The Enhancement Effect of Salt Bath Chromizing for P20 Steel

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.