Study On Thermal Diffusion On Cold Extrusion Die

The rapid development of the national economy made mould industry rising demand,prompt mould techonology rapid development,mould is the important instrument to the each product of industrial and domestic,mould have become a very important industry. Since the beginning of the 1980s, the development of china's mould industry is very rapid. Over the past 20 years, Output of mould industry grow at an annual rate of around 15%.China's mould industrial output value in 2000 reached 28 billion yuan.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 and economic benefits of products. As the development of the industry, the requirement of the performance of moulds becomes higher and higher. The mechanical properties and the service life of moulds can be improved largely by appropriate application of the surface strengthening technique. Thus the surface strengthening technique plays a very important role in the mould industry, and attracts widely attentions.Salt-bath vanadising by TD method(thermal diffusion) belongs to the TD method. The coating formed by this process is very stable at room temperature. The coating shows good wear property. And high service life obtained in applying to cold work die.The bonding strength of the coating formed by this process is also much higher than which formed by PVD or CVD process. 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 at china.Theories concerning the probability and the velocity of coating reaction were studied in this paper. On the basis of conclusion of previous experiment that mixed salt bath vanadinizing to the cold die, use the acid borax salt of bath in the TD process to several typical cold steel, compared the thickness ,hardness and other parameters that the same steel use the mixed salt of bath and the acid borax salt of bath,analysis the components of the salt of bath's impact to the coating's hardness andthickness.The steel used in this experiment incloudCrl2MnV, TICK CrWMru 6W6Mo5Cr4V. Use the acid borax salt of bath in this experiment. The aim is research the relation between coating thickness and carbon content and holding time. 6W6Mo5Cr4V is Low -carbon alloyed steel,theelment W, Mo, V is Strong carbide, these elments will Influence coating's growth. So use the process carbonization to part of 6W6Mo5Cr4V Research the coating's thickness and hardness between the 6W6Mo5Cr4V have used theprocess carbonization and no by the acid borax salt of bath.Use the SEM observe the metallographic,Use the Micro sclerometer measure the hardness of the coating. Use the electron probe micro-analysis(EMPA) analysis the element and content.The coating formed by TD method has many advantages, such as compact coating, uniform thickness, very high hardness, good bonding strength and power saving property. This technology has obtained the anticipated target in the experimental stage.