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Research of Wear-resistant and Finite Element Analysis of ADI for Track Rollers

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Tutor: GuoXuHong
School: Suzhou University
Course: Mechanical Manufacturing and Automation
Keywords: ADI,Track rollers,Sliding wear,Impact abrasive wear,ANSYS
CLC: TG156.3
Type: Master's thesis
Year:  2011
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Abstract:
It¡¯s a brand-new attempt that producing the track roller of crawler excavators by austempered ductile iron (ADI). In the open air, track rollers contact with sand and soil directly, the working environment of the track roller is very complex, and the wear is very prominent. The track rollers require excellent mechanical properties and wear resistance. So far it has been few of articles about this application. In this paper, the systematic study of ADI material was carried out by experimental and finite element analysis, thus the feasibility of the production of track roller by ADI was confirmed and the heat treatment process of ADI was obtained for producing the track roller.The ductile cast iron (QT500-7) was austenitized at 900¡æfor 2 h and then austempered for 2 h at three different temperatures: 260¡æ, 310¡æand 360¡æ.Then three different ADI materials of different mechanical properties were obtained. The microstructure was qualitatively and quantitatively analyzed by using optical microscopy (OM), scanning electron microscope (SEM) and X-ray diffraction method (XRD). And the effect of different austempering temperatures on the microscope, composition and mechanical properties was studied.The wear resistance of 50Mn and 3 different ADI materials was investigated by MM-200 wear test machine and MLD-10 impact abrasion tester in the paper. The effect of the hardness, the content of retained austenite on the ADI wear resistance was studied, and the ADI wear mechanism was analyzed by SEM.Contact stress and von Mises stress under the situation of walking and working were investigated based on the study of contact mechanics and the finite element software ANSYS. The feasibility of producing the track roller by ADI is proved with simulation.The results showed that: a) Austempering temperature greatly affects microstructure and mechanical properties. As the austempering temperature increases, microstructure of ADI get coarser and coarser; the amount of residual austenite and its carbon content increases, while the hardness and yield strength decreases. At lower temperature of 260¡æ, the microstructure consisted of very fine ferrite needles with thin layers of austenite between them while the hardness and the yield strength is the largest. At higher austempering temperature of 360¡æ, the microstructure consisted of very coarse and feathery ferrite with relatively large amount of bulky austenite while the hardness and the yield strength is the smallest.b) As the austempering temperature increases, the wear-resistance of ADI materials decreases under dry sliding wear and impact abrasive wear. The wear mechanism of the former is mainly adhesive wear while the latter is mainly the impact plastic deformation wear and micro cutting. The wear resistance of ADI increases while the impact energy increases in the impact abrasive wear tests.c) In the wear process,the work hardening of the surface happens while the retained austenite is transformed to martensite, and the retained austenite can prevent the crack initiation and propagation, so the wear resistance is improved. Under the same wear condition, coarse ausferrite microstructure exhibited higher wear rate than fine ausferrite microstructure.d) ADI material can be used to produce the track roller of crawler excavators by the calculation results of ANSYS, and the edge of the track rollers is easier damaged.e) For the track rollers, in normal conditions, austempering temperature between 260¡æand 310¡æof ADI materials can replace 50Mn material as the material of track rollers, but if working conditions are seriously bad and the impact load is very large, upper bainite ADI material should be considered. The weight of ADI tracker rollers is 10% less than that of 50Mn tracker rollers.
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