The Influence of Surface-Active Elements on Grains Boundary Structure and Resistance Against Intergranular Corrosion of Austenitic Cr–Ni and Cr–Ni–Mo Steels

The maximum permissiblse 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, was established. To ensure high resistance against IGC when tested in boiling 65% HNO₃ (according to ISO 3651-1), the carbon content in 03Kh18N11 (304L) and 03Kh17N14M3 (316L) steels should not exceed 0.025% and 0.015%, respectively, and when tested in boiling H₂SO₄ (ISO 3651-2, method B) should not exceed 0.03%. The nitrogen amount up to 0.2% does not influence negatively 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°C was shown. Technologies for increasing the resistance against IGC of pipes made of the studied steels were developed, taking into account the principle of grain boundary engineering of polycrystalline materials.