On the low temperature strain aging of bainite in the TRIP steel

Ilana Timokhina, Hossein Beladi, Xiang-Yuan Xiong, Peter D Hodgson

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Abstract

The aging behavior of a thermomechanically processed Mo-Al-Nb transformation-induced plasticity steel with ultrafine microstructure was investigated using transmission electron microscopy and atom probe tomography (APT). Strain aging at 73 K (200 C) for 1800 seconds led to a significant bake-hardening response (up to 222 MPa). Moreover, aging for 1800 seconds at room temperature after 4 pct pre-strain also revealed a bake-hardening response ( 60 MPa). The experimental results showed the formation of carbon Cottrell atmospheres around dislocations and the formation of carbon clusters/fine carbides in the bainitic ferrite during aging. It is proposed that this is associated with the high dislocation density of bainitic ferrite with formation of a complex dislocation substructure after pre-straining and its high average carbon content ( 0.35 at. pct). The segregation of carbon and substitutional elements such as Mn and Mo to the retained austenite/bainitic ferrite interface during aging was observed by APT. This segregation is likely to be the preliminary stage for Mo-C particles formation. The aging after pre-straining also induced the decomposition of retained austenite with formation of ferrite and carbides.
Original languageEnglish
Pages (from-to)5177 - 5191
Number of pages15
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume44
Issue number11
DOIs
Publication statusPublished - 2013

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