Structural anomalous zones in the coating arc-deposited by powder tape ПЛ АН-111

The article describes the microstructure features of wear-resistant 500Cr40Ni40Si2Zr alloy, which was obtained by electric arc surfacing with the use of ПЛ АН-111 powder strip. The coating was arc-weld deposited in two layers deposited with 50% bead overlapping. The methods of investigation include optical and electron scanning microscopy, energy-dispersive spectroscopy, microhardness measurements. It is shown that coating microstructure changes from the «substrate/coating» boundary towards the overlay top. Apart from primary and eutectic carbides M7C3 with hexagonal lattice, austenite (FCC lattice) and graphite some large anomalous features (LAF) were found in the microstructure. LAFs are big roundish carbide-free «white» spots of 120-300 mm in diameter which do not corrode under etching. LAFs lie mostly within the fusion interlayer zone. LAF zone microhardness was measured as 350-455 HV. According to the data of EPMA analyses, the average contents of chromium, nickel and iron in LAF zone are 20,37%, 21,79% and 49,24% respectively. The formation of large anomalous features can be explained by the heterogeneity of the thickness of the steel shell of the tape, which could cause the enrichment of melt with iron in the places of tape thickening. In contact with thick tape the melt was «frozen», which resulted in its crystallization by metastable mechanism to form a supersaturated solid solution without carbides