| Duplex stainless steel has good corrosion resistance in the application process due to the fine structure of ?+? chromium nickel duplex stainless steel.It is well known that the nickel belongs to expensive elements,so containing much nickel will increase the cost of production.To our delight,the latest-developed duplex stainless steel which contains only 1%~4% of the nickel has solved the problem.Without doubt,the duplex stainless steel become a kind of potential and economic application material.Super duplex stainless steel S32760 is a new type of stainless steel adding W and Cu elements,however,the relationship between the macroscopic properties and its microstructure in different acid system remains to be investigated.In this paper,OM,XRD,SEM and XPS were used to explore the effect of different heat treatment processes on the microstructure of duplex stainless steel S32760.By measuring the corrosion rate of weight loss,polarization curves and impedance spectra,the corrosion resistance of duplex stainless steel S32760 after 950?,1000?,1050?,1100?and 1150? solid solution treatment and 650?,750?,850? and 950?aging treatment materials were researched in sulfuric acid and phosphoric acid at different temperatures and concentrations.And the corrosion morphology of the material was observed by SEM.The optimal heat treatment conditions and the most suitable acid making system environment are analyzed.In this paper,it is shown that the microstructure of S32760 stainless steel is mainly ferrite and austenite phase,which is distributed uniformly and has no impurity precipitation.With the increasing of the concentration of sulfuric acid solution,the corrosion rate of S32760 stainless steel showed a trend of accelerating first and then slowing down.When the concentration reached 40%,the corrosion rate of the material was the fastest,reaching 44.3824mm/a.With the increase of temperature of sulfuric acid,the corrosion resistance of the material is weakened first and then enhanced.When the temperature reached 125?,corrosion resistance is the worst,and the corrosion rate reached 0.9634mm/a,but when the temperature rises to 200?,the corrosion rate is only 0.1686mm/a,the corrosion resistance is greatly improved.According to the electrochemical corrosion test,With the temperature gradually increasing to 15?,30? and 50?,capacitive arc radius of material is reducing,the corrosion resistance becomes worse.At 40?,with concentration of phosphoric acid increased to 10%,30%,50%,the corrosion potential Ecorr decreases and the corrosion current Icorr increases gradually,the corrosion resistance of material decreased.S32760 in the temperature range of 950?~1150?(temperature difference between the progressive interval of 50?)followed by solution treatment,material structure mainly in ferrite and austenite phase,but the ferrite content increased gradually.When the temperature rising to 1050?,using XRD combining with metallographic image analysis shows that the ferrite phase changes from the strip structure into the bamboo structure.When the temperature continues to rise,duplex stainless steel S32760 precipitated carbides and nitrides in organization.Corrosion resistance test,of which the material after solution treatment in 98% sulfuric acid show that with the solution temperature increasing,the corrosion resistance performance becomes better then worse.The 1050? is the best corrosion resistance,and the corrosion rate is only 0.0981mm/a.Compared with the results of electrochemical corrosion test,the corrosion resistance of the duplex stainless steel S32760 treated by 1050? in the solution of 20% dilute sulfuric acid and 40%phosphoric acid solution is the best.After the treatment of 1050? solid solution,conduct 1 hour aging treatment in the temperature range of 650?~950?(temperature difference between the progressive interval of 100?).The experimental results show that with the increasing of aging temperature,the precipitation of ? phase increased first and then decreased.?phase is an important factor affecting the properties of materials,850? is the nose temperature of ? phase precipitation in S32760 duplex stainless steel.When the temperature increases,the corrosion rate of the material becomes larger and then smaller,and the corrosion resistance of the sample after 850? aging treatment is worst,with 0.1635mm/acorrosion rate,which is increased by 40% than that of the solid solution.The results of electrochemical corrosion test showed that samples after850? aging treatment,the corrosion resistance of S32760 is the worst,because the corrosion potential Ecorr of S32760 reached the maximum potential and the corrosion current Icorr reached the maximum.Meanwhile the electrochemical capacitive arc radius is minimum at this temperature in 20% dilute sulfuric acid and 30% phosphoric acid.This is the same as immersion corrosion test.The relationship between corrosion resistance and microstructure of S32760 duplex stainless steel based on the original state and after different heat treatment were researched under different conditions.The corrosion data of duplex stainless steel S32760 under different conditions were obtained.Finally,the optimal heat treatment process was determined.Hope to provide reference for future industrial design and production. |
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