| The slurry pumps are suffered from serious erosion-corrosion (E-C) in liquid-solid two-phase flow of zinc hydrometallurgy slurry containing solid particles such as silica , and diluted sulfuric acid as well as the impurities of Cl–,F–,Zn2+,Fe3+ and so on. Especially due to the rapid damages of the impellers, the plant is forced to stop production frequently so as to repair or replace spare parts. It results in decrease of productive efficiency and increase of production cost, together with the huge economic loss. Although many efforts were made such as improving the configurations and replacing the materials of the impellers, in which better performance metallic materials such as copper alloy and titanium alloy, engineering plastic and ceramic material were used, the difficult problem has not been still satisfactorily solved. By now ,there are few research reports on E-C behavior of the materials used in zinc hydrometallurgy environment, therefore the basic research on it is urgent. In this thesis, three kinds of stainless steels were selected as research object and zinc hydrometallurgy slurry as medium, systemic researches were carried out on E-C mechanism and effect factors and so on, the purpose is to provide a guide for rational selection of the impeller materials of slurry pump. At the same time the research results should be of benefit not only to the development of E-C resistant materials, but also to the richness of tribology theory.Failure analysis of the impeller of slurry pump was firstly carried out, at the same time corrosion behavior of slurry ions composition and dynamics characteristic of erosion action at different position of the impeller were simulated by using electrochemical method and rotating disc E-C apparatus. The results showed that the failure of austenite stainless steel (0Cr25Ni18Mo) impeller used in zinc hydrometallurgy environment was due to the interaction of corrosion and erosion-wear, erosion-wear was dominating, low hardness of the impeller material namely poor wear resistance was main reason that resulted in rapid damage of it. Moreover erosion damage of the impeller at different place depended on flow velocity of the slurry and concentration of solid particles, i.e. the momentum of particles. Erosion rate in the margin of the impeller was higher because of higher flow velocity and bigger particles concentration ,namely bigger impact momentum, while erosion rate near the center of the impeller was lower because of lower flow velocity and smaller particles concentration,namely smaller impact momentum.The results of electrochemical analysis showed that with the increase of acidic ions such as SO42-,Cl-, F- in the slurry , the critical passivation current density ip or ipp of stainless steel was increased and passive potential range was shortened , therefore corrosive mass loss rate and E-C mass loss rate of the material were increased; While with the increase of the cations such as Zn2+ and Fe3+ in the slurry, passivation current density ip was decreased and passive potential range was widened, therefore corrosion mass loss rate and E-C mass loss rate of the material were reduced. The conclusion should be of benefit not only to the development of E-C resistant materials, but also to the richness of E-C research.The research results on the simulated tests of the several corrosion resistant or wear resistant materials showed that under the condition of zinc hydrometallurgy selecting the traditional materials as that of the impellers of slurry pumps couldn't ensure longer service life. But stainless steel series materials possessing certain corrosion resistance and good deformation resistance or wear resistance should be likely to become the first selection of the impeller materials. Three kinds of candidate materials, i.e. nitrogen-containing duplex stainless steel (DSS), 17-4PH precipitation-hardening stainless steel (17-4PH) and austenite stainless steel strengthened byσphase were screened out as three kinds of candidate materials of the impeller from the simulated test.The research results on nitrogen-containing DSS showed that in the simulated slurry corrosion current density ic of the tested materials was decreased and passive potential range was enlarged, and pure corrosion rate (Vc) was decreased with the increase of N content. While pure erosion rate (Ve) and total E-C rate (Vt) weren't decreased with the increase of N content in the studied the range of N content. DSSs containing nitrogen contents from 0.1% to 0.3% had the microstructures of austenite (γ) contents from 30% to 70% and ferrite (α), the ratio ofγandαwas appropriate, their Ve and Vt were lower, their E-C resistant performance were more excellent, moreover Ve and Vt of DSS containing the microstructure of nearly equal content ofγandαwere lowest, therefore its E-C resistant performance is most excellent. Hardness of DSS is not be the determinant factor, deformation strengthening ability is just a key factor on E-C resistance.The research results on 17-4PH steel showed that under the simulated slurry medium owing to dispersive precipitate of a number of Cu-rich particle aged at 460℃,the hardness of the material was highest and its E-C resistance was most excellent. Effect of corrosion factor on E-C rate was more remarkably compared with failure impeller material. When sulfuric acid concentration was lower, 17-4PH steel showed better E-C resistance than that of failure impeller, while sulfuric acid concentration was higher, its E-C resistance was poorer than that of failure impeller.The research results on austenite stainless steel strengthened byσphase showed that they exhibited better wear resistance due to the protecting action ofσphase on soft matrix as well as excellent corrosion resistance owing to higher main corrosion-resistant alloy element inσphase and little difference of electrode voltage with austenite matrix, therefore they showed excellent E-C resistance. The steels aged had been reinforced further owing to the dispersive precipitate of fine needle and flakeσphase in the matrix, at the same time it held good corrosion resistance due to the slight decrease of main corrosion resistant elements in the matrix, therefore E-C resistance of the improved materials had been significantly promoted. 57% of E-C rate of the improved materials was decreased compared with that of failure impeller in the simulated zinc hydrometallurgy slurry.The systemic research of main environmental parameters on E-C behavior of austenite stainless steel strengthened byσphase and failure impeller was performed. The results showed that under the test condition, flow velocity (υ) dependency of E-C rate (VE-C) was as follows: VE-C = K1·υn1 ,n1 in the test was between 1 and 2.5, n1 is smaller than velocity exponent (2～5) of general gas-solid E-C. VE-C was markedly increased with the concentration of silica(Cp) of about 5% or 20%. VE-C was approximately linerly increased with the increase of granularity of silica (Dp). When sulphuric acid concentration (Ca) was lower, E-C resistances of the tested materials mainly depended on erosion resistance, while Ca was higher, E-C resistances depended on not only erosion resistance but also corrosion resistance, especially synergistic rate (Vs) between erosion and corrosion besides erosion resistance. Material loss mechanism maps of flow velocity-silica granularity, flow velocity-silica particles concentration and flow velocity-sulphuric acid concentration are drawn by the research results,thereby material loss trend could be forecasted by them when the condition change of the material occurs.E-C test result of three kinds of stainless steels and failure impeller material confirmed that under the zinc hydrometallurgy slurry, E-C resistance of austenite stainless steel strengthened byσphase was most excellent, much more excellent than the impeller material used now. It should be an effective approach to develop the material of flow-handling component of slurry pump such as the impeller and prolong its service life to make use of such method that the material is strengthened by second phase with weak cathode.
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