Electrochemical Corrosion Behavior of Spray-Formed Boron-Modified Supermartensitic Stainless Steel

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STAINLESS steel is widely used in the oil industry due to its corrosion resistance properties linked with appropriate mechanical properties. The supermartensitic stainless steel (SMSS) grades, or super 13Cr martensitic stainless steel, have increasingly been used in seamless pipes for drilling, casing, and tubing subjected to application in the corrosive environments of oil and gas fields. Such stainless steel grades are based on the Fe-Cr-Ni-Mo system with up to 13 wt pct Cr, 4-6 wt pct Ni, 0.5 to 2.5 wt pct Mo, low amounts of carbon, nitrogen, phosphorus, and sulfur (C £ 0.02 wt pct, N, P, S £ 0.03 wt pct). SMSS grades are divided into three classes: Low alloy SMSS (11Cr-2Ni); Medium alloy SMSS (12Cr-4.5Ni-1.5Mo); and High alloy SMSS (13Cr-6Ni-2.5Mo).[1] The optimized microstructures of these alloys are free from d-ferrite and offers good corrosion resistance in environments containing CO2 and H2S.[2–4] Kondo et al.

GUILHERME ZEPON, CLAUDIO S. KIMINAMI, WALTER J. BOTTA FILHO, and CLAUDEMIRO BOLFARINI are with the Departamento de Engenharia de Materiais, Universidade Federal de Sa˜o Carlos, Rod. Washington Luiz, Km 235, 13565-905, Sa˜o Carlos, SP, Brazil. Contact e-mail: [email protected] RICARDO P. NOGUEIRA is with the University of Grenoble Alpes, LEPMI, 38000 Grenoble, France, and also with the Department of Chemical Engineering, Gas Research Center, The Petroleum Institute, Abu Dhabi, UAE. Manuscript submitted September 13, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

have studied the corrosion resistance of the SMSS grades in chloride medias containing CO2 (such as seawater in off-shore fields).[4] However, pipes and pumps used in the exploitation and production of oil, in addition to corrosive environments, are often subjected to extreme wear conditions. In those cases, the application of stainless steels is greatly limited due to their low hardness or poor wear resistance properties. The exploitation of oil in ultra-deep water regions, as in the case of pre-salt fields at the Brazilian coast, has increased the demand of materials comprising both high wear and corrosion resistance. Based on this scenario, much effort is being devoted to develop materials, which combine the good corrosion resistance of the stainless steel grades with improved wear resistance. Different approaches have been used to increase the wear resistance of stainless steel parts. Nanostructured and amorphous alloys with high wear and corrosion resistance, alloys with high hardness and high fraction of hard intermetallic, and alloys with strain induced phase transformation are some of the approaches used by different researches around the world.[5–20] In the context of this paper, the approach used is to increase the wear resistance of stainless steel grades through the modification of their chemical composition. Such modification aims to conscientiously induce the formation of hard phases, increasing the wear resistance, while maintaining the corrosion resistance of the stainless steel matrix. Spray forming is an advanced casting process usefu