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The cavitation erosion-corrosion behaviour of CrMnB overlay was investigated in comparison with 0Cr13Ni5Mo stainless steel in 0.5 M NaCl and 0.5 M HCl solutions by using a magnetostrictive-induced cavitation facility. The micrographs of damaged surfaces were observed by scanning electron microscope (SEM), and the polarization curves were measured under quiescent and cavitating condition. The results showed that the cavitation erosion-corrosion resistance of CrMnB overlay was 14 times higher than that of 0Cr13Ni5Mo steel in NaCl solution, but, the cavitation erosion-corrosion resistance was 5.7 times lower in HCl solution. For CrMnB overlay in NaCl solution, the excellent cavitation erosion-corrosion resistance could be attributed to strain-induced martensite transformation and its "skeleton" structure of borides. For CrMnB overlay in HCl solution, the electrochemical dissolution promoted the borides to drop out. The martensite transformation was retarded by cushion effect of H(2) gas. Material removal in massive chunks (independent on the microstructural features) was accelerated by connection of cavitation cracks, which was enhanced by hydrogen embrittlement. These results suggested that developing steels with high martensite transformability and boride strengthening is an important method to design coatings or steels used in neutral cavitation environments, but which is not suitable for acidic environments. (C) 2008 Elsevier Ltd. All rights reserved.