The effects of heat treatment on the sensitization and SCC behavior of INCONEL 600 alloy
- PDF / 4,334,687 Bytes
- 12 Pages / 590.28 x 785 pts Page_size
- 78 Downloads / 235 Views
I.
INTRODUCTION
I N C O N E L * 600 alloy is now being widely used as the *INCONEL is a trademark of the INCO family of companies.
steam generator tubing material for pressurized water reactors (PWR's) because of its good mechanical strength, thermal conductivity, and corrosion resistance. H o w ever, if it is used under an improper environment, intergranular attack (IGA) and SCC will occur which will induce tubing failure during normal operation. Since 1970, broken tubes in steam generators have become a vital defect for P W R ' s . From the statistics presented by Tatone, m it is observed that SCC is becoming the most serious cause for the failure of PWR steam generator tubes. Researchers lz,3,41 have proposed that sulfur compounds and material sensitizatiofi were responsible for the extensive degradation observed in the steam generators of TMI-1 in late 1981. Berge and Donati lzl reported that sulfur-bearing species did induce IGA. Bandy e t a l . E31 found that the sulfur contents had a great effect on the sensitized I N C O N E L 600 specimens and caused SCC failure in this alloy. Rajan and Was t< reported that IGSCC failure of I N C O N E L 600 could occur in 0.017 M sodium tetrathionate solution at room temperature. Although this problem has been noticed for a period of time, an additional contribution can still be made by studying the effect of heat treatment on the chromium depletion near the grain boundary area and on the SCC failure of INCONEL 600 under sulfur-contaminated environments. This study was aimed to investigate the effect of thermal treatment on the sensitization of I N C O N E L 600 and to study the SCC behavior of this alloy in a sulfurJ.J. KAI, Associate Professor, C.H. TSAI, Professor, and T.A. HUANG and M.N. LIU, Graduate Students, are with the Department of Nuclear Engineering, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China. Manuscript submitted May 25, 1988. METALLURGICAL TRANSACTIONS A
contaminated environment using the constant load test. The results of this study can be used to correlate the SCC susceptibility to the degree of sensitization of this alloy by defining a critical chromium concentration under the test condition.
II.
EXPERIMENTAL
PROCEDURES
The plate-type I N C O N E L 600 alloy used in this study was supplied by Huntington Alloys, Inc., and the chemical composition is shown in Table I. T w o types of specimens were cut from the plate. Specimens of 3 m m diameter discs were used for S T E M / E D S examinations. The dimensions of the specimens used in the constant load tests are shown in Figure 1. Each specimen was solution-annealed at 1120 ~ for 30 minutes, followed by a water quench and then an isothermal heat treatment (621 ~ 700 ~ or 800 ~ for various periods of time: 621 ~ 700 ~ 800 ~
10, 24, 100 h + water quench 3, 5, 15, 24, 100 h + water quench 5, 10, 24 h + water quench
The microstructural analysis and the precipitate identification were performed using a JEOL-200CX transmission electron microscope (TEM). The TEM specimens were
Data Loading...
