Preparation Of Fe-based High Chromium Coatings And Carbon Dioxide Corrosion Behavior

This paper selects the325powder which Chinese laborers technology product, addingproper amount of pure Fe, Cr powder, using the method of laser cladding prepare threecoatings：Fe-20Cr, Fe-30Cr, Fe-40Cr, then test P110steel and three kinds of coating oflinear polarization, potentiodynamic polarization curves, electrochemical impedancespectroscopy, The rules of CO₂corrosion behavior at different temperature, Cl-concentrationwas studied systematic. At last, analyze and test microstructure, phase composition,performance of three cladding layer by scanning electron microscopy （SEM）, energydispersive spectrometer （EDS）, X ray diffraction （XRD）. Explain the role and corrosionmechanism of cladding layer in the CO₂corrosion medium and the effect of Cr in the claddinglayer.The results show that: the corrosion potential of three kinds of coating was negative shift,and the corrosion current density decreases in a simulated saturation formation water. Afterentering CO₂, corrosion trend of coating increased, CO₂and Ca²⁺, Mg²⁺ forms a kind ofprotection film on the coating surface improves the corrosion resistance of the coating. Whilethe corrosion rate increases of P110steel in the CO₂system, with time passing the protectivefilm formed on the surface of P110steel shedding caused corrosion current density increased.In the saturation formation water of simulated pumping in CO₂, P110steel and three kinds ofcorrosion rate increases with temperature increasing, decrease with Cl-concentrationincreased, Cl-concentration and corrosion resistance existence a critical value, when theCl-concentration reached1mol/L, the corrosive reached the maximum. At85degrees, In thesaturation formation water of simulated pumping in CO₂, coating has the lower corrosiontendency and the superior corrosion resistance than P110steel. In the present experimentpreparation technology conditions, three kinds of coating corrosion resistance did not showthe better anticorrosive property with the increase of the Cr content. With the increase of theCr content, the corrosion potential shifted negatively, corrosion current density increased,Fe-30Cr and Fe-40Cr coating passive current density decreased dramatically, passive currentdensity and passive potential increase. Fe-20Cr has the most excellent corrosion resistance,higher than that of Fe-30Cr and Fe-40Cr over the passive potential.The results of metallographic microscope（MM） and scanning electron microscope （SEM）of micro features, organization show that: three cladding layer is metallurgical combination,good quality of cladding layer. Energy spectrometer （EDS） and X ray diffraction （XRD） phase analysis results show that: the micro domain organization are typical organization, Fe-20Crcladding region mainly for gamma-（Ni, Fe）, Cr, Ni-Cr-Fe three phase, and Fe-30Cr, Fe-40Crcladding layer is too much Cr with the C element has a certain affinity, gradually formed aCr₇C₃, Cr₂₃C₆etc. Fe-30Cr and Fe-40Cr cladding layer has a lower corrosion resistance islargely because of excess Cr₇C₃, Cr₂₃C₆formation, caused by grain boundary is generatedaround the chromium depleted zone, resulting in corrosion resistance greatly reduced. But atthe same time, the cladding layer was formed in excess of the Cr₇C₃, Cr₂₃C₆carbide belongsto hard phase, in reducing the corrosion resistance at the same time, improve the hardness ofcladding layer, Fe-30Cr and Fe-40Cr hardness is higher than that Fe-20Cr cladding layer.