| Nowadays carbon steels and low alloy steels are often used for basic materials of chemical industry pipes,acid-resistant pumps,ships and turbines, while 304 and 321 stainless steel(SS) are worked as the main component of ship propellers and turbine vanes. But in some corrosive environment (such as flowing phase),they are still seriously corroded. Therefore further research about corrosion resistance mechanism of steels in flowing phase plays an important role for developing lately anti-erosion materials and new technologies of stainless steel surface modification.In the paper,the electrochemical behaviors of 45 # steel,20SiMn steel,304 and 321 stainless steel under the conditions of quiescence and flowing phase in 1mol/L HCl and 3.5% NaCl solutions have been studied by using PGSTAT30 instrument,8S-1magentic stirring apparatus and metallurgical microscope CMM-20. In order to furthher study the corrosion mechanism in the flowing phase,the relationships between velocity and corrosion resistance have been explored by means of polarization curve , EIS , Bode chart and metallographic photo. The results for the electrochemical corrosion of 20SiMn steel and 45# steel show that:(1) With the flowing rates increasing,impedance arc radius and dispersion coefficient of 45 # steel and 20SiMn steel were sharply decreased,so their dispersion coefficients were sharply decreased. When the flowing rates increasing,Icorr was increased,especially reaching critical velocity of 200 r / min. Meanwhile there was an decreasing trend for Maximum value of phase angle and the placement values at entire region of frequencies in Bode charts.(2) The pitting spots were observed in metal surface by the photos of corrosion tests.With the flowing rates increasing,the number and radius of pitting spots were significantly increased. So the electrochemical corrosion was changed localized corrosion into uniform corrosion. The order of the corrosion resistance is :20SiMn steel>45 # steel. (3)With increasing concentration of UP,the corrosion current density of 45 # steel decreased,however the corrosion potential increased. When the concentration of UP is 0.01 mol/L,the maximum of inhibition efficiency was observed. When the concentration of UP was greater than 0.1 mol /L,UP desorbed from the steel surface and made inhibition efficiency decreased . Increasing the corrosion potential indicates that UP was an anodic inhibitor.The results for the electrochemical corrosion of 304SS and 321SS indicate that:(1) the results of polarization curve indicated that 304SS and 321SS in 1 M HCl solution were passivated. With the flow rate increasing,Icorr increased, especially reaching critical velocity of 800 r/ min. (2)the results of EIS indicated that with the increasing of stirring rates,304SS and 321SS'impedance arc radius, the passive film resistance and dispersion coefficient were sharply decreased, while the passivated solution resistance and capacitance and metal surface roughness were increased, so dispersion coefficient were sharply decreased. (3) There was a decreasing trend for Maximum value of phase angle and the placement values at entire region of frequencies in Bode charts. (4) The pitting spots were observed in metal surface by the photos of corrosion tests. With the flowing rates increasing,the number and radius of pitting spots were significantly increased. So the electrochemical corrosion was changed localized corrosion into uniform corrosion. The order of the corrosion resistance is : 321SS>304SS.In a word,analyzing the experimental datas for the electrochemical behaviors of four kinds of steels under the conditions of quiescence and flowing phase through the corrosion rate,diffusion coefficient and the Bode chart,The order of the corrosion resistance is:321 SS> 304 SS> 20SiMn Steel> 45 # steel.
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