Study On Intergranular Corrosion Of Low Ni, Cr, Mn, N Austenitic Stainless Steel

Austenitic stainless steel has been applied in various industries because of its goodcomprehensive performance, accounting for about70%of the stainless steel production.Inaustenitic stainless steel， Low nickel chromium manganese nitrogen stainless steelbecause of its low price advantage has become a trend in today’s study and use. However,austenitic stainless steel could have sensitized reaction happened in a certain temperaturerange heating or use, resulting in the occurrence of intergranular corrosion behavior,Rare earth can purify the steel in the stainless steel and microalloyed inclusionImprovement the action such as organization, therefore, the research of rare earth of lownickel austenite stainless steel corrosion resistance is of great importance.In this paper, we research based on the low nickel and chromium manganese nitrogenaustenitic stainless steel as the object, using the hot acid immersion test, ac impedance(EIS), electrochemical potentiodynamic method of reactivation (EPR) to study the effectsof different amount and specics of rare earth (La and Ce), different heat treatment systemto low nickel austenite stainless steel intergranular corrosion.Firstly, we study the causes of steel intergranular corrosion. The sample heated to650℃cold insulation2hours junior and air cooling, make it in the sensitized state, andthen use the scanning electron microscope (SEM) to observation and analysis, andcomparing with an allergy treated sample. The research shows that the samples treated bysensitizing generate plenty of deposition of irregular shape in the grain boundary, theenergy spectrum detection on it found that it is chromium and iron compounds.comparing the Cr content of deposition with its around, the grain boundary precipitateshigher chromium content in the grain within7~8%, and at the same time, higher Crcontent than the area around it about10percentage points. this tell us with the generationof grain boundary precipitation of chromium compounds, it form the narrow poorchrome area near the grain boundary, thus cause intergranular corrosion. In addition,to detect the effect of sensitization processing to low nickel austenitestainless steel intergranular corrosion, this article uses the Cu-CuSO4-16%H2SO4solution boiling method and electrochemical corrosion method (corrosion solution is0.5mol/L H2SO4+0.01mol/L KSCN) to detect.when the sensitizing temperature within550℃~750℃, the sensitization degree risewith the increase of temperature; Therefore, in the process of production use, austeniteshould be avoided in this temperature range, in order to prevent the occurrence ofintergranular corrosion behavior. When the sensitizing temperature reaches950℃, samplehave not sensitization trend; When sensitization temperature is650℃heat preservation0.5～12hours, sensitized with increased with the extension of heat preservation time.The most important, rare earth can effectively purify grain boundary, reduce thenumber of grain boundary precipitates, in my paper,we can see that the content of rareearth La was0.0049%, maximum intergranular corrosion resistance; Rare earth Ce contentis0.053%, the maximum intergranular corrosion resistance; A glut of two kinds of rareearth, rare earth inclusions also will increase, and at the grain boundary precipitates, reduceaustenitic stainless steel intergranular corrosion resistance. In addition, the sameconcentration of La and Ce, La slightly stronger the intergranular corrosion resistantcapacity.