The Research Of Electrochemical Corossion Resistances Of Stainless Steels

Stainless steel is widely used in industry production and daily life with the corrosion resistance as the most important performance of it. The corrosion resistance of hot-rolled sheet has been researched combined with its microstructure on steel type austenitic stainless steel 304 and ferritic stainless steel 430,410S and 409L to improve the performance and technology and guide the production with theroy.First, the oxidizing, deoxygenizing, alkaline, corrosion resistance in salt solution and oxidation-reduction solution of hot-rolled 304,430,410S and 409L has been researched by elechemistry method.Polarization curves in different corrosive media were obtained to judge the corrosion resistance by parameters.The victoria passivation current is the evaluation criteria of corrosion resistance when corrosion potential is the criteria of the corrosion tendency due to the existence of passivation platform in oxidizing medium.The high content of Cr in 304 induced the high passive ability and better corrosion resistance of it. The corrosion resistance of the stainless steel types mentioned above in the different corrosion media is NaOH,FeCl3,10%HCl,Mixed acid,80%H2SO4 from high to low.Second, polarization curves of stainless steel in 5 different corrosion media was classified to three species in this project judged by the difference of the positions of the junctions of cathodic polarization curves and anodic polarization curves:Curve with a passivation platform; Curve of multi transitions of activation and passivation; Curve of none passivation platform. Different types of polarization curves show the characteristics of different media and the corrosion behavior of different materials also show the difference influnence of immersion test. Complete passivation platform exists in 80% H2SO4 in all of these tainless steel types and passivation occurred in immersion. Only the short small passivation platform exists by anode passivation when tainless steel cannot be passivated in 10% HCl.The polarization curve of tainless steel overall downward in the alkaline solution and immersion corrosion rate declined with an apassivation platform exists.The corrosion of ferrite is more serious than austenitic when an apassivation platform exists in the polarization curve of austenitic stainless steel in FeCl3 solution but ferritic stainless steel.A mutilple passivation found in the curve of mixed acid when nitric acid passivated the stainless steel and hydrochloric acid damage the passive film.Resistance to intergranular corrosion and pitting corrosion of these 4 types of stainless steel has been determinated by cyclic voltammetry. The Ir/Ia ratio shows the better resistance to intergranular corrosion of 304 and 430,409L,410S follows in a decline sequence. T The stability of metal passivation and potential to pitting corrosion rise with the Eb value in the pitting corrosion experiment which shows a better passive film repair capacity. The corrosion resistance to pitting corrosion of 410S and 409L, 304,430 arrangs in a decline sequence judged from scanning electron microscope result and Eb-Ep value.