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Metals
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Microstructure Evolution and Mechanical Properties of Microalloyed Steels
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Microstructure Evolution and Mechanical Properties of Microalloyed Steels

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

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 6760

Special Issue Editor

Dr. Antti Kaijalainen

E-Mail Website
Guest Editor
Centre for Advanced Steels Research, University of Oulu, Oulu, Finland
Interests: direct quenching; formability; mechanical properties; microstructure characterization; thermomechanical modeling; ultrahigh-strength steels

Special Issue Information

Dear Colleagues,

New steel products and improvement of current grades are vital steps in increasing the efficiency of new energy production methods. Higher strength, excellent toughness and outstanding weldability, corrosion, and even wear resistance properties are some of the essential improvements that need to be made, both in new products and in the current generation of high-strength steels, which can further be improved to provide better usability and mechanical properties. The ductility and toughness properties of steels are not on par with the latest structural steels, and therefore, research work should be done to upgrade the property balance. These balanced properties make them ideal for critical applications under severe conditions or in aggressive environments, e.g., automotive components, offshore and bridge structures, or construction machinery and pipelines. Following that, it is therefore essential to deeply understand the relations between properties and microstructure and how to drive them via a specific process. In this framework in particular, the role of heat treatments in obtaining even more complex microstructures is still quite an open matter, also thanks to the design of innovative heat treatments.

In this Special Issue, we seek to provide a wide set of articles on various aspects of microalloyed steels. The idea is to demonstrate the broad range of properties and applications of these steels. Articles covering the physical metallurgy, production methods, defect elimination, modeling, and performance in final products of microalloyed steels are desired.

Dr. Antti Kaijalainen
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

  • microstructural characterization
  • toughness
  • formability
  • anisotropy
  • heat treatments
  • quenching
  • thermomechanical modeling
  • cellular automata modeling

Published Papers (3 papers)

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Research

19 pages, 6447 KiB  
Article
Flow Stress Behaviour and Static Recrystallization Characteristics of Hot Deformed Austenite in Microalloyed Medium-Carbon Bainitic Steels
by Pentti M. Kaikkonen, Mahesh C. Somani, Leo Pentti Karjalainen and Jukka I. Kömi
Metals 2021, 11(1), 138; https://doi.org/10.3390/met11010138 - 12 Jan 2021
Cited by 9 | Viewed by 1887
Abstract
In the past decade, efforts have been focused on developing very fine, medium-carbon bainitic steels via the low-temperature (typically 300–400 °C) ausforming process, which not only enables shorter isothermal holding times for bainitic transformation at low temperatures, but also offers significantly improved strength. [...] Read more.
In the past decade, efforts have been focused on developing very fine, medium-carbon bainitic steels via the low-temperature (typically 300–400 °C) ausforming process, which not only enables shorter isothermal holding times for bainitic transformation at low temperatures, but also offers significantly improved strength. This paper describes static recrystallization (SRX) characteristics of austenite in four medium-carbon 2%Mn-1.3%Si-0.7%Cr steels with and without microalloying intended for the development of these steels. The stress-relaxation method on a Gleeble simulator resulted in recrystallization times over a wide range of temperatures, strains and strain rates. Also, the occurrence of precipitation was revealed. Powers of strain (−1.7 to −2.7) and strain rate (−0.21 to −0.28) as well as the apparent activation energies (225–269 kJ/mol) were in the ranges reported in the literature for C-Mn and microalloyed steels with lower Mn and Si contents. The new regression equations established for estimating times for 50% SRX revealed the retardation effects of microalloying and Mo addition showing reasonable fits with the experimental data, whereas the previous model suggested for ordinary microalloyed steels tended to predict clearly shorter times on average than the experimental values for the present coarse-grained steels. The Boratto equation to estimate the non-recrystallization temperature was successfully modified to include the effect of Mo alloying and high silicon concentrations. Full article
(This article belongs to the Special Issue Microstructure Evolution and Mechanical Properties of Microalloyed Steels)
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16 pages, 7535 KiB  
Article
Optimization of Niobium Content in Direct Quenched High-Strength Steels
by Jaakko Hannula, David Porter, Antti Kaijalainen, Mahesh Somani and Jukka Kömi
Metals 2020, 10(6), 807; https://doi.org/10.3390/met10060807 - 17 Jun 2020
Cited by 4 | Viewed by 1977
Abstract
This paper focuses on understanding the effect of niobium content on the phase transformation behavior and resultant mechanical properties of thermomechanically rolled and direct-quenched low carbon steels containing 0.08 wt.% carbon. Investigated steels contained three different levels of niobium: 0, 0.02 and 0.05 [...] Read more.
This paper focuses on understanding the effect of niobium content on the phase transformation behavior and resultant mechanical properties of thermomechanically rolled and direct-quenched low carbon steels containing 0.08 wt.% carbon. Investigated steels contained three different levels of niobium: 0, 0.02 and 0.05 wt.%. The continuous cooling transformation (CCT) diagrams covering cooling rates in the range 3–96 °C/s constructed based on the dilatometer studies showed only a minor effects of Nb on the phase transformation characteristics. In addition, experiments were performed for reheating and soaking the slabs at 1050–1200 °C and the results revealed that for these low-carbon steels, Nb failed to prevent the austenite grain growth during slab reheating. In the case of hot rolling trials, two different finish rolling temperatures of 820 °C and 920 °C were used to obtain different levels of pancaking in the austenite prior to direct quenching. The resultant microstructures were essentially mixtures of autotempered martensite and lower bainite imparting yield strengths in the range 940–1070 MPa. The lower finish rolling temperature enabled better combinations of strength and toughness in all the cases, predominantly due to a higher degree of pancaking in the austenite. The optimum level of Nb in the steel was ascertained to be 0.02 wt.%, which resulted not only in marginally higher strength but also without any significant loss of impact toughness. Full article
(This article belongs to the Special Issue Microstructure Evolution and Mechanical Properties of Microalloyed Steels)
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13 pages, 7500 KiB  
Article
Insight to the Influence of Ti Addition on the Strain-Induced Martensitic Transformation in a High (about 7 wt.%) Mn Stainless Steel
by Saeed Sadeghpour, Vahid Javaheri, Ahmad Kermanpur and Jukka Kömi
Metals 2020, 10(5), 568; https://doi.org/10.3390/met10050568 - 27 Apr 2020
Cited by 1 | Viewed by 2395
Abstract
The kinetics of strain-induced martensite (SIM) formation in a Ti-bearing 201L stainless steel were evaluated and compared to the existing results of two conventional stainless steel grades; i.e., 201L and 304L AISI. The effects of strain rate and rolling pass reduction on the [...] Read more.
The kinetics of strain-induced martensite (SIM) formation in a Ti-bearing 201L stainless steel were evaluated and compared to the existing results of two conventional stainless steel grades; i.e., 201L and 304L AISI. The effects of strain rate and rolling pass reduction on the kinetics of SIM formation during cold rolling were investigated. The Ti-microalloying was found to be intensifying the transformation due to lowering the stacking fault energy. It was seen that decreasing the rolling pass reduction strongly affected the variation of SIM volume fraction. Furthermore, a close correlation between the hardness and strain-induced transformation was found arising from microstructural evolution during the cold rolling process. Three stages in the hardening behavior were detected associated with lath-type martensite formation, transition stage of martensite laths break up and formation of dislocation-cell-type martensite. Full article
(This article belongs to the Special Issue Microstructure Evolution and Mechanical Properties of Microalloyed Steels)
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