PSI - Issue 23

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ScienceDirect

Procedia Structural Integrity 23 (2019) 155–160 Structural Integrity Procedia 00 (2019) 000–000 Structural Integrity Procedia 00 (2019) 000–000

www.elsevier.com / locate / procedia www.elsevier.com / locate / procedia

© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers Abstract The increased use of renewable energy pushes steam turbines toward a more frequent operation schedule. Consequently, compo nents must endure more severe fatigue loads which, in turn, requires an understanding of the deformation and damage mechanisms under high-temperature cyclic loading. Based on this, low cycle fatigue tests were performed on a creep resistant steel, FB2, used in ultra-supercritical steam turbines. The fatigue tests were performed in strain control with 0.8–1.2 % strain range and at temperatures of 400 ◦ C and 600 ◦ C. The tests at 600 ◦ C were run with and without dwell time. The deformation mechanisms at di ff erent tem peratures and strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter di ff raction. Microscopy revealed that specimens subjected to 600 ◦ C showed signs of creep damage, in the form of voids close to fracture surface, regardless of whether the specimen had been exposed to dwell time or been purely cycled. In addition, the amount of low angle grain boundaries was lower at 600 ◦ C than at 400 ◦ C. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed to being all plastic strain. c 2019 The Authors. Published by Elsevier B.V. his is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committe of the IC MSMF organizers. Keywords: Low cycle fatigue; Steam turbine steel; FB2; EBSD; Creep-fatigue interaction 9th International Conference on Materials Structure and Micromechanics of Fracture Characterisation of deformation and damage in a steam turbine steel subjected to low cycle fatigue Ahmed Azeez a, ∗ , Robert Eriksson a , Mattias Calmunger a a Department of Management and Engineering, Linko¨ping University, Linko¨pings universitet, Linko¨ping 58183, Sweden Abstract The increased use of renewable energy pushes steam turbines toward a more frequent operation schedule. Consequently, compo nents must endure more severe fatigue loads which, in turn, requires an understanding of the deformation and damage mechanisms under high-temperature cyclic loading. Based on this, low cycle fatigue tests were performed on a creep resistant steel, FB2, used in ultra-supercritical steam turbines. The fatigue tests were performed in strain control with 0.8–1.2 % strain range and at temperatures of 400 ◦ C and 600 ◦ C. The tests at 600 ◦ C were run with and without dwell time. The deformation mechanisms at di ff erent tem peratures and strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter di ff raction. Microscopy revealed that specimens subjected to 600 ◦ C showed signs of creep damage, in the form of voids close to fracture surface, regardless of hether the specimen had been exposed to dwell time or been purely cycled. In addition, the amount of low angle grain boundaries was lower at 600 ◦ C than at 400 ◦ C. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed to being all plastic strain. c 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. Keywords: Low cycle fatigue; Steam turbine steel; FB2; EBSD; Creep-fatigue interaction 9th International Conference on Materials Structure and Micromechanics of Fracture Characterisation of deformation and damage in a steam turbine steel subjected to low cycle fatigue Ahmed Azeez a, ∗ , Robert Eriksson a , Mattias Calmunger a a Department of Management and Engineering, Linko¨ping University, Linko¨pings universitet, Linko¨ping 58183, Sweden

1. Introduction 1. Introduction

Steam turbine materials need to be designed to endure both cyclic and prolonged static loading at high temperatures. Higher temperatures and pressures are desired in steam turbines to increase thermal e ffi ciency. The challenge, however, is to achieve materials with su ffi cient strength under such conditions. The 9–12 % Cr steel family has been widely used in steam turbines due to good mechanical properties. The newly developed 9 % Cr steel called FB2, under the European program COST 522, showed a significant improvement over several other materials and was able to satisfy requirements for use in ultra super-critical (USC) turbine conditions with temperatures up to 620 ◦ C. This mainly due to the stability of its martensitic structure at high temperatures Kern et al. (2008). Steam turbine materials need to be designed to endure both cyclic and prolonged static loading at high temperatures. Higher temperatures and pressures are desired in steam turbines to increase thermal e ffi ciency. The challenge, however, is to achieve materials with su ffi cient strength under such conditions. The 9–12 % Cr steel family has been widely used in steam turbines due to good mechanical properties. The newly developed 9 % Cr steel called FB2, under the European program COST 522, showed a significant improvement over several other materials and was able to satisfy requirements for use in ultra super-critical (USC) turbine conditions with temperatures up to 620 ◦ C. This mainly due to the stability of its martensitic structure at high temperatures Kern et al. (2008).

2452-3216 © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the ICMSMF organizers 10.1016/j.prostr.2020.01.079 ∗ Corresponding author. Tel.: + 46-13-281993. E-mail address: ahmed.azeez@liu.se 2210-7843 c 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the IC MSMF organizers. ∗ Corresponding author. Tel.: + 46-13-281993. E-mail address: ahmed.azeez@liu.se 2210-7843 c 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http: // creativecommons.org / licenses / by-nc-nd / 4.0 / ) Peer-review under responsibility of the scientific committee of the IC MSMF organizers.