Metallurgical and Materials Transactions A

, Volume 45, Issue 11, pp 4960–4971 | Cite as

Microstructural Features Controlling Mechanical Properties in Nb-Mo Microalloyed Steels. Part I: Yield Strength

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


Low carbon Nb-Mo microalloyed steels show interesting synergies between the “micro”-alloying elements when high strength–high toughness properties are required. Strain accumulation in austenite is enhanced, and therefore grain sizes are refined in the final microstructures. The presence of Mo facilitates the presence of non-polygonal phases, and this constituent modification induces an increment in strength through a substructure formation as well as through an increase in the dislocation density. Regarding fine precipitation and its strengthening effect, the mean size of NbC is reduced in the presence of Mo and their fraction increased, thus enhancing their contribution to yield strength. In this paper, a detailed characterization of the microstructural features of a series of microalloyed steels is described using the electron-backscattered diffraction technique. Mean crystallographic unit sizes, a grain boundary misorientation analysis, and dislocation density measurements are performed. Transmission electron microscopy is carried out to analyze the chemical composition of the precipitates and to estimate their volume fraction. In this first part, the contribution of different strengthening mechanisms to yield strength is evaluated and the calculated value is compared to tensile test results for different coiling temperatures and compositions.


Austenite Yield Strength Dislocation Density Unit Size Polygonal Ferrite 
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The financial support of the Spanish Ministry of Economy and Competitiveness (MAT2009-09250 and MAT2012-31056) and Basque Government (PI2011-17) is gratefully acknowledged.


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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2014

Authors and Affiliations

  • Nerea Isasti
    • 1
  • Denis Jorge-Badiola
    • 1
  • Mitra L. Taheri
    • 2
  • Pello Uranga
    • 1
  1. 1.CEIT and TECNUN (University of Navarra)Donostia-San SebastiánSpain
  2. 2.Department of Materials ScienceDrexel UniversityPhiladelphiaUSA

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