Das, Samar and Joarder, A (1997) Effect of long-term service exposure at elevated temperature on microstructural changes of 5Cr-0.5Mo steels. Metallurgical and Materials Transactions A, 28 (8). pp. 1607-1616.
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Effects of long-term service exposure at elevated temperature on microstructural changes have been studied for both virgin and service-exposed process heater tube pipes of 5Cr-0.5Mo steels used in oil refineries. Samples selected for this study had experienced a nominal temperature range of 450 °C to 500 °C for about 20 to 25 years. Two different initial virgin microstructures were taken and designated by steel A and steel B. The virgin microstructure of steel A exhibited fine platelets of fibrous or hairlike M2C carbides within the ferrite grains and occasionally irregularly shaped M23C6, both along the grain boundaries and at the grain interiors, and very few spheroidally shaped M3C, either along the grain boundaries or at the grain interiors. The size, shape, position, distribution, and type of carbides in virgin steel A changed significantly due to 220,000 hours of service exposure in the temperature range of 450 °C to 500 °C. Massive M23C6 carbides precipitated along the grain boundaries. In addition, regular geometrically shaped M23C6 carbides, such as hexagonal, square, and triangular type, were observed to form at the grain interiors. The virgin steel B microstructure exhibited predominantly M23C6 carbides, either along the grain boundaries or at the lath boundaries. Occasionally, fine platelets of M2C carbides were also observed within the laths. The position, shape, distribution, and type of carbides did not change significantly due to 172,000 hours of service exposure in the temperature range of 450 °C to 500 °C. The average interparticle spacings of the carbides increased from 0.35 to 1.2 µm due to 172,000 hours of exposure.
|Uncontrolled Keywords:||M23C6 carbides; 5Cr-0.5Mo steels|
|Divisions:||Material Science and Technology|
|Deposited By:||Dr. A K Sahu|
|Deposited On:||09 Oct 2009 10:40|
|Last Modified:||14 Dec 2011 14:52|
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