Intergranular Corrosion Mechanism of Slightly-sensitized and UNSM-treated 316L Stainless Steel
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316L stainless steels have been widely used in many engineering fields, because of their high corrosionresistance and good mechanical properties. However, welding or aging treatment may induce intergranularcorrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formationof chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering ofcarbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism ofslightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at 650 ℃ in N2 gas atmosphere. Subsequently UNSMtreatments were carried out on the surface of the samples. The results were discussed on the basis of thesensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Eventhough chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel wasdrastically increased with aging time, and it was confirmed that the increased intergranular corrosion rateof slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation alongthe grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of agedstainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinementof the outer surface, including the introduction of compressive residual stress.
Abstract
316L stainless steels have been widely used in many engineering fields, because of their high corrosionresistance and good mechanical properties. However, welding or aging treatment may induce intergranularcorrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formationof chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering ofcarbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism ofslightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at 650 ℃ in N2 gas atmosphere. Subsequently UNSMtreatments were carried out on the surface of the samples. The results were discussed on the basis of thesensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Eventhough chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel wasdrastically increased with aging time, and it was confirmed that the increased intergranular corrosion rateof slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation alongthe grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of agedstainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinementof the outer surface, including the introduction of compressive residual stress.
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