The influence of surfactant elements on grain boundary structure of grain boundaries and resistance against intergranular corrosion of austenitic Cr–Ni and Cr–Ni–Мо steels

The maximum permissible content of surface-active elements of carbon, nitrogen and boron in low-carbon Cr–Ni and Cr–Ni–Mo steels, which provide high resistance against intergranular corrosion (IGC) when tested in strongly and weakly oxidizing environments, have been established. It has been proven that in order to ensure high resistance against IGC when tested in boiling 65% HNO3 (according to ISO 3651-1), the carbon content in 03Х18Н11 (304L) and 03Х17Н14М3 (316L) steels should not exceed 0.025% and 0.015%, respectively, and when tested in boiling H2SO4 (ISO 3651-2, method B) – 0.03%. It іs established that nitrogen in the amount of up to 0.2% does not have a negative effect on the IGC of the studied steels, and the simultaneous increase of nitrogen and carbon gives a negative synergistic effect. The negative influence of 0.003% and, to a greater extent, 0.03% boron on the grain boundary structure and resistance against IGC of steels hardened at temperatures >1100° is shown. Technologies for increasing the resistance against IGC of pipes made of the studied steels have been developed, taking into account the principle of grain boundary engineering of polycrystalline materials.