What is Intergranular Corrosion and how is it caused?
If austenitic stainless steel at temperature 1035Cis cooled slowly in the temperature range 425-815C it may undergo Intergranular corrosion. It occurs because at high temperature chromium carbides are completely dissolved in austenitic stainless steel but on cooling in the temperature range 815-425C, they are completely precipitated at grain boundary. Normally the austenitic stainless steel has 18% chromium but after precipitation chromium is less than 12% in the matrix and it is depleted of chromium. The diffusion rate of chromium in austenite is slow at the precipitation temperature. The depleted zones have higher corrosion rates than the matrix. Hence Intergranular corrosion occurs.
