Avaliação da microestrutura, macroestrutura e microdureza ao adicionar carboneto de boro (B4C) em ligas Fe-Mn-Cr-Si

Abstract

The cavitation mass loss of the turbine blades is a phenomenon that occurs in the most of the hydroelectric plants. The cavitation appears when the liquid form a difference of pressure along the blades which bump against the metallic surface, releasing energy and promoting the mass loss of the components’ surface. The best way to control the erosion is keep it under control, being carried out through the replacement of the eroded material. The main problem regarding the replacement of the eroded material is the elaboration of resistant alloys to this phenomenon. The chemical element boron, when deposited on metallic surfaces provides an increase of the mechanical and cavitation resistance. Thus, this paper has as a goal to determine an ideal amount of composite B4C to elevate the resistance to cavitation of the surfaces subjects to this phenomenon. The methodology applied in this research is classified as a methodology of experimental feature. An alloy Fe-Mn-Cr-Si with additions of B4C was chosen to the analysis, being placed by the plasma process PTA in austenitic stainless steel plates ABNT 304 with composition 0,08%C, 2%Mn, 0,75%Si, 0,045%P, 0,03%S, 19%Cr, 9%Ni and 0,10%N. The percentage of the composite B4C in each alloy varied between 10 and 20% in weight. The welding velocity was varied to verify the influence of the dilution in the macrostructure and microstructure of the deposited alloys and it was verified that the velocity influenced significantly the microstructure of the alloys. It can be concluded that the composite B4C when deposited in the alloys Fe-Mn-Cr-Si present a phase in the form of needles or blocks riches in Iron-Boron. These needles are responsible to the microhardness increase of the materials. Thus, the ideal amount of the composite B4C must be determined accurately to increase the efficiency way the resistance to cavitation of the surfaces subjects to this phenomenon.