Microstructure And Properties Of Laser Repair Layer For Coal-winning Machine Framework

With the development of coal-mining industry, coal mining machine and spare parts are always in extremely complex and demanding working conditions, a lot of equipments are scrapped as corrosion or abrasion, especially the wear failure. Low alloy wear resistant cast steel materials applied to coal-winning machine framework (as ZG30Mn2), the existence of many casting defects, accelerated the failure process of the framework. In order to improve its service life, the vulnerable places need to be repaired and reinforced. Cladding technology and thermal spray technology are important ways to improve surface properties of parts. Laser cladding technology can get high-performance alloy coatings, with good industrial application prospect. In the subject, the process and organization of coal-winning machine framework laser cladding were being researched.The microstructures of cladding layer are observed by OP, SEM, EDS and the micro-hardness tester was used for hardness analysis. According to the cladding alloy forming, porosity and crack technology test and laser process parameters optimization test results, Fe308、Fe313、 Fe45、Ni26、Ni35 alloy and ZG30Mn2 can achieve a good metallurgical bonding, the optimized laser parameters is P=2.5～4.0kW, v=2.5mm/s～ 4.5mm/s; Fe55、Fe60、Ni55、Ni60 alloy with ZG30Mn2 effect generally tend to be larger and cladding layer crack, P=3.0～3.8kW, v=2.5mm/s-3.5mm/s; Fe316 alloy and Co base alloy are hardly combined with ZG30Mn2, to keep the close union of cladding layer and substrate, meet the requirements of different working conditions, appropriate process parameters of laser cladding and alloy transition layer are needed, and adjust the cladding material composition; containing WC cladding layer hardness, crack tendency was also significantly increased, to improve the laser power or lower scanning speed and comply with preheating; cladding layer hardness value between 320 HV to 600 HV, and can satisfy the requirement of coal winning machine frame on wear resistance.Laser cladding alloy fused cold process is fast, a lot of nucleation in liquid metal crystallization, in areas of solid-liquid interface is a very narrow form a layer of planar fine grain area, because of the positive growth of a rapidly towards, grow up to become a priority cellular crystal and perpendicular to the interface, the cellular crystal growth, generate numbers of dendrites, formed the primary phase has a certain direction and dendrites close cladding layer microstructure characteristics of the mixture, the cellular crystal growth and branch out to other components of the epitaxial is preserved in eutectic organization or solid solution form.Ni60+WC compound alloy cladding layer microstructure morphology, there were significant differences in different thermal cycling effect, when Fe308 alloy transition layer have a preheating effect on Ni60+WC compound alloy, Ni base alloy layer in a large number of forms of lamellar eutectic organization and irregular mass alloy compounds, multi-element alloy boride, Cr-C alloy compounds, improve the wear resistance of cladding layer at the same time, as a precipitate eutectic organization formed between the trunk and eutectic organization potential "micro-crack source" and "crack channel", reduce the anti-cracking performance of cladding alloy layer.In the process of laser cladding repair of coal winning machine framework, cast steel substrate layer of loose, holes, and micro crack defect, will increase the cracking tendency of cladding layer, to choose appropriate methods to reduce the effects of substrate defect on cladding layer quality. Through the test of the micro-hardness of different cladding organization, the characteristics of the microstructure, morphology of crack, crack propagation path, to analysis the mechanism of laser cladding layer crack briefly. Discuss the cladding alloy composition, process parameters of laser cladding, constraint form, transition layer, and preheating treatment on the influence law of cladding layer cracking. Cladding layer crack control measures are put forward, as the coal-winning machine framework provide experiment basis for the establishment of laser cladding repairing process. Promote the laser cladding technology to the cast steel structure repair production.