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Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing

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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: 31 December 2025 | Viewed by 13313

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Special Issue Editors

Prof. Dr. Samuel F. Rodrigues

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Department of Mechanical and Materials Engineering, Federal Institute of Education, Science and Technology of Maranhão - IFMA, Sao Luis 65030-005, MA, Brazil
Interests: dynamic transformation; phase transformation; development of new alloys; thermomechanical process;mechanical properties and deformation behavior of materials; physical metallurgy

Dr. Clodualdo Aranas

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Department of Mechanical Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada
Interests: thermomechanical processing; development of novel alloys; mechanical properties and deformation behavior of materials; phase transformation in metal alloys; static and dynamic materials testing; high-strain rate deformation; static and dynamic recrystallization; materials characterization; texture and anisotropy of materials; thermodynamics of materials; additive manufacturing of metallic materials
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Dr. Fulvio Siciliano

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Dynamic Systems Inc., Poestenkill, NY 12140, USA
Interests: thermomechanical processing; steels; recrystallization; mathematical modeling; microalloying

Special Issue Information

Dear Colleagues,

Dynamic and/or static softening is known to occur during the thermomechanical processing of metals and alloys. Some of these phenomena include recovery, recrystallization and phase transformation, which have been of great interest to academia and industry for decades. It is well known that understanding and controlling the softening behavior during the manufacturing of metals and alloys will lead to optimization of the final product mechanical properties. Additionally, these softening mechanisms can be modelled to guarantee improved properties for specific applications and the development of new materials. Regardless of significant research and progress in this field, the limit of our ability to improve material properties and the variety of different applications is far from being reached.

This Special Issue of Metals invites experts to submit papers related to experimental research, simulation and modelling of the various softening mechanisms. All steel families, alloys of titanium, magnesium, aluminum, nickel-based, high-entropy and additive-manufactured alloys are the primary target materials, although other alloy systems will also be considered.

Prof. Dr. Samuel F. Rodrigues
Dr Clodualdo Aranas
Dr. Fulvio Siciliano
Guest Editors

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Keywords

phase transformation
thermomechanical processing
static and dynamic recovery
static and dynamic recrystallization
materials characterization
physical metallurgy

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Published Papers (9 papers)

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Research

21 pages, 57255 KB

Open AccessArticle

Solidification Microstructure and Secondary-Phase Precipitation Behavior of 310S Austenitic Stainless Steel

by Jun Xiao, Di Wang, Shaoguang Yang, Kuo Cao, Siyu Qiu, Jianhua Wei and Aimin Zhao

Metals 2025, 15(10), 1091; https://doi.org/10.3390/met15101091 - 29 Sep 2025

Viewed by 265

Abstract

In this study, the solidification behavior of 310S stainless steel was systematically investigated by combining high-temperature confocal laser scanning microscopy (HT-CLSM), microstructural characterization, and thermodynamic calculations. The focus was on the formation and transformation of ferrite, secondary-phase precipitation, and elemental segregation behavior, with comparisons made with 304 stainless steel. The effects of an Al addition and cooling rate were also explored. The results show that the solidification sequence of 310S stainless steel is L → L + γ → L + γ + δ → δ + γ, in which austenite nucleates early and grows rapidly, followed by the precipitation of a small amount of δ-ferrite in the later stages of solidification. In contrast, 304 stainless steel solidifies according to L → L + δ → L + δ + γ → δ + γ, with a rapid δ → γ transformation occurring after solidification. Compared with 304, 310S stainless steel exhibits a reduced ferrite fraction and a significantly increased σ phase content. The σ phase primarily precipitates directly from δ-ferrite (δ → σ), while M₂₃C₆ preferentially forms at grain boundaries and δ/γ interfaces, where δ-ferrite not only provides fast diffusion pathways for Cr but also nucleation sites. The solidification segregation sequence in 310S stainless steel is Cr > Ni > Fe, with Cr and Ni showing positive segregation and Fe showing negative segregation. The addition of Al does not alter the solidification mode of 310S stainless steel but refines austenite grains, reduces interdendritic solute enrichment, decreases segregation, lowers both the size and fraction of ferrite, and suppresses the precipitation of σ and M₂₃C₆ phases. This effect is mainly attributed to the reduction of δ/γ interfaces, which weakens the preferred nucleation sites for M₂₃C₆. Increasing the cooling rate enhances non-equilibrium solute segregation, promotes ferrite formation, inhibits the δ → γ transformation, and ultimately retains more ferrite; the intensified segregation further accelerates the δ → σ transformation. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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22 pages, 7700 KB

Open AccessArticle

Towards a Global Constitutive Formulation for Modeling the Hot Working Behavior of Low-Carbon Steels

by Unai Mayo, Sergio Fernandez-Sanchez, Isabel Gutierrez, Denis Jorge-Badiola and Amaia Iza-Mendia

Metals 2025, 15(9), 1044; https://doi.org/10.3390/met15091044 - 19 Sep 2025

Viewed by 379

Abstract

The current study explores the applicability of a single constitutive equation, based on the Arrhenius hyperbolic sine model, to a wide range of chemical compositions and test conditions by using a unique approximation. To address this challenge, a mixed model is proposed, integrating a physical model with phenomenological expressions to capture the strain and strain rate hardening, forming temperature, dynamic recovery (DRV) and dynamic recrystallization (DRX). The investigation combines high-temperature mechanical testing with modeling in order to understand the hot deformation mechanisms. Hot torsion tests were conducted on ten different low-carbon steels with distinct microalloying additions to capture their responses under diverse initial austenite grain sizes, deformation temperatures and strain rate conditions (d₀ = 22–850 µm, T = 800–1200 °C and

\dot{ε}

= 0.1–10 s⁻¹). The developed constitutive equation has resulted in a robust expression that effectively simulates the hot behavior of various alloys across a wide range of conditions. The application of an optimization tool has significantly reduced the need for adjustments across different alloys, temperatures and strain rates, showcasing its versatility and effectiveness in predicting the flow behavior in a variety of scenarios with excellent accuracy. Moreover, the model has been validated with experimental torsion data from the literature, enhancing the applicability of the developed expression to a broader spectrum of chemical compositions. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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10 pages, 1023 KB

Open AccessArticle

Research on the Solidification Structure of the Zn-19Al-6Mg Alloy

by Jianhua Wei, Jun Xiao, Shaoguang Yang, Kuo Cao, Di Wang and Aimin Zhao

Metals 2025, 15(7), 769; https://doi.org/10.3390/met15070769 - 8 Jul 2025

Viewed by 471

Abstract

This paper deals with “Zn-19Al-6Mg” coatings and their solidification structure is the basis for the study of the alloy’s properties. The solidification equilibrium phase diagram of this alloy was calculated using thermodynamic software. Samples were taken from the billets of this alloy for differential thermal analysis experiments. By combining the phase diagram and the experimental results of differential thermal analysis, the solidification structure of the Zn-19Al-6Mg alloy was obtained. The phases in the solidified structure were identified by means of SEM, EDS, XRD, etc. The research finds that the solidification structure of the Zn-19Al-6Mg alloy is composed of the β-Al phase, the α-Al phase, the MgZn₂ phase, and the Mg₂Zn₁₁ phase. During the actual solidification process of the alloy, due to the large cooling rate, Zn-rich phases will appear in the microstructure. The research results provide a basis for the regulation of the coating structure when preparing Zn-19Al-6Mg-coated sheets and strips. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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18 pages, 3769 KB

Open AccessArticle

Effect of Inter-Pass Temperature and Time on Martensite Formation in the Heat-Affected Zone During Multi-Pass Welding of P91 Steel

by Druce Dunne, Huijun Li and Elena Pereloma

Metals 2025, 15(5), 501; https://doi.org/10.3390/met15050501 - 30 Apr 2025

Viewed by 1042

Abstract

Dilatometry was used to simulate and analyze martensite formation in the grain-coarsened heat-affected zone (GCHAZ) of P91 steel for high inter-pass temperatures during multi-pass welding. The inter-pass temperature of 360 °C was within the dual-phase temperature range (~400 °C to 240 °C), but because of the unexpected formation of isothermal martensite, the microstructure at the inter-pass temperature was substantially martensitic and similar in microstructure and hardness to those obtained using lower, conventional inter-pass temperatures (about 250 °C). The results for martensite formation indicate that kinetic classifications for transformation in carbon and alloyed steels should take into account the overlapping effects of the diffusionless transformation and thermally activated processes associated with dislocation motion and the diffusion of interstitial elements. Furthermore, the M_S temperature was found to be highly sensitive to the microstructural state of the austenite and the availability of nucleating sites for martensite formation. The data for the kinetics of martensite formation were inconsistent with the widely used Koistinen and Marburger (KM) equation for predicting the volume fraction of martensite as a function of quench temperature. It is concluded that the KM equation has limited applicability Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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20 pages, 21573 KB

Open AccessArticle

Thermo-Mechanical Properties and Oxidation Behavior of FeCrAl Alloys with Si and Y Addition

by Yanzhao Ni, Wen Qi, Liangshuo Zhao, Dong Li, Yingjie Qiao, Jingxue Zhou, Peng Wang and Kun Yang

Metals 2025, 15(4), 433; https://doi.org/10.3390/met15040433 - 12 Apr 2025

Cited by 2 | Viewed by 1465

Abstract

The chemical composition of FeCrAl alloy significantly influences its thermal-mechanical as well as anti-corrosive properties. This study investigates the impact of silicon and yttrium additions on the thermal-mechanical properties and high-temperature oxidation resistance of FeCrAl alloy. The results indicate that thermal conductivity gradually decreases with the incorporation of Y or Si into the lattice, whereas the mechanical strength of the alloy can be enhanced through the addition of Y. A trace amount of Y can improve the alloy’s high-temperature oxidation resistance by mitigating the spallation of the surface oxidation film and promoting the growth of the film, characterized by heterogeneous chemical composition and microstructure. It is observed that Y possesses a higher charge density than FeCrAl, suggesting that Y can lose electrons more readily than other elements, which implies a reduction in oxygen diffusion. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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26 pages, 53754 KB

Open AccessArticle

Microstructure Evolution of Cold-Rolled Carbide-Free Bainite Steel Sheets During Continuous Annealing Process

by Bahareh Mobedpour, Fateh Fazeli and Hatem Zurob

Metals 2025, 15(2), 125; https://doi.org/10.3390/met15020125 - 27 Jan 2025

Viewed by 1460

Abstract

A modified carbide-free bainite (CFB) steel has been developed, building on existing alloys for compatibility with commercial continuous annealing lines (CALs), featuring a low austenitization temperature and short overaging time. The microstructural features of such candidate CFB sheets are compared with those of conventional CFB steel sheets that require higher reheating temperatures and longer overaging times. The effects of annealing parameters such as reheating temperatures and overaging temperatures on phase transformation kinetics and microstructure evolution are presented. The annealing process was simulated in a Gleeble thermomechanical processing simulator, and the microstructural characterization was carried out using XRD, SEM, and EBSD. Reconstruction of parent austenite grains from EBSD data did not reveal any variant selection, regardless of changes in the austenitization temperature, overaging temperature, or carbon content. It was observed that the V1–V2 variant pairing is the most common at the lower overaging temperature for reheating at 950 °C; however, this pairing decreases as the isothermal overaging temperature increases, with variant pairings involving low misorientation boundaries—such as V1–V4 and V1–V8—becoming more frequent. Steels with higher carbon content exhibit no significant changes in their variant pairing, regardless of variations in the austenitizing or isothermal temperatures. The XRD results show that the retained austenite fraction is reduced by increasing the isothermal transformation temperature. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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13 pages, 23660 KB

Open AccessArticle

In Situ Microstructural Evolution and Precipitate Analysis of High-Nickel Shipbuilding Steel Using High-Temperature Confocal Laser-Scanning Microscopy

by Guojin Sun, Shengzhi Zhu, Zhenggui Li and Qi Wang

Metals 2024, 14(9), 1085; https://doi.org/10.3390/met14091085 - 22 Sep 2024

Cited by 2 | Viewed by 1641

Abstract

This study investigates the microstructural evolution and mechanical properties of high-nickel shipbuilding steel during thermal processing using high-temperature confocal laser-scanning microscopy (HTCLSM). An in situ observation of the heating and holding processes reveals critical insights into phase transformations, grain-growth behavior, and the formation of precipitates. The experimental results demonstrate that austenitization begins at approximately 700 °C, with significant grain-boundary nucleation. At 900 °C, the formation of black precipitates was observed, and their persistence up to temperatures exceeding 1000 °C was confirmed. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses identified these precipitates as chromium carbides (Cr₇C₃), which significantly contribute to the material’s strength. A comprehensive analysis using transmission electron microscopy (TEM) confirmed the presence and distribution of Cr₇C₃ within the grains and along grain boundaries. These findings provide a deeper understanding of the microstructural dynamics in high-nickel steels, guiding the optimization of heat-treatment processes to enhance mechanical properties for maritime applications. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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20 pages, 5679 KB

Open AccessArticle

Microstructural and Texture Evolution of Pearlite-Drawn Wires for Flexible Marine Pipelines: Investigating the Effect of Heat Treatments on Mechanical Properties

by Pedro H. Pinheiro, Mohammad Masoumi, Luís Flávio G. Herculano, João Victor B. Xavier, Samille Kricia B. de Lima, Eden S. Silva, Gedeon S. Reis, Samuel F. Rodrigues and Hamilton F. Gomes de Abreu

Metals 2023, 13(4), 805; https://doi.org/10.3390/met13040805 - 20 Apr 2023

Cited by 4 | Viewed by 2819

Abstract

Flexible pipelines connect offshore platforms to subsea production systems due to their high flexibility, applicability, and recycling. Flexible armor layers in flexible pipelines are constructed using the parallel helical wrapping of several rectangular wires. The complex stress modes to which pipelines are subjected provide complex failure modes that are mostly unpredictable, requiring expensive pipeline integrity verification methods. This work investigates texture and microstructure evolution in pearlite-drawn wires due to different heat treatments. The material was subjected to annealing and isothermal heat treatments to obtain changes in its microstructure and texture. The changes were characterized using SEM, XRD, and EBSD techniques. Samples were subjected to tensile testing to evaluate their mechanical properties. This work revealed that annealing and isothermal treatments mainly modify the material microstructure, whereas annealing provides a material with grains with ease of deformation. In contrast, isothermal treatment provides grain growth with high internal energy and more deformation resistance. Annealing increases the intensity of all texture components, while isothermal treatment reduces intensity. These findings provide insights into the relationship between material properties and heat treatments, which can be used to optimize the design and performance of flexible pipelines, thereby reducing the need for expensive integrity verification methods. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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17 pages, 23237 KB

Open AccessArticle

Dynamic Ferrite Formation and Evolution above the Ae₃ Temperature during Plate Rolling Simulation of an API X80 Steel

by Francisco Romário de S. Machado, João C. Ferreira, Maria Veronica G. Rodrigues, Marcos Natan da S. Lima, Rodrigo de C. Paes Loureiro, Fulvio Siciliano, Eden S. Silva, Gedeon S. Reis, Regina C. de Sousa, Clodualdo Aranas, Jr., Hamilton F. Gomes de Abreu and Samuel Filgueiras Rodrigues

Metals 2022, 12(8), 1239; https://doi.org/10.3390/met12081239 - 22 Jul 2022

Cited by 3 | Viewed by 2411

Abstract

Thermo-mechanically controlled rolling is a technique used to produce steel strips and plates. One of the steels widely used in the production of heavy plates for application in oil and gas pipelines is API X80. The hot rolling process of this family of steels consists of applying deformation passes at high temperatures, mainly above Ae₃, inside the austenite phase field. It has been shown that during deformation, the phenomenon of dynamic transformation (DT) of austenite into ferrite leads to lower hot deformation resistance within the stable austenite region. In this investigation, hot torsion simulations of an industrial rolling process under continuous cooling conditions were used to monitor the formation of ferrite by DT. Stress–strain flow curves and equivalent mean flow stresses followed by sample characterization via optical and electron microscopy showed the inevitable formation of ferrite above the Ae₃. The employed 10-pass deformation schedule was divided into 5 roughing and 5 finishing passes, thereby promoting an increased volume fraction of ferrite and decreased critical strain for the onset of DT and dynamic recrystallization (DRX). A microstructural analysis confirmed the formation of ferrite from the first roughing strain until the last finishing pass. The volume fraction of DT ferrite increased due to strain accumulation, an increased number of deformation passes and as the temperature approached the Ae₃, leading to a characteristic torsion texture at the end of the simulation. Full article

(This article belongs to the Special Issue Phase Transformation and Softening Mechanisms of Metals and Alloys during Thermomechanical Processing)

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