Ferritic 310S Stainless Steel Tube Intergranular Corrosion Phenomenon Ferrite 310S Stainless Steel Tubes Similar to austenitic 316L stainless steel tubes, intergranular corrosion also occurs, but the sensitization treatment and heat treatment to avoid such corrosion are just like the austenitic steels. in contrast. Ferritic 310S stainless steel tubes are susceptible to intergranular corrosion from rapid cooling above 925°C (eg, water quenching); this state of susceptible to intergranular corrosion (sensitized state) can be eliminated by brief tempering at 650-815°C. Or reduce the effect of heat treatment on intergranular corrosion of Cr17 and Cr18Ni8 stainless steels.
Intergranular corrosion of ferritic 310S stainless steel pipes is caused by precipitation of carbides on the grain boundaries. At present, it is widely accepted to explain the phenomenon of intergranular corrosion of ferritic 310S stainless steel pipes by the chromium-depleted mechanism: due to the effect of solid solubility At temperatures above 925°C, the adsorption of carbon in the α-phase at the grain boundary tends to be larger than the γ-phase. Since it can be adsorbed at the grain boundary of the γ-phase, the carbon will have greater adsorption at the grain boundary of the α-phase (because carbon The solid solubility of the alpha phase is much smaller than its solid solubility in the gamma phase; diffusion of carbon in the alpha phase is much faster than diffusion in the gamma phase). Only extremely fast cooling does not result in intergranular corrosion due to the suppression of the precipitation of chromium carbides in the grain boundary. However, in the case of water quenching or air cooling, the adsorption of carbon on the grain boundary and the chromium adjacent to the grain boundary cannot be inhibited from depositing in the grain boundary in the form of chromium carbide, and there is a chromium-depleted region around, so there is intergranular corrosion. Due to the rapid diffusion of chromium in α2Fe, a short tempering in the range of 650-815°C can reduce the degree of chromium depletion in the very narrow chromium-depleted zone through diffusion; in addition, tempering within this temperature range, the grain boundary Spheroidization of carbides; these two factors explain the reason for the disappearance of intergranular corrosion.
Intergranular corrosion based on ferrite 310S stainless steel pipe is mainly caused by the precipitation of carbides in the grain boundary. It is an effective measure to prevent the intergranular corrosion of ferritic 310S stainless steel pipe in the industry and to prevent the austenitic 316L stainless steel pipe. The method of intergranular corrosion is similar, mainly including:
(1) The carbon content and the nitrogen content are reduced to a very low level, for example, less than 0.005%C and less than 0.015%N.
(2) Tempered at 700-800°C for a short time.
(3) Add enough titanium or niobium to fix the carbon and nitrogen in the steel.
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