Effect of Nb on Microstructural Evolution and Mechanical Properties of Hot-Rolled Quenching and Partitioning Steels Containing Bainite

Zhisong Chai, Jun Hu, Chenchong Wang, Lingyu Wang, Weihua Sun, Sybrand van der Zwaag, Wei Xu*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Herein, the effect of Nb content on the phase transformation kinetics, microstructure, and mechanical properties of hot-rolled quenching and partitioning (Q&P) steel is investigated. The characteristics of three C–Mn–Si–Ti steels (0.18C, 2.0Si, 2.6Mn, and 0.015Ti) containing 0, 0.027, or 0.061 wt% Nb are compared. Results reveal that grain boundary pinning by precipitates and Nb solute drag effects refine the austenite grain size during the hot-rolling process; the microstructural refinement is carried over to the final microstructure subjected to the Q&P treatment. The remaining supersaturated Nb suppresses the bainite formation and decreases the final bainite fraction formed in the Q&P process. The microstructural evolution leads to an increase in the ultimate tensile strength (UTS) of the steel containing 0.027 wt% Nb from 1169 to 1228 MPa, while keeping the total elongation at 18%. When the Nb content is increased to 0.061 wt%, the UTS of the steel increases to 1313 MPa, but the elongation at break drops to 16%. The effect is due to the carbon consumption by the Nb precipitates, which causes a decrease in the stability of the retained austenite and reduces the strain hardening at high strain levels.

Original languageEnglish
Article number2100247
Pages (from-to)10
JournalSteel Research International
Volume92
Issue number12
DOIs
Publication statusAccepted/In press - 2021

Bibliographical note

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care
Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Keywords

  • bainitic transformation
  • Nb microalloying
  • quenching and partitioning steel
  • retained austenite
  • strength and total elongation

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