The effect of soaking time after ultrafast heating on the microstructure and mechanical behavior of a low carbon steel

M. A. Valdes-Tabernero, R. H. Petrov, M. A. Monclus, J. M. Molina-Aldareguia, I. Sabirov

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1 Citation (Scopus)

Abstract

The main objective of this study is to understand the effect of the soaking time during the ultrafast heat treatment of a low carbon steel on its complex multi-phase microstructure, tensile mechanical behavior and properties of individual microconstituents. Tensile tests were performed to determine the macro-mechanical properties. Nanoindentation testing was carried out on individual microconstituents (martensite, recrystallized ferrite and non-recrystallized ferrite) identified a priori via EBSD analysis to measure their properties. It is shown that ultrafast heating combined with short soaking times results in improved macro-mechanical properties due to finer grain size and higher fraction of non-recrystallized ferrite, that has a higher nanohardness than recrystallized ferrite. Prolonged soaking times eliminate the advantages of the ultrafast heat treatment. This occurs because, even though a long soaking time promotes a higher volume fraction of martensite than a short one, it also induces substantial grain growth and complete recrystallization of the ferritic matrix. On the micro-scale, the ferritic grains show two different types of mechanical response. The recrystallized ferritic grains are prone to show pop-in events on the nanoindentation curves that are associated to dislocation nucleation events as a consequence of their low dislocation density, while non-recrystallized ferritic grains demonstrate a continuous response. The relationship between microstructure and mechanical properties on the macro- and micro-scales is discussed with respect to the microstructure, which in turn strongly depends on the applied heating rate and soaking time. A general recipe for microstructural design to improve the tensile mechanical behavior of low carbon steels implementing controlled heating and soaking conditions is outlined.

Original languageEnglish
Article number138276
Number of pages10
JournalMaterials Science and Engineering A
Volume765
DOIs
Publication statusPublished - 2019

Keywords

  • Mechanical properties
  • Microstructure
  • Nanoindentation
  • Pop-in
  • Steel
  • Ultrafast heating

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