Metallurgical and Materials Transactions A

, Volume 33, Issue 5, pp 1331–1349

Effect of composition and austenite deformation on the transformation characteristics of low-carbon and ultralow-carbon microalloyed steels

  • P. Cizek
  • B. P. Wynne
  • C. H. J. Davies
  • B. C. Muddle
  • P. D. Hodgson
Article

DOI: 10.1007/s11661-002-0059-8

Cite this article as:
Cizek, P., Wynne, B.P., Davies, C.H.J. et al. Metall and Mat Trans A (2002) 33: 1331. doi:10.1007/s11661-002-0059-8

Abstract

Deformation dilatometry has been used to simulate controlled hot rolling followed by controlled cooling of a group of low- and ultralow-carbon microalloyed steels containing additions of boron and/or molybdenum to enhance hardenability. Each alloy was subjected to simulated recrystallization and nonrecrystallization rolling schedules, followed by controlled cooling at rates from 0.1 °C/s to about 100 °C/s, and the corresponding continuous-cooling-transformation (CCT) diagrams were constructed. The resultant microstructures ranged from polygonal ferrite (PF) for combinations of slow cooling rates and low alloying element contents, through to bainitic ferrite accompanied by martensite for fast cooling rates and high concentrations of alloying elements. Combined additions of boron and molybdenum were found to be most effective in increasing steel hardenability, while boron was significantly more effective than molybdenum as a single addition, especially at the ultralow carbon content. Severe plastic deformation of the parent austenite (>0.45) markedly enhanced PF formation in those steels in which this microstructural constituent was formed, indicating a significant effective decrease in their hardenability. In contrast, in those steels in which only nonequilibrium ferrite microstructures were formed, the decreases in hardenability were relatively small, reflecting the lack of sensitivity to strain in the austenite of those microstructural constituents forming in the absence of PF.

Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 2002

Authors and Affiliations

  • P. Cizek
    • 2
  • B. P. Wynne
    • 3
  • C. H. J. Davies
    • 4
  • B. C. Muddle
    • 4
  • P. D. Hodgson
    • 5
  1. 1.Department of Materials EngineeringMonash UniversityClaytonAustralia
  2. 2.Department of MaterialsUniversity of OxfordOxfordUnited Kingdom
  3. 3.Institute of Microstructural and Mechanical Process Engineering (IMMPETUS)University of SheffieldSheffieldUnited Kingdom
  4. 4.the School of Physics and Materials EngineeringMonash UniversityAustralia
  5. 5.the School of Engineering and TechnologyDeakin UniversityVictoriaAustralia