The effect of post-heat treatment on the microstructure and microhardness of laser cladded high Co-Ni secondary hardening steel coating was investigated. The microstructure of the coating was analyzed using a scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS), and the microhardness was measured with a Vickers indenter. Decomposition of the retained austenite in the coating occurred during the post-heat treatment. As the temperature increased from 200 ℃ to 600 ℃, the quantity of the retained austenite at the boundaries decreased significantly, while that of the needleshaped M₃C cementite and M₂C carbides increased. The M₂C carbides evidently coarsened when the temperature was 550 ℃ and 600 ℃. The microhardness of high Co-Ni steel coating increased as the temperature of heat treatment increased from 200 ℃ to 400 ℃ because the fine-scale M₂C carbides were coherent with the matrix and increased distinctly in this temperature range. While the microhardness decreased sharply when the temperature was improved from 500 ℃ to 600 ℃ due to both the incoherency of the coarsened M₂C carbides and the recovery of dislocations in the carbon-supersaturated matrix.

heat treatment  /  laser cladding  /  high Co-Ni steel  /  coating  /  microhardness