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Applied Sciences
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Heat Treatment of Metals
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Heat Treatment of Metals

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Additive Manufacturing Technologies".

Deadline for manuscript submissions: 30 June 2024 | Viewed by 4770

Special Issue Editors

Dr. Giulia Stornelli

E-Mail Website
Guest Editor
Dipartimento di Ingegneria, Università di Perugia, Via G. Duranti 93, 06125 Perugia, Italy
Interests: metal additive manufacturing; steel; heat treatment; metals for nuclear fusion application; alloy design
Dr. Andrea Di Schino

E-Mail Website
Guest Editor
Dipartimento di Ingegneria, Università di Perugia, Via G. Duranti 93, 06125 Perugia, Italy
Interests: steels; microstructure; properties; additive materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The use of heat treatments represents one of the most common and effective methods used to modify the internal structure of metals and thus obtain or tune the required properties. Almost all metals and alloys respond to heat treatments but their response is often significantly different, resulting in different performances. The identification and development of process technologies and analysis methods have created possibilities for new research efforts and practical applications. As an example, the development of additive manufacturing has promoted research efforts on the use of heat treatment methods for as-built alloys or for ultra-fast heat treatments having a strong industrial impact in terms of affordability and reliability. This Special Issue contains contributions on the microstructural influence of innovative and/or traditional heat treatments for different classes of metals and alloys.

Furthermore, the application of different techniques and technologies of investigation is strongly encouraged since the possibility of combining information from various methods of analysis provides unique insights into the performance–microstructure relationship in metallic materials (e.g., the influence of the microstructure on mechanical and/or magnetic properties).

Contributions related to simulation models of microstructural evolution are also welcome.

Dr. Giulia Stornelli
Prof. Dr. Andrea Di Schino
Guest Editors

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. Applied Sciences is an international peer-reviewed open access semimonthly 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 2400 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

  • microstructure
  • metals and alloys
  • heat treatments
  • properties
  • simulation model

Published Papers (5 papers)

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Research

16 pages, 10783 KiB  
Article
An Industrial-Scale Study of the Hardness and Microstructural Effects of Isothermal Heat Treatment Parameters on EN 100CrMo7 Bearing Steel
by Annalisa Fortini, Emanuele Bertarelli, Manuel Cassola and Mattia Merlin
Appl. Sci. 2024, 14(2), 737; https://doi.org/10.3390/app14020737 - 15 Jan 2024
Viewed by 620
Abstract
The 100CrMo7, commonly employed for bearings in rotating machinery, relies on precise heat treatment parameters to ensure an optimal microstructure and, in turn, mechanical properties. Typically, an austenitizing treatment, followed by rapid cooling in a salt bath for martempering or austempering, is crucial [...] Read more.
The 100CrMo7, commonly employed for bearings in rotating machinery, relies on precise heat treatment parameters to ensure an optimal microstructure and, in turn, mechanical properties. Typically, an austenitizing treatment, followed by rapid cooling in a salt bath for martempering or austempering, is crucial in achieving the desired microstructure and hardness. The present industrial-scale study involved a comparative analysis between martempering and austempering routes regarding the hardness and microstructure evolution of EN 100CrMo7 large-size rings. The investigation delves into the effects of austempering temperatures, holding times, and austenitizing temperature. Furthermore, the role of tempering in reducing the amount of retained austenite was also considered. The results indicate that martempering yielded the highest hardness values while austempering exhibited a decrease in hardness at the center of the rings, though a lower amount of retained austenite (in the range of 3.0–4.9 vol.%) was detected in comparison with martempering. In addition, a 850 °C austenitizing temperature reduced the hardness by 16% in the center of the rings and promoted a high content of upper bainite, thus suggesting its inefficacy for the involved large-size rings. In contrast, a 880 °C austenitizing temperature maintained consistently high HRC values across the ring’s height. Lastly, the analysis highlighted that the cooling rate played a more crucial role than the austempering holding time. Such industrial-scale investigations performed on real components improve the knowledge and control of heat treatment parameters in comparison with the nominal guidelines provided by steel suppliers. These outcomes offer insights for optimizing industrial heat treatment parameters, with practical implications for enhancing steel bearings’ microstructural and mechanical performance and lifespan. Full article
(This article belongs to the Special Issue Heat Treatment of Metals)
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15 pages, 9931 KiB  
Article
Influence of Heat Treatment Parameters on the Microstructure of 17-4 PH Single Tracks Fabricated by Direct Energy Deposition
by Mattia Merlin, Cindy Morales, Matteo Ferroni, Annalisa Fortini and Chiara Soffritti
Appl. Sci. 2024, 14(2), 700; https://doi.org/10.3390/app14020700 - 14 Jan 2024
Viewed by 701
Abstract
Post-fabrication heat treatment (PFHT) is one of the most applied strategies for achieving the desired microstructure and mechanical resistance on additive manufactured components because of the non-equilibrium microstructural state of the material in the as-built condition. In particular, during PFHT, 17-4 PH martensitic [...] Read more.
Post-fabrication heat treatment (PFHT) is one of the most applied strategies for achieving the desired microstructure and mechanical resistance on additive manufactured components because of the non-equilibrium microstructural state of the material in the as-built condition. In particular, during PFHT, 17-4 PH martensitic stainless steel is mainly strengthened by the precipitation of Cu-rich nanometric particles and Nb carbides into the metal matrix. In this work, the influence of specifically designed PFHTs on the microstructural and mechanical properties of 17-4 PH single tracks fabricated via direct energy deposition was studied. Different solubilization and aging times, as well as a direct aging strategy, were considered. Optical microscopy, X-ray diffractometry, and transmission electron microscopy were used to investigate the microstructure evolution induced by the PFHTs. Moreover, Vickers microhardness measurements were performed to evaluate the increase in mechanical strength. In all cases, the heat-treated single tracks showed a mean microhardness higher than that of the depositions in the as-built condition. In the single tracks subjected to solution treatment, followed by aging for about 100 h, the presence of both Cu-rich precipitates and Nb carbides was assessed; conversely, when directly aged from the as-built condition, only Nb carbides were detected. In the latter case, the carbides were finer and closer to each other than those in the single tracks aged after the solution treatment. Full article
(This article belongs to the Special Issue Heat Treatment of Metals)
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17 pages, 8355 KiB  
Article
Ultra-Fast Heating Treatment Effect on Microstructure, Mechanical Properties and Magnetic Characteristics of Non-Oriented Grain Electrical Steels
by Matteo Gaggiotti, Luciano Albini, Giulia Stornelli, Giulia Tiracorrendo, Luca Landi and Andrea Di Schino
Appl. Sci. 2023, 13(17), 9833; https://doi.org/10.3390/app13179833 - 30 Aug 2023
Viewed by 800
Abstract
This paper focuses on the effect of rapid annealing on Non-Grain Oriented Electrical Steel (NGO) in terms of microstructure, mechanical properties, and magnetic properties. The Ultra-Fast Heating (UFH) tests were performed by a transversal induction heater on NGO electrical steel samples (cold rolled [...] Read more.
This paper focuses on the effect of rapid annealing on Non-Grain Oriented Electrical Steel (NGO) in terms of microstructure, mechanical properties, and magnetic properties. The Ultra-Fast Heating (UFH) tests were performed by a transversal induction heater on NGO electrical steel samples (cold rolled down to 0.5 mm), varying the heating power (80 kW and 90 kW) and the speed of the strip through the induction heater. This allowed us to exploit heating rates (HR) in the range of 200–300 °C/s and targeting peak temperature (Tpeak) up to a maximum of 1250 °C. The comparison between the microstructure as obtained by conventional annealing and the ultra-fast heating process highlights a clear effect in terms of grain size refinement provided by the UFH. In particular, the average grain size as obtained by UFH ranges two/three times lower than by a conventional process. The results show the possibility of applying UFH to NGO steels, targeting mechanical properties such as those obtained by the standard process, combined with the benefits from this innovative heat treatment in terms of green energy and the minimization of CO2 emissions. Magnetic characterization performed by a single sheet tester (30 × 90 mm) showed that the values of core losses are comparable with conventional NGO grades. Full article
(This article belongs to the Special Issue Heat Treatment of Metals)
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12 pages, 6037 KiB  
Article
Strengthening Mechanisms in a Medium-Carbon Steel Subjected to Thermo-Mechanical Processing
by Valeriy Dudko, Diana Yuzbekova and Rustam Kaibyshev
Appl. Sci. 2023, 13(17), 9614; https://doi.org/10.3390/app13179614 - 25 Aug 2023
Cited by 1 | Viewed by 833
Abstract
Strengthening mechanisms were examined in a Fe-0.43C-1.60Si-0.01Mn-1.1Cr-0.95Mo-0.08V-0.05Nb steel exhibiting a yield strength (YS) of 1310 MPa after tempering and 1550 MPa after tempforming. The dislocation strengthening gave a major contribution to the overall YS of the steel in the tempered condition, whereas dispersion [...] Read more.
Strengthening mechanisms were examined in a Fe-0.43C-1.60Si-0.01Mn-1.1Cr-0.95Mo-0.08V-0.05Nb steel exhibiting a yield strength (YS) of 1310 MPa after tempering and 1550 MPa after tempforming. The dislocation strengthening gave a major contribution to the overall YS of the steel in the tempered condition, whereas dispersion strengthening was a major contributor to the YS of the steel in the tempformed condition. High values of dislocation strengthening after tempering were attributed to dislocations composing the lath boundaries. A high density of free dislocations provided nearly the same dislocation strengthening after tempforming. Warm rolling after tempering led to alignment of intercrystallite boundaries along the rolling direction that decreased the interparticle spacing between M23C6 carbides located at these boundaries and thus increased the magnitude of dispersion strengthening. The boundary strengthening contributed to overall YS significantly due to small lath thickness after tempering and nanoscale spacing between lamellar boundaries after tempforming. Full article
(This article belongs to the Special Issue Heat Treatment of Metals)
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19 pages, 11595 KiB  
Article
The In-House Method of Manufacturing a Low-Cost Heat Pipe with Specified Thermophysical Properties and Geometry
by Michał Rogowski, Maciej Fabrykiewicz, Paweł Szymański and Rafał Andrzejczyk
Appl. Sci. 2023, 13(14), 8415; https://doi.org/10.3390/app13148415 - 20 Jul 2023
Viewed by 1075
Abstract
Various types of heat pipes are available to purchase off the shelf, from various manufacturers, but most of them have strictly defined geometry and technical parameters. However, when there is a need to use a heat pipe (HP) with an unusual size and [...] Read more.
Various types of heat pipes are available to purchase off the shelf, from various manufacturers, but most of them have strictly defined geometry and technical parameters. However, when there is a need to use a heat pipe (HP) with an unusual size and shape or working conditions other than the standard ones, it becomes very costly to order them from manufacturers, especially in small quantities, and only a few producers are willing to fulfill such an order. This paper presents a detailed description and step-by-step method of manufacturing and testing a low-cost HP with specific properties and geometry, cooperating with a modular heat recovery system based on the use of phase change materials (PCM) for electromobility applications. The presented heat pipes were made entirely by hand, primarily with the use of basic workshop tools, without the use of specialized and automated CNC machines. Utensils used during the process were either made by hand or using desktop FDM 3D printers. During the evaluation of heat pipes’ performance within PCM (coconut oil), simple statistical functions were used. One-dimensional and two-dimensional histograms were used to visualize data obtained during this research. The presented method allows the manufacturing of heat pipes that are, on average, able to melt about 35% more PCM than an empty copper pipe with the exact same geometry. The HPs’ performance in coconut oil was evaluated on the basis of their future applications. Full article
(This article belongs to the Special Issue Heat Treatment of Metals)
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