FORMATION OF WEAR-RESISTANT WELD SURFACE LAYERS

The protective coating on low-alloy steels Hardox 400 has been welded by electric arc method using the fl ux cored wire SK A 70-G. Such coating works effectively in conditions of strong abrasive wear and shock loads and is used in various industries. Chemical and phase composition and defect substructure condition of the coatings has been investigated using scanning electron microscopy with EDA-technique and x-ray phase analysis. The coatings can be divided in three layers by morphological features. The surface layer with the thickness of 3.5 mm has the property cellular structure crystallization and can be characterized by the presence of faceted particles enriched in niobium. The intermediate layer (0.4 mm) has the structure of an islet type. Transition layer (to 0.02 mm) adjacent to the interface with the substrate, is characterized by columnar and dendritic structure. Heat-affected zone has a total thickness of 4 mm. It has been established that the wear resistance of the coatings is in 2.3 times higher than of the substrate. This is due to the formation of the submicrodimensional structure of crystallization, the release of large amounts of high strength particles of hardening phases and forming a martensitic structure of the α-phase of the coating. The reinforcing phases are Fe3C, the volume fraction of which is 10 %, the carbides of niobium and chromium NbC and Cr3C2 , with total volume fraction of 20 %, and iron boride Fe3B, with volume fraction of 10 %.

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