PSI - Issue 28

Available online at www.sciencedirect.com Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2019) 000–000

www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 28 (2020) 93–100

© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo Abstract Three nanostructured bainitic steels have been produced by austempering at 250, 300 and 350°C respectively after a similar austenitization treatment at 950°C. It has been found that a decrease in austempering temperature causes increase in content of bainitic ferrite (BF) as well as refinement of BF and retained austenite (RA) resulting in strengthening of the steel. However, results of sub-critical fatigue crack growth rate tests on these steels revealed that the steel transformed at higher austempering temperature which showed coarser morphology of BF and RA and also higher content of RA are more damage tolerant. It appeared that the thickness of BF plates and its volume fraction in the microstructure plays a major role in enhancing the strength whereas improved damage tolerance has been attributed to higher content of ductile phase RA. Scanning electron microscopy, nano-indentation and surface profilometry techniques revealed that the larger plastic zone size, higher amount of strain energy consumed during austenite to martensite transformation (TRIP effect) and tortuous crack path are the main factors for slower fatigue crack propagation rates in steel with the coarser morphology and higher retained austenite content. © 2020 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo Keywords: Bainite; fatigue; nano-indentaion; damage tolerance 1. Introduction Nano-structured bainitic steels have a dual phase structure comprising of nano-scaled slender plates of bainitic ferrite (BF) and retained austenite (RA). BF provides excellent strength whereas RA enhances ductility through TRIP e / 1st Virtual European Conference on Fracture The Role of Microstructure on Damage Tolerance in Nano-Bainitic Steels Avanish Kumar, Aparna Singh * Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai, 400076, India

* Corresponding author. Tel.: +91-22-2576-7605; fax: +91 22 2572 3480. E-mail address: aparna_s@iitb.ac.in

2452-3216 © 2020 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo

2452-3216 © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExCo 10.1016/j.prostr.2020.10.012