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Metals
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Advanced High-Strength Bainitic Steels
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Advanced High-Strength Bainitic Steels

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 17002

Special Issue Editor

Dr. Lucia Morales-Rivas

E-Mail Website
Guest Editor
University of Kaiserslautern, Materials Testing Group, Gottlieb-Daimler-Str., Kaiserslautern 67663, Germany
Interests: nanostructured bainite; metallic alloys; microstructural characterization; fatigue
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Advanced bainitic steels have attracted the attention of steel makers and end users in recent years, owing to the simplicity of their chemical composition and their processing, as well as their ability to achieve both high strength and excellent toughness values.

Bainite has many similarities to martensite from a crystallographic perspective. However, bainitic transformation does not involve severe quenching, which often leads to the formation of cracks in martensite and even failure during subsequent treatment.  On the other hand, transformation at higher temperatures comes with the detrimental carbide precipitation typical of conventional bainite. This promising steel concept depends on the elimination of the massive precipitation of carbides by the rational addition of silicon, enabling the presence of a heterogeneous distribution of retained austenite at room temperature, which opens a window of applications to bainitic steels that has never been seen before.

Technological research is still needed for the implementation of advanced bainitic steels in sectors like the automotive, where the use of high-strength steels seeks weight reduction to comply with the increasingly strict regulations on greenhouse gas emissions. Likewise, safety standards and in-use life extension requirements for many applications involve the necessity of further studies on wear and fatigue. Fundamental studies on transformation, deformation, and damage mechanisms will guide the development of new advanced high-strength bainitic microstructures.

The scope of this Special Issue is to share novel findings on advanced high-strength bainitic steels regarding the following aspects: the design of the alloy and processing routes, advanced microstructural characterization, and mechanical testing.

Dr. Lucia Morales-Rivas
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 submissions that pass pre-check are 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 2600 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

  • Advanced steels
  • High-strength steels
  • Bainitic microstructures
  • Carbide-free bainitic steels
  • Retained austenite
  • Alloy design
  • Processing routes
  • Microstructural characterization
  • Mechanical performance
  • In-use properties

Published Papers (7 papers)

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Research

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14 pages, 7699 KiB  
Article
Microstructure and Mechanical Properties of Cast and Hot-Rolled Medium-Carbon Steels under Isothermal Heat-Treatment Conditions
by Byungsue Shin, Kwangyuk Kim, Sung Yi, Sanggyu Choi and Soongkeun Hyun
Metals 2021, 11(12), 1950; https://doi.org/10.3390/met11121950 - 03 Dec 2021
Cited by 2 | Viewed by 3065
Abstract
In this study, the changes in the microstructure and mechanical properties during isothermal heat treatment of cast steel before and after hot deformation were investigated using medium-carbon steel with low alloy content. The microstructural characteristics of the cast and hot-rolled medium-carbon steel under [...] Read more.
In this study, the changes in the microstructure and mechanical properties during isothermal heat treatment of cast steel before and after hot deformation were investigated using medium-carbon steel with low alloy content. The microstructural characteristics of the cast and hot-rolled medium-carbon steel under isothermal heat-treatment conditions were examined using optical microscopy and scanning electron microscopy in conjunction with electron backscatter diffraction. The variation in the mechanical properties was evaluated using Rockwell hardness and tensile tests. After maintaining an austenitizing condition at 1200 °C for 30 min, an isothermal heat treatment was performed in the range 350–500 °C, followed by rapid cooling with water. Both the cast steel and hot-rolled steel did not completely transform into bainitic ferrite during isothermal heat treatment. The partially untransformed microstructure was a mixture of martensite and acicular ferrite. At 500 °C, the prior austenite phase changed to Widmanstätten ferrite and pearlite. At 450 °C, bainitic ferrite and cementite were coarsened by the coalescence of ferrite and subsequent diffusive growth. The mechanical properties increased as the isothermal heat-treatment temperature decreased, and the hardness of the cast steel was generally higher than that of the hot-rolled steel. Hardness and strength showed similar trends, and overall mechanical properties tend to decrease as the isothermal heat-treatment temperature increases, but there are slight differences depending on complex factors such as various phase fractions and grain size. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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21 pages, 17184 KiB  
Article
Controlling the Content and Morphology of Phase Constituents in Nanobainitic Steel Containing 0.6%C to Obtain the Required Ratio of Strength to Plasticity
by Jarosław Marcisz, Bogdan Garbarz, Aleksandra Janik and Władysław Zalecki
Metals 2021, 11(4), 658; https://doi.org/10.3390/met11040658 - 17 Apr 2021
Cited by 6 | Viewed by 2138
Abstract
The phase composition of nanobainitic steel 0.56–0.60%C, 1.68–1.95%Mn, 1.58–1.80%Si, 1.30–1.47%Cr, 0.57–0.75%Mo is described in this paper. The phase composition is controlled in order to obtain diversified mechanical properties for specific applications, such as armor plates. The effect of temperature and time of isothermal [...] Read more.
The phase composition of nanobainitic steel 0.56–0.60%C, 1.68–1.95%Mn, 1.58–1.80%Si, 1.30–1.47%Cr, 0.57–0.75%Mo is described in this paper. The phase composition is controlled in order to obtain diversified mechanical properties for specific applications, such as armor plates. The effect of temperature and time of isothermal heat treatment on both the microstructure and the mechanical properties of the steel were determined. Dilatometric studies, as well as measurements of volume fraction and size distribution of retained austenite were carried out. Analysis of the kinetics of isothermal transformation in the temperature range of 200–225 °C for times of up to 144 h were also carried out, and the parameters of the production process of the steel were determined. A microstructure consisting of nanolathy carbideless bainite and blocky and lathy retained austenite, providing tensile strength of at least 2000 MPa, yield strength of at least 1300 MPa, and total elongation of at least 10% has been found. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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14 pages, 20964 KiB  
Article
Revealing the Dynamic Transformation of Austenite to Bainite during Uniaxial Warm Compression through In-Situ Synchrotron X-ray Diffraction
by William Lemos Bevilaqua, Jérémy Epp, Heiner Meyer, Juan Dong, Hans Roelofs, Alexandre da Silva Rocha and Afonso Reguly
Metals 2021, 11(3), 467; https://doi.org/10.3390/met11030467 - 12 Mar 2021
Cited by 3 | Viewed by 1834
Abstract
In this work, the microstructural evolution during the dynamic transformation of austenite to bainite was directly observed by in-situ high energy synchrotron X-ray diffraction measurements during warm uniaxial compression performed at the P07 beamline of PETRA III, DESY (Deutsches Elektronen-Synchrotron). Plastic deformation triggers [...] Read more.
In this work, the microstructural evolution during the dynamic transformation of austenite to bainite was directly observed by in-situ high energy synchrotron X-ray diffraction measurements during warm uniaxial compression performed at the P07 beamline of PETRA III, DESY (Deutsches Elektronen-Synchrotron). Plastic deformation triggers the phase transformation, which is continuously stimulated by the introduction of dynamic dislocations into the austenite. This scenario accelerates the kinetics of bainite formation in comparison with conventional isothermal treatment. No mechanical stabilization of austenite was observed during dynamic transformation. Evidence of carbon partitioning between phases during plastic deformation was obtained. Further post-process investigations suggest that the bainitic microstructure developed during compression is oriented perpendicular to the loading direction. The findings open up new possibilities to design carbide-free bainitic microstructures directly via thermomechanical processing. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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13 pages, 3045 KiB  
Article
A New Systematic Approach Based on Dilatometric Analysis to Track Bainite Transformation Kinetics and the Influence of the Prior Austenite Grain Size
by David San-Martin, Matthias Kuntz, Francisca G. Caballero and Carlos Garcia-Mateo
Metals 2021, 11(2), 324; https://doi.org/10.3390/met11020324 - 13 Feb 2021
Cited by 7 | Viewed by 1468
Abstract
This investigation explores the influence of the austenitisation heat treatment and thus, of the prior austenite grain size (PAGS), on the kinetics of the bainitic transformation, using as A case study two high-carbon, high-silicon, bainitic steels isothermally transformed (TIso = 250, [...] Read more.
This investigation explores the influence of the austenitisation heat treatment and thus, of the prior austenite grain size (PAGS), on the kinetics of the bainitic transformation, using as A case study two high-carbon, high-silicon, bainitic steels isothermally transformed (TIso = 250, 300, 350 °C), after being austenised at different temperatures (γTγ = 925–1125 °C). A methodology, based on the three defining dilatometric parameters extracted from the derivative of the relative change in length, was proposed to analyse the transformation kinetics. These parameters are related to the time to start bainitic transformation, the time lapse for most of the transformation to take place and the transformation rate at the end of the transformation. The results show that increasing the PAGS up to 70 µm leads to an increase in the bainite nucleation rate, this effect being more pronounced for the lowest TIso. However, the overall transformation kinetics seems to be weakly affected by the applied heat treatment (γTγ and TIso). In one of the steels, PAGS > 70 µm (γTγ > 1050 °C), which weakly affects the progress of the transformation, except for TIso = 250 °C, for which the enhancement of the autocatalytic effect could be the reason behind an acceleration of the overall transformation. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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31 pages, 9832 KiB  
Article
Effect of Microsegregation and Bainitic Reaction Temperature on the Microstructure and Mechanical Properties of a High-Carbon and High-Silicon Cast Steel
by Alejandro Basso, Adriana Eres-Castellanos, Nicolás Tenaglia, David San-Martin, José Antonio Jimenez and Francisca G. Caballero
Metals 2021, 11(2), 220; https://doi.org/10.3390/met11020220 - 27 Jan 2021
Cited by 5 | Viewed by 2070
Abstract
Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently of great interest. Microstructural evolution and the bainitic transformation kinetics of a high-carbon and high-silicon cast steel held at 280, 330, and 380 °C was analyzed using dilatometry, X-ray diffraction, optical [...] Read more.
Bainitic microstructures obtained in high-carbon (HC) and high-silicon (HSi) steels are currently of great interest. Microstructural evolution and the bainitic transformation kinetics of a high-carbon and high-silicon cast steel held at 280, 330, and 380 °C was analyzed using dilatometry, X-ray diffraction, optical and scanning electron microscopy, and electron backscatter diffraction (EBSD). It is shown that the heterogeneous distribution of silicon (Si), manganese (Mn), and chromium (Cr) associated to microsegregation during casting has a great impact on the final microstructure. The transformation starts in the dendritic zones where there is a lower Mn concentration and then expands to the interdendritic ones. As Mn reduces the carbon activity, the interdendritic areas with a higher Mn concentration are enriched with carbon (C), and thus, these zones contain a greater amount of retained austenite plus martensite, resulting in a heterogeneous microstructure. Higher transformation temperatures promote higher amounts of residual austenite with poor thermal/mechanical stability and the presence of martensite in the final microstructure, which has a detrimental effect on the mechanical properties. Tensile tests revealed that the ultra-fine microstructure developed by the transformation at 280 °C promotes very high values of both tensile and yield stress (≈1.8 GPa and 1.6 GPa, respectively), but limited ductility (≈2%). Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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Review

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15 pages, 1232 KiB  
Review
Viewpoints on Technological Aspects of Advanced High-Strength Bainitic Steels
by Lucia Morales-Rivas
Metals 2022, 12(2), 195; https://doi.org/10.3390/met12020195 - 21 Jan 2022
Cited by 7 | Viewed by 2986
Abstract
The development of advanced high-strength bainitic steels has been preceded and linked to different metallurgical advances, both in the field of fundamental materials science and in technological fields closer to the production and final application. The diversity and abundance of documents in literature [...] Read more.
The development of advanced high-strength bainitic steels has been preceded and linked to different metallurgical advances, both in the field of fundamental materials science and in technological fields closer to the production and final application. The diversity and abundance of documents in literature has favored the co-existence of extensive terminology in the context of advanced high-strength steels and bainitic steels. In this work, the concept of advanced high-strength bainitic steels is briefly revisited from a wide perspective, with the aim of highlighting the main limitations and challenges for further development of these microstructures. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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19 pages, 2476 KiB  
Review
Future Trends on Displacive Stress and Strain Induced Transformations in Steels
by Adriana Eres-Castellanos, Carlos Garcia-Mateo and Francisca G. Caballero
Metals 2021, 11(2), 299; https://doi.org/10.3390/met11020299 - 09 Feb 2021
Cited by 9 | Viewed by 2349
Abstract
Displacive stress and strain induced transformations are those transformations that occur when the formation of martensite or bainitic ferrite is promoted by the application of stress or strain. These transformations have been shown to be one of the mechanisms by which the mechanical [...] Read more.
Displacive stress and strain induced transformations are those transformations that occur when the formation of martensite or bainitic ferrite is promoted by the application of stress or strain. These transformations have been shown to be one of the mechanisms by which the mechanical properties of a microstructure can be improved, as they lead to a better ductility and strength by the transformation induced plasticity effect. This review aims to summarize the fundamental knowledge about them, both in fully austenitic or in multiphase structures, pointing out the issues that—according to the authors’ opinion—need further research. Knowing the mechanisms that govern the stress and strain induced transformation could enable to optimize the thermomechanical treatments and improve the final microstructure properties. Full article
(This article belongs to the Special Issue Advanced High-Strength Bainitic Steels)
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