Phase-Dependent Tensile Properties of 9Cr-1Mo(V, Nb) Ferritic/Martensitic Steel
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ensitic steel [9Cr-1Mo(V, Nb)] and its reduced activation variants are materials of interest to ultra-supercritical power plants and advanced nuclear reactor systems including fusion reactors.[1–3] These steels show hysteresis in the phase field as they transform from tempered martensite (TM) to austenite (A) in the temperature range 1100 K to 1160 K (823 °C to 887 °C) while heating and then on cooling from austenite to martensite (M) in the 650 K to 473 K (377 °C to 200 °C) range.[4–6] Thus, depending on the thermal cycle that these steels are subjected to, there are two regimes of phase field hysteresis—Regime I [300 K to 650 K (27 °C to 377 °C)] in which either TM or M can exist and Regime II [650 K to 1073 K (377 °C to 800 °C)] in which either TM or A can exist. Such thermal cycles, causing excursion through the three different phase fields—TM, A, and M—are associated
SANTOSH KUMAR, Scientific Officer-F, RAM PRATAP KUSHWAHA, Technical Officer-C, and BIKAS CHANDRA MAJI, Scientific Officer-F, are with the Bhabha Atomic Research Centre, Mumbai 400085, India. Contact e-mails: [email protected]; [email protected] KARANAM BHANUMURTHY, Head, is with the Scientific Information and Resources Division, Bhabha Atomic Research Centre. GAUTAM KUMAR DEY, Head, is with the Materials Science Division, Bhabha Atomic Research Centre. Manuscript submitted June 4, 2013. Article published online December 20, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
with several thermomechanical processes including welding of these steels. Therefore, these steels are subjected to hysteresis in the phase field with each welding pass. The three phase fields—TM, A, and M—differ substantially in terms of the basic crystal structure as well as the microstructure. As the structure of a material forms the basis of its mechanical properties, it is natural that structural hysteresis in these steels will induce phase dependence in their tensile behavior. Phase-dependent tensile properties are expected to have a strong influence on the evolution of displacement and stress fields during welding. Therefore, quantitative assessment of phase-dependent tensile behavior is essential for modeling and simulation endeavors, for computing the displacement and stress fields, resulting from welding of these steels. Though substantial literature exists on the phase transformation behavior of the metastable austenitic phase field of different grades of steel under stress as well as plastic deformation,[7–11] and tensile tests of supercooled austenite in high hardenability low carbon steel have also been reported,[12] there is no published literature quantifying the phase dependence in the tensile behavior of these ferritic/martensitic steels. Due to non-availability of information on the phase-dependent mechanical properties of these steels, computational efforts in this direction have relied on published literature on elevated temperature mechanical properties of either austenitic stainless steel or those of the TM condition of these steels.[13–15] Inferences drawn from such computa
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