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Application of yttrium-based REMg spheroidizing agent in wind power castings

Application of yttrium-based REMg spheroidizing agent in wind power castings

(Summary description)

Application of yttrium-based REMg spheroidizing agent in wind power castings


Hu Linghai 1, Dong Chengyu 1, Zhong Weichang 2, Li Chunhong 2, Liu Guanghui 2
(1. FAW Casting Co., Ltd., Changchun, Jilin 130011; 2. Longnan Longyttrium Heavy Rare Earth Technology Co., Ltd., Ganzhou, Jiangxi 341700)

Abstract: The requirements and casting process of the main box of QT400-18AL and the 3 MW planet carrier castings of QT450-10 are introduced, as well as the issues that must be paid attention to in the production of thick ductile iron castings. The test results show that the application of Y basis weight REMg spheroidization It produces large-section wind power ductile iron castings with strong resistance to spheroidization and recession. The mechanical properties of the castings fully meet the material requirements. Analyze the reasons for the anti-spheroidization decline of the Y basis weight REMg nodulizer: ①The heavy RE element has a high boiling point; ②No spheroidization decline caused by the phenomenon of returning S will occur; ③It has strong resistance to graphite distortion; ④Sufficient It takes advantage of the superimposing and compounding effects between RE elements and Mg, Ba, and Ca.

Key words: Y basis weight REMg spheroidizing agent; large section wind power ductile iron castings; resistance to spheroidization decline
Chinese Library Classification Number: TG255 Document Identification Code: B Article Number: 1003-8345 (2012) 01-0033-04
DOI: 10.3969/j.issn.1003-8345.2012.01.006

Application of Y-Base Heavy Rare Earth-Containing REMgFeSi Nodularizing Alloy to Wind-Power Castings

HU Lin-hai1, Dong Cheng-yu1, ZHONG Wei-chang2, LI Chun-hong2, LIU Guang-hui2

(1. First Automotive Foundry Co. Ltd., Changchun 130011, China; 2. Longnan Longyi Rare-earth Material Co. Ltd., Ganzhou 341700, China)

Abstract:Technical r equirements, casting process and the main points of the QT400 -18AL grade nodular iron main case
body and the QT450-10 grade nodular iron planet support was introduced. The test result showed that the heavy section wind
power nodular iron castings produced by using Y -base heavy RE -Mg nodularizer have relatively strong ability to prevent
nodularization degeneration, and all the mechanical properties fully met the material requirements. The reasons why the heavy
RE-Mg nodularizing alloy has strong ability to prevent nodularization fading were analyzed as follows: (a) the heavy rare earth elements have high boiling point; (b) it's impossible to occur that the S returning from the slag to the iron melt would cause nodularization degeneration; (c) the heavy RE has relatively high ability to prevent the nodular graphite degeneration; (d) the mutual complementation effect and combination effect of the RE and Mg, Ba, Ca was fully utilized.

Key words: Y-base heavy RE-Mg-Si-Fe nodularzing alloy; heavy section wind power nodular iron castings; anti-nodularizing
degeneration capacity

In recent years, the large parts workshop of FAW Foundry Co., Ltd. Technology Center has applied Y basis weight REMg nodularizer to produce large-section wind power ductile iron castings. The performance indicators fully meet the material requirements. Below are examples of two castings, the main box body and the 3 MW planet carrier.

Casting products and processes
1.1 Casting and its requirements
Table 1 shows the requirements for the main box casting and planet carrier casting. The outline of the casting is shown in Figure 1.

references
[1] Wei Bing. Balanced solidification technology and application of castings [M]. Beijing: Mechanical Industry Press, 1998: 60.
[2] Huang Liequn, Pan Dongjie, He Zhimei, etc. Sand-coated iron casting and its development [J]. Modern Cast Iron, 2006, (3): 12-14.

[3] He Zhimei, Pan Dongjie, Huang Liequn, etc. Sand-coated iron casting process and equipment for wheel castings[J]. Modern Cast Iron, 2009, (5): 46-49.
(Editor: Wang Feng, E-mail: xdzt_wf@fawfc.com; Editor: Zhou Gen, E-mail: zhougen_embx@163.com)

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1.2 The chemical composition of the original molten iron is smelted by an intermediate frequency electric furnace. The chemical composition of the original molten iron is shown in Table 2.
1.3 Spheroidizing process
The spheroidizing treatment is carried out by the flushing method. (1) Choose Y-based REMg spheroidizing agent DY-4 brand product of Longnan Longyttrium Company, the main chemical components are: w (Y) 2.4%~3.2%, w (Mg) 6%~8%, w (Ca) 2%~3%, w(Si) 43%~45%. (2) Spheroidizing treatment: Add 1.5% of molten iron, 0.4% of Ba-containing high-efficiency inoculant, and 0-0.4% 75SiFe into the bottom pit of the spheroidizing package. , Iron filings cover. The molten iron discharge temperature is 1 460~1 520 ℃ (choose according to the pouring temperature required by different parts). The amount of Cu, Mn, Sn alloy is adjusted in the bag or furnace according to the required amount of each material. (3) The final composition of molten iron after spheroidization is shown in Table 3.
1.4 Pouring temperature and unpacking time
Table 4 shows the pouring temperature and unpacking time.

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2 Results and analysis
2.1 Mechanical properties and metallographic testing Take the attached test block of the cast product for mechanical performance and metallographic testing. The results are shown in Table 5 and Figures 2-5.
2.2 Issues that must be paid special attention to in the production of thick ductile iron castings
(1) Spheroidization decline. The production of thick ductile iron castings adopts furan resin self-hardening sand, which has limited heat dissipation conditions. In addition, the solidification speed and long solidification time of the thick ductile iron castings themselves are very slow, which can easily cause the spheroidization of the castings to decline. Therefore, it is necessary to ensure high-temperature and pure raw iron liquid, and to select a spheroidizing agent with strong resistance to spheroidization and recession. (2) Breeding with the flow. The inoculation of thick ductile iron castings during pouring is very important. If the inoculation is insufficient, the number of graphite balls will decrease, the diameter of the balls will increase, the shape will deteriorate, and even the spheroidization will decline. It is recommended to adopt the inoculation method with bag incubator (see Figure 6), which can easily and reliably ensure the quality of inoculation. The author’s company uses Ba-containing high-efficiency inoculants with a particle size of 0.2~0.7 mm, and the inoculation amount is molten iron

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0.1%~0.15% of the amount. (3) Chemical composition. In order to ensure that the low temperature impact value of QT400-18AL material meets the standard, the content of Si, Mn, P, As, and V in the molten iron must be strictly controlled.

2.3 Reasons for the anti-spheroidization decline of Y basis weight REMg nodulizer
① The heavy RE element in the Y basis weight REMg spheroidizing agent has a high boiling point (3 038 ℃), which is much higher than that of the Ce-based light RE. The vapor pressure generated by adding to the molten iron is only 0.001 atmosphere, and the burning loss is small. 75 min after the spheroidization reaction, the content of heavy RE elements in the molten iron does not decrease. Therefore, in the case of rapid decay of Mg, due to the existence of the total amount of RE, the minimum w (Mg residual) necessary to ensure spheroidization is reduced, and spheroidization decay is avoided. To
②When treating ductile iron with light REMg spheroidizing agent, there is a phenomenon of returning S. This is because the de-S product interacts with O in the air on the surface of the molten iron to release S again, and the released S returns to the molten iron to capture the ball Therefore, S, as a vehicle, continuously circulates and consumes the spheroidizing element in the molten iron, causing the spheroidization of ductile iron to decline. The affinity between heavy RE elements and S is very strong, and it is an irreversible reaction. Therefore, the use of Y basis weight REMg spheroidizing agent basically does not cause the spheroidization to decline due to the phenomenon of returning to S.
③Y basis weight REMg spheroidizing agent has strong anti-graphite distortion ability. There is a certain residual amount of spheroidizing elements in the molten iron, and graphite can be spheroidized; insufficient spheroidizing elements can easily cause poor spheroidization or spheroidization decline. However, the spheroidizing elements are all elements that promote the increase of white mouth. Excessive spheroidizing elements not only make the ductile iron have a large white mouth tendency and more cementite, but also easily produce casting defects such as slag inclusion and subcutaneous pores, and seriously deteriorate the graphite morphology. . In actual production, it has been proved that such problems often occur in the production of ductile iron using light REMg nodulizer. For thick and large section castings and electric furnace thermal insulation molten iron, in order to prevent spheroidization from decay, it is necessary to maintain a relatively high amount of w (Mg residual) or w (RE residual), and because of the slow cooling rate of large castings, spheroidizing elements Segregation is easy to occur, leading to increase in the amount of w (RE) and w (Mg) in the local or central part. The increase of the content of these elements severely deteriorates the graphite morphology, produces graphite distortion, and produces a tendency to white mouth.
The solid solubility of Y in cast iron is greater than that of light RE elements, and the concentration can reach 0.5%. Through electron scanning microscopic analysis, Y forms a Y-Fe metal bond compound with iron in the ductile iron matrix to form a microalloy, and it is impossible to adsorb at the spin outlet of the screw dislocation of the graphite crystal, instead of the interference effect of S and O. . Due to the wide range of Y basis weight RE residues, there is more RE content for attenuation, thus greatly improving its resistance to spheroidization and recession. In addition, if the residual heavy RE in the molten iron does not exceed the solid solubility, it will not cause graphite distortion.


④由于 Y 基重 REMg 球化剂中的 RE 组分除了以重 RE 元素为主(含 Y50%)以外,还包含了其它 RE 元素,同时由于配加了 Mg、Ca、Ba、Si等,并充分利用了 RE 元素间和 Mg、Ba、Ca 之间互为补充的叠加作用及复合作用,使得 Y 基重REMg 球化剂的球化能力强、球化质量高,而且反应平稳。
曾有一段时间,由于熔炼设备生产能力不足,用户又急待供件,不得已只能在相距 500 m以外的另一铸造厂熔炼车间求援铁液,球化处理后经 30 min 运回进行厚大球铁铸件浇注,结果铸件完成达到要求,满足了用户需求, 获得了使用其它球化剂难以想像的效果。 
3 结语Y 基重REMg 球化剂应用于大断面风电球铁铸件生产,具有较强的抗球化衰退能力,铸件的各项力学性能指标完全符合材料要求。
(编辑:王 峰,E-mail:xdzt_wf@fawfc.com;编审:周 亘,E-mail:zhougen_embx@163.com)

 

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