Theoretical Analysis of Intergranular Corrosion

• Posted by Yin Tuo April 21, 2021 - Filed in Other - #ferritic stainless steel seamless pipe and tube  - 1,154 views

   

  Intergranular corrosion is common localized corrosion, which extends to the inside along the interface between metal grains. The mechanism of intergranular corrosion mainly includes "Cr-poor theory" and "Selective dissolution theory of grain boundary impurities".

  1. Poor Cr theory

  The saturated solubility of C in austenite is less than 0.02%. Generally, the C content of stainless steel is higher than this value. When the stainless steel is cooled from the solid solution temperature, C is supersaturated. When subjected to sensitization treatment, C and Cr form The carbide precipitates at the grain boundary. Because the formed carbide contains a high Cr content, and the diffusion rate of Cr in austenite is low, a Cr-poor zone is formed. There is a significant difference between the grain boundary zone and the grain body. , Forming a live-passive micro-couple structure, causing grain boundary corrosion.

  2. Theory of selective dissolution of grain boundary impurities

  Stainless steel will also undergo intergranular corrosion in a strong oxidizing medium, but the intergranular corrosion does not occur on the stainless steel that has undergone sensitization treatment, but on the stainless steel that has undergone solid solution treatment. It is explained by the theory of selective dissolution in the boundary. When impurities segregate on the grain boundaries, selective dissolution will occur, resulting in intergranular corrosion.

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