Effect of the Holding Time during Solution Heat Treatment on Intergranular Corrosion of Unstabilized Austenitic Stainless Steels

다국어 초록 (Multilingual Abstract)

The holding time during solution heat treatment of unstabilized austenitic stainless steels as specified in the nuclear regulatory requirements was investigated. The sensitized 2.54㎝ thick specimens held at 675℃ for 1 h were rejected by ASTM A262 test, due to the large amount of chromium carbide precipitated in the form of 50~300㎚ particles at the grain boundaries. They also showed about 10.8% of DOS in the DL-EPR test. However, solution heat treatment of the sensitized specimens at 1,038℃ and 1,121℃ for at least 1 min resulted in the complete dissolution of chromium carbide into the grains, and they passed ASTM A262 test and showed less than 0.01% of DOS in the DL-EPR test. As a result of solution heat treatment at 1,038℃ for 5 h of the 25.4㎝ thick specimen sensitized at 675℃ for 10 h, it passed ASTM A262 and DL-EPR test at any position in the specimen thickness. While the specimen surface showed a step structure without the precipitation of chromium carbide and a DOS less than 0.01%, towards the center, a dual structure was observed. It exhibited about 0.6% of DOS due to the longer exposure time to the sensitization range of 427~816℃. Considering the minimum time in which the chromium carbide precipitated at the grain boundary at 1,038℃ was completely dissolved into the grain, and the maximum delay time for the center of the specimen to reach 1,038℃ rather than the surface, the holding time for complete solution heat treatment to the center was found to be up to 2 min per 2.54㎝ of material thickness. The solution heat treatment for 0.5~1.0 h per 2.54㎝ of material thickness at 1,038~1,121℃, which is employed in the nuclear power industry, was proven to prevent grain boundary corrosion by inhibiting the sensitization of unstabilized austenitic stainless steels.

목차 (Table of Contents)

• Abstract
• 1. Introduction
• 2. Experimental Method
• 3. Test Results and Discussion
• 4. Conclusion
• References