Special Issue "Bainite and Martensite: Developments and Challenges"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 31 May 2017

Special Issue Editor

Guest Editor
Dr. Carlos Garcia-Mateo

Physical Metallurgy Department, Spanish National Center for Metallurgical Research, Madrid 28040, Spain
Website | E-Mail
Interests: phase transformations in steels; bainite; microstructural characterization; microstructure-mechanical properties relationships; alloy design

Special Issue Information

Dear Colleagues,

Nowadays, when modern high strength steels come to play, it is not strange to find that their microstructure contains austenite and either bainite or martensite, a combination of both, or more sophisticated variations such as Q&P and nanostructured bainitic steels.

There is no doubt that there are certain similarities in the mechanisms ruling such transformations, and therefore it is not surprising that parameters at play controlling the mechanical properties also overlap.

The development of new and powerful scientific techniques and equipment (EBSD, APT, HRTEM, etc.) allow us to gain fundamental insights that help to establish some of the principles by which those microstructures are known. The developments accompanying such findings lead to further developments and intensive research providing the required metallurgical support.

There is a very significant number of publications and some scattered conferences and workshops devoted to these type steels. However, there is no forum that brings together the latest developments, taking place in the framework of these microstructures and their properties.

Papers on recent advances and review articles, particularly related to the most challenging aspects of the use of bainitic and martensitic microstructures, in any of their forms, are invited for inclusion in this Special Issue on "Bainite and Martensite: Developments and Challenges".

Dr. Carlos Garcia-Mateo
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Phase transformation
  • Modelling
  • Alloy and process design
  • Thermal treatment
  • Mechanical and in-use properties
  • Crystallography
  • Microstructural (advanced) characterization

Published Papers (4 papers)

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Research

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Open AccessArticle Evaluating Strengthening and Impact Toughness Mechanisms for Ferritic and Bainitic Microstructures in Nb, Nb-Mo and Ti-Mo Microalloyed Steels
Metals 2017, 7(2), 65; doi:10.3390/met7020065
Received: 10 February 2017 / Revised: 17 February 2017 / Accepted: 17 February 2017 / Published: 22 February 2017
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Abstract
Low carbon microalloyed steels show interesting commercial possibilities by combining different “micro”-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this
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Low carbon microalloyed steels show interesting commercial possibilities by combining different “micro”-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this paper, a detailed characterization of the microstructural features of three different microalloyed steels, Nb, Nb-Mo and Ti-Mo, is described using mainly the electron backscattered diffraction technique (EBSD) as well as transmission electron microscopy (TEM). The contribution of different strengthening mechanisms to yield strength and impact toughness is evaluated, and its relative weight is computed for different coiling temperatures. Grain refinement is shown to be the most effective mechanism for controlling both mechanical properties. As yield strength increases, the relative contribution of precipitation strengthening increases, and this factor is especially important in the Ti-Mo microalloyed steel where different combinations of interphase and random precipitation are detected depending on the coiling temperature. In addition to average grain size values, microstructural heterogeneity is considered in order to propose a new equation for predicting ductile–brittle transition temperature (DBTT). This equation considers the wide range of microstructures analyzed as well as the increase in the transition temperature related to precipitation strengthening. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Open AccessArticle Phase Equilibrium and Austenite Decomposition in Advanced High-Strength Medium-Mn Bainitic Steels
Metals 2016, 6(10), 248; doi:10.3390/met6100248
Received: 15 September 2016 / Revised: 11 October 2016 / Accepted: 14 October 2016 / Published: 20 October 2016
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Abstract
The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature
[...] Read more.
The work addresses the phase equilibrium analysis and austenite decomposition of two Nb-microalloyed medium-Mn steels containing 3% and 5% Mn. The pseudobinary Fe-C diagrams of the steels were calculated using Thermo-Calc. Thermodynamic calculations of the volume fraction evolution of microstructural constituents vs. temperature were carried out. The study comprised the determination of the time-temperature-transformation (TTT) diagrams and continuous cooling transformation (CCT) diagrams of the investigated steels. The diagrams were used to determine continuous and isothermal cooling paths suitable for production of bainite-based steels. It was found that the various Mn content strongly influences the hardenability of the steels and hence the austenite decomposition during cooling. The knowledge of CCT diagrams and the analysis of experimental dilatometric curves enabled to produce bainite-austenite mixtures in the thermomechanical simulator. Light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to assess the effect of heat treatment on morphological details of produced multiphase microstructures. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Review

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Open AccessReview Transferring Nanoscale Bainite Concept to Lower C Contents: A Perspective
Metals 2017, 7(5), 159; doi:10.3390/met7050159
Received: 27 March 2017 / Revised: 16 April 2017 / Accepted: 28 April 2017 / Published: 4 May 2017
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Abstract
The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the
[...] Read more.
The major strengthening mechanisms in bainitic steels arise from the bainitic ferrite plate thickness rather than the length, which primarily determines the mean free slip distance. Both the strength of the austenite from where the bainite grows and the driving force of the transformation, are the two factors controlling the final scale of the bainitic microstructure. Usually, those two parameters can be tailored by means of selection of chemical composition and transformation temperature. However, there is also the possibility of introducing plastic deformation on austenite and prior to the bainitic transformation as a way to enhance both the austenite strength and the driving force for the transformation; the latter by introducing a mechanical component to the free energy change. This process, known as ausforming, has awoken a great deal of interest and it is the object of ongoing research with two clear aims. First, an acceleration of the sluggish bainitic transformation observed typically in high C steels (0.7–1 wt. %) transformed at relatively low temperatures. Second, to extend the concept of nanostructured bainite from those of high C steels to much lower C contents, 0.4–0.5 wt. %, keeping a wider range of applications in view. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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Other

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Open AccessFeature PaperTechnical Note Tensile Ductility of Nanostructured Bainitic Steels: Influence of Retained Austenite Stability
Metals 2017, 7(1), 31; doi:10.3390/met7010031
Received: 19 December 2016 / Revised: 9 January 2017 / Accepted: 16 January 2017 / Published: 23 January 2017
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Abstract
High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 °C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of
[...] Read more.
High silicon (>1.5%) steels with different compositions were isothermally transformed to bainite at 220 and 250 °C to produce what is often referred to as nanostructured bainite. Interrupted tensile tests were carried out and the retained austenite was measured as a function of strain. Results were correlated with tensile ductility. The role of retained austenite stability is remarkably underlined as strongly affecting the propensity to brittle failure, but also the tensile ductility. A simple quantitative relationship is proposed that clearly delimitates the different behaviours (brittle/ductile) and correlates well with the measured ductility. Conclusions are proposed as to the role of retained austenite fraction and the existence of a threshold value associated with tensile rupture. Full article
(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)
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