| With the development of economy, the traditional steel can not satisfy therequirements of large projects, so the performance of steel should be improved. Thecorrosion resistance is an important indicator which has a vital significance toimprove the performance of steel. This paper studied the corrosion performance ofX80pipeline steel with strain-based design and analyzed the corrosion mechanismand corrosion resistance factors. Then, the P20corrosion behavior in3.5%NaClsolution by different heat treatment processes was studied, at last, by optimizing heattreatment processes, the corrosion performance of304austenitic stainless steel wasstudied, the results are as follows:The corrosin behavior of X80pipeline steel with strain-based design was studiedby the electrochemical measurement, weight loss experiment and copper acceleratedacetic acid salt spray test. The result shows that in the electrochemical experiment,the X80pipeline steel with strain-based design has a better corrosion resistance thanthat of acicular ferrite X80pipeline steel in NaCl solution. In the copper acceleratedacetic acid salt spray test, the degree of corrosion and pitting of the two kinds ofpipeline steel increase with time prolonging. However, the X80pipeline steel withstrain-based design has little corrosion pits, and shows an excellent corrosionresistance. The small dislocation density, microstructure of PF and BM, and coarsegrains contribute to the excellent corrosion resistance of X80pipeline steel withstrain-based design.By electrochemical test, electrochemical impedance spectrum experiment,weightloss test, neutral salt spray test and SEM、 EDS、 XRD, the corrosionperformance and pitting mechanism of P20steels by different heat treatmentprocesses were studied. It is found that the bainite/martensite microstructure obtainedby quenching at860oC followed by air cooling and the martensite microstructureobtained by quenching at860oC followed by oil cooling have a better corrosionresistance than ferritic/martensitic microstructure obtained by quenching at785oC followed by oil cooling. When the samples with bainite/martensite microstructure andmartensite microstructure are tempered at450oC and620oC, respectively, themartensite and bainite decompose and a lot of carbides precipitate, leading to a poorcorrosion resistance. After electrochemical experiment, the outer layer of corrosionproduct is loose FeOOH and the inner layer is relatively dense Fe3O4. The anodereaction is mainly dissolution of Fe and cathode reaction is hydrogen evolutionreaction. It is shown that pitting mainly originates from inclusions in3.5%NaClsolution.Through SEM and electrochemical experiment, the corrosion behavior of AISI304austenitic stainless steel was studied, it is found that the original rolling sampleand the samples under200oC~500oC stress-relieve treatment have an excellentcorrosion resistance, Then, the corrosion performance of specimens after860oC~900oC stabilization treatment is almost same as the samples under lowtemperature stress-relieve treatment. Among the samples by1000oC~1100oC solidsolution treatment, the corrosion performance is good through water colling and thecorrosion resistance is bad after oilling cooling or air cooling. Through SEM, theresults show that after solid solution treatment, the microstructure is austenite and thecorrosion resistance becomes badly with the content of carbide precipitates increasing.After stabilizing treatment, the organization is austenite, but it still keeps the lathform of martensite, and the corrosion performance has a little change. Afterstress-relieve treatment, the microstructure is austenite and martensite and it has alittle change before500oC, the corrosion behavior is good, but after500oC, themartensite laths become wider and the martensite begins to decompose, it iscompletely dissolved when the temperature arrived at800oC, at the same time, thequantity and the size of precipitates in microstructure increase gradually with thetemperature increasing. |
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