The intergranular corrosion of stainless steel is a corrosion damage phenomenon, shown as the loss of binding force between the grains, so that the strength of the material deteriorates. For intergranular corrosion causes, there are many different theories, such as chromium depletion theory, the grain boundary adsorption theory, theory of metastable precipitates, metastable phase dissolution theory, stress theory, theory and morphology of precipitates electrochemical corrosion theory. Among of them, chromium depletion theory is a theory first proposed and widely accepted. For 18-8 stainless steel, lattice grain boundaries is not complete, which is conducive to the spread of metal atoms; the Cr shall lack in the grain boundary and adjacent area due to the carbide Cr23C6 precipitation in the grain boundaries, which resulting in chromium depleted zone around grain boundaries, and when the Cr content is reduced to about 12%, and in some corrosive medium corrosion along the grain boundary, so that the binding force between the grains losses, producing intergranular corrosion phenomenon.
In Europe and other developed regions, TP321 stainless steel seamless pipe has gradually been replaced by TP304L, TP316L and other low-carbon, ultra-low carbon stainless seamless steel pipe; but in our country, TP321 stainless steel seamless steel pipe demand remains high, according to the International Stainless Steel data Forum (ISSF) released data show that in 2012,
the apparent consumption of TP321 stainless steel seamless pipe is about 100 000 t. Due to restrictions on the production process and test conditions, the current domestic production of TP321 stainless steel seamless pipe resistance to intergranular corrosion pass rate is not high, a test pass rate of about 80%.
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