Ferritic 310S stainless steel pipes, like austenitic 316L stainless steel pipes, also undergo intergranular corrosion, but sensitization treatment and heat treatment to prevent this corrosion are exactly the opposite of austenitic steel. Ferrite 310S stainless steel pipes experience intergranular corrosion during rapid cooling (such as water quenching) above 925 ℃; This susceptibility to intergranular corrosion (sensitized state) can be eliminated or reduced by short-term tempering at 650-815 ℃, and the effect of heat treatment on intergranular corrosion of Cr17 and Cr18Ni8 stainless steel can be minimized.
The intergranular corrosion of ferritic 310S stainless steel pipes is caused by the accumulation of carbides at grain boundaries. Nowadays, it is widely accepted to use the chromium deficient mechanism to explain the intergranular corrosion phenomenon of ferritic 310S stainless steel pipes: due to the influence of solid solubility, when kept above 925 ℃, the adsorption trend of carbon at the grain boundaries of the alpha phase will be greater than that of the gamma phase, and it can already be adsorbed at the grain boundaries of the gamma phase. Therefore, carbon will have greater adsorption at the grain boundaries of the alpha phase (because the solid solubility of carbon in the alpha phase is much lower than its solid solubility in the gamma phase); The dispersion of carbon in the alpha phase is much faster than in the gamma phase. Only extremely fast cooling is needed, as the accumulation of chromium carbide at grain boundaries is restrained, there is no intergranular corrosion. In the case of water quenching or air cooling, it is also impossible to resist the accumulation of carbon adsorbed on the grain boundary and adjacent chromium in the form of chromium carbide at the grain boundary, with a chromium deficient zone around it, resulting in intergranular corrosion. Due to the rapid dispersion of chromium in α 2Fe, short-term tempering in the range of 650-815 ℃ can reduce the degree of chromium deficiency in a narrow chromium deficient zone through dispersion; In addition, tempering within this temperature range results in spheroidization of carbides at grain boundaries; These two elements explain the reason for the disappearance of intergranular corrosion.
The intergranular corrosion of ferritic 310S stainless steel pipes is mainly caused by the accumulation of carbides at grain boundaries. Effective measures to prevent intergranular corrosion of ferritic 310S stainless steel pipes in industry are similar to those to prevent intergranular corrosion of austenitic 316L stainless steel pipes, mainly including:
(1) Reduce the carbon and nitrogen content to very low levels, such as less than 0.005% C and less than 0.015% N.
(2) Temper briefly at 700-800 ℃.
(3) Participate in the fixation of carbon and nitrogen in titanium or niobium fixed steel.

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