Evolution of Carbide Precipitates in 2.25Cr-1Mo Steel during Long-Term Service in a Power Plant

Abstract

Carbide precipitation from the steel matrix during long-term high-temperature exposure can adversely affect the fracture toughness and high-temperature creep resistance of materials with implications on the performance of power plant components. In the present work, carbide evolution in 2.25Cr-1Mo steel after long-term aging during service was investigated. Boiler pipe samples of this steel were removed from a supercritical water-cooled coal-fired power plant after service times of 17 and 28 years and a mean operational temperature of 810 K (537°C). The carbide precipitation and coarsening effects were studied using the carbon extraction replica technique followed by analysis using transmission electron microscopy and energy dispersive X-ray spectroscopy. The carbides extracted using an electrolytic technique were also analyzed using X-ray diffraction to evaluate phase transformations of the carbides during long-term service. Small ball punch and Vickers hardness were used to evaluate the changes in mechanical performance after long-term aging during service.

Microstructure and Properties of Fe-2Cr-Mo-0.12C (Wt Pct)-Tempered Steel Plate at Different Normalizing Temperature After Hot Rolling

“…Additionally, many martensite and austenite islands (M/A) could be found in the bainite matrix, [6] which contributed to improving the toughness and ductility. [24][25][26] 3. Normalized and tempered steel Figure 4 shows the OM and SEM microstructures of the samples normalized at 880°C, 930°C, 980°C, and 1030°C for 1 hour and then tempered at 700°C for 50 minute.…”

Effect of Trace Mg on Impact Toughness of 2.25Cr1Mo Steel Doped with 0.056% P at Medium Temperature Aging Process

“…Thus, it is difficult to distinguish them only by SAED, but they can be distinguished from the element content. Based on literature reports [37][38][39], the Mo-rich element is the M 6 C phase, and the Cr-rich element is the M 23 C 6 phase. Therefore, the individual type of carbides can be clarified based on the element map distributions of these two carbides (see Figure 12).…”

X-ray analysis of nano-carbide transformations for actual life assessment of service-exposed 2.25Cr–1Mo boiler tubes in a thermal power station

“…The carbide phase changes happening in 2.25Cr -1Mo steel is a topic of continued interest [3,4] and are related to the temperature and time to which it is exposed [5,6]. The general sequence of carbide transformations in this steel is given below [5] M 7 C 3 ?M 6 C :…”