Abstract
High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening, and whereas usually lead to degraded toughness for especially ferritic steels. Hence, it is important to understand the formation behaviors of the Cu precipitates. High-resolution transmission electron microscopy (TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy (HSLA) steel. The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations. The Cu precipitates in the same aging condition have various structure of BCC, 9R and FCC, and the structural evolution does not greatly correlate with the actual sizes. The presence of different structures in an individual Cu precipitate is observed, which reflects the structural transformation occurring locally to relax the strain energy. The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe–Cu alloys with Ni or Mn additions. This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.
Highlights
The nanoscale Cu precipitates often endows alloyed steels with dramatically high strength but simultaneously lead to degraded impact toughness especially at cryogenic temperature [1,2,3]
Several nanoscale Cu precipitates can be recognized by the strain field contrast arose from lattice distortion and by the somewhat weak fringe contrast where the atomic columns are mostly ill-arranged
These precipitates are formed in association with linear dislocation as they generally distributed in an arc curve, which is consistent with the APT observation of Cu precipitates in a similar steel [19]
Summary
The nanoscale Cu precipitates often endows alloyed steels with dramatically high strength but simultaneously lead to degraded impact toughness especially at cryogenic temperature [1,2,3]. The nature of Cu precipitation in α-Fe matrix have been comprehensively investigated in aspect of mutual development of composition, structure and morphology [4]. With the precipitation reaction proceeding, Fe atoms are gradually expelled into the matrix and Ni and. Mn tend to segregate at the precipitate/α-Fe boundaries [8, 9]. The structure of Cu precipitates evolves following a complicated BCC→9R→3R→FCC sequence [10, 11], and the BCC Cu precipitates are considered to be originate from the growth of B2 ordered domains, as reported by Wen et al [12]. Accompanying the compositional and structural evolution, the morphology of Cu precipitates generally changes from spherical to ellipsoidal to rod-like shape [4, 13]. The transformations in course of Cu precipitation collectively take place in order to reduce the related coherent strain energy, interfacial energy and inherent energy of Cu precipitates
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
