Martensitic stainless steel (420B) microstructure show carbides precipitate at grain boundaries. Chromium, present in the matrix to guarantee corrosion resistance, is taken away to form chromium carbides. This causes a strong reduction in the corrosion resistance just near the carbides. This form of corrosion is called intergranular corrosion and the aspect is represented in the picture. Corrosion develops mainly along the grains boudaries, that is the chromium impoverished area, susceptible to the corrosion attack. The component in figure has failed also because the presence of tensile stresses.