| High chromium cast irons (HCCI), as an excellent wear-resistant materials material, are commonly used for wear resistant applications in the mining, cement and other industries. However, conventional casting techniques produce structures containing coarse metal matrix grains and carbides, which cause the properties such as strength and toughness drops. As a result, conventional cast not only cannot make full use of its outstanding wear resistance, but also difficult to meet the requirements in harsh conditions. Presently, a sintered hypoeutectic high chromium cast iron (SHCCI) with fine and uniform microstructures was fabricated by powder metallurgy (PM) technology with air/water atomized powders as raw materials.Firstly, the influence of the sintering process itself on microstructure and properties, were studied systematically, and compared with an as-cast high chromium cast iron (CHCCI) with the same composition. The results show that, different atomizing media has a great impact on morphology, microstructure and sintering properties of powders. The sintering window of air and water atomized powders are respectively 1230??1270? and 1205??1254?. The phase of SHCCI are mainly M7C3-type carbides, martensite and residual austenite, and the carbides are uniformly distributed in the matrix. As the sintering temperature rises, the increase of liquid phase cause the densification process of SHCCI rapidly progressive before slow down, grain and carbide gradually grow up. The maximum sintered density of SHCCI was fabricated with air or water atomized powders is 7.63g/cm2, and the maximum hardness respectively HRC 63.0 and HRC 64.5. With the dramatical improvement of microstructure, SHCCI presented evident advantages of bending strength and impact toughness compared with CHCCI. The best sintering temperature of air atomized powders is 1245?, the impact toughness and bending strength are respectively 7.8J/cm2 and 2365MPa, and the best sintering temperature of water atomized powders under 1210? were reached respectively 6.4J/cm2 and 2110MPa. Nevertheless, for CHCCI it accounted for 7.8J/cm2 and 2365MPa of the impact toughness and bending strength respectively.Secondly, the quenching temperature and tempering temperature on microstructure and mechanical properties of SHCCI were studied. With the quenching temperature, the secondary carbides showed first precipitation then dissolved, the primary carbides in aggregation and growth, spheroidizing, and grains has no obvious grow. Martensite lath size grew gradually and the amount of retained austenite increased. The hardness of SHCCI present growth rose at the beginning then dropped later, and obtained a peak 66.5HRC. The maximum impact toughness and bending strength were achieved at 950?, respectively 6.4J/cm2 and 2110MPa, and the impact toughness and bending strength significantly decreased above 950?.And then, with the tempering temperature increasing, quenched SHCCI gradually formed a mixed structure composed of a phase and secondary carbides, and secondary carbides grow and coarsening. Close to the eutectoid temperature, SHCCI formed eutectoid structure. The hardness rises sharply at first and then slowly increased accompany the tempering temperature rising. The maximum hardness is 62HRC at 450?. The maximum impact toughness and bending strength were obtained at 250?, respectively 8.0J/cm2 and 2452MPa.Finally, the impact abrasive wear resistance and mechanisms obtained from the impact abrasive wear experiment, and compared with an as-cast high chromium cast iron (CHCCI) with the same composition. In the low impact energy state, the higher proportion is short cutting wear. The increase of impact energy lead to the fatigue spalling wear intensifies or even brittle fracture, but the fatigue spalling wear is the main cause of weight loss during the process of impact wear. Compared to CHCCI, SHCCI obtain a favorable match between hardness and strength and toughness so that it has a more excellent impact abrasive wear resistance. |
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