Structure and properties of strengthening layer on Hardox 450 steel

The microstructure and microhardness distribution in the surface of low-carbon Hardox 450 steel coated with alloyed powder wires of different chemical compositions are studied. It is shown that the microhardness of 6-8 mm-thick surfaced layer exceeds that of base metal by more than two times. The increased mechanical properties of surfaced layer are caused by the submicro and nanoscale dispersed martensite, containing the niobium carbides Nb2C, NbC and iron borides Fe2B. In the bulk plates, a dislocation substructure of the net-like type with scalar dislocation density of 10(11) cm(-2) is observed. The layer surfaced with the wire containing B possesses highest hardness. The possible mechanisms and temperature regimes of niobium and boron carbides in surfacing are discussed.