| This paper is a second part of the study on the effects of processing parameters on characteristics of the laser surface alloyed chromium carbide layer on the stainless steel. This Part II correlates surface properties (hardness, erosion and corrosion) with microstructures of alloyed layer. Further, a possible operation mechanism in particle erosion of the substrate and alloyed layer is also proposed based on the observation of erroded surface. Microstructures of the laser alloyed layer consisted of three different layers. In the layer I , adjacent to the bond line, applied Cr₃C₂ completely dissolved and mixed with the melted substrate and formed C saturated austenite matrix and carbides (Cr_7C₃ and Cr_(23)C_6) along dendrite boundaries during rapid cooling. In the layer II which is a mid-region of the alloyed layer, Cr₃C₂ also dissolved but did not appear to mix with the substrate completely, and transformed as metastable phase of M₃C₂ during cooling, In the layer III near surface, some of the Cr₃C₂ were not dissolved and embedded in the C, Fe enriched austenitic solid solution. Erosion and Cl^- corrosion resistance of the laser alloyed layer was found to be far superior to that of martensitic strainless steel substrate and plasma coating. Small amount of pores in the Layer III did not influence on the pitting corrosion resistance. |
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