Study On Process Of Vanadizing In Salt-Bath Of Borax

Moulds are important equipments in mass production of all kinds of product in modern industry. The quality of moulds is a key factor which influences the quality of products. As the development of the industry, the requirement of the performance of moulds becomes higher and higher. The mechanical properties and service life of moulds can be improved largely by appropriate application of the surface strengthening technique.Salt bath vanadinzing belongs to salt bath surface alloying by TD(thermail diffusion) process. The process has been given more and more attention since it was put forward by Japanese Toyota research center. The process has become a mature technology and been widely used in the field of cold working die surface hardening. The bonding strength of the coating formed by this process is also much higher than which formed by PVD or CVD process. The coating formed by this process is very stable at room temperature and shows excellent wear resistance. But this method has some limitations such as the very short service life, hard corrosion of salt bath, large deformation of work piece and bad surface finish. So this process has not been used widely in China.In this dissertation, the initial behavior, growth course and microstructure has been systematically studied by SEM/EDS on the base of successful development of device with industrial value for TD process and technology. The micro—hardness of cross—section was determined by Victor hardness tester. Abrasion resistance of vanadium carbide coating was tested by MM200abrasion tester. The salt bath with the rare earth content of0.3%,0.8%,1.3%,1.8%wt had been observed on the influence of TD process.The coating formed by TD method has many advantages, such as compact coating, uniform thickness, very high hardness, good bonding strength.At the same time, through to the traditional salt bath equipment improvement. The control accuracy of salt bath equipment has been raised. The service life of salt bath equipment has been lengthened. Energy consumption has been down.By studying the effects of rare earth on vanadizing technology and microstructure of coating, the conclusions can be drawn that there is an optimal addition amount of rare earth. Moreover, the addition of rare earth can decrease the size of grain. In this dissertation, some main problems concerning TD vanadizing process were solved by theoretical and experiment study. It paves the way from a technique in laboratory to application of this surface strengthening method in industry.