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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 (20 February 2020) | Viewed by 49346

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Prof. Dr. José María Rodríguez-Ibabe

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President and Researcher at CEIT, CEIT, 20018 Donostia-San Sebastian, Basque Country, Spain
Professor at Universidad de Navarra-Tecnun, Materials Science and Metallurgy, Universidad de Navarra-Tecnun, M. Lardizabal 15, 20018 Donostia-San Sebastian, Basque Country, Spain
Interests: microstructure; microscopy; thermomechanical processing; microalloying; steels; metallurgy; modelling

Dr. Pello Uranga

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Materials and Manufacturing Division, CEIT-BRTA and Universidad de Navarra-Tecnun, 20018 Donostia-San Sebastian, Basque Country, Spain
Interests: thermomechanical processing; microstructural evolution modeling; microalloying; microstructure–property relationship
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Dear Colleagues,

The combination of hot working technologies with a thermal path, under controlled conditions, i.e., thermomechanical processing, provides opportunities to achieve required mechanical properties at lower costs. The replacement of conventional rolling plus post-rolling heat treatments by integrated controlled forming and cooling strategies implies important reductions in energy consumption, increases in productivity and more compact facilities in the steel industry. The metallurgical challenges that this integration implies, though, are relevant and impressive developments that have been achieved over the last 40 years. The development of new steel grades and processing technologies devoted to thermomechanically-processed products are increasing and their implementation is being expended to higher value added products and applications.

The achievement of mechanical properties and process stability during a Thermomechanical Controlled Process (TMCP), depend on the chemical composition, process parameter control and optimization, as well as post-forming cooling strategy and thermal treatments. Therefore, this Special Issue would like to combine contributions on different fields, topics, steel grades and forming technologies applying TMCP processes to steels. Papers regarding forming technologies, such as rolling, forging, hot-stamping, etc., using microalloyed, medium/high Mn or alternative high alloyed grades will be welcome. New technologies, such as near-net-shape production, innovative cooling strategies, such as direct quenching, quenching and partitioning or additional controlled cooling strategies will be the base for current and future new product developments.

In addition to the metallurgical peculiarities and relationships between chemical composition, process and final properties, the impact of advanced characterization techniques and innovative modelling strategies provides new tools to achieve further deployment of the TMCP technologies.

For this Special Issue on "Thermomechanical Processing of Steels", we would like to invite researchers from the steel industry and academia to submit their latest developments and achievements in the field.

Prof. Dr. José María Rodríguez-Ibabe
Dr. Pello Uranga
Guest Editors

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Keywords

Thermomechanical processing
Steels
Hot working
Phase transformations
Microstructure
Mechanical properties
Modelling

Published Papers (13 papers)

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Editorial

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4 pages, 186 KiB

Open AccessEditorial

Thermomechanical Processing of Steels

by Pello Uranga and José María Rodríguez-Ibabe

Metals 2020, 10(5), 641; https://doi.org/10.3390/met10050641 - 15 May 2020

Cited by 8 | Viewed by 2933

Abstract

The combination of hot working technologies with a thermal path, under controlled conditions (i [...] Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

Research

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19 pages, 7494 KiB

Open AccessFeature PaperArticle

The Influence of Vanadium Additions on Isothermally Formed Bainite Microstructures in Medium Carbon Steels Containing Retained Austenite

by Irina Pushkareva, Babak Shalchi-Amirkhiz, Sébastien Yves Pierre Allain, Guillaume Geandier, Fateh Fazeli, Matthew Sztanko and Colin Scott

Metals 2020, 10(3), 392; https://doi.org/10.3390/met10030392 - 19 Mar 2020

Cited by 13 | Viewed by 3506

Abstract

The influence of V additions on isothermally formed bainite in medium carbon steels containing retained austenite has been investigated using in-situ high energy X-ray diffraction (HEXRD) and ex-situ electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX) techniques in the transmission electron microscope (TEM). No significant impact of V in solid solution on the bainite transformation rate, final phase fractions or on the width of bainite laths was seen for transformations in the range 375–430 °C. No strong influence on the dislocation density could be detected, although quantitative analysis was impeded by ferrite tetragonality. A reduction in the carbon content of retained austenite C_γ that is not believed to be due to competition with VC or cementite precipitation was observed. No influence of V on the carbon supersaturation in bainitic ferrite C_b could be directly measured, although carbon mass balance calculations suggest C_b slightly increases. A beneficial refinement of blocky MA and a corresponding size effect induced enhancement in austenite stability were found at the lowest transformation temperature. Overall, V additions result in a slight increase in strength levels. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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19 pages, 12065 KiB

Open AccessFeature PaperArticle

Hot Strip Mill Processing Simulations on a Ti-Mo Microalloyed Steel Using Hot Torsion Testing

by Caleb A. Felker, John G. Speer, Emmanuel De Moor and Kip O. Findley

Metals 2020, 10(3), 334; https://doi.org/10.3390/met10030334 - 03 Mar 2020

Cited by 9 | Viewed by 2744

Abstract

Precipitation strengthened, fully ferritic microstructures in low-carbon, microalloyed steels are used in applications requiring enhanced stretch-flange formability. This work assesses the influence of thermomechanical processing on the evolution of austenite and the associated final ferritic microstructures. Hot strip mill processing simulations were performed on a low-carbon, titanium-molybdenum microalloyed steel using hot torsion testing to investigate the effects of extensive differences in austenite strain accumulation on austenite morphology and microstructural development after isothermal transformation. The gradient of imposed shear strain with respect to radial position inherent to torsion testing was utilized to explore the influence of strain on microstructural development for a given simulation, and a tangential cross-section technique was employed to quantify the amount of shear strain that accumulated within the austenite during testing. Greater austenite shear strain accumulation resulted in greater refinement of both the prior austenite and polygonal ferrite grain sizes. Further, polygonal ferrite grain diameter distributions were narrowed, and the presence of hard, secondary phase constituents was minimized, with greater amounts of austenite strain accumulation. The results indicate that extensive austenite strain accumulation before decomposition is required to achieve desirable, ferritic microstructures. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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22 pages, 6174 KiB

Open AccessArticle

Tracing Microalloy Precipitation in Nb-Ti HSLA Steel during Austenite Conditioning

by Johannes Webel, Adrian Herges, Dominik Britz, Eric Detemple, Volker Flaxa, Hardy Mohrbacher and Frank Mücklich

Metals 2020, 10(2), 243; https://doi.org/10.3390/met10020243 - 12 Feb 2020

Cited by 20 | Viewed by 3611

Abstract

The microalloying with niobium (Nb) and titanium (Ti) is standardly applied in low carbon steel high-strength low-alloy (HSLA) steels and enables austenite conditioning during thermo-mechanical controlled processing (TMCP), which results in pronounced grain refinement in the finished steel. In that respect, it is important to better understand the precipitation kinetics as well as the precipitation sequence in a typical Nb-Ti-microalloyed steel. Various characterization methods were utilized in this study for tracing microalloy precipitation after simulating different austenite TMCP conditions in a Gleeble thermo-mechanical simulator. Atom probe tomography (APT), scanning transmission electron microscopy in a focused ion beam equipped scanning electron microscope (STEM-on-FIB), and electrical resistivity measurements provided complementary information on the precipitation status and were correlated with each other. It was demonstrated that accurate electrical resistivity measurements of the bulk steel could monitor the general consumption of solute microalloys (Nb) during hot working and were further complemented by APT measurements of the steel matrix. Precipitates that had formed during cooling or isothermal holding could be distinguished from strain-induced precipitates by corroborating STEM measurements with APT results, because APT specifically allowed obtaining detailed information about the chemical composition of precipitates as well as the elemental distribution. The current paper highlights the complementarity of these methods and shows first results within the framework of a larger study on strain-induced precipitation. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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14 pages, 8373 KiB

Open AccessArticle

Casting and Constitutive Hot Flow Behavior of Medium-Mn Automotive Steel with Nb as Microalloying

by Perla Julieta Cerda Vázquez, José Sergio Pacheco-Cedeño, Mitsuo Osvaldo Ramos-Azpeitia, Pedro Garnica-González, Vicente Garibay-Febles, Joel Moreno-Palmerin, José de Jesús Cruz-Rivera and José Luis Hernández-Rivera

Metals 2020, 10(2), 206; https://doi.org/10.3390/met10020206 - 01 Feb 2020

Cited by 6 | Viewed by 2512

Abstract

A novel medium-Mn steel microstructure with 0.1 wt.% Nb was designed using Thermo-Calc and JMatPro thermodynamic simulation software. The pseudo-binary equilibrium phase diagram and time–temperature transformation (TTT) and continuous cooling transformation (CCT) diagrams were simulated in order to analyze the evolution of equilibrium phases during solidification and homogenization heat treatment. Subsequently, the steel was cast in a vacuum induction furnace with the composition selected from simulations. The specimens were heat-treated at 1200 °C and water-quenched. The results of the simulations were compared to the experimental results. The microstructure was characterized using optical microscopy (OM) and scanning electron microscopy (SEM). We found that the as-cast microstructure consisted mainly of a mixture of martensite, ferrite, and a low amount of austenite, while the microstructure in the homogenization condition corresponded to martensite and retained austenite, which was verified by X-ray diffraction tests. In order to design further production stages of the steel, the homogenized samples were subjected to hot compression testing to determine their plastic flow behavior, employing deformation rates of 0.083 and 0.83 s⁻¹, and temperatures of 800 and 950 °C. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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17 pages, 10765 KiB

Open AccessFeature PaperArticle

Defect Reduction and Quality Optimization by Modeling Plastic Deformation and Metallurgical Evolution in Ferritic Stainless Steels

by Silvia Mancini, Luigi Langellotto, Paolo Emilio Di Nunzio, Chiara Zitelli and Andrea Di Schino

Metals 2020, 10(2), 186; https://doi.org/10.3390/met10020186 - 27 Jan 2020

Cited by 27 | Viewed by 2724

Abstract

Manufacturing of ferritic stainless steels flat bars is an important industrial topic and the steel 1.4512 is one of the most commonly used grades for producing this component. In this paper, the origin of some edge defects occurring during hot rolling of flat bars of this grade is analyzed and thermomechanical and microstructural calculations have been carried out to enhance the quality of the finished products by reducing the jagged borders defect on hot rolled bars. An accurate investigation has been carried out by analyzing the defects on the final product from both the macroscopic and microstructural point of view through the implementation of thermomechanical and metallurgical models in a finite element (FE) MSC Marc commercial code. Coupled metallurgical and damage models have been implemented to investigate the microstructural evolution of ferritic grain size and material damaging. Three levels of prior ferritic grain size (PFGS) and three furnace discharge temperatures have been considered in the thermo-mechanical simulations of the roughing passes. Rheological laws for modeling the evolution of ferritic grain have been modified to describe the specific cases simulated. Results have shown that the defect is caused by processing conditions that trigger an anomalous heating which, in turn, induces an uncontrolled grain growth on the edges. The work-hardened and elongated grains do not recrystallize during hot deformation. Consequently, they tend to squeeze out the surrounding softer and recrystallized matrix towards the edges of the bar where the fractures that characterizes the surface defect occur. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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24 pages, 7944 KiB

Open AccessFeature PaperArticle

Effect of High Ti Contents on Austenite Microstructural Evolution During Hot Deformation in Low Carbon Nb Microalloyed Steels

by Leire García-Sesma, Beatriz López and Beatriz Pereda

Metals 2020, 10(2), 165; https://doi.org/10.3390/met10020165 - 22 Jan 2020

Cited by 4 | Viewed by 4411

Abstract

This work has focused on the study of hot working behavior of Ti-Nb microalloyed steels with high Ti contents (> 0.05%). The role of Nb during the hot deformation of low carbon steels is well known: it mainly retards austenite recrystallization, leading to pancaked austenite microstructures before phase transformation and to refined room temperature microstructures. However, to design rolling schedules that result in properly conditioned austenite microstructures, it is necessary to develop models that take into account the effect of high Ti concentrations on the microstructural evolution of austenite. To that end, in this work torsion tests were performed to investigate the microstructural evolution during hot deformation of steels microalloyed with 0.03% Nb and different high Ti concentrations (0.05%, 0.1%, 0.15%). It was observed that the 0.1% and 0.15% Ti additions resulted in retarded softening kinetics at all the temperatures. This retardation can be mainly attributed to the solute drag effect exerted by Ti in solid solution. The precipitation state of the steels after reheating and after deformation was characterized and the applicability of existing microstructural evolution models was also evaluated. Determined recrystallization kinetics and recrystallized grain sizes reasonably agree with those predicted by equations previously developed for Nb-Ti microalloyed steels with lower Ti concentrations (<0.05%). Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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17 pages, 8117 KiB

Open AccessArticle

Tensile Properties and Microstructural Evolution of an Al-Bearing Ferritic Stainless Steel at Elevated Temperatures

by Ying Han, Jiaqi Sun, Yu Sun, Jiapeng Sun and Xu Ran

Metals 2020, 10(1), 86; https://doi.org/10.3390/met10010086 - 04 Jan 2020

Cited by 7 | Viewed by 3248

Abstract

The influence of temperature and strain rate on the hot tensile properties of 0Cr18AlSi ferritic stainless steel, a potential structural material in the ultra-supercritical generation industry, was investigated at temperatures ranging from 873 to 1123 K and strain rates of 1.7 × 10⁻⁴–1.7 × 10⁻² s⁻¹. The microstructural evolution linked to the hot deformation mechanism was characterized by electron backscatter diffraction (EBSD). At the same strain rate, the yield strength and ultimate tensile strength decrease rapidly from 873 K to 1023 K and then gradually to 1123 K. Meanwhile, both yield strength and ultimate tensile strength increase with the increase in strain rate. At high temperatures and low strain rates, the prolonged necking deformation can be observed, which determines the ductility of the steel to some extent. The maximum elongation is obtained at 1023 K for the strain rates of 1.7 × 10⁻³ and 1.7 × 10⁻² s⁻¹, while this temperature is postponed to 1073 K once decreasing the strain rate to 1.7 × 10⁻⁴ s⁻¹. Dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX) are found to be the main softening mechanisms during the hot tensile deformation. With the increase of temperature and the decrease of strain rate (i.e., 1123 K and 1.7 × 10⁻⁴ s⁻¹), the sub-grain coalescence becomes the main mode of CDRX that evolved from the sub-grain rotation. The gradual decrease in strength above 1023 K is related to the limited increase of dynamic recrystallization and the sufficient DRV. The area around the new small recrystallized grains on the coarse grain boundaries provides the nucleation site for cavity, which generally results in a reduction in ductility. Constitutive analysis shows that the stress exponent and the deformation activation energy are 5.9 and 355 kJ·mol⁻¹ respectively, indicating that the dominant deformation mechanism is the dislocations motion controlled by climb. This work makes a deeply understanding of the hot deformation behavior and its mechanism of the Al-bearing ferritic stainless steel and thus provides a basal design consideration for its extensive application. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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10 pages, 5672 KiB

Open AccessArticle

Study on σ Phase in Fe–Al–Cr Alloys

by Jintao Wang, Shouping Liu and Xiaoyu Han

Metals 2019, 9(10), 1092; https://doi.org/10.3390/met9101092 - 11 Oct 2019

Cited by 9 | Viewed by 4867

Abstract

In this paper, a method of using the second phase to control the grain growth in Fe–Al–Cr alloys was proposed, in order to obtain better mechanical properties. In Fe–Al–Cr alloys, austenitic transformation occurs by adding austenitizing elements, leading to the formation of the second phase and segregation at the grain boundaries, which hinders grain growth. FeCr(σ) phase was obtained in the Fe–Al–Cr alloys, which had grains of several microns and was coherent and coplanar with the matrix (Fe₂AlCr). The nucleation of σ phase in Fe–Al–Cr alloy was controlled by the ratio of nickel to chromium. When the Ni/Cr (eq) ratio of alloys was more than 0.19, σ phase could nucleate in Fe–Al–Cr alloy. The relationship between austenitizing and nucleation of FeCr(σ) phase was given by thermodynamic calculation. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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17 pages, 8413 KiB

Open AccessFeature PaperArticle

Interaction between Microalloying Additions and Phase Transformation during Intercritical Deformation in Low Carbon Steels

by Unai Mayo, Nerea Isasti, Jose M. Rodriguez-Ibabe and Pello Uranga

Metals 2019, 9(10), 1049; https://doi.org/10.3390/met9101049 - 27 Sep 2019

Cited by 7 | Viewed by 2658

Abstract

Heavy gauge line pipe and structural steel plate materials are often rolled in the two-phase region for strength reasons. However, strength and toughness show opposite trends, and the exact effect of each rolling process parameter remains unclear. Even though intercritical rolling has been widely studied, the specific mechanisms that act when different microalloying elements are added remain unclear. To investigate this further, laboratory thermomechanical simulations reproducing intercritical rolling conditions were performed in plain low carbon and NbV-microalloyed steels. Based on a previously developed procedure using electron backscattered diffraction (EBSD), the discretization between intercritically deformed ferrite and new ferrite grains formed after deformation was extended to microalloyed steels. The austenite conditioning before intercritical deformation in the Nb-bearing steel affects the balance of final precipitates by modifying the size distributions and origin of the Nb (C, N). This fact could modify the substructure in the intercritically deformed grains. A simple transformation model is proposed to predict average grain sizes under intercritical deformation conditions. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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16 pages, 8826 KiB

Open AccessArticle

Microstructure Formation of Low-Carbon Ferritic Stainless Steel during High Temperature Plastic Deformation

by Yi Shao, Xiaohua Li, Junjie Ma, Chenxi Liu and Zesheng Yan

Metals 2019, 9(4), 463; https://doi.org/10.3390/met9040463 - 20 Apr 2019

Cited by 7 | Viewed by 7078

Abstract

In this paper, the effects of the deformation temperature, the deformation reduction and the deformation rate on the microstructural formation, ferritic and martensitic phase transformation, stress–strain behaviors and micro-hardness in low-carbon ferritic stainless steel were investigated. The increase in deformation temperature promotes the formation of the fine equiaxed dynamic strain-induced transformation ferrite and suppresses the martensitic transformation. The higher deformation temperature results in a lower starting temperature for martensitic transformation. The increase in deformation can effectively promote the transformation of DSIT ferrite, and decrease the martensitic transformation rate, which is caused by the work hardening effect on the metastable austenite. The increase in the deformation rate leads to an increase in the ferrite fraction, because a high density of dislocation remains that can provide sufficient nucleation sites for ferrite transformation. The slow deformation rate results in dynamic recovery according to the stress–strain curve. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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13 pages, 25991 KiB

Open AccessArticle

Exploring the Difference in Bainite Transformation with Varying the Prior Austenite Grain Size in Low Carbon Steel

by Liangyun Lan, Zhiyuan Chang and Penghui Fan

Metals 2018, 8(12), 988; https://doi.org/10.3390/met8120988 - 24 Nov 2018

Cited by 12 | Viewed by 6047

Abstract

The simulation welding thermal cycle technique was employed to generate different sizes of prior austenite grains. Dilatometry tests, in situ laser scanning confocal microscopy, and transmission electron microscopy were used to investigate the role of prior austenite grain size on bainite transformation in low carbon steel. The bainite start transformation (Bs) temperature was reduced by fine austenite grains (lowered by about 30 °C under the experimental conditions). Through careful microstructural observation, it can be found that, besides the Hall–Petch strengthening effect, the carbon segregation at the fine austenite grain boundaries is probably another factor that decreases the Bs temperature as a result of the increase in interfacial energy of nucleation. At the early stage of the transformation, the bainite laths nucleate near to the grain boundaries and grow in a “side-by-side” mode in fine austenite grains, whereas in coarse austenite grains, the sympathetic nucleation at the broad side of the pre-existing laths causes the distribution of bainitic ferrite packets to be interlocked. Full article

(This article belongs to the Special Issue Thermomechanical Processing of Steels)

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1 pages, 164 KiB

Open AccessErratum

Erratum: Pushkareva, I., et al. The Influence of Vanadium Additions on Isothermally Formed Bainite Microstructures in Medium Carbon Steels Containing Retained Austenite. Metals 2020, 10, 392

by Irina Pushkareva, Babak Shalchi-Amirkhiz, Sébastien Yves Pierre Allain, Guillaume Geandier, Fateh Fazeli, Matthew Sztanko and Colin Scott

Metals 2020, 10(5), 565; https://doi.org/10.3390/met10050565 - 27 Apr 2020

Viewed by 1427

Abstract

The authors wish to make the following erratum to this paper [...] Full article

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