For stainless steel, there is another special local electrochemical corrosion called intergranular corrosion. The corrosion develops along the grain boundary of the metal or alloy or its adjacent area. The grain itself corrodes very slightly. This kind of corrosion is called intergranular corrosion. corrosion.
For austenitic stainless steel, the diffusion rate of chromium from the grain is lower than that of chromium along the grain boundary, and the internal chromium has no time to diffuse to the grain boundary, so the chromium required for the chromium carbide formed in the intergranular is not mainly from the austenitic stainless steel. Inside the tensite grain, but from the vicinity of the grain boundary, the result is that the content of chromium near the grain boundary is greatly reduced. ”, under the action of corrosive medium, the chromium-depleted area will lose its corrosion resistance, resulting in intergranular corrosion.
The stainless steel that produces intergranular corrosion, when subjected to stress, will fracture along the grain boundary and the strength will almost completely disappear, which is one of the most dangerous forms of damage to stainless steel. Intergranular corrosion can occur in the heat affected zone (HAZ), weld seam or fusion line of welded joints, respectively.
