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The microstructure and pitting performance of high-carbon martensitic stainless steel (HMSS) samples, which were produced via laser cladding (LC) and hot isostatic pressing (HIP) were comparatively investigated via electrochemical measurements and electron microscopies. Dendritic and network connected M23C6 carbides are the main precipitates in the HMSS coating, while the M23C6 carbides in HMSS bulk are spherical or elongated in shape. Pitting resistance of the HMSS coating is dramatically deteriorated. The Cr-depleted region induced by the Cr-enriched and dendritic M23C6 carbides are considered as underlying factor for the “LOP” effect of the HMSS coating.

Recently, laser cladding (LC) technology has become a cost-effective and convenient method to protect metal substrate from corrosion by producing metal coating with high corrosion resistance. In order to fully investigate the pitting mechanism for high-carbon martensitic stainless steel (HMSS) coating, the microstructure and pitting performance of HMSS samples produced via LC and hot isostatic pressing were comparatively investigated via electrochemical measurements and electron microscopies. Dendritic and network connected M23C6 carbides are the main precipitates in the HMSS coating, while the M23C6 carbides in HMSS bulk are spherical or elongated in shape. Pitting resistance of the HMSS coating is dramatically deteriorated. The massive and continuously distributed dendritic M23C6 carbides could form a large-area cathode and cause the micro-galvanic corrosion of the HMSS-LC coating matrix, thus can be considered as underlying factor for the “loss of passivation” effect of the HMSS coating.

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