Laser-fabricated Fe-Ni-Co-Cr-B austenitic alloy on steels. Part II. Corrosion behaviour and corrosion-erosion synergism

A cobalt-containing hardfacing alloy NiCoCrB (Ni-17.1% Co-19.6% Cr-14.5% Fe-3.5% B-1% C-0.9% Si) was surface-alloyed on mild steel AISI 1050 and stainless steel AISI 316L as presented in Part I, together with their microstructures and cavitation erosion behaviour in deionised water. In Part II, the corrosion and cavitation erosion-corrosion behaviour in 3.5% NaCl at 23°C was studied with a potentiodynamic polarisation technique and ultrasonic vibration tester, respectively. The corrosion resistance of mild steel 1050 was somewhat increased, owing to the presence of Cr in the alloyed layer, while that of stainless steel 316L decreased, due to the presence of borides and boro-carbides which weakened the passive film. The cavitation erosion-corrosion resistance Recin 3.5% NaCl was improved by a factor of 8.3 and 9.9 for 1050 316L, respectively. Corrosion and erosion-corrosion synergism played a significant role in the overall cavitation erosion-corrosion resistance, leading to a drop in resistance of approximately 50-70% for laser-alloyed 1050 specimens and approximately 20% in the case of laser-alloyed 316L specimens. Thus, it might be concluded that it is difficult to simultaneously achieve significant improvements in both erosion and corrosion resistance.