The Research Of The Logging Surface Material Corrosing Causes And Mechanism

The logging instrument surface material commonly used17-4PH stainless steel, whichhas good corrosion resistance and mechanical properties. But in the practical, there are a fewinstrument surface material exists pitting corrosion and leakage phenomenon. Once thematerial fractures, loss caused incalculable. In order to ensure the equipment life, improveproduction technology, this paper analyzes the mechanical properties and microstructure of thepitting corrosion of17-4PH stainless steel by means of macroscopic mechanical analysis andXPS, XRD, SEM, metallographic analysis, found the17-4PH stainless steel final pittingcorrosion reasons, and failure mechanism. The main conclusions are as follows：Pitting is caused by intergranular corrosion. The micro crack along grain boundaries, andexposed the parent material and the formation of oxide film Two crack through China Unicomwill be here from parent metal mining. With Cl ion corrosion in acid solution, when the parentmaterial was digging out, exposing the metal base, corrosion caused by corrosion product filmformed a large cathode, anode and no corrosion product film covering areas. Because of Clions in this area due to enrichment and the corrosion speeds up, A new formation of corrosionfilm is grown rapidly.Leakage is generated in the pits around. Due to poor chrome area forming in the forgingprocess, the reason is Cr₂₃C₆actually not solid solution, and the solid precipitation in the500⁸00degrees. The reduce of the content of chrome and near the grain boundary corrosion ofmetals. Finally in the role of internal pressure, when the grain boundary corrosion thicknesscut to less than the yield strength limit and eventually into leakage.