Metallurgical and Materials Transactions A

, Volume 44, Issue 8, pp 3552–3563 | Cite as

Phase Transformation Study in Nb-Mo Microalloyed Steels Using Dilatometry and EBSD Quantification

  • Nerea Isasti
  • Denis Jorge-Badiola
  • Mitra L. Taheri
  • Pello Uranga

A complete microstructural characterization and phase transformation analysis has been performed for several Nb and Nb-Mo microalloyed low-carbon steels using electron backscattered diffraction (EBSD) and dilatometry tests. Compression thermomechanical schedules were designed resulting in the undeformed and deformed austenite structures before final transformation. The effects of microalloying additions and accumulated deformation were analyzed after CCT diagram development and microstructural quantification. The resulting microstructures ranged from polygonal ferrite and pearlite at slow cooling ranges, to a combination of quasipolygonal ferrite and granular ferrite for intermediate cooling rates, and finally, to bainitic ferrite with martensite for fast cooling rates. The addition of Mo promotes a shift in the CCT diagrams to lower transformation start temperatures. When the amount of Nb is increased, CCT diagrams show little variations for transformations from the undeformed austenite and higher initial transformation temperatures in the transformations from the deformed austenite. This different behavior is due to the effect of niobium on strain accumulation in austenite and its subsequent acceleration of transformation kinetics. This article shows the complex interactions between chemical composition, deformation, and the phases formed, as well as their effect on microstructural unit sizes and homogeneity.


Austenite Bainitic Ferrite Polygonal Ferrite Continuous Cool Transformation Diagram Transformation Start Temperature 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The financial support of the Spanish Ministry of Economy and Competitiveness (MAT2009-09250 and MAT2012-31056) and Basque Government (PI2011-17) is acknowledged.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2013

Authors and Affiliations

  • Nerea Isasti
    • 1
  • Denis Jorge-Badiola
    • 1
  • Mitra L. Taheri
    • 2
  • Pello Uranga
    • 1
  1. 1.CEIT and TECNUN, University of NavarraDonostia-San SebastiánSpain
  2. 2.Drexel UniversityPhiladelphiaUSA

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