Microstructural evolution and stability during strain-controlled fatigue in a multiphase microalloyed steel

Sankaran, S and Madhavan, R and Suwas, S and Ray, RK and Padmanabhan, KA (2022) Microstructural evolution and stability during strain-controlled fatigue in a multiphase microalloyed steel. In: Materials Science and Engineering A, 861 .

PDF mat_sci_eng_861_2022.pdf - Published Version Restricted to Registered users only Download (25MB) | Request a copy

Abstract

Multiphase ferrite-bainite-martensite (F-B-M) microstructure processed through rolling and two-step cooling in a V-microalloyed steel exhibited excellent stability under strain-controlled fatigue. The steel exhibited a steady state response and even cyclic hardening up to a total strain amplitude of 0.6% and displayed a cyclic softening response at total strain amplitudes >0.7%. To understand and determine the degradation mechanisms, a detailed transmission electron microscopic investigation was carried out in fatigue tested samples as a function of total strain amplitude. At low strain amplitudes (<0.4%), microstructural constituents such as the bainite/martensite colonies, and the inter-lath films of retained austenite remained stable. The deformation occurred only in the polygonal ferrite and the lamellar retained austenite, which was sheared into fine, smaller strips. Only some boundaries of bainite/martensite colonies were subjected to shearing. At an intermediate strain amplitude (0.6%), all the coarse bainite/martensite colonies exhibited shear deformation with very fine retained austenite segments distributed over large regions. The bainite/martensite lath interiors were filled with dislocation substructures and sheared inter-lath austenite layers. Austenite grain rotation was noticed, and the grain interior exhibited sheared or segmented layers. Selective inter-lath austenite layers transformed into acicular martensite. At higher amplitudes (0.8%), the F-B-M microstructure displayed homogeneous deformation and cyclic softening. Carbides and lath debris were distributed throughout the matrix and consisted of decomposed bainite and martensite. Formation of acicular and twinned martensite was present due to the TRIP effect. The F-B-M microstructure comprising small colonies of bainite/martensite with fine lath morphology, polygonal ferrite (∼20%), retained austenite with lamellar morphology and inter-lath films (∼5%) along with a fine dispersion of carbonitride precipitates in the matrix appears to be highly resistant to fatigue damage. Hot rolling processes aimed at promoting these microstructural features in the steel, which is also accompanied by texture strengthening, seem to be effective against cyclic softening in fatigue. © 2022 Elsevier B.V.

Item Type:	Journal Article
Publication:	Materials Science and Engineering A
Publisher:	Elsevier Ltd
Additional Information:	The copyright for this article belongs to Elsevier Ltd.
Keywords:	Austenite; Bainite; Carbides; Carbon nitride; Degradation; Fatigue testing; Ferrite; Microalloying; Microstructural evolution; Morphology; Steel metallography, Cyclic softening; Fatigue damage mechanism; Ferrite bainite martensites; Micro-alloyed steels; Microstructure stability; Multi-phase steels; Multiphases; Retained austenite; Strain controlled fatigue; Total strain amplitude, Martensite
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	07 Feb 2023 06:52
Last Modified:	07 Feb 2023 06:52
URI:	https://eprints.iisc.ac.in/id/eprint/80119

Actions (login required)

View Item