Influence of Prior Fatigue Cycling on Creep Behavior of Reduced Activation Ferritic-Martensitic Steel
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NTRODUCTION
REDUCED Activation Ferritic-Martensitic (RAFM) steels, derived from the conventional modified 9Cr-1Mo steel with the replacement of Mo and Nb by W and Ta, respectively, exhibit lower residual radioactivity under neutron irradiation and are considered as the prime structural materials for the Test Blanket Module (TBM) to be tested in International Thermonuclear Experimental Reactor (ITER). The choice of the material is based on its excellent resistance to neutron irradiation induced swelling and helium embrittlement and adequate high-temperature mechanical properties.[1–4] In India, an extensive research program has been underway at Indira Gandhi Centre for Atomic Research, Kalpakkam (IGCAR) in collaboration with Institute for Plasma Research, Gandhinagar for the development of India-specific RAFM steel as one of the potential structural materials for TBM-based LeadLithium Cooled Ceramic Breeder (LLCB).[5] This steel is designated as Indian Reduced Activation FerriticMartensitic (INRAFM) steel.
ARITRA SARKAR, Scientific Officer-D, V.D. VIJAYANAND, Scientific Officer-D, P. PARAMESWARAN, Scientific Officer-G, VANI SHANKAR, Scientific Officer-F, R. SANDHYA, Head Fatigue Studies Section, K. LAHA, Head Creep Studies Section, M.D. MATHEW, Head Mechanical Metallurgy Division, and T. JAYAKUMAR, Director, are with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India. Contact e-mail: [email protected], aritra147@gmail. com E. RAJENDRA KUMAR, Scientist-F, is with the Institute for Plasma Research, Bhat, Gandhinagar, Gujrat, India. Manuscript submitted October 8, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
The blanket module facing the plasma operates at a temperature of 623 K to 823 K (350 C to 550 C). It is exposed to the simultaneous effects of mechanical and thermo-mechanical stresses due to the pulsed operating nature of plasma.[6] Hence, in design procedures, creep, fatigue, and creep–fatigue interaction data are required. The creep and fatigue behavior of INRAFM steel has already been extensively studied.[7,8] However, combinations of both fatigue and creep exposure are very common in reactor operating condition, which may have deleterious implications to the service life of the reactor. Thus, assessment of creep–fatigue lifetime becomes a prime consideration in design codes,[9,10] particularly to meet the long service lifetime of components. A conventional way of carrying out creep–fatigue interaction is by introducing a hold period in fatigue tests under strain control where creep damage is superimposed on fatigue damage in each cycle. However, the effect of extensive cyclic softening or microstructural changes[11,12] encountered during fatigue stage for RAFM steels on creep deformation is unknown. Some of the previous investigations did throw some light in this matter by carrying out hold-time tests where the fatigue part was simulated through strain controlled cycling, and then the testing mode was changed to load control (hold time) which simulated the creep dam
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