| 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 home.To solve these problems, the theories concerning to TD method and some former experience were deduced at first. Recipe of salt-bath, the selection of mould substrate, integrative treating of the work piece were observed for Seeking a simple, stable and effective surface strengthening process suitable for cold work die.Theories concerning the probability and the velocity of coating reaction were studied in the first part of this paper. The salt-bath with the borax content of 25,35,45 and 55 wt. pct. had been observed on the capability of coating and the advantage of cleaning up. The result shows that the salt-bath containing 45% borax performs well in integrative properties. On the basic of former experiment, a series of carbon steels containing 02 to 1.7 wt. pet C was examined on the relation between carbon content of substrate and attainable coating thickness. The relations between carbon content and velocity, thickness and time of treating were educed.The crystal lattice and element of coating were observed by XRD, XRF, SEM, EPMA and Victor hardness tester. The result reveals that the coating is made up of VC. The experiment examining the technologic parameter of Crl2MoV coating process was scheduled by optimization method. And the influence of each technologic parameterto coating process was examined by corresponding analytical method. Finally, experiment study of TD-QT integrative process on Crl2MoV precision press ram was carried out. Compact and uniform coating, expectant thickness, good surface finish and high hardness of substrate were obtained.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. And this process is without social effects of pollution. The application of TD method on cold work die and other kind of parts takes great effects, and it works well on low-temperature hot work die. So, the application of this method will carry out many benefits.In this paper, some main problems concerning TD vanadising process were solved by theoretical and experiment study. It paves the way from a technique in lab. to application of this surface strengthening method in industry.
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