The Effect Of Cu On The Structure And Properties Of 6Mo Super Austenitic Stainless Steel

6Mo superaustenitic stainless steel?SASS?was widely used in the Cl^-ion harsh environments because of its excellent mechanical properties and corrosion resistance.However,for the steel with high contents of Cr,Mo,it is easier to promote the precipitation of intermetallic phase during the process of hot working with welding and result in the deterioration of both mechanical properties and corrosion resistance,which greatly limits the further development of SASS.Therefore,we have studied and discussed the hot rolled plate of 20Cr-25Ni-6Mo SASS.The effects of solid solution temperature and different Cu contents?0Cu,1.5Cu,3Cu,4.5Cu and 6Cu?on the structure and properties of SASS were studied.The solidsolution behaviour of 3Cu stainless steel was studied by using the methods of Scanning Electron Microscopy?SEM?,Transmission Electron Microscopy?TEM?and physicochemical phase analysis,and quantitative analysis was made on the precipitates 0Cu,3Cu and 6Cu stainless steels.The results have shown that hot rolled plate matrix microstructure is primarily austenite after high temperature solid treatment.There is a small amount of sigma phase precipitation,its content decreases with the solution temperature,and the precipitation increases with the increasing of copper content at each solution temperature.The grain coarsening of SASS happened when the temperature beyond 1150?.The activation energies of grain growth for 0Cu,3Cu and 6Cu stainless steels were Q₀=320.33k J/mol,Q₃=299.16k J/mol and Q₆=306.75k J/mol,respectively.The Cu has no effect on the grain growth of SASS.With the increase of Cu contents,the SASS has increased uniform corrosion resistance in the H₂SO₄ solution,but the pitting corrosion resistance reduced in the Fe Cl₃ solution.In addition,it can improve corrosion resistance in the mixed solution.EPR results have shown that stainless steel does not have intergranular corrosion in general corrosive medium,The Cu has no effect on the corrosion performance of stainless steel sensitized.The semiconducting properties of passive film of stainless steels in 1mol/LH₂SO₄solution were investigated by Mott-Schottky test.The passive film in?-0.1V⁰.69V?has n-type semiconductor characteristics and that in?0.69V¹.0V?p-type semiconductor properties.The composition of passive film formed at 80?,60% H₂SO₄ solution soak was analyzied by Auger Elctron Spcetroscopy.The results have shown that the cooperation reaction between the enriched surface copper and chromium,molybdenum,nickel compounds in membrane is the reason that the stainless steels have excellent uniform corrosion resistance.