Study On Gray Iron Surface Alloyed By Pressureless Infiltration

Infiltration process is widely used in surface hardening because of their good combination of low cost, short production cycle, as well as wear resistance and corrosion resistant. To date, it is currently used more pressure infiltration, the process due to the effect of negative pressure, the exhaust is good,not easy to produce blowhole defects, can not make the prefabricating alloyed layer adhesive strength, there is no porosity, slag hole binder decomposition caused by defects. But pressure infiltration process is narrowly used in industry because it needs special equipment and suitable casting is rarely used in process of casting production. Most of the casting is produced by pressureless infiltration process. Therefore, to solve the key technical problems under pressureless infiltration process is significant. Coating layer is asked to have sufficient strength, binder must be used in pressureless infiltration process. While, the binder produces pores and slag hole. Therefore, reducing the number of pores and slag hole is a pressing problem on condition that the strength of coating layer is enough.The effects of particle size of high carbon ferrochrome powder and coating thickness on quality of infiltrated layer were discussed. The samples with good infiltrated layer were prepared by pressureless infiltration process and the microstructure and composition of infiltrated layer were investigated. And the wear performance of samples was tested.In this study, the effects of bond strength and gas evolution of four typic binder (water glass, aluminum dihydrogen phosphate, polyvinyl alcohol and polyvinyl butyral) on quality of surface alloying were investigated. Compared to aluminum dihydrogen phosphate, polyvinyl alcohol and polyvinyl butyral, water glass is the most suitable for pressureless infiltration process in this study. When water glass content is 7 wt.%, infiltrated layer thickness is 5 mm. The effects of particle size of high carbon ferrochrome powder and coating thickness on infiltrated layer thickness were investigated. While, high carbon ferrochrome powder of 100 mesh size, coating layer thickness of 4 mm is the optimal parameter.Material properties and performance were investigated by Optical Microscope, Field-emission scanning electron microscopy, X-ray diffractometer, Energy-dispersive X-ray spectrometer and Vickers hardness testing machine. There are three obvious different zones and the differences in microstructure and composition of above zones is attributed to the diffusion between high carbon ferrochrome powder and liquid metal. While, the effects of coating thickness on microstructure of infiltrated layer and three-body abrasive wear behaviour were investigated. It indicates that the larger coating thickness, the greater hardness and wear resistance. For infiltrated layer thickness is 5 mm, the surface hardness of composite achieves 840 HV and the wear performance of composite is one time that of gray iron.