| Because the liners in wet ball mill for mineral processing industry must bear abrasive wear and corrosive wear, which made expenditure for liners become a major part of production costs. Service life of the liner made from traditional material, such as Hadfield steel, alloyed steel etc., is less than eight months. HCCI(high Cr white cast iron) is the most abrasive resistant material today, which is very suitable for serving in wet ball mill according to its performance and microstructure. But fracture toughness of singular HCCI couldn’t meet requirement of impact wear conditions in ball mill. To overcome the bottleneck, bimetal liner possessing superior properties, which are high hardness, high corrosive wear resistance and reasonable fracture toughness, has been researched and developed in this paper.Several key alloy elements in HCCI and carbon steel have been analyzed and optimized. Microstructure of HCCI has been modified by the complex modifier contains RE, Si, Ca etal.,Several kinds of compound have been generated which have same crystal coherency with M7C3. During solidification, small compound act as crystallization nuclei which make the large sized primary carbides change into smaller rods and blocks, and the hollow eutectic carbides tubes were modified to be solid carbides rods, and the morphology of these carbides was turned to be more regular.The result showed that by adding the complex modifier,the hardness of the HCCI increased slightly, while the impact toughness improved significantly.Systematic research focused on LFC with composing processing has been done:It is feasible that bimetal liner could be well produced by LFC according to couple analysis between thermal field and structure field on ANSYS. The pouring interval of two metals is75s by computation of heat trafer model. Several key process methods have confirmed, which include horizontal pouring without isolated plate, pouring sequence,composite position etal. Sotfware used to LFC with composing process is achieved by C#program and ACCESS database, which improve the efficiency of processing design signally.④Foam pattern have been made ultilizing three dimensional CAD/CAM technology. Pouring has been finished at three different intervals after coating, vibrating and molding. Bimetal liner, made from HCCI and carbon steel, has been produced successfully by lost foam casting with liquid-liquid composing processThe Microstructure and interface of composite were analyzed with optical microscope, SEM, EDX and XRD. According to micrograph:the typical as-cast microstructure of HCCI layer is hypoeutectic and consist of eutectic carbides in a mainly austenitic matrix, the typical as-cast microstructure of carbon steel layer is hypoeutectoid, it is composed of ferrite and pearlite. After the destabilization heat treatment, the secondary carbide precipitation has contributed to change the microstructure from an austenitic matrix to a mainly martensitic one with some retained austenite. Moreover, the newly formed matrix has been reinforced with secondary carbides of the type M7C3. The boundary of bimetal combination regions was staggered like dogtooth, two liquid metals were not mixed and the interface presented excellent metallurgical bonding state. Comprehensive mechanical property were studied, the results show that:the hardness of HRC>61, the fracture toughness ak>16.5J/cm2, and bending strength>1600MPa.Finally,Wear resistant comparison between liners made from bimetal composite and alloyed steel was made in industrial hematite ball mill of WISCO, the results of eight months test in wet grinding environment prove that the service life of bimetal composite liner is three times as long as that of one made from alloyed steel. |
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