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Status and process characteristics of stainless steel precision casting industry in my country

Edit:Xiangyang Liqiang Machinery Co., Ltd.UpDate:2019-10-09

1. Mainland ChinaStainless steel precision castingThe scale of operation of the manufacturing industry Although the precision casting manufacturing industry in mainland China has long been established in the mid to late 1950s and is slowly gaining application and promotion, the real rapid development is indeed in the decades since the early 90s of the 20th century. Very much in the last two years. At this stage, my country's investment casting has two major types of processing technology. The first is that the company uses medium temperature mold material to make molds and silica sol or ethyl silicate adhesive to make shells. Flexible investment casting process. The second is the use of ultra-low temperature mold materials and sodium silicate adhesive to make the shell processing technology. The precision and roughness of the casting specifications are worse than the first, which is not up to the international investment casting standard. According to the conditions in the mainland, there are also medium-temperature or ultra-low temperature molding materials used for molding, the surface layer is made of silica sol, and the structural reinforcement layer is made of sodium silicate. The composite processing technology can be controlled while ensuring high specification precision and process performance. cost. According to the survey, in 2001, more than 350 manufacturers selected the first type, with a total output of 75,000 tons, and annual sales of 3.28 billion US dollars; the second type of processing technology (including composite processing technology) exceeded 1,350, with a total output Nearly 200,000 tons, with annual sales of 1.5 billion US dollars. In 2002, the production volume exceeded 321,000 tons and the annual output value exceeded 5.49 billion U.S. dollars. The production volume in 2002 was 6.4 times that of 1988. The annual output value is 16.6 times of 330 million in 1988.

2. The technical level, quality of castings and product types are currently in my country in terms of main uses and quality standardsStainless steel precision castingThe key to the production of castings is: the use of the first processing technology to produce castings for airlines and gas turbines, the quality exceeds international standards, there are 50 manufacturers with a total output of 5,000 tons and annual sales of 400 million U.S. dollars; precision castings for commercial services produced by using the first and compound processing technology. The new quality inspection items and specifications are smaller than those of aviation parts. There are 300 companies with a total output of 70,000 tons and annual sales of 2.88 billion US dollars. ; The second processing technology is used to produce investment casting rough parts with low specification precision and roughness. There are 1,350 companies with a total output of nearly 200,000 tons and annual sales of 1.5 billion US dollars. It can be seen from the proportion of castings of several quality levels that the production volume of high-standard airlines' precision castings is very small, accounting for only 1.8% of the total output value. Usually commercial precision castings account for 25.6%, and the quality is not up to According to national standards, sodium silicate castings accounted for 72.6% of the total output value. Compared with the market concentration of investment castings in excellent countries and regions such as the United Kingdom, the United States, Europe and Japan, there is a significant difference. The proportion of high-quality precision castings is still very low. Even so, the important links of investment casting processing technology in China still have long-term development, and there are many new materials, new technologies, new processes, and new machinery and equipment that have great harm to the development trend of investment casting, such as water-soluble cores and porcelain types. Core, stainless steel material improvement, large and medium-sized investment casting technology, titanium investment casting, fixed-item condensation and polysilicon forging, filtering technology, heat and other negative pressure, rapid prototyping technology, and the application and specialization of electronic computers in investment casting Technological development trends such as automation technology enable investment casting not only to produce small and medium-sized castings, but also to produce large castings. The contour specifications of larger investment castings have been 2m, but the minimum wall thickness is not high. 2mm. In addition, investment castings are becoming increasingly high-precision. In addition to linear dimensional tolerances, parts can also exceed higher geometrical dimensional tolerances. The roughness value of investment castings is getting smaller and smaller, which can exceed Ra0.4um.

3. The business process of supporting facilities is gradually complete. The rapid development of the precision casting manufacturing industry has promoted the rapid development trend of the business process of related supporting facilities. It is specifically manifested in mold manufacturing, machinery and equipment manufacturing, and raw material procurement and manufacturing. According to preliminary statistics, professional factories for the production of precision casting abrasive tools dominated by production equipment have long been established in areas where precision casting plants are concentrated, such as Guangdong Province, Shandong Province, and Wuhan City. There are many professional equipment manufacturers; The raw material procurement manufacturers and distributors have already developed a trend to nearly a hundred, and because of the first precision casting process, the mold materials, zircon powder, abrasive belt and other auxiliary materials and some excellent machinery and equipment are not yet available. It can be manufactured in China, and hundreds of tons of raw materials have to be imported from overseas over the years. However, because the basic industrial production and resource standards in my country are much better than those in other developed countries, in addition to the development of the investment casting industry, it will also expand and develop their sales markets to crooked places and even the world.

4. The difference and advantages between the manufacturing industry and the international standards and the comparison with the international investment casting standards. my country's precision casting industry uses the first processing technology to produce airline precision castings. The production volume is very small and high-quality precision castings There are also very few parts. Most of the pipes, hardware accessories, harnesses and auto parts with too low precision requirements are produced. The types of aluminum alloys are singular, and the proportion of high-temperature alloys and non-ferrous plate aluminum alloys is very small. The level of precision casting in our country is still very outdated. However, our country's human capital costs are relatively low, and the raw materials are rich in variety, which occupies a great advantage in product quotation. If the product quality is improved, it will still have considerable competitiveness in the international arena. In addition, with the prevalence of China’s national high-tech, the machinery manufacturing industry is moving towards precision and practicality, and certain policies, regulations and local regulations issued by the construction industry one after another, the use of cast copper and aluminum alloy die castings to replace cast iron drainage pipes is The investment casting manufacturing industry presents unprecedented business opportunities for entrepreneurship. In addition, the franchise agent and rapid development of my country's private investment casting industry have introduced fresh charm to my country's investment casting industry, and it has long become the strongest and most practical competitor in the country's investment casting industry. From the 1980s to the early 1990s, this kind of company used joint ventures and individual proprietorship to import silica sol shell processing technology from Taiwan, Japan and other places. The key is to spread in coastal areas and surrounding cities. Most of them are exported to foreign markets, and because of its excellent system, flexible system, and efficient management methods, the economic benefits are very good. Although there is only a development trend of more than 20 years, it has become a new force in the investment casting industry in mainland China to undertake the import and export business process. At the same time, because of the high level of machinery and equipment, the processing technology and quality standards are excellent in China, most of which exceed the usual overseas standards, with immediate import and export order information and sales market alliances, and the use value of goods is maintained at a high level. Standard, basic and international combination. Regardless of technical strength or sales channels, they are all powerful competitors for state-owned capital investment casting companies. Manufacturers such as Chefeng Precision Castings Co., Ltd. are the second and third processing technology companies. In recent years, regardless of the processing technology strength, product quality and output rate, they have accelerated their promotion to foreign markets and will once again To improve the standard of my country's precision casting industry is proactive and diligent.

In recent years, the number of stainless steel castings used at ultra-low temperatures has been increasing. Many of them are pressure-bearing parts at ultra-low temperatures. Most of these castings have strict requirements on ultra-low temperature impact toughness. Among the many regulations on stainless steel castings, for many steel casting plants, the more difficult to qualify is impact toughness. Generally, the countermeasures used to improve impact toughness are as follows: ◆Reduce carbon content; ◆Appropriately increase manganese to carbon ratio (Mn/c); ◆Add aluminum alloy elements, such as Ni, Cr, Mo, etc.; ◆ Reduce the sulfur content; ◆Reduce the sulfur content in the steel and improve the shape of the sulfide hybrid; ◆Select the scouring process outside the furnace; ◆Improve the quenching and tempering treatment among the corresponding measures, the improvement of the quenching and tempering treatment should be a high degree The value of the optimal plan is: ◆Does not cause major adjustments in the entire forging process; ◆No need to add machinery and equipment; ◆The production cost rises very little. In 1978, E.? G.? Nisbett, RDASP and D.? E.? Morgan et al. published the results of scientific research on the dual-phase quenching and tempering treatment of forged carbon steel. After the carbon steel castings used in nuclear power plants are quenched and tempered in the dual-phase zone, the impact toughness is approximately doubled, while the compressive strength is only slightly reduced. Since then, the steel casting industry in Australia and certain companies in Europe have carried out scientific research on the dual-phase quenching and tempering treatment of steel castings, and have obtained relatively satisfactory practical results.

1. What is the dual-phase zone quenching and tempering treatment? The dual-phase zone quenching and tempering treatment of castings is based on the quenching or heat treatment that was originally performed on the castings. In many ways, only the dual-phase area is heated again by quenching or heat treatment. The dual-phase zone is between A1 and A3. The steel is not completely ferritized in this category. The mechanism is composed of α and γ two phases, so it is called the dual-phase zone. Eutectoid steel has no dual phase zone, so this type of solution is only applicable to hypoeutectoid steel. The lower the carbon content of steel, the wider the range of its dual-phase region. The microscope mechanism is a hypoeutectoid steel with metallographic structure and ferrite, heated to a temperature of about A1, and the changes in the mechanism are roughly given: a. Just beyond A1 (727℃), most of the metallographic structure remains unchanged , Ferrite gradually changes to ferrite. The new ferrite crystals nucleate on the boundaries of the ferrite clusters, and the massive martensite in the ferrite thickens and becomes spherical. Following the development of the whole process of change, carbon diffuses from spherical martensite to ferrite that has grown up continuously. In that way, new metallographic structure crystals are produced in the original spherical body. The time required for such changes in ferrite varies with the water content and temperature of the aluminum alloy element in the steel. However, it can take about 90% in an hour in a dual-phase residential area. The original carbon content of ferrite produced by ferrite is close to the eutectoid component (that is, 0.77%). b. Heating to a higher temperature in the dual-phase residential area. If the steel is heated to a higher temperature, the ferrite area will deepen and expand into the original metallographic structure, and the carbon content of the ferrite will gradually decrease. To be close to the composition of steel. The original metallographic structure will also produce some small and helpless ferrite. When stainless steel castings are cooled by water after heat insulation in the dual phase zone, the transformed austenitic body changes into ferrite and metallographic structure. The key practical effect of the solution is the optimization of the crystal mechanism, which can improve the ductility of the steel.

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