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Application of Nano SiC in Large Diameter CADI Casting Ball

YAO Yong-mao 1 ZHANG Fen-hong 1, HUANG Yong 1, CHEN Quan-xin 2, GUI Jinsong 1, CHEN Can-guang 2

1 Hefei Keln Nano Energy Technology Co., Ltd. 2 Ningguo Huafeng Wear-resistant Material Co., Ltd.


  Abstract: Nano-SiC powder is a hard spot, its stability is good, the melting point is higher. When added to the CADI melt, the SiC powder as a heterogeneous heterogeneous nucleation, an increase of the graphite core, cast ball heart of the number of graphite ball increased by 12-29%, to promote the graphite ball refinement, graphite ball diameter can be reduced 11.2% or more, the impact value increased by 18.76%.

  Ductile iron isothermal quenching heat treatment, the microstructure is: acicular ferrite + carbon austenite + graphite ball mixed organization, known as isothermal ductile iron (Austempered Ductile Iron, referred to as ADI), it is this unique Of the microstructure, so that isothermal quenching ductile iron has excellent comprehensive mechanical properties. Carbidic Austempered Ductile Iron (CADI) is a new type of ductile iron material derived from ADI in recent years. CADI not only inherited the many advantages of ADI, but also show more than ADI wear resistance, more suitable for demanding wear resistance and toughness of the working conditions, wear-resistant materials industry is widely used.

  But the CADI and ADI compared to the hardness has improved significantly, while the toughness has a more substantial reduction, especially for thick sections of the castings, due to slow heart cooling, crystallization time is long, resulting in spheroidization, graphite ball growth, The decrease in the number of graphite balls due to the poor spheroidization caused by the decline of mechanical properties, especially the lack of toughness, seriously affect the application of CADI large diameter cast ball, which is large cross-section ductile iron production in a common problem.

  Ningguo Huafeng wear-resistant materials Co., Ltd. since 2013, oil quenching and other isothermal treatment of CADI casting ball since the main production of φ120 the following CADI cast ball-based, for φ150 above the large diameter CADI cast ball found the heart of the ball recession, Toughness is low, the use of the process prone to crushing phenomenon, in order to solve this technical problems, Hefei Kel and Ningguo Huafeng company, nano-SiC metamorphic technology applied to CADI large diameter CADI cast ball, and achieved initial results.

1, test method

  Using 0.75 tons of intermediate frequency electric furnace smelting, each furnace out of hot metal 800Kg, according to the company Austrian iron cast ball the normal process requirements selection, smelting, spheroidization and breeding, rare earth magnesium nodular addition 1.1%.

  Preparation of nano-SiC: nano-SiC powder and nodular powder mixed with granulation, mixed with the original ballification agent added to the ball pits. Nano content of 0.06%. Spheroidized molten iron directly cast products φ80 balls and φ150 test ball. Heat treatment is carried out in the heat treatment line with normal products. The sample is sampled from the center using a wire cut from the center of the cast ball, and the impact test specimen is cut from the center of the cast ball to detect the spheroidized state and mechanical properties of the core.

2, detection and analysis

2.1 Chemical composition

  Due to test more furnace, the chemical composition can not be exactly the same, within the scope of control fluctuations, chemical composition requirements as shown in Table 1

Table 1 Chemical composition control range


2.2 Spheroid state analysis

 In order to verify the repeated performance of the test data, the same test was carried out three times, each test spherulite state analysis in Table 2, Figure 1.

 Table 2 Analysis of three tests of spheroidization


Fig.1 Comparison of spheroidization parameters of the three centers



From the above three test data analysis, adding nano-mixed nodularizing agent on the φ150 cast ball core graphite ball diameter can be reduced by 4.5-12.4%, increase the number of graphite ball 9-24.5% .Three tests φ150 casting ball heart graphite ball are In more than 300.

2.3 metallographic pictures


2.4 mechanical properties of impact toughness and hardness testing in Table 3

     Table 3 150 core impact strength and hardness


From the test data analysis: φ150 cast ball after adding nano-nodular impact toughness increased by 18.76%, while the hardness change is not.

3, analysis and conclusions

  3.1 Comparison of the graphite morphology with the addition of nano-spherulite can be seen, without adding nano-SiC powder, the casting of the core of the organization of the graphite ball is not rounded, the surrounding crack, was blooming or sharp-like convex , Graphite ball diameter is relatively large, it is because the heart cooling speed is slow, resulting in ball decay and graphite ball distortion. After adding nano-SiC nodularizer, the roundness of the graphite ball is improved and the dispersion is better. The diameter of the graphite ball becomes smaller and the number increases. For the production of large ductile nodular cast iron, the mechanical properties can be improved and improved.

  3.2 nano-SiC powder is a hard spot, its stability is good, high melting point. When added to the ductile iron melt, SiC powder as a heterogeneous heterogeneous nucleation, an increase of graphite core, the number of graphite ball increased by 12-29%, to promote the refinement of graphite ball, graphite ball diameter can be reduced More than 11.2%.