Degradation mechanisms of a Colbalt-base Alloy and stainless steel UNS S17400 used for drilling tools by the oil industry

Two materials which are candidates in the construction of drill bits have been studied in severe liquid-solid impingement conditions. Analysis of the total weight loss was carried out on Stellite X40 (Co-base) and UNS S17400 (stainless steel) materials at 30°, 60° and 90° angles of impingement under erosion-corrosion conditions at the free corrosion potentials and with applied cathodic protection. A preliminary analysis of the corrosion behaviour of the materials in static conditions was the starting point for the electrochemistry analysis. A more extensive corrosion analysis under erosion-corrosion conditions was carried out through DC potentiodynamic tests while varying angle of impingement to detect the effect on their corrosion behaviour. The results were used to identify the contribution of mechanical erosion and electrochemical corrosion for both materials under different angles of impingement and to determine the extent of interaction between corrosion and mechanical erosion processes.