Growth Mechanism Of Chromizing Coatings By TD

In order to investigate the coating thickness variation on TD treatment time and TD treatment temperature,and the growth mechanism of chromizing coatings,the TD salt bath chromizing and chromboridizing experiments were carried out on 5Cr Ni Mo alloy steels at 1173,1223 and 1273 K for 0~6 h,respectively.The phase of the coating was analyzed by XRD and the morphology of the coating was observed by SEM-EDS.The results show that the chromizing coating consists of M7C3 and Cr7C3,and the chromizing coating is dense and well bonded to the substrate.When the TD treatment time is greater than 1 h,the chromizing coating thickness,TD treatment temperature and TD treatment time follow the parabolic law: (92=5743exp(-18492/T)t,and the diffusion activation energy is 154.3 k J/mol.According to the chromizing coating thickness variation relationship with TD treatment time and TD treatment temperature,the contour diagram of chromizing coating thickness for 5Cr Ni Mo alloy steel in salt bath is drawn,which is convenient for predicting the coating thickness in actual production.According to the unsteady state diffusion theory and regular solution sub-lattice theory,the theoretical solution of the mathematical model of the chromizing coating thickness is obtained L2=4570exp(-17185/T)t.When the TD treatment time is greater than 1 h,the chromboridizing coating thickness,TD treatment temperature and TD treatment time follow the parabolic law: (92=8909.1exp(-21550/T)t,and the diffusion activation energy is 179.2 k J/mol.Under the same conditions,the thickness of chromboridizing layer is much thicker than that of chromizing coating.