Background and Objectives: The down hole application environment is highly corrosive due to the presence of hydrogen sulfide and carbon dioxide in brines. To handle this environment, special materials with a high resistance to pitting corrosion and a high capability of repassivation are used such as steels containing molybdenum, chromium and nickel. The cost of the metallic constituents in these alloys can preclude their use in some applications. The objective of this study is to provide cheaper materials withstanding these conditions. The materials developed in this study are high interstitial stainless steels (HISS) with high nitrogen and carbon content. Methods: Several studies showed that the addition of nitrogen and carbon in stainless steels enhance their pitting corrosion resistance, increase their critical pitting temperature and also increase their repassivation rates. In order to develop high nitrogen and carbon content stainless steels we employed the air-casting techniques developed by the Colorado School Mines. In these techniques, the nitrogen is added to the melt using nitrogen-bearing additives (nitrided manganese). In this case, the nitrided manganese is placed in cavities in the mold, and melts when the liquid metal enters the mold. In order to characterize the chemical and mechanical properties of the HISS several tests were performed. The XRF and the EDX techniques were used to determine the chemical composition. The microstructure was observed using an inverted optical microscope and a scanning electron microscope. The corrosion resistance to 3.5% sodium chloride solution was studied using weight loss and electrochemical tests. The corrosion tests under sour environment will be performed as soon as the sour gas research laboratory will be constructed. The hardness of the HISS was measured using the Rockwell hardness test. Results: Preliminary investigations show that the microstructure of the developed materials contain nitrites and carbides which have a bad effect on the pitting corrosion. This problem can be solved by applying the adequate heat treatments. These results also show that the developed stainless steels are harder than nickel-molybdenum.


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