Special Issue "Advances in Microalloyed Steels"

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

Deadline for manuscript submissions: closed (30 September 2018)

Special Issue Editor

Guest Editor
Dr. Pello Uranga

Associate Director of the Materials and Manufacturing Division at CEIT and Associate Professor at Universidad de Navarra-Tecnun;
CEIT and Universidad de Navarra-Tecnun, M. Lardizabal 15, 20018 Donostia-San Sebastian, Basque Country, Spain
Website | E-Mail
Interests: phase transformations; microstructure; microscopy; microalloying; steels; metallurgy; materials science; modelling

Special Issue Information

Dear Colleagues,

In response to the demanding requirements of different sectors, such as construction, transportation, energy, manufacturing, and mining, new generations of microalloyed steels are being developed and brought to market. The addition of microalloying elements, such as Niobium, Vanadium, Titanium, Boron and/or Molybdenum have become a key tool in the steel industry to reach economically-viable grades with increasingly higher mechanical strengths, toughness properties, good formability and weldable products.

The challenges that microalloying steel production face can be successfully solved with a deeper understanding of the effects that these microalloying additions and combinations of them have during the different steps of the steelmaking process. Their influence in softening mechanisms, such as recrystallization and grain growth during hot working, precipitation kinetics, phase transformation during cooling, and the relationship between the final microstructure and mechanical properties are just some examples of subjects of interest for research in industry and academia.

The availability of advanced characterization techniques together with innovative modelling strategies provides new tools to understand these open issues and achieve valid answers for the development of new microalloyed grades and the optimization of the processing routes.

For this Special Issue on "Advances in Microalloyed Steels", I would like to invite researchers from steel industry and academia to submit their latest developments and achievements in this field.

Assoc. Prof. Pello Uranga
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 1500 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

  • Niobium
  • Vanadium
  • Titanium
  • Boron
  • Molybdenum
  • Thermomechanical Processing
  • Phase Transformations
  • Microstructure
  • Mechanical Properties
  • Modelling

Published Papers (12 papers)

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Editorial

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Open AccessEditorial
Advances in Microalloyed Steels
Metals 2019, 9(3), 279; https://doi.org/10.3390/met9030279
Received: 22 February 2019 / Accepted: 27 February 2019 / Published: 28 February 2019
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Abstract
Microalloyed steels are one of the core alloy steels in the development of modern advanced high-strength steels [...] Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)

Research

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Open AccessArticle
Effect of Cold-Deformation on Austenite Grain Growth Behavior in Solution-Treated Low Alloy Steel
Metals 2018, 8(12), 1004; https://doi.org/10.3390/met8121004
Received: 28 October 2018 / Revised: 19 November 2018 / Accepted: 21 November 2018 / Published: 1 December 2018
Cited by 1 | PDF Full-text (1823 KB) | HTML Full-text | XML Full-text
Abstract
The occurrence of abnormal grain growth (AGG) of austenite during annealing is a serious problem in steels with carbide and/or nitride particles, which should be avoided from a viewpoint of mechanical properties. The effects of cold deformation prior to annealing on the occurrence [...] Read more.
The occurrence of abnormal grain growth (AGG) of austenite during annealing is a serious problem in steels with carbide and/or nitride particles, which should be avoided from a viewpoint of mechanical properties. The effects of cold deformation prior to annealing on the occurrence of AGG have been investigated. It was found that the temperature range of the occurrence of AGG is shifted toward a low temperature region by cold deformation, and that the shift increases with the increase of the reduction ratio. The lowered AGG occurrence temperature is attributed to the fine and near-equilibrium AlN particles that are precipitated in the cold-deformed steel, which is readily dissolved during annealing. In contrast, coarse and non-equilibrium AlN particles precipitated in the undeformed steel, which is resistant to dissolution during annealing. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
Influence of Vanadium on the Microstructure and Mechanical Properties of Medium-Carbon Steels for Wheels
Metals 2018, 8(12), 978; https://doi.org/10.3390/met8120978
Received: 31 October 2018 / Revised: 14 November 2018 / Accepted: 21 November 2018 / Published: 23 November 2018
Cited by 1 | PDF Full-text (4677 KB) | HTML Full-text | XML Full-text
Abstract
Steels used for high-speed train wheels require a combination of high strength, toughness, and wear resistance. In 0.54% C-0.9% Si wheel steel, the addition of 0.075 or 0.12 wt % V can refine grains and increase the ferrite content and toughness, although the [...] Read more.
Steels used for high-speed train wheels require a combination of high strength, toughness, and wear resistance. In 0.54% C-0.9% Si wheel steel, the addition of 0.075 or 0.12 wt % V can refine grains and increase the ferrite content and toughness, although the influence on the microstructure and toughness is complex and poorly understood. We investigated the effect of 0.03, 0.12, and 0.23 wt % V on the microstructure and mechanical properties of medium-carbon steels (0.54% C-0.9% Si) for train wheels. As the V content increased, the precipitation strengthening increased, whereas the grain refinement initially increased, and then it remained unchanged. The increase in strength and hardness was mainly due to V(C,N) precipitation strengthening. Increasing the V content to 0.12 wt % refined the austenite grain size and pearlite block size, and increased the density of high-angle ferrite boundaries and ferrite volume fraction. The grain refinement improved the impact toughness. However, the impact toughness then reduced as the V content was increased to 0.23 wt %, because grain refinement did not further increase, whereas precipitation strengthening and ferrite hardening occurred. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
Modeling of Precipitation Hardening during Coiling of Nb–Mo Steels
Metals 2018, 8(10), 758; https://doi.org/10.3390/met8100758
Received: 21 August 2018 / Revised: 19 September 2018 / Accepted: 21 September 2018 / Published: 25 September 2018
Cited by 1 | PDF Full-text (12177 KB) | HTML Full-text | XML Full-text
Abstract
Nb–Mo low-alloyed steels are promising advanced high strength steels (AHSS) because of the highly dislocated bainitic ferrite microstructure conferring an excellent combination of strength and toughness. In this study, the potential of precipitation strengthening during coiling for hot-strip Nb–Mo-bearing low-carbon steels has been [...] Read more.
Nb–Mo low-alloyed steels are promising advanced high strength steels (AHSS) because of the highly dislocated bainitic ferrite microstructure conferring an excellent combination of strength and toughness. In this study, the potential of precipitation strengthening during coiling for hot-strip Nb–Mo-bearing low-carbon steels has been investigated using hot-torsion and aging tests to simulate the hot-rolling process including coiling. The obtained microstructures were characterized using electron backscatter diffraction (EBSD), highlighting the effects of Nb and Mo additions on formation and tempering of the bainitic ferrite microstructures. Further, the evolution of nanometer-sized precipitates was quantified with high-resolution transmission electron microscopy (HR-TEM). The resulting age hardening kinetics have been modelled by combining a phenomenological precipitation strengthening model with a tempering model. Analysis of the model suggests a narrower coiling temperature window to maximize the precipitation strengthening potential in bainite/ferrite high strength low-alloyed (HSLA) steels than that for conventional HSLA steels with polygonal ferrite/pearlite microstructures. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessFeature PaperArticle
Effect of Microstructure on Post-Rolling Induction Treatment in a Low C Ti-Mo Microalloyed Steel
Metals 2018, 8(9), 694; https://doi.org/10.3390/met8090694
Received: 18 July 2018 / Revised: 30 August 2018 / Accepted: 1 September 2018 / Published: 4 September 2018
Cited by 1 | PDF Full-text (17343 KB) | HTML Full-text | XML Full-text
Abstract
Cost-effective advanced design concepts are becoming more common in the production of thick plates in order to meet demanding market requirements. Accordingly, precipitation strengthening mechanisms are extensively employed in thin strip products, because they enhance the final properties by using a coiling optimization [...] Read more.
Cost-effective advanced design concepts are becoming more common in the production of thick plates in order to meet demanding market requirements. Accordingly, precipitation strengthening mechanisms are extensively employed in thin strip products, because they enhance the final properties by using a coiling optimization strategy. Nevertheless, and specifically for thick plate production, the formation of effective precipitation during continuous cooling after hot rolling is more challenging. With the aim of gaining further knowledge about this strengthening mechanism, plate hot rolling conditions were reproduced in low carbon Ti-Mo microalloyed steel through laboratory simulation tests to generate different hot-rolled microstructures. Subsequently, a rapid heating process was applied in order to simulate induction heat treatment conditions. The results indicated that the nature of the matrix microstructure (i.e., ferrite, bainite) affects the achieved precipitation hardening, while the balance between strength and toughness depends on the hot-rolled microstructure. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
The Integration of Process and Product Metallurgy in Niobium Bearing Steels
Metals 2018, 8(9), 671; https://doi.org/10.3390/met8090671
Received: 15 July 2018 / Revised: 12 August 2018 / Accepted: 14 August 2018 / Published: 28 August 2018
Cited by 1 | PDF Full-text (5591 KB) | HTML Full-text | XML Full-text
Abstract
A review of the technological integration of both the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels have evolved into the development of higher quality steels for more demanding end user requirements. The connection of process [...] Read more.
A review of the technological integration of both the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels have evolved into the development of higher quality steels for more demanding end user requirements. The connection of process and physical metallurgy is evolving through the integration of research that is aimed at improving product quality. However, often the connection of the process metallurgical parameters is not reported, especially with industrial data. The importance of this innovative metallurgical connection is validated by the market demand for reduced fuel consumption, improved quality, and CO2 emissions in both the automotive and construction sectors. This situation has further increased the demand for new higher quality Nb-bearing steel grades. This integrative process/physical metallurgical (IP/PM) approach applies to both low and high strength steel grades in numerous applications. Often, the transition from laboratory melted and TMCP to the production scale is challenging. The methodology, process control, and key production steps that are required during the melting, ladle metallurgy, continuous casting, thermal, and hot rolling production conditions often vary significantly from the laboratory conditions. Understanding the reasons and corrective action for these variations is a critical product development success factor. These process metallurgy parameters for the industrial melting, casting, reheating, and hot rolling of Nb grades are connected and correlated to the resultant microstructures, physical metallurgy, and mechanical properties. These advanced high strength steels are microalloyed with Nb, V, Ti and/or other elements, which affect the austenite-ferrite transformation. Niobium enables the achievement of substantial grain refinement when the plate or sheet is rolled with the proper reheat, hot reduction, and thermal schedule. A recently developed key metallurgical transition is in progress applying this integrative approach with the use of MicroNiobium. A reduction of Mn and C levels with the complementary refinement of the microstructural grain size through MicroNiobium additions improves the robustness of the steel to better accommodate some process metallurgy variations. Applications are evolving in lower strength steels with Nb to achieve complementary grain refinement. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
Local Characterization of Precipitation and Correlation with the Prior Austenitic Microstructure in Nb-Ti-Microalloyed Steel by SEM and AFM Methods
Metals 2018, 8(8), 636; https://doi.org/10.3390/met8080636
Received: 30 July 2018 / Revised: 8 August 2018 / Accepted: 8 August 2018 / Published: 13 August 2018
Cited by 1 | PDF Full-text (2468 KB) | HTML Full-text | XML Full-text
Abstract
Precipitation is one of the most important influences on microstructural evolution during thermomechanical processing (TMCP) of micro-alloyed steels. Due to precipitation, pinning of prior austenite grain (PAG) boundaries can occur. To understand the mechanisms in detail and in relation to the thermomechanical treatment, [...] Read more.
Precipitation is one of the most important influences on microstructural evolution during thermomechanical processing (TMCP) of micro-alloyed steels. Due to precipitation, pinning of prior austenite grain (PAG) boundaries can occur. To understand the mechanisms in detail and in relation to the thermomechanical treatment, a local characterization of the precipitation state depending on the microstructure is essential. Commonly used methods for the characterization, such as transmission electron microscopy (TEM) or matrix dissolution techniques, only have the advantage of local or statistically secured characterization. By using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques, both advantages could be combined. In addition, in the present work a correlation of the precipitation conditions with the prior austenite grain structure for different austenitization states could be realized by Electron Backscatter Diffraction (EBSD) measurement and reconstruction methods using the reconstruction software Merengue 2. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
Physically-Based Modeling and Characterization of Hot Flow Behavior in an Interphase-Precipitated Ti-Mo Microalloyed Steel
Metals 2018, 8(4), 243; https://doi.org/10.3390/met8040243
Received: 21 March 2018 / Revised: 1 April 2018 / Accepted: 3 April 2018 / Published: 6 April 2018
Cited by 2 | PDF Full-text (22236 KB) | HTML Full-text | XML Full-text
Abstract
In this contribution, a series of hot compression tests was conducted on a typical interphase-precipitated Ti-Mo steel at relatively higher strain rates of 0.1~10 s−1 and temperatures of 900~1150 °C using a Gleeble-2000 thermo-mechanical simulator. A combination of Bergstrom and Kolmogorov–Johnson–Mehl–Avrami models [...] Read more.
In this contribution, a series of hot compression tests was conducted on a typical interphase-precipitated Ti-Mo steel at relatively higher strain rates of 0.1~10 s−1 and temperatures of 900~1150 °C using a Gleeble-2000 thermo-mechanical simulator. A combination of Bergstrom and Kolmogorov–Johnson–Mehl–Avrami models was first used to accurately predict the whole flow behaviors of Ti-Mo steel involving dynamic recrystallization, under various hot deformation conditions. By comparing the characteristic stresses and material parameters, especially at the higher strain rates studied, the dependence of hot flow behavior on strain rate and deformation temperature was further clarified. The hardening parameter U and peak density ρp exhibited an approximately positive linear relationship with the Zener–Hollomon (Z) parameter, while the softening parameter Ω dropped with increasing Z value. The Avrami exponent nA varied between 1.2 and 2.1 with lnZ, implying two diverse nucleation mechanisms of dynamic recrystallization. The experimental verification was performed as well based on the microstructural evolution and mechanism analysis upon straining. The proposed constitutive models may provide a powerful tool for optimizing the hot working processes of high performance Ti-Mo microalloyed steels with interphase precipitation. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
Comparative Effect of Mo and Cr on Microstructure and Mechanical Properties in NbV-Microalloyed Bainitic Steels
Metals 2018, 8(2), 134; https://doi.org/10.3390/met8020134
Received: 4 January 2018 / Revised: 10 February 2018 / Accepted: 13 February 2018 / Published: 16 February 2018
Cited by 4 | PDF Full-text (4681 KB) | HTML Full-text | XML Full-text
Abstract
Steel product markets require the rolled stock with further increasing mechanical properties and simultaneously decreasing price. The steel cost can be reduced via decreasing the microalloying elements contents, although this decrease may undermine the mechanical properties. Multi-element microalloying with minor additions is the [...] Read more.
Steel product markets require the rolled stock with further increasing mechanical properties and simultaneously decreasing price. The steel cost can be reduced via decreasing the microalloying elements contents, although this decrease may undermine the mechanical properties. Multi-element microalloying with minor additions is the route to optimise steel composition and keep the properties high. However, this requires deep understanding of mutual effects of elements on each other’s performance with respect to the development of microstructure and mechanical properties. This knowledge is insufficient at the moment. In the present work we investigate the microstructure and mechanical properties of bainitic steels microalloyed with Cr, Mo, Nb and V. Comparison of 0.2 wt. % Mo and Cr additions has shown a more pronounced effect of Mo on precipitation than on phase balance. Superior strength of the MoNbV-steel originated from the strong solid solution strengthening effect. Superior ductility of the CrNbV-steel corresponded to the more pronounced precipitation in this steel. Nature of these mechanisms is discussed. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessArticle
The Influence of La and Ce Addition on Inclusion Modification in Cast Niobium Microalloyed Steels
Metals 2017, 7(9), 377; https://doi.org/10.3390/met7090377
Received: 7 August 2017 / Revised: 28 August 2017 / Accepted: 29 August 2017 / Published: 15 September 2017
Cited by 9 | PDF Full-text (5515 KB) | HTML Full-text | XML Full-text
Abstract
The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In [...] Read more.
The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In this study, different amounts of RE were added to a niobium microalloyed steel in as-cast condition to investigate its influence on: (i) type of inclusions and (ii) precipitation of niobium carbides. The characterization of the microstructure by optical, scanning and transmission electron microscopy shows that: (1) the addition of RE elements change the inclusion formation route during solidification; RE > 200 ppm promote formation of complex inclusions with a (La,Ce)(S,O) matrix instead of Al2O3-MnS inclusions; (2) the roundness of inclusions increases with RE, whereas more than 200 ppm addition would increase the area fraction and size of the inclusions; (3) it was found that the presence of MnS in the base and low RE-added steel provide nucleation sites for the precipitation of coarse niobium carbides and/or carbonitrides at the matrix–MnS interface. Thermodynamic calculations show that temperatures of the order of 1200 °C would be necessary to dissolve these coarse Nb-rich carbides so as to reprecipitate them as nanoparticles in the matrix. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Review

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Open AccessReview
Microalloyed Steels through History until 2018: Review of Chemical Composition, Processing and Hydrogen Service
Metals 2018, 8(5), 351; https://doi.org/10.3390/met8050351
Received: 22 March 2018 / Revised: 20 April 2018 / Accepted: 25 April 2018 / Published: 14 May 2018
Cited by 5 | PDF Full-text (17796 KB) | HTML Full-text | XML Full-text
Abstract
Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of [...] Read more.
Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of gas and hydrocarbons transport. As a result of this, microalloyed steels present a good combination of high strength and ductility obtained through the addition of microalloying elements, thermomechanical processing, and controlled cooling, processes capable of producing complex microstructures that improve the mechanical properties of steels. These controlled microstructures can be severely affected and result in catastrophic failures, due to the atomic hydrogen diffusion that occurs during the corrosion process of pipeline steel. Recently, a martensite–bainite microstructure with acicular ferrite has been chosen as a viable candidate to be used in environments with the presence of hydrogen. The aim of this review is to summarize the main changes of chemical composition, processing techniques, and the evolution of the mechanical properties throughout recent history on the use of microalloying in high strength low alloy steels, as well as the effects of hydrogen in newly created pipelines, examining the causes behind the mechanisms of hydrogen embrittlement in these steels. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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Open AccessReview
Property Optimization in As-Quenched Martensitic Steel by Molybdenum and Niobium Alloying
Metals 2018, 8(4), 234; https://doi.org/10.3390/met8040234
Received: 8 February 2018 / Revised: 21 March 2018 / Accepted: 28 March 2018 / Published: 3 April 2018
Cited by 3 | PDF Full-text (26796 KB) | HTML Full-text | XML Full-text
Abstract
Niobium microalloying is the backbone of modern low-carbon high strength low alloy (HSLA) steel metallurgy, providing a favorable combination of strength and toughness by pronounced microstructural refinement. Molybdenum alloying is established in medium-carbon quenching and tempering of steel by delivering high hardenability and [...] Read more.
Niobium microalloying is the backbone of modern low-carbon high strength low alloy (HSLA) steel metallurgy, providing a favorable combination of strength and toughness by pronounced microstructural refinement. Molybdenum alloying is established in medium-carbon quenching and tempering of steel by delivering high hardenability and good tempering resistance. Recent developments of ultra-high strength steel grades, such as fully martensitic steel, can be optimized by using beneficial metallurgical effects of niobium and molybdenum. The paper details the metallurgical principles of both elements in such steel and the achievable improvement of properties. Particularly, the underlying mechanisms of improving toughness and reducing the sensitivity towards hydrogen embrittlement by a suitable combination of molybdenum and niobium alloying will be discussed. Full article
(This article belongs to the Special Issue Advances in Microalloyed Steels)
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