Issue 48

S.C.S.P. Kumar Krovvidi et alii, Frattura ed Integrità Strutturale, 48 (2019) 577-584; DOI: 10.3221/IGF-ESIS.48.56 577 Focused on “Showcasing Structural Integrity Research in India” Low cycle fatigue and creep-fatigue response of the 316Ti stainless steel S.C.S.P. Kumar Krovvidi, Sunil Goyal, A. K. Bhaduri Indira Gandhi Centre for Atomic Research, Kalpakkam- 603102, India krovvidi@igcar.gov.in , goyal@igcar.gov.in , bhaduri@igcar.gov.in A BSTRACT . SS 316Ti is widely used in bellows industry and is a good candidate material for high temperature bellows in sodium cooled fast reactor (SFR) systems. Typical operating temperature experienced by SFR systems is around 823K. Design of bellows for nuclear applications need to be in compliance with the standard design codes such as ASME section-III and RCC-MR. The fatigue data and cyclic stress strain curve of SS316Ti are not available in design codes such as RCC-MR or ASME section-III/NH. Hence, the material data required for high temperature design of bellows are generated experimentally. Initially, the basic tensile data such as yield strength, ultimate tensile strength and % elongation of the material were obtained from tensile testing at 823K. Low cycle fatigue tests were carried out in strain controlled mode on SS316Ti at 823K different strain ranges in air and variation of number of cycles with strain range was obtained. Creep-fatigue interaction (CFI) experiment was also conducted at 823K and strain amplitude of ± 0.4% with 1 minute hold time in peak tensile strain. The stress response (peak stress variation with number of cycles) of the material showed continuous hardening up to saturation followed by crack nucleation and final failure. The fatigue life was found to decrease with increase in strain range. The fatigue life decreased in presence of hold period in tension. The design fatigue curve for SS316Ti at 823K has been generated using the LCF data by incorporating factors of safety on strain and number of cycles. Cyclic stress strain curve was generated for the material at 823K. The tensile, LCF and CFI data generated will be useful in design of SS316Ti bellows for SFR systems. K EYWORDS . SS 316Ti; Bellows; Low cycle fatigue; Creep-fatigue interaction. Citation: Kumar Krovvidi, S.C.S.P., Goyal, S., Bhaduri, A. K., Low cycle fatigue and creep- fatigue response of the 316Ti stainless steel, Frattura ed Integrità Strutturale, 48 (2019) 577-584. Received: 27.11.2018 Accepted: 28.02.2019 Published: 01.04.2019 Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION 16Ti stainless steel is a titanium-stabilized grade of Type 316 austenitic stainless steel. Type 316 stainless steels are generally susceptible to sensitization in the temperature range of 500ºC to 850ºC due to the formation of grain boundary chromium carbides resulting in reduction in corrosion resistance [1]. Resistance to sensitization is achieved 3