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

Edit:Xiangyang Liqiang Machinery Co., Ltd.UpDate:2019-10-25

1. Mainland ChinaStainless steel precision castingThe scale of operation of the manufacturing industry Although the investment casting manufacturing industry in mainland China has been established in the early and mid-1950s of the 20th century and has been slowly gaining application and promotion, the real rapid development has indeed occurred in the more than ten years since the beginning of the 1990s in the 20th century. Very much in the last two years. At this stage, China's investment casting has two levels of technology. The first type of company uses medium-temperature molding material to mold and silica sol or ethyl silicate adhesive to make the shell. Mold casting process. The second category is the use of ultra-low temperature mold materials and sodium silicate adhesive to make the shell process. The precision and roughness of the casting specifications are worse than the first category, which is not up to the international alliance 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. This can control costs while ensuring high specification precision and process performance. . According to the survey, in 2001, more than 350 manufacturers selected the first category, with a total output of 75,000 tons and annual sales of 3.28 billion US dollars; the second category of process manufacturers (including composite processes) exceeded 1,350, with a total output of nearly 20 10,000 tons, with annual sales of 1.5 billion US dollars. In 2002, the production volume reached 321,000 tons and the annual output value reached 5.49 billion US 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. Technical level, quality of castings and product types. From the perspective of main use and quality level, the key to castings produced in China's precision casting at this stage is: the quality of castings for airlines and gas turbines produced by the first-class process To achieve the level of the international alliance, there are 50 manufacturers with a total output of 5,000 tons and annual sales of 400 million US dollars; the first-class and composite technology is used to produce precision castings for commercial services, and its new quality inspection items and The specification is smaller than that of aerospace parts. There are 300 companies with a total output of 70,000 tons and annual sales of 2.88 billion US dollars. The second-class process 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 proportions of castings of the three 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, and general 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 key link of China's investment casting process still has long-term development, and there are many new materials, new technologies, new processes, and new machinery and equipment that are very harmful to the development trend of investment casting, such as water-soluble cores and porcelain cores. , 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, computer application in investment casting and its specialized automation technology Other technological development trends 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 are nearly 2m, but the minimum wall thickness is less than 2mm. . In addition, investment castings are becoming increasingly high-precision. In addition to linear dimensional tolerances, parts can also achieve higher geometrical dimensional tolerances. The roughness value of investment castings is getting smaller and smaller, which can reach Ra0.4um.

3. The business process of supporting facilities is gradually complete Because 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, raw material procurement and manufacturing. According to preliminary statistics, professional factories for the production of precision casting abrasive tools led 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 purchasing and processing plants and distributors of casting raw materials have already developed a trend to nearly one hundred, and because of the first type of precision casting process, the mold materials, zircon powder, abrasive belt and other auxiliary materials and some excellent machinery and equipment are not available in China. For manufacturing, hundreds of tons of raw materials are imported from overseas every year. However, because the basic manufacturing and resource standards in my country are much better than those of other developed countries, in addition to the development of the investment casting industry, it will also expand and develop their sales markets in Southeast Asia and even the world.

4. The differences and advantages between the manufacturing industry and the level of the international alliance compared with the level of the international alliance investment casting. China's investment casting industry uses the first-class process to produce airlinesStainless steel precision castingThe production volume of parts is very small, and there are few high-quality precision castings. Most of the production and manufacture of pipes, hardware, harnesses and auto parts with too low precision requirements, the type of aluminum alloy is single, very high-temperature alloys and non-ferrous plate aluminum alloys The proportion is very small, and the level of precision casting in our country is still very outdated. However, China's human capital costs are relatively low, and the raw materials are rich and varied, and have a great advantage in product quotation. If the product quality is improved, it will still have considerable competitiveness in the international alliance. In addition, with the prevalence of China’s national high-tech, the machinery manufacturing industry is developing towards precision and practicality, and some policies, regulations and local regulations successively promulgated by the construction industry, the use of cast copper and aluminum alloy die castings to replace cast iron drainage pipes is a refined The casting manufacturing industry presents unprecedented business opportunities for entrepreneurship. In addition, the franchise chain and rapid development of China's private investment casting industry have introduced fresh charm to China's investment casting industry, and it has long become the most powerful and practical opponent of the national investment casting industry. From the 1980s to the early 1990s, this kind of company used joint ventures and individual proprietorships to introduce silica sol shell technology from Taiwan, Japan and other places. The key is spread in coastal areas and surrounding cities, and its products are extremely large. Most of them are exported to foreign markets, and because of their excellent system, system flexibility, and high efficiency of management methods, their 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 business process of the export department. On the other hand, because of the high level of machinery and equipment, the level of craftsmanship and quality are excellent in China, most of them have reached the general level of overseas, with immediate export order information and sales market alliances, and the use value of goods is maintained at a high level. The level, foundation and international alliance are combined. Regardless of their technical strength or the way of marketing and promotion, they are all powerful opponents of state-owned capital investment companies. However, Chefeng Precision Casting Co., Ltd. and other manufacturers are part of the second and third types of technology companies that have accelerated their promotion to foreign markets in recent years, regardless of process technology strength, product quality, and labor productivity, and will once again contribute to improving China The 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 for ultra-low temperature impact toughness. Among the various 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 furnace refining process; ◆Improve the quenching and tempering treatment among the corresponding measures, the improvement of the quenching and tempering treatment should be valued The preferred plan is because: ◆It does not cause major adjustments in the entire forging process; ◆There is 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. released the results of scientific research on the dual-phase quenching and tempering treatment of forged alloy steel. After the alloy 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 the United States and some companies in France 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 quenching and tempering treatment of castings? The dual-phase quenching and tempering treatment of castings is basically the quenching or heat treatment originally implemented in the castings. In many ways, only the dual-phase area is heated for the second 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 does not have a 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 ferrite and metallographic structure. It is heated to a temperature of about A1. The changes in the mechanism are approximately as follows: a. Just beyond A1 (727℃), the metallographic structure is mostly consistent. The ferrite gradually changes to ferrite. The new ferrite crystals nucleate on the boundaries of the ferrite clusters, and the plate-like carbides in the ferrite become thicker and become spherical. With the development of the whole process of change, carbon diffuses from the spherical carbide to the ferrite that has grown 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 elements in the steel. However, it can be approximately 90% in a dual-phase residential area within an hour. The original carbon content of ferrite produced by ferrite is close to the eutectoid component (that is, up to 0.77%). b. Heat to a higher temperature in the dual-phase residential area. If the steel is heated to a higher temperature, the ferrite area will further 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 changes into ferrite and metallographic structure. The key practical effect of the solution is the optimization of the crystal structure, which can improve the ductility of the steel.

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