addition of rare earth elements (Ce.La.Pr) and keeping it in proportion with sulfur is the key to spheroidization technology, while strictly controlling P≤0.04%. -0.06%, Be = 0.003% - 0.007%. Experiments have confirmed that when Mg/S ≥ 5, white mouth is easily formed; and when RE/S ≤ 2 (when spheroidization occurs; when RE/S ≥ 2.5, white mouth is also prone to occur. Therefore, sulfur is generally required. The lower the content, the better the cast iron. At this time (thin wall state), in order to achieve a certain spheroidization rate, grain refinement and reduction of white mouth, it is necessary to maintain a certain proportion of sulfur content. This point is for scrap steel (S less) Special attention should be paid to the smelting plant that is the main raw material.
(2) Continue to develop and apply Austria-Bei iron. Ao-bei ductile iron is one of the major achievements in the research of cast iron metallurgy in recent decades. It is the ductile iron with the best comprehensive performance so far, especially the high bending fatigue performance and good wear resistance. A wide range of attention and development applications. The matrix structure of austempered ductile iron consists of 25%-50% stable retained austenite and carbide of platy or acicular ferrite, sometimes with a small amount of martensite, generally passing 850-900 degrees austenite. It is obtained by isothermal quenching at 300-450 degrees, and its conventional chemical composition is the same as that of ordinary ferrite or pearlite ductile iron. Austempered quenching is used to obtain the Austrian-bead ductile iron, which has high heat treatment cost and is difficult to popularize, and the work hardening phenomenon due to the transformation of retained austenite to martensite makes processing difficult. In foreign countries, new production of Austrian-bee ball iron technology, such as interrupting the hot falling sand method and interrupting the normalizing method, has emerged. These production processes have low cost, low energy consumption, and are feasible, so they have practical significance for research and promotion.
(3) Development of austenitic ductile iron. Austenitic ductile iron has broad application prospects in many fields such as petroleum, chemical, marine and marine, instrumentation, food, power and refrigeration, and nuclear engineering, and thus has become a new research focus in the field of ductile iron in recent years. . Although the current production is still small, some countries have developed rapidly, especially in Germany, which is increasing at a rate of 10% per year, and a weldable austenitic ductile iron with the GGG-NiGrNb20-2 grade is already in Germany. The chemical composition (%) is: C≤3.0, Si1.5-2.6, Mn0.5-1.5, P≤0.4, Nb0.1-0.2, Ni18-22, Gr1.2-2.5,
Mg0.08. The new Ni-Mn austenitic ductile iron developed by Sulzer in Switzerland still has good impact toughness at -196 °C. Recently, 15% Ni-5% Mn has appeared. The economy of 20% Ni-4% Mn is very economical. Good, low temperature austenitic ductile iron. GGG-NiMn137 grades have also been used to manufacture thermonuclear reactor shell load-bearing structures, nuclear submarine high-pressure shells, etc. Our nickel storage of accounting for the world, and the study of austenitic ductile iron or a weakness, and therefore to be developed, especially for high Ni austenitic ductile iron.
(4) Adopt a new ductile iron production process.
In terms of melting, preferably using an induction furnace or cupola - duplex melting furnace, in particular a cupola - furnace desulfurization - electric insulation of high temperature process to provide high-quality low sulfur base iron is made of ductile iron taken. In the sphere of processing, now existing methods at home and abroad for more than eight kinds, widely used abroad GF subcontract law and clad law, the country is also widely used. In terms of inoculation, the inoculant should be selected so that the ball at a certain cooling rate of the casting - bred there is an optimal match. The gestation method is better than instant gestation. In the past ten years, five or six new instant gestation techniques have been developed at home and abroad. In addition, the development of molten iron filtration purification technology in recent years has also been promoted and applied, and has become a good measure to improve the quality of ductile iron.
2.2.3 Development of gestation technology The development of high-strength gray cast iron promoted the production of ductile iron and vermicular cast iron. Cast iron that has been inoculated has the characteristics of graphite refinement, uniform organization and small wall thickness sensitivity. With the development of industry, there is bound to be a large amount of scrap steel to be utilized, and electric furnace smelting has become increasingly prominent in the melting of cast iron. In this kind of smelting and charging conditions, gestation is even more essential. Inoculation has become an important means of producing high quality cast iron products. In the production of modern cast iron, the importance of gray cast iron and ductile iron inoculation is receiving more and more attention, and this situation will certainly continue. In the past, the development of new breeds tend to hope inoculant, which is undoubtedly necessary. However, in recent years, improvements in gestation methods, especially late birth, have received attention. Therefore, in the future, while developing the inoculant, attention to the breeding problem may shift to the development of new methods of breeding. In addition, measures must be taken in the aspects of molten iron quality, molten iron composition, charge composition, inoculation technology, rapid test and control before furnace, to overcome the contradiction between casting performance, white mouth tendency, mechanical properties and high carbon equivalent.
2.2.4 Development of alloy cast iron Alloying is one of the important means to improve the performance of cast iron. With the development of production, cast iron alloying or microalloying will play an important role. It is necessary to continuously develop new varieties of alloy cast iron in combination with local resources, and use advanced methods to continuously deepen the understanding of the existing alloy cast iron.
2.2.5 Development of surface strengthening technology for cast iron parts For special applications, it is often desirable to have special properties on the surface of the casting. The overall strengthening of the traditional castings leads to deterioration of the process performance of the parts as a whole, complicated production process, increased scrap rate and waste of alloying elements, and increases the cost, thereby limiting the advantages of the cast iron material. The laser strengthening treatment of the surface layer of cast iron parts and the alloying technology of casting surface can form a metallurgical bonded alloy layer on the surface of ordinary castings, so that the castings have composite properties to suit special applications. The above technology has been gradually used in the production of wear-resistant parts and has achieved remarkable results. In short, the above-mentioned cast iron technology is not isolated. Strengthening the research and application of cast iron composite technology, taking comprehensive measures from the perspective of system engineering is the fundamental guarantee for obtaining high-quality, high-strength castings. On this basis, strengthening quality management, adopting advanced testing methods, and improving the dimensional accuracy and surface quality of castings are also essential.
3 Future development direction The arrival of the new century has brought great development opportunities and severe challenges to China's foundry industry. Similarly, the cast iron industry is actively adopting high-tech to transform traditional industries, and fully exploiting the huge potential of cast iron materials will certainly keep pace with the times. It is expected that the following aspects will be developed in the following aspects.
(1) Taking the machine tool industry, energy industry, nuclear energy industry, petrochemical industry and marine engineering as the main objectives, the basic theoretical research of major technical equipment and casting technology is carried out with the characteristics of heavy, high, large and difficult. The development of numerical simulation, physical simulation and expert systems to make cast iron technology from "experience" to "quantitative".
(2) Taking the automotive industry, aerospace and nuclear energy industry as the main objectives, and focusing on strengthening, lightening, precision, and high efficiency, research on new materials and processes for cast iron.
(3) In order to improve product quality and productivity, enhance the competitiveness of China's industrial products in the international market, carry out research on automation of casting process, flexible production unit and system and integrated manufacturing technology.
(4) Encourage the research on the basic theory of cast iron technology application with potential application prospects.
(1) Take specialized production roads, increase the operating rate of cupola, and develop in the direction of large-scale, intelligent and long-term operation;
(2) Specialization and scale of charge supply;
(3) Vigorously develop the supporting technology of the cupola, and at the same time strengthen the control and detection of the cushioning furnace;
(4) Development of cupola furnace. Electric furnace double smelting technology;
(5) Obtaining high-temperature and high-quality molten iron is the fundamental task of cupola melting.
1.2 Electric Furnace Technology Induction furnaces are used to smelt cast iron. Since it has the advantages of high temperature, stable composition, less pollution and easy adjustment of molten iron composition, it has been popularized in some industrialized countries since the early 1960s. In recent years, the rapid development of medium frequency induction melting furnaces has injected new vitality into cast iron production. The development and application of induction melting furnaces has brought cast iron production to a new stage. Despite some shortcomings of the power frequency induction melting furnace, it is still widely used in metal melting, iron composition adjustment, metal liquid heating and heat preservation, especially as a double furnace for other melting furnaces. The medium frequency induction melting furnace is suitable for melting cast iron, especially alloy cast iron, ductile iron and compacted graphite iron. Its rapid development and superiority have made it a new trend in cast iron production in recent years. It has energy saving, high productivity, and great production flexibility. It is very advantageous for industrial metal repair shops such as iron and steel metallurgical enterprises and other small-volume production. It is highly automated and equipped with dual power supply and control system. At the same time, it has the dual functions of smelting and heat preservation. It is very suitable for continuous operation such as automobile casting and cast iron pipe production; it is suitable for both cold smelting and double smelting furnaces, and has broad application prospects.
2 Cast iron alloy 2.1 Overview of cast iron alloy At present, the production status and trend of the world's cast iron parts is that the proportion of gray iron castings is significantly reduced, but still dominates. The output of ductile iron castings continues to grow, and the creeping iron and special cast iron have also developed considerably. The global production of gray cast iron tends to decline year by year, but the proportion of high-strength cast iron in gray cast iron is increasing, and it is widely used in the manufacture of automobiles, tractors, agricultural machinery, machine tools and general machinery. China's gray cast iron accounts for more than 80% of the total output of cast iron parts, while the high-strength gray cast iron has a small proportion. For example, domestic diesel engine block castings are more than 30% heavier than foreign countries, and the tensile strength is 1-2 lower than foreign countries under the same carbon equivalent. Under the same carbon equivalent conditions, the tensile properties of gray cast iron produced in China are 1-2 grades lower than those in developed countries. In the future, the experimental research on strengthening high-strength gray cast iron should undoubtedly be the development direction of China's gray cast iron. China's total output of malleable cast iron is among the best in the world. Although the output of malleable cast iron in China is large, the demand in the future will increase. Therefore, in the future, China's malleable cast iron will have a big development.
At present, the production of malleable cast iron in China is mainly compared with that of foreign countries. a small variety, only black heart malleable cast iron. Foreign pearlite malleable cast iron is produced in a lot, and has good whitening malleable cast iron. b is of poor quality. Most of the foreign countries mainly use electric furnace or cupola* electric furnace double smelting, and have advanced furnace control and testing technology. The domestic small-scale cupola is the mainstay, and the inspection and control of raw materials is not strict. The experience in front of the furnace and the lack of advanced testing equipment are all important reasons for the unstable quality of the products. c galvanizing process is backward. d lacks an ideal annealing furnace with low energy consumption, good heat preservation and low pollution. The above gaps have to be caught up so that China's malleable cast iron can develop to a higher level. In the case of reduced cast iron production, the proportion of ductile iron in cast iron parts is still increasing. In the 1950s, the world's ductile iron production was still very small. In 1960, it was only 500,000 tons. In 1970, it increased to 5 million tons. By 1980, it had reached 7.6 million tons. In western developed countries, some gray iron castings and malleable casting balls are usually replaced by ductile iron. The output of ductile iron castings in China is relatively low, and the proportion of cast iron parts is much smaller than that of developed countries. In addition, the gap between the quality and production stability of ductile iron castings in China is also large. At present, the problem of the production of ductile iron in China is that the material has poor toughness and many defects. The reason is that in addition to the charge, spheroidization treatment method and spheroidizing agent, the sulphur content of the molten iron is too loose before the spheroidization treatment. In the production of ductile iron in developed countries, when double-smelting with cupola or electric furnace and cupola is used, desulfurization outside the furnace is indispensable, so that the sulfur content of the original iron liquid reaches ≤0.001%, which greatly reduces the level of sulfur. The spheroidizing agent consumption during spheroidization and the content of sulfide inclusions in the cast iron. In order to enable China's ductile iron production to grow substantially, it is necessary to vigorously promote the implementation of supporting technologies that can stably provide high quality ductile iron parts with reliable quality. At home and abroad, the research on the creeping process and the humectant has reached a very high level, and the variety of osmotic agents developed has reached a variety of up to nearly one hundred. China's rare earth resources are abundant. Nowadays, the creeping agents used in production are mainly rare earth silicon iron magnesium alloys, rare earth silicon calcium alloys and rare earth magnesium titanium alloys. The existing creep treatment processes at home and abroad mainly include the punching method, the flow method, the pneumatic method, and the internal method. Vermicular graphite iron has been used in mass production, and a production line (melted by induction furnace) has been built, and the quality is basically stable. China has also gained some experience in the stable production of creep iron, especially in the cylinder head and exhaust pipe. Domestically, it is usually melted in a cupola furnace. The quality of the original molten iron is poor. Although the rare earth magnesium spheroidizing agent is used to ensure the quality of the casting, the dynamic mechanical properties and elongation of the material are lower than the foreign level. At present, the key issue affecting the development of domestic writhing iron is still the problem of production stability, which is mainly reflected in the technical level and production management level of smelting and processing. With the development of modern industry, the demand for materials with special properties is increasing, while the development speed of special cast iron (anti-wear, corrosion-resistant and heat-resistant cast iron) in China is slow, and the technical level is far from the foreign countries. In order to meet the needs of national economic development under the new situation, the research of special cast iron will become an important direction for the development of cast iron in China.
2.2 Development of cast iron alloy 2.2.1 High strengthening and thin walling is the development direction of China's gray cast iron.
Compared with foreign countries, the main gap between high-strength gray iron castings in China is low strength, poor wear resistance, low life, large section sensitivity and poor processability. High intensity gray cast iron to improve the focus of carbon equivalent, to obtain a high strength to ensure good castability simultaneously. However, in order to obtain iron castings with high strength, stable performance and uniform quality, the carbon equivalent must be strictly controlled and guaranteed from the aspects of melting and testing. At present, the production of high-strength gray cast iron in foreign countries, in addition to routine testing, also proposed ten new test indicators, namely molten iron temperature, molten iron purity, eutectic group number, eutectic degree, relative hardness, relative strength, quality Factor, modulus of elasticity, degree of undercooling, ratio of undercooling. Among them, the eutecticity is generally about 0.8-1.0; the relative strength is 1.15-1.20, the performance of cast iron is the most ideal; the relative hardness is 0.8-1.0, the cutting performance is good. The higher the quality factor, the better the material. The degree of subcooling is generally controlled between 6-8 degrees, at which time the best effect is produced; the degree of supercooling is usually controlled between 1.5 and 2.5; the greater the value of the elastic modulus, the greater the tensile strength of cast iron; The finer the crystallites, the higher the strength of the cast iron. Stable quality can be achieved through strict control of the above indicators. The research focus of high-strength gray cast iron in China is: a increase the temperature of molten iron, improve the metallurgical quality of cast iron, adopt synthetic cast iron smelting process; b strengthen the inoculation treatment technology, especially strengthen the research and promotion of cast iron; c research and promote low alloying Inoculate cast iron; d adjust chemical composition, control the Si/C ratio of cast iron to obtain high-strength low-stress cast iron. Domestic practice shows that if the Si/c ratio is 0.5-0.9, and then properly inoculated and alloyed, high-strength gray cast iron with good comprehensive mechanical properties can be obtained. Further, by adjusting the Mn and Si contents so that the Mn content is 0.2% to 1.3% or more higher than the Si content, another high strength low stress cast iron can be obtained. At present, most of the factories in China do not have the instrument to quickly measure the C and Si content before the furnace, so the C and Si changes cannot be grasped in time. The Si content fluctuates greatly, which makes the casting quality difficult to stabilize. This is an urgent problem to be solved in the future. . The thinning, lightweight, and toughening of cast iron is to meet the requirements of the engineering community for energy conservation and reusability of engineering materials, and to meet the needs of the "human sustainable development strategy." For the automotive industry, reducing the weight of the entire vehicle is critical to energy conservation and emission reduction. The “thin wall high strength†of castings is becoming a trend in the engineering field, and its technical application will be increasingly mature and rapidly expanded. In the foreseeable future, 3-5mm high-strength thin-walled ductile iron parts will appear in a large number of general mechanical and electrical products. . The so-called "thin wall high strength", that is, the wall thickness referred to in production is 4-6mm (3.0-3.5mm abroad), and the tensile strength is greater than 250MPa. At present, most of the factory engines in China still use the HT200 grade material standard. As far as materials are concerned, the main reason is that most factories use cupola smelting, and the iron liquid index does not meet the requirements. In particular, the low temperature of the molten iron and the fluctuation of chemical composition make the castings of such products difficult to control, resulting in high scrap rate. . Among them, the material is mainly due to the fact that the performance does not meet the requirements of high grades, the uniformity of the section is poor, the leakage is serious, and the thermal fatigue performance is poor. During the period from the "Sixth Five-Year Plan" to the "Eighth Five-Year Plan" period, China's research on high-strength thin-walled iron castings has made great progress through the joint research of research institutes, universities and manufacturers, and shortened the gap with advanced foreign countries. . Compared with similar foreign products, there is still a big gap in the performance and quality stability of castings. For example, in terms of material wear resistance, foreign vehicles generally have the first major overhaul mileage, with gasoline engines of 300,000 km and diesel engines of more than 500,000 km. The domestic is 10-15 thousand km and 250,000 km respectively. The service life of the cylinder liner can reach 6000-8000h abroad, while the domestic only has 3000-5000h. Since the wear resistance is closely related to the comprehensive performance of the material, it has become the current to meet the ever-increasing requirements of the engine, improve the structure and performance of the cylinder, research new materials and processes of the cylinder, and improve the wear resistance and service life of the cylinder. One of the focuses of research by domestic and foreign scholars and engineers.
2.2.2 Develop new ductile iron varieties and adopt new ductile iron production process (1) Strengthen the development and application of thin-walled and large-section as-cast ductile iron technology. It is necessary to ensure that the mechanical strength and cutting properties of the casting are not reduced by the reduction of the wall thickness. The basic way is to improve the mechanical properties of the ductile iron. The two most important aspects are the reduction and suppression of the tendency of white mouth and the improvement of graphite structure. The rational selection of spheroidizing agents and the addition of rare earth (RE) elements are the key to achieving high strength thin-walled ductile iron casting. The core of the technology is to ensure RE/S = 2-2.5 in the casting (melting) process. The spheroidizing agent should use Fe-Si-Mg-RE-Ca-based materials. The addition of rare earth elements (Ce.La.Pr) and keeping it in proportion with sulfur is the key to spheroidization technology, while strictly controlling P≤0.04%. -0.06%, Be = 0.003% - 0.007%. Experiments have confirmed that when Mg/S ≥ 5, white mouth is easily formed; and when RE/S ≤ 2 (when spheroidization occurs; when RE/S ≥ 2.5, white mouth is also prone to occur. Therefore, sulfur is generally required. The lower the content, the better the cast iron. At this time (thin wall state), in order to achieve a certain spheroidization rate, grain refinement and reduction of white mouth, it is necessary to maintain a certain proportion of sulfur content. This point is for scrap steel (S less) Special attention should be paid to the smelting plant that is the main raw material.
(2) Continue to develop and apply Austria-Bei iron. Ao-bei ductile iron is one of the major achievements in the research of cast iron metallurgy in recent decades. It is the ductile iron with the best comprehensive performance so far, especially the high bending fatigue performance and good wear resistance. A wide range of attention and development applications. The matrix structure of austempered ductile iron consists of 25%-50% stable retained austenite and carbide of platy or acicular ferrite, sometimes with a small amount of martensite, generally passing 850-900 degrees austenite. It is obtained by isothermal quenching at 300-450 degrees, and its conventional chemical composition is the same as that of ordinary ferrite or pearlite ductile iron. Austempered quenching is used to obtain the Austrian-bead ductile iron, which has high heat treatment cost and is difficult to popularize, and the work hardening phenomenon due to the transformation of retained austenite to martensite makes processing difficult. In foreign countries, new production of Austrian-bee ball iron technology, such as interrupting the hot falling sand method and interrupting the normalizing method, has emerged. These production processes have low cost, low energy consumption, and are feasible, so they have practical significance for research and promotion.
(3) Development of austenitic ductile iron. Austenitic ductile iron has broad application prospects in many fields such as petroleum, chemical, marine and marine, instrumentation, food, power and refrigeration, and nuclear engineering, and thus has become a new research focus in the field of ductile iron in recent years. . Although the current production is still small, some countries have developed rapidly, especially in Germany, which is increasing at a rate of 10% per year, and a weldable austenitic ductile iron with the GGG-NiGrNb20-2 grade is already in Germany. The chemical composition (%) is: C≤3.0, Si1.5-2.6, Mn0.5-1.5, P≤0.4, Nb0.1-0.2, Ni18-22, Gr1.2-2.5,
Mg0.08. The new Ni-Mn austenitic ductile iron developed by Sulzer in Switzerland still has good impact toughness at -196 °C. Recently, 15% Ni-5% Mn has appeared. The economy of 20% Ni-4% Mn is very economical. Good, low temperature austenitic ductile iron. GGG-NiMn137 grades have also been used to manufacture thermonuclear reactor shell load-bearing structures, nuclear submarine high-pressure shells, etc. Our nickel storage of accounting for the world, and the study of austenitic ductile iron or a weakness, and therefore to be developed, especially for high Ni austenitic ductile iron.
(4) Adopt a new ductile iron production process.
In terms of melting, preferably using an induction furnace or cupola - duplex melting furnace, in particular a cupola - furnace desulfurization - electric insulation of high temperature process to provide high-quality low sulfur base iron is made of ductile iron taken. In the sphere of processing, now existing methods at home and abroad for more than eight kinds, widely used abroad GF subcontract law and clad law, the country is also widely used. In terms of inoculation, the inoculant should be selected so that the ball at a certain cooling rate of the casting - bred there is an optimal match. The gestation method is better than instant gestation. In the past ten years, five or six new instant gestation techniques have been developed at home and abroad. In addition, the development of molten iron filtration purification technology in recent years has also been promoted and applied, and has become a good measure to improve the quality of ductile iron.
2.2.3 Development of gestation technology The development of high-strength gray cast iron promoted the production of ductile iron and vermicular cast iron. Cast iron that has been inoculated has the characteristics of graphite refinement, uniform organization and small wall thickness sensitivity. With the development of industry, there is bound to be a large amount of scrap steel to be utilized, and electric furnace smelting has become increasingly prominent in the melting of cast iron. In this kind of smelting and charging conditions, gestation is even more essential. Inoculation has become an important means of producing high quality cast iron products. In the production of modern cast iron, the importance of gray cast iron and ductile iron inoculation is receiving more and more attention, and this situation will certainly continue. In the past, the development of new breeds tend to hope inoculant, which is undoubtedly necessary. However, in recent years, improvements in gestation methods, especially late birth, have received attention. Therefore, in the future, while developing the inoculant, attention to the breeding problem may shift to the development of new methods of breeding. In addition, measures must be taken in the aspects of molten iron quality, molten iron composition, charge composition, inoculation technology, rapid test and control before furnace, to overcome the contradiction between casting performance, white mouth tendency, mechanical properties and high carbon equivalent.
2.2.4 Development of alloy cast iron Alloying is one of the important means to improve the performance of cast iron. With the development of production, cast iron alloying or microalloying will play an important role. It is necessary to continuously develop new varieties of alloy cast iron in combination with local resources, and use advanced methods to continuously deepen the understanding of the existing alloy cast iron.
2.2.5 Development of surface strengthening technology for cast iron parts For special applications, it is often desirable to have special properties on the surface of the casting. The overall strengthening of the traditional castings leads to deterioration of the process performance of the parts as a whole, complicated production process, increased scrap rate and waste of alloying elements, and increases the cost, thereby limiting the advantages of the cast iron material. The laser strengthening treatment of the surface layer of cast iron parts and the alloying technology of casting surface can form a metallurgical bonded alloy layer on the surface of ordinary castings, so that the castings have composite properties to suit special applications. The above technology has been gradually used in the production of wear-resistant parts and has achieved remarkable results. In short, the above-mentioned cast iron technology is not isolated. Strengthening the research and application of cast iron composite technology, taking comprehensive measures from the perspective of system engineering is the fundamental guarantee for obtaining high-quality, high-strength castings. On this basis, strengthening quality management, adopting advanced testing methods, and improving the dimensional accuracy and surface quality of castings are also essential.
3 Future development direction The arrival of the new century has brought great development opportunities and severe challenges to China's foundry industry. Similarly, the cast iron industry is actively adopting high-tech to transform traditional industries, and fully exploiting the huge potential of cast iron materials will certainly keep pace with the times. It is expected that the following aspects will be developed in the following aspects.
(1) Taking the machine tool industry, energy industry, nuclear energy industry, petrochemical industry and marine engineering as the main objectives, the basic theoretical research of major technical equipment and casting technology is carried out with the characteristics of heavy, high, large and difficult. The development of numerical simulation, physical simulation and expert systems to make cast iron technology from "experience" to "quantitative".
(2) Taking the automotive industry, aerospace and nuclear energy industry as the main objectives, and focusing on strengthening, lightening, precision, and high efficiency, research on new materials and processes for cast iron.
(3) In order to improve product quality and productivity, enhance the competitiveness of China's industrial products in the international market, carry out research on automation of casting process, flexible production unit and system and integrated manufacturing technology.
(4) Encourage the research on the basic theory of cast iron technology application with potential application prospects.
API 602 Globe Valve is samll forging shut off valve which widely used in all type system of thermal power plant. API 602 globe valve with bolt bonnet or welding bonnet type as well as full port or reduce port. Valve size from 1/2"(PN15) to 2"(PN50) matching pressure class 150(PN16) to class 2500(PN420). Valve connection can be NPT, BW, SW, RF.
Api 602 Globe Valve,Forged Steel Globe Valve,Api Globe Valve,Api Forged Globe Valve
Yongjia South Trading Co.,Ltd , https://www.n-lvalve.com