Development of high strength and ductile martensitic stainless steel coatings with Nb addition fabricated by laser cladding

Abstract

Abstract In the present work, martensitic stainless steel (MSS) coatings with niobium (Nb) contents of 0–1.0 wt%, combining high strength and ductility with improved corrosion resistance, have been developed and fabricated by a laser cladding technique. The effects of Nb-microalloying on the microstructure and properties of the laser-cladded MSS coatings have been carefully investigated. The results show that the original Nb-free MSS coating is mainly composed of martensite and austenite, along with nano-M2N and M23C6. With the addition of Nb, the lath-shaped martensite is refined, and an increasing occurrence of nano-sized Nb-enriched precipitates (NbC and Nb(C,N)) is observed in the coatings with increasing Nb content. With the successive addition of Nb, the microhardness of the specimens is found to increase from the 437 HV0.2 of the Nb-free coating to the 502 HV0.2 of the 1.0 wt% Nb-alloyed coating. At the same time, the tensile mechanical properties and corrosion resistance are found to increase with increasing Nb content of up to 0.5 wt% and subsequently decrease with further addition of Nb. Thus, the addition of 0.5 wt% Nb provides a laser-cladded MSS coating that is superior to those reported in the literature, combining the optimum tensile properties of high strength (1780 MPa) and high ductility (EL = 10.5%) along with excellent corrosion resistance. The remarkable overall properties of the as-prepared MSS coatings can be ascribed to the combined effects of solid solution, microstructural refinement, and nano-precipitation.