Abstract
The TD (Thermal Diffusion) salt bath process is used to obtain a super hard carbide coating on the material surface by utilizing the mechanism of metal thermal diffusion. In this paper, chromium carbide coating was prepared on P20 hot-pressing die steel by the TD salt bath chromizing process. Characterization of the modified surface layer was made by means of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), a micro-hardness tester and an automatic scratch tester. The influence rules of different salt bath times and temperatures on the growth thickness of the cladding layer were explored through experiments, and the optimum salt bath process scheme was determined as a temperature of 960 °C and time of 6 h. The chromium carbide coating with a thickness similar to that of chromium plating was prepared, and the average thickness of the coating was about 8–10 μm. The results showed that hardness and bonding strength of chromium carbide coating are higher than that of electroplated chromium coating. The combination of chromium carbide coating and matrix is metallurgical, while the electroplated chromium coating is physical. Immersion corrosion test results show that both coatings have good corrosion resistance in a 65% nitric acid solution.
Highlights
Salt bath chromizing is a kind of valuable chemical heat treatment technology that is widely used for steels to obtain the required properties [1,2,3]
Researchers have derived the growth kinetics equation of chromium carbide coating on high chromium steel surface by TD heat treatment, and proposed that the structure of carbide coating is several or one of Cr7 C3, (Cr,Fe)7 C3 and Cr23 C6 ; there is a lack of research on the structure growth process of carbide coating [7]
Another researcher found that sub-micron CrN agglomeration area and CrN nano-crystal agglomeration area exist in the compound obtained by chromizing 20 steel in a low temperature composite salt bath for
Summary
Salt bath chromizing is a kind of valuable chemical heat treatment technology that is widely used for steels to obtain the required properties [1,2,3]. Researchers have derived the growth kinetics equation of chromium carbide coating on high chromium steel surface by TD heat treatment, and proposed that the structure of carbide coating is several or one of Cr7 C3 , (Cr,Fe) C3 and Cr23 C6 ; there is a lack of research on the structure growth process of carbide coating [7] Another researcher found that sub-micron CrN agglomeration area and CrN nano-crystal agglomeration area exist in the compound obtained by chromizing 20 steel in a low temperature composite salt bath for. A TD salt bath chromizing process was developed to solve the problem of insufficient surface performance of the mold and replace the existing polluting chromium plating process, in order to improve the service life of hot-pressing die and comply with the requirements of energy saving, environmental protection and industrial green development. The structure growth process of chromium carbide was analyzed and the improvement of its matrix performance was discussed
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