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In order to reveal the microstructure transformation mechanism of the process of depositing dissimilar material on the surface of mold steel containing Cr, the 316L stainless steel was deposited on two kinds of mold steel. The microstructure and hardness were characterized by SEM, EPMA, XRD etc, moreover, the mechanism of microstructure transformation in the interface and deposition zone was analyzed by the combination of melting-solidification dynamic process and Schaeffler diagram. The results show that the microstructure near the deposition interface shows obviously different characters due to the difference of matrix element composition and phase distribution. The thickness of transition zone of high Cr ledeburite steel is 200 μm, the transition zone is obviously different from other areas of the deposition layer in terms of its morphology and phase; the carbides in the transition zone undergo complex changes, such as local aggregation and growth at first, and then uniform distribution among dendrites. However, the thickness of microstructure transition zone of the deposition layer in P20 steel is less than 20 μm, the microstructure grows in the form of dendrite and is connected with the non transition zone of the deposition layer, meanwhile, dispersed granular carbides are found in the dendrites. Under the action of the dynamic changes of C, Cr, Ni and other elements in the molten pool, the composition phase of the non transition zone in the two kinds of steel deposition layers is also obviously different;the matrix phases of deposition layers in high Cr ledeburite steel and P20 steel are austenite phase and martensite phase respectively, as a result, the range of hardness variation is 295-325HV0.2 and 500-575HV0.2,respectively.