Effect of Nitrogen Content on the Corrosion Resistance of High- nitrogen Austenitic Stainless Steel for Nonmagnetic Drill Collar in a Harsh Service Environment

Abstract

In this work, the effect of N content on the corrosion resistance of high-nitrogen austenitic stainless steels for nonmagnetic drill collars in a harsh service environment was investigated by immersion tests in simulated service environment and XPS analysis. The number and morphology of corrosion pits on 0.63N, 0.79N and 0.83N steels were evaluated using the methods of probability and statistics. The composition of the passive films on 0.63N and 0.83N steels was analysed by XPS, and the mechanism of high N content improving corrosion resistance was discussed. The results show that increasing the N content not only reduced the number of pits but also greatly limited the growth of pit width and depth. In addition, it made pits more likely to appear as a relatively less harmful “shallow disk”. The XPS analysis results show that N increased the ratio of chromium oxides and iron oxides in the passive film and promoted the enrichment of CrN, which was beneficial to improving the stability and protection ability of the passive film. This work provides some experience and inspiration for the development of high-nitrogen austenitic stainless steel for nonmagnetic drill collars.