| Wear resistance of high manganese steels are commonly used in the manufacture of iMPAct abrasion wear parts because of its special work hardening properties. High manganese steels are widely used in mining industry, its abrasion resistance is poor in low stress and without work hardening. Conventional hard particle reinforced Fe-based coating can significantly improve the wear resistance of high manganese steel under low stress, but it is easy to form cracks under high stress and abrasive wearing. This paper presents the plasma cladding nickel-based alloy surface strengthening technology is one of the best methods to improve the performance and life of high manganese steels. Plasma cladding processing is a fast cooling and heating process, plasma cladding nickel-based alloy on the high manganese steel surface is a nonequilibrium solidification process. Improper process controling is easy to cause excessive stress which will result in the cracks of the coating, meanwhile, it is difficult to use the method of experiment to measure the temperature field and stress field of the process. In this paper, ANSYS software analysis method was used in plasma cladding nickel-based alloy on surface of the high manganese steel. By combining the numerical simulation and experimental methods, the process of plasma cladding temperature field and stress field distribution and parameters optimization of the cladding were explored. The nickel-based alloy coating organization and phase composition of forming condition, hardness, friction and wear properties and the mechanism of cracks forming were analyzed, in order to provide experimental and theoretical basis on the preparation and application of high manganese steel surface plasma cladding wear-resistant strong toughness nickel-based alloy coating.Using ANSYS finite element analysis software, sending nickel-based alloy powder plasma cladding mathematical model was set up by combining the actual machining condition. The different process parameters and the influence of the substrate preheating temperature on the temperature fields were analyzed. The results show that changing the cladding process parameters, the highest temperature of nodes in temperature fields and the size of the molten pool, dilution rate will change accordingly. The substrate preheating temperature can also affect of temperature and cracks formation and a proper cladding parameters are shown below:plasma arc power P=2.0kw, plasma arc scanning speed V=150mm/min, arc radius R=4mm, preheating temperature T=250℃.The temperature field distribution, temperature-time curve and temperature gradient of nodes in the cladding layer as well as substrate preheating temperature on the influence of the temperature field were analyzed. Nodes in the cladding layer shown fast cooling after rapid heating up. On both ends of the cladding layer the node highest temperature were higher than the intermediate nodes, which presents a phenomenon of "end effect". Cladding process produces enormous temperature gradient, up to 105℃/m, and the solidification cooling rate shows 4000℃/s, which tend to form small grains. The preheating process can improve nodes highest temperature, as the preheating temperature increase, the node temperature gradient and cooling rate present decline.Based on temperature field simulation results, the plasma cladding stress field was investigated. The results show that:the location of biggest stress value is the bonding area of cladding and substrate which is near the molten pool, where is a high incidence zone of forming cracks. After the sample cooling down, the residual stress in the cladding is about 235 MPA, and the maximum tensile stress presents along the plasma arc scan direction, which is 225 MPA. Cladding layer internal nodes show tensile stress and most residual stress are thermal stress, which tends to form transverse cracks. Cladding layer cracks caused by thermal strain and plastic strain, most residual stress in the cladding layer is thermal stress. In the X direction shows tensile stress, however, in Y, Z direction the resultant force presents compressive stress. Plastic strain of cladding processing along the scanning direction shows the maximum positive value, making the materials producing plastic deformation of elongation. It is the reason that the transverse cracks often appear in the cladding layer after cooling process.The effect of the cracks and stress field on different substrate preheating temperature were studied through experimental observation. The results show that:Stress distributions under different substrate preheating temperature vary markedly and when preheat to 250 ℃ the stress concentration phenomenon in the cladding layer and the surrounding area eliminate. Experimental observation discovery that cladding layer surface appears obvious macroscopic cracks under 20℃ substrate temperature, and micro cracks show after preheating to 150℃. When the preheating temperature rise to 250 ℃, the cladding layer do not form cracks. Analysis of the reason is that with the substrate temperature rising, the temperature gradient reducing by 104℃/m and cooling rate reducing a lot.Experimentally measured the molten pool sizes and cladding layer nodes residual stress values, respectively coMPAred with the molten pool sizes and node stress values ANSYS software simulated, so as to validate the accuracy of the established model. Cladding layer hardness, friction and wear resistance were investigated. The studies show that:cladding layer organization from top to bottom respectively are fine isometric, dendrites and cellular crystal. In the solidification process, carbide precipitation and intermetallic compound diffuse distribution, making second phase strengthening. The hardness of cladding layer is about 900 HV, growing six times to the hardness of substrate material. The width and depth of grinding crack are about a third of the substrate and the abrasion loss of the substrate is 58 times than the cladding layer. It is obvious that cladding processing has refined the grain and improved the hardness, wear resistance of the specimen. |
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