New Progress in Production Technology of Austempered Ductile Iron

Zeng Yicheng (General Institute of Mechanical Science Research, Beijing 100044, China) Abstract: The new development of ADI production technology in China was introduced, mainly in:

(1) CADI grinding ball has made great progress;

(2) Heavy truck chassis parts may become a new growth point of ADI output in China;

(3) ADI (CADI) has made a breakthrough in the application of anti-wear and wear parts; (

4) The establishment of the isothermal quenching heat treatment center makes the heat treatment equipment with stable quality and reasonable price become a concern again;

(5) The improvement of the quality of raw and auxiliary materials for the production of ductile iron and the improvement of the blank quality of ductile iron will increase confidence in the re-use of ADI for gear, crankshaft and other parts. At the same time, the problems of poor product stability and consistency in ADI production process and the future development direction are put forward. Key words: isothermal quenched ductile iron; Production technology; Development Direction CLC Number: TG255 Document Code: A Article Number: 1003-8345 (2015) 05-0019-07 DOI: 10.3969/j.issn.1003-8345.2015.05.001 New Progress of Isothermally Quenched Ductile Iron Production Technology ZENG Yi-cheng (China Academy of Machinery Science & Technology, Beijing 100044, China) Abstract: An introduction was conducted to the new progress of ADI production technology in China, the main progresses were as follows: (1) CADI grinding balls production technology had relatively obvious progress. (2) It was possible that the chassis parts of heavy trucks would become the new growth point of ADI production in China. (3) The application of ADI (CADI) to abrasion-resistant and anti-abrasion parts has got breakthrough. (4) The establishment of isothermally-quenching center caused the heat treating equipments with stable quality and rational price to become the problem attracting public  attentions. (5) Quality improvement of raw and accessorial materials used for ductile iron production and quality elevation of rough ductile iron castings strengthened confidence to re-use ADI for making important parts such as gears, crankshafts et al. In addition, the problem of poor quality stability and consistency of products existing in the ADI production process, as well as the future development direction of ADI were proposed. Key words: isothermally quenched ductile iron; production technology; ADI from the system research, development has been 40 years, the development of ADI has gone through three stages: experimental research, development and application and industrial production. Due to its high strength (up to more than 1 600 MPa), good plasticity (maximum elongation >11%), high dynamic load capacity (bending fatigue strength of 420 ~ 500 MPa, contact fatigue strength of 1 600 ~ 2 100 MPa), good wear resistance and shock absorption and many other advantages, it has developed rapidly. The scope of application is gradually expanding. In the foreign ADI application market, automotive castings account for the main position, about 45% of the total output of ADI parts, especially the chassis parts of heavy trucks. According to reports, at least 500 kg of ADI castings in every heavy truck in the United States. After decades of production and application, we have accumulated rich experience and data. The application of ADI has been developed from general substitution to the optimization of product structure by using finite element analysis and other modern design technology according to the performance characteristics and service conditions of ADI, so as to achieve the purpose of reducing the wall thickness of parts, reducing the quality and saving energy and materials. In our ADI application, anti-wear and wear-resistant parts are still the main, especially the grinding ball, CADI grinding ball and Obei grinding ball still account for a large part of our ADI output. Rough statistics, China's ADI (including CADI) annual output of about 130,000 t, of which about 70,000 t grinding ball, accounting for Received date: 2014-12-30 Revised date: 2015-06-27 Author Profile: Zeng Yicheng (1934.11-), male, born in Nanhai, Guangdong Province, professor-level senior engineer, mainly engaged in the research of cast iron smelting and isothermal quenching ductile iron technology. Nodular Iron 19 Modern cast iron 2015/5 more than 50%; Engineering structural parts (including tooth plates, lining plates) accounted for about 42%, of which heavy truck suspension parts, brackets accounted for 50%, anti-wear, wear-resistant parts accounted for 25% to 30%, gear, crankshaft accounted for 5% to 10%, which accounted for 10%. The production of ADI consists of three main parts: ductile iron blank, heat treatment and machining, and the provision of sound and stable quality ductile iron blank is the foundation. Without a good quality and stable ductile iron blank, it is impossible to produce qualified ADI parts. Numerous production practices show that ADI parts with remarkable effects and good economic benefits are often defeated because of high scrap rate and unstable quality in mass production. In recent years, China's ductile iron production technology has made great progress, the performance and quality level of ductile iron has been greatly improved, the quality stability has increased year by year, the supply and quality of raw and auxiliary materials have been greatly improved, especially the large supply of high-purity pig iron, due to the impurity element content is very low, the purity of liquid iron is high. It can change the situation that the plastic (toughness) index of ductile iron production in China is lower than that of the same brand abroad; Develop and improve various treatment technologies to effectively control the roundness, size and quantity of graphite balls; The strict control of each process of the production process greatly improves the stability of ductile iron quality; The application of ultrasonic, magnetic powder, ray and other non-destructive testing technology, especially in mass production to achieve online testing, to ensure the quality of each product. It can be seen that the quality of nodular cast iron billet provided for ADI production has been basically solved, and it can be expected that the promotion and application of ADI will be greatly developed in the next few years. CADI grinding ball has made great progress CADI grinding ball has a history of 6 ~ 7 years from research and development, is jointly developed by Hebei University of Technology and Qianxi Aodi Ai Machinery Casting Co., LTD., years of use results prove: Compared with high Cr ball and low Cr ball, CADI grinding ball has the advantages of low wear, low crushing rate, power saving and low noise. At present, Qianxi Aodi Ai Company has 4 iron type and sand-coated iron type grinding ball lines, 4 heat treatment production lines (one of which is a special continuous production line for grinding ball), It can produce CADI grinding balls of φ40 mm, φ50 mm, φ60 mm, φ80 mm, φ100 mm, φ120 mm, φ130 mm, φ150 mm and even φ180 mm, with an annual production capacity of 50,000 tons of CADI grinding balls. At present, it is the largest CADI grinding ball manufacturer in China. Hebei Chengde Qiuye Vanadium Titanium anti-wear Technology Material Co., LTD., using V, Ti and C, N compounds and other hard points produced CADI grinding ball, in use has also achieved good results. Due to the obvious use effect of CADI grinding ball, many grinding ball manufacturers are racing to adopt, but because of the production process, equipment is not standardized, technical essentials are not mastered, some CADI grinding ball quality instability, use effect is not ideal and other problems, must be paid attention to, such as not guiding, improving, improving quality, etc. Will affect the reputation of CADI mill. According to the domestic and foreign market situation, CADI grinding ball is mainly developed in the following aspects: (1) Standardize the production process, form CADI grinding ball complete set of production technology (including equipment), ensure the quality of the grinding ball, and gradually expand the market. (2) Due to the current slowdown in demand for iron ore fine powder, the market condition of pig iron is not good, and the payment of CADI grinding ball is difficult, and its application scope has gradually expanded from iron ore to copper, gold, cement, coal and other aspects. (3) From the domestic market to the foreign market. (4) In order to ensure quality and reduce costs, heat treatment process and equipment have become the key under the condition of ensuring the quality of ductile iron blanks. In recent years, around the establishment of a special heat treatment production line for grinding balls with an annual output of 10,000 t, the wear-resistant cast iron branch of the China Casting Association and ADI Technical Committee have organized 7 heat treatment equipment plants to discuss and put forward various schemes. The requirements for the heat treatment production line are: the production capacity is 10,000 t/ year, the hardness is >56 HRC, the circumference hardness difference is 2%, w (Mo) is > 0.3%, the hardness is 280 ~ 310 HB, the casting quality is 4.3t, and the net weight after processing is 2.4t. Usually these parts have a diameter of 1 200 mm, but as the turbine continues to develop into a larger, more efficient, casting diameter is predicted to reach 3 000 mm. The Mezhan plant has been equipped with the largest isothermal quenching furnace for commercial use, which can handle large castings weighing 7 t, with a diameter of 1 840 mm and a height of 1 430 mm. In addition to planetary gears, 1 500 kW and 3 000 kW transmission gears are also produced by ADI. ADI parts are limited by wall thickness, which is generally less than 25 mm and can be quenched without adding alloying elements. According to the process technology previously mastered, using effective measures to improve the hardenability, the maximum wall thickness that can stably obtain the quenching effect is 150 mm. Through the investigation of ADI manufacturers in China, it can be seen that the progress of ADI production technology in China is: (1) CADI grinding ball has made great progress;

(2) The application of heavy truck chassis parts has gradually expanded, and the output has increased year by year. With the implementation of the lightweight policy of transportation equipment, it is possible to become a new growth point of ADI output in China;

(3) ADI (CADI) in the application of anti-wear wear parts to achieve burst;

(4) The establishment of the isothermal quenching heat treatment center, made a great contribution to the development of ADI in our country, in the case of fierce competition in the market, stable quality and reasonable price of heat treatment equipment, and again become a concern;

(5) The improvement of the quality of raw and auxiliary materials used in the production of ductile iron and the improvement of the blank quality of ductile iron have boosted confidence in the re-use of ADI for gear wheels, crankshafts and other parts. Although ADI production technology in China has made great progress, there are also problems of poor quality stability and consistency, which need to be solved urgently.

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