Comparative Evaluation of Creep-Rupture Behavior of P9 Steel Plate and Thick Section Tubeplate Forging
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JMEPEG https://doi.org/10.1007/s11665-019-04346-y
Comparative Evaluation of Creep-Rupture Behavior of P9 Steel Plate and Thick Section Tubeplate Forging B.K. Choudhary, Isaac Samuel E., Christopher J., and S.D. Yadav (Submitted September 4, 2018; in revised form July 20, 2019) In the present investigation, creep-rupture behavior of P9 steel in two different product forms of 20-mm plate and 300-mm-thick tubeplate forging has been studied at 793 and 873 K. It has been found that steadystate creep rate and rupture life followed power law dependence on applied stress at low and high stress regimes for both forms of products. At high stress regime, P9 steel plate exhibited better creep strength with respect to tubeplate forging in terms of lower creep rate and higher rupture life at 793 and 873 K. On contrary, both product forms exhibited similar creep rate and rupture behavior in the low stress regime at 873 K. Difference in creep ductility has been found to be insignificant in both product forms. Irrespective of test conditions and product forms, fracture appearance remained transgranular ductile characterized by dimples. The comparative evaluation of creep-rupture properties of both product forms has also been described in terms of creep rate-rupture life relationships of Monkman–Grant type, creep damage tolerance and tertiary creep characteristics at 793 and 873 K. Keywords
creep damage, P9 steel, rupture life, steady-state creep rate, tubeplate forging
1. Introduction Creep-resistant steels are the class of steels those can be used for long durations at elevated temperatures, which are important for the construction of electricity generating power plants, and chemical and petroleum industries. Among the creep-resistant steels, P9 steel and its modified version such as P91 and P92 are favored structural materials for steam generator (SG) applications in nuclear and thermal power plants, respectively. The modified version is developed by adding strong carbide/nitride-forming elements such as vanadium and niobium along with controlled addition of nitrogen in P9 steel. In general, P91 steel exhibits significantly higher tensile and creep strengths than P9 steel. The choice of 9% Cr steels for steam generator applications in power plants is primarily based on its better high-temperature mechanical properties compared to alternate 2.25Cr-1Mo steel in addition to low thermal expansion coefficient and high resistance to stress corrosion cracking in water-steam systems compared to austenitic stainless steels (Ref 1, 2). Progress in recent years has led to the further development of 9% Cr steels for achieving higher creep strength with enhanced weld characteristics at elevated temperatures. One of the major developments is the controlled addition of boron in P91 steel for stabilizing the
B.K. Choudhary and Christopher J., Materials Development and Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu 603102, India; and Homi Bhabha National Institute, Kalpakkam, Tamil Nadu 603102, India; and Isaa
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