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Metals
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Heat Treatment of Steels
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Heat Treatment of Steels

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 (30 April 2021) | Viewed by 45876

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

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
Dr. Claudio Testani

E-Mail Website
Guest Editor
CALEF-ENEA CR Casaccia, Via Anguillarese 301, Santa Maria di Galeria, 00123 Rome, Italy
Interests: light alloys; titanium alloys; aluminium alloys; ODS steels; thermal treatments powder metallurgy; additive manufacturing; forging; extrusion; hot isostatic pressing; superplastic forming
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Steels represent a quite interesting material family, both from a scientific and commercial point of view, following many applications they can be devoted to. Following that, it is therefore essential to deeply understand the relations between properties and microstructure and how to drive them via a specific process. Despite their diffusion as a consolidated material, many research fields are active regarding new applications. In this framework in particular, the role of heat treatments in obtaining even complex microstructures is still quite an open matter, also thanks to the design of innovative heat treatments.

The Special Issue scope embraces interdisciplinary work covering physical metallurgy and processes, reporting on experimental and theoretical progress concerning microstructural evolution during heat treatments of steels.

Prof. Dr. Andrea Di Schino
Dr. Claudio Testani
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. 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

  • Steel
  • Heat treatments
  • Microstructure
  • Mechanical properties
  • Q&P

Published Papers (15 papers)

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Editorial

Jump to: Research, Review

3 pages, 181 KiB  
Editorial
Heat Treatment of Steels
by Andrea Di Schino and Claudio Testani
Metals 2021, 11(8), 1168; https://doi.org/10.3390/met11081168 - 23 Jul 2021
Cited by 5 | Viewed by 2360
Abstract
Steels represent an interesting family of materials, both from a scientific and commercial point of view, considering the many innovative applications they can be used for [...] Full article
(This article belongs to the Special Issue Heat Treatment of Steels)

Research

Jump to: Editorial, Review

15 pages, 9211 KiB  
Article
Heat Treatment Design for a QP Steel: Effect of Partitioning Temperature
by Marcel Carpio, Jessica Calvo, Omar García, Juan Pablo Pedraza and José María Cabrera
Metals 2021, 11(7), 1136; https://doi.org/10.3390/met11071136 - 19 Jul 2021
Cited by 18 | Viewed by 4319
Abstract
Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels [...] Read more.
Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels display an excellent relationship between strength and formability, making them able to fulfill the requirements of safety, while reducing automobile weight to enhance the performance during service. The main attribute of QP steels is the TRIP effect that retained austenite possesses, which allows a significant energy absorption during deformation. The present study is focused on evaluating some process parameters, especially the partitioning temperature, in the microstructures and mechanical properties attained during a QP process. An experimental steel (0.2C-3.5Mn-1.5Si (wt%)) was selected and heated according to the theoretical optimum quenching temperature. For this purpose, heat treatments in a quenching dilatometry and further microstructural and mechanical characterization were carried out by SEM, XRD, EBSD, and hardness and tensile tests, respectively. The samples showed a significant increment in the retained austenite at an increasing partitioning temperature, but with strong penalization on the final ductility due to the large amount of fresh martensite obtained as well. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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18 pages, 10670 KiB  
Article
Microstructures and Properties of Auto-Tempering Ultra-High Strength Automotive Steel under Different Thermal-Processing Conditions
by Han Jiang, Yanlin He, Li Lin, Rendong Liu, Yu Zhang, Weisen Zheng and Lin Li
Metals 2021, 11(7), 1121; https://doi.org/10.3390/met11071121 - 14 Jul 2021
Cited by 9 | Viewed by 2546
Abstract
Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the [...] Read more.
Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the steels under water quenching, there was approximately a 70% increase in the strength and elongation of steels under air cooling, in which the martensite was well-tempered. Although the elongation of the steel with a microstructure composed of ferrite, well-tempered martensite and less-tempered martensite could exceed 15%, the hole expansion ratio was still lower because of the undesirable hardness distribution between the hard phases and the soft phases. It followed from the calculation results based on SEM, TEM and XRD analyses, that for the steel under air cooling, the strengthening mechanism was dominated by the solid solution strengthening and the elongation was determined by the auto-tempering of martensite. Experiments and analyses aimed to explore the strengthening and plasticity mechanisms of auto-tempering steels under the special process of flash heating. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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19 pages, 5209 KiB  
Article
The Effect of Different Annealing Strategies on the Microstructure Development and Mechanical Response of Austempered Steels
by Eliseo Hernandez-Duran, Luca Corallo, Tanya Ros-Yanez, Felipe Castro-Cerda and Roumen H. Petrov
Metals 2021, 11(7), 1041; https://doi.org/10.3390/met11071041 - 29 Jun 2021
Cited by 6 | Viewed by 2024
Abstract
This study focuses on the effect of non-conventional annealing strategies on the microstructure and related mechanical properties of austempered steels. Multistep thermo-cycling (TC) and ultrafast heating (UFH) annealing were carried out and compared with the outcome obtained from a conventionally annealed (CA) 0.3C-2Mn-1.5Si [...] Read more.
This study focuses on the effect of non-conventional annealing strategies on the microstructure and related mechanical properties of austempered steels. Multistep thermo-cycling (TC) and ultrafast heating (UFH) annealing were carried out and compared with the outcome obtained from a conventionally annealed (CA) 0.3C-2Mn-1.5Si steel. After the annealing path, steel samples were fast cooled and isothermally treated at 400 °C employing the same parameters. It was found that TC and UFH strategies produce an equivalent level of microstructural refinement. Nevertheless, the obtained microstructure via TC has not led to an improvement in the mechanical properties in comparison with the CA steel. On the other hand, the steel grade produced via a combination of ultrafast heating annealing and austempering exhibits enhanced ductility without decreasing the strength level with respect to TC and CA, giving the best strength–ductility balance among the studied steels. The outstanding mechanical response exhibited by the UFH steel is related to the formation of heterogeneous distribution of ferrite, bainite and retained austenite in proportions 0.09–0.78–0.14. The microstructural formation after UFH is discussed in terms of chemical heterogeneities in the parent austenite. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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18 pages, 10725 KiB  
Article
Precipitation Criterion for Inhibiting Austenite Grain Coarsening during Carburization of Al-Containing 20Cr Gear Steels
by Huasong Liu, Yannan Dong, Hongguang Zheng, Xiangchun Liu, Peng Lan, Haiyan Tang and Jiaquan Zhang
Metals 2021, 11(3), 504; https://doi.org/10.3390/met11030504 - 18 Mar 2021
Cited by 5 | Viewed by 2341
Abstract
AlN precipitates are frequently adopted to pin the austenite grain boundaries for the high-temperature carburization of special gear steels. For these steels, the grain coarsening criterion in the carburizing process is required when encountering the composition optimization for the crack-sensitive steels. In this [...] Read more.
AlN precipitates are frequently adopted to pin the austenite grain boundaries for the high-temperature carburization of special gear steels. For these steels, the grain coarsening criterion in the carburizing process is required when encountering the composition optimization for the crack-sensitive steels. In this work, the quantitative influence of the Al and N content on the grain size after carburization is studied through pseudocarburizing experiments based on 20Cr steel. According to the grain structure feature and the kinetic theory, the abnormal grain growth is demonstrated as the mode of austenite grain coarsening in carburization. The AlN precipitate, which provides the dominant pinning force, is ripened in this process and the particle size can be estimated by the Lifshitz−Slyosov−Wagner theory. Both the mass fraction and the pinning strength of AlN precipitate show significant influence on the grain growth behavior with the critical values indicating the grain coarsening. These criteria correspond to the conditions of abnormal grain growth when bearing the Zener pinning, which has been analyzed by the multiple phase-field simulation. Accordingly, the models to predict the austenite grain coarsening in carburization were constructed. The prediction is validated by the additional experiments, resulting in accuracies of 92% and 75% for the two models, respectively. Finally, one of the models is applied to optimize the Al and N contents of commercial steel. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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14 pages, 6601 KiB  
Article
Evolution of Microstructure during Isothermal Treatments of a Duplex-Austenitic 0.66C11.4Mn.9.9Al Low-Density Forging Steel and Effect on the Mechanical Properties
by Idurre Kaltzakorta, Teresa Gutierrez, Roberto Elvira, Pello Jimbert and Teresa Guraya
Metals 2021, 11(2), 214; https://doi.org/10.3390/met11020214 - 26 Jan 2021
Cited by 5 | Viewed by 1619
Abstract
In the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of [...] Read more.
In the last decades, low-density steels for forging have increasing interest in the automotive industry, and good mechanical properties are required for their real application. This paper describes the results obtained for a 0.66C11.4Mn9.9Al duplex austenitic low-density steel after applying a set of isothermal treatments at different combinations of time and temperature, aimed to promote kappa carbide precipitation, and improve the mechanical properties obtained with a water quenching treatment. The effects of the different isothermal treatments on the microstructure and on the mechanical properties have been analyzed and compared to those obtained from a quenching heat treatment. We found that isothermal treatments in the range temperature between 550–750 °C promoted the profuse precipitation of coarse kappa carbides at grain boundaries, which dramatically reduced the ductility of the alloy, whereas a traditional quenching treatment resulted in a better combination of ductility and mechanical strength. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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15 pages, 5673 KiB  
Article
Correlation between Microstructures and Ductility Parameters of Cold Drawn Hyper-Eutectoid Steel Wires with Different Drawing Strains and Post-Deformation Annealing Conditions
by Jin Young Jung, Kang Suk An, Pyeong Yeol Park and Won Jong Nam
Metals 2021, 11(2), 178; https://doi.org/10.3390/met11020178 - 20 Jan 2021
Cited by 5 | Viewed by 2079
Abstract
The relationship between microstructures and ductility parameters, including reduction of area, elongation to failure, occurrence of delamination, and number of turns to failure in torsion, in hypereutectoid pearlitic steel wires was investigated. The transformed steel wires at 620 °C were successively dry-drawn to [...] Read more.
The relationship between microstructures and ductility parameters, including reduction of area, elongation to failure, occurrence of delamination, and number of turns to failure in torsion, in hypereutectoid pearlitic steel wires was investigated. The transformed steel wires at 620 °C were successively dry-drawn to drawing strains from 0.40 to 2.38. To examine the effects of hot-dip galvanizing conditions, post-deformation annealing was performed on cold drawn steel wires (ε = 0.99, 1.59, and 2.38) with a different heating time of 30–3600 s at 500 °C in a salt bath. In cold drawn wires, elongation to failure dropped due to the formation of dislocation substructures, decreased slowly due to the increase of dislocation density, and saturated with drawing strain. During annealing, elongation to failure increased due to recovery, and saturated with annealing time. The variation of elongation to failure in cold drawn and annealed steel wires would depend on the distribution of dislocations in lamellar ferrite. The orientation of lamellar cementite and the shape of cementite particles would become an effective factor controlling number of turns to failure in torsion of cold drawn and annealed steel wires. The orientation and shape of lamellar cementite would become microstructural features controlling reduction of area of cold drawn and annealed steel wires. The density of dislocations contributed to reduction of area to some extent. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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19 pages, 11353 KiB  
Article
Effect of Intercritical Annealing and Austempering on the Microstructure and Mechanical Properties of a High Silicon Manganese Steel
by Mattia Franceschi, Luca Pezzato, Claudio Gennari, Alberto Fabrizi, Marina Polyakova, Dmitry Konstantinov, Katya Brunelli and Manuele Dabalà
Metals 2020, 10(11), 1448; https://doi.org/10.3390/met10111448 - 29 Oct 2020
Cited by 22 | Viewed by 2494
Abstract
High Silicon Austempered steels (AHSS) are materials of great interest due to their excellent combination of high strength, ductility, toughness, and limited costs. These steel grades are characterized by a microstructure consisting of ferrite and bainite, accompanied by a high quantity retained austenite [...] Read more.
High Silicon Austempered steels (AHSS) are materials of great interest due to their excellent combination of high strength, ductility, toughness, and limited costs. These steel grades are characterized by a microstructure consisting of ferrite and bainite, accompanied by a high quantity retained austenite (RA). The aim of this study is to analyze the effect of an innovative heat treatment, consisting of intercritical annealing at 780 °C and austempering at 400 °C for 30 min, on the microstructure and mechanical properties of a novel high silicon steel (0.43C-3.26Si-2.72Mn wt.%). The microstructure was characterized by optical and electron microscopy and XRD analysis. Hardness and tensile tests were performed. A multiphase ferritic-martensitic microstructure was obtained. A hardness of 426 HV and a tensile strength of 1650 MPa were measured, with an elongation of 4.5%. The results were compared with those ones obtained with annealing and Q&T treatments. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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13 pages, 3688 KiB  
Article
Heat Treatment Effect on Microstructure Evolution in a 7% Cr Steel for Forging
by Andrea Di Schino, Matteo Gaggiotti and Claudio Testani
Metals 2020, 10(6), 808; https://doi.org/10.3390/met10060808 - 17 Jun 2020
Cited by 28 | Viewed by 3467
Abstract
Well-defined heat-treatment guidelines are required to achieve the target mechanical properties in high-chromium steels for forgings. Moreover, for this class of materials, the microstructure evolution during heat treatment is not clearly understood. Thus, it is particularly important to assess the steel microstructure evolution [...] Read more.
Well-defined heat-treatment guidelines are required to achieve the target mechanical properties in high-chromium steels for forgings. Moreover, for this class of materials, the microstructure evolution during heat treatment is not clearly understood. Thus, it is particularly important to assess the steel microstructure evolution during heat treatment, in order to promote the best microstructure. This will ascertain the safe use for long-term service. In this paper, different heat treatments are considered, and their effect on a 7% Cr steel for forging is reported. Results show that, following the high intrinsic steel hardenability, significative differences were not found versus the cooling-step treatment, although prior austenite grain size was significantly different. Moreover, retained austenite (RA) content is lower in double-tempered specimens after heat treatments at higher temperatures. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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17 pages, 8378 KiB  
Article
Analytical Model to Compare and Select Creep Constitutive Equation for Stress Relief Investigation during Heat Treatment in Ferritic Welded Structure
by Mengjia Hu, Kejian Li, Shanlin Li, Zhipeng Cai and Jiluan Pan
Metals 2020, 10(5), 688; https://doi.org/10.3390/met10050688 - 23 May 2020
Cited by 5 | Viewed by 2985
Abstract
The one-dimensional analytical model was promoted to help select the creep constitutive equation and predict heat treatment temperature in a ferritic welded structure, along with neglecting the impact of structural constraint and deformation compatibility. The analytical solutions were compared with simulation results, which [...] Read more.
The one-dimensional analytical model was promoted to help select the creep constitutive equation and predict heat treatment temperature in a ferritic welded structure, along with neglecting the impact of structural constraint and deformation compatibility. The analytical solutions were compared with simulation results, which were validated with experimental measurements in a ferritic welded rotor. The as-welded and post weld heat treatment (PWHT) residual stresses on the inner and outer cylindrical surfaces were measured with the hole-drilling method (HDM) for validation. Based on the one-dimensional analytical model, different effects of Norton and Norton-Bailey creep constitutive equation on stress relief during heat treatment in a ferritic welded rotor were investigated. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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14 pages, 7782 KiB  
Article
Influence of Vacuum Heat Treatments on Microstructure and Mechanical Properties of M35 High Speed Steel
by Chiara Soffritti, Annalisa Fortini, Ramona Sola, Elettra Fabbri, Mattia Merlin and Gian Luca Garagnani
Metals 2020, 10(5), 643; https://doi.org/10.3390/met10050643 - 15 May 2020
Cited by 12 | Viewed by 3980
Abstract
Towards the end of the last century, vacuum heat treatment of high speed steels was increasingly used in the fabrication of precision cutting tools. This study investigates the influence of vacuum heat treatments at different pressures of quenching gas on the microstructure and [...] Read more.
Towards the end of the last century, vacuum heat treatment of high speed steels was increasingly used in the fabrication of precision cutting tools. This study investigates the influence of vacuum heat treatments at different pressures of quenching gas on the microstructure and mechanical properties of taps made of M35 high speed steel. Taps were characterized by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, apparent grain size and Vickers hardness measurements, and scratch tests. Failure analysis after tapping tests was also performed to determine the main fracture mechanisms. For all taps, the results showed that microstructures and the values of characteristics of secondary carbides, retained austenite, apparent grain size and Vickers hardness were comparable to previously reported ones for vacuum heat treated high speed steels. For taps vacuum heat treated at six bar, the highest plane strain fracture toughness was due to a higher content of finer small secondary carbides. In contrast, the lowest plane strain fracture toughness of taps vacuum heat treated at eight bar may be due to an excessive amount of finer small secondary carbides, which may provide a preferential path for crack propagation. Finally, the predominant fracture mechanism of taps was quasi-cleavage. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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14 pages, 17371 KiB  
Article
Corrosion Behavior and Mechanical Properties of AISI 316 Stainless Steel Clad Q235 Plate
by Andrea Di Schino and Claudio Testani
Metals 2020, 10(4), 552; https://doi.org/10.3390/met10040552 - 24 Apr 2020
Cited by 37 | Viewed by 5223
Abstract
This paper deals with carbon steel and stainless steel clad-plate properties. Cladding is performed by the submerged-arc welding (SAW) overlay process. Due to element diffusion (Fe, Cr, Ni, and Mn), a 1.5 mm wide diffusion layer is formed between the stainless steel and [...] Read more.
This paper deals with carbon steel and stainless steel clad-plate properties. Cladding is performed by the submerged-arc welding (SAW) overlay process. Due to element diffusion (Fe, Cr, Ni, and Mn), a 1.5 mm wide diffusion layer is formed between the stainless steel and carbon steel interface of the cladded plate affecting corrosion resistance. Pitting resistance is evaluated by measuring the critical-pitting temperature (CPT), as described in the American Society for Testing and Materials (ASTM) G-48 standard test. Additionally, Huey immersion tests, in accordance with ASTM A262, Type C, are carried out to evaluate the intergranular corrosion resistance. Some hardness peaks are detected in microalloyed steel close to the molten interface line in the coarse-grained heat-affected zone (CGHAZ). Results show that stress-relieving treatments are not sufficient to avoid hardness peaks. The hardness peaks in the CGHAZ of the microalloyed steel disappear after quenching and tempering (Q and T). Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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12 pages, 3062 KiB  
Article
Compound Layer Design for Deep Nitrided Gearings
by Stefanie Hoja, Matthias Steinbacher and Hans-Werner Zoch
Metals 2020, 10(4), 455; https://doi.org/10.3390/met10040455 - 31 Mar 2020
Cited by 11 | Viewed by 3807
Abstract
Deep nitriding is used to obtain a nitriding hardness depth beyond 0.6 mm. The long nitriding processes, which are necessary to reach the high nitriding hardness depths, mostly have a negative influence on the hardness and strength of the nitrided layer as well [...] Read more.
Deep nitriding is used to obtain a nitriding hardness depth beyond 0.6 mm. The long nitriding processes, which are necessary to reach the high nitriding hardness depths, mostly have a negative influence on the hardness and strength of the nitrided layer as well as on the bulk material. The compound layer often is considered less, because in most practical cases, it is removed mechanically after nitriding, to avoid spalling in service. However, in former investigations, it was shown, that thick and compact compound layers have the potential for high flank load capacity of gears. The investigations focus on the simultaneous formation of a high nitriding depth and a thick and compact compound layer. Beside the preservation of the strength, a challenge is to control the porosity of the compound layer, which should be as low as possible. The investigations were carried out using the common nitriding and heat treatable mild steel 31CrMoV9, which is often used for gear applications. The article gives an insight on the development of multistage nitriding processes studied by short- and long-term experiments aiming for a specific compound layer build-up with low porosity and high strength of the nitride layer and core material. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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Review

Jump to: Editorial, Research

17 pages, 1686 KiB  
Review
A Review of the Boiling Curve with Reference to Steel Quenching
by Manuel de J. Barrena-Rodríguez, Francisco A. Acosta-González and María M. Téllez-Rosas
Metals 2021, 11(6), 974; https://doi.org/10.3390/met11060974 - 17 Jun 2021
Cited by 5 | Viewed by 2283
Abstract
This review presents an analysis and discussion about heat transfer phenomena during quenching solid steel from high temperatures. It is shown a description of the boiling curve and the most used methods to characterize heat transfer when using liquid quenchants. The present work [...] Read more.
This review presents an analysis and discussion about heat transfer phenomena during quenching solid steel from high temperatures. It is shown a description of the boiling curve and the most used methods to characterize heat transfer when using liquid quenchants. The present work points out and criticizes important aspects that are frequently poorly attended in the technical literature about determination and use of the boiling curve and/or the respective heat transfer coefficient for modeling solid phase transformations in metals. Points to review include: effect of initial workpiece temperature on the boiling curve, fluid velocity specification to correlate with heat flux, and the importance of coupling between heat conduction in the workpiece and convection boiling to determine the wall heat flux. Finally, research opportunities in this field are suggested to improve current knowledge and extend quenching modeling accuracy to complex workpieces. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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7 pages, 384 KiB  
Review
Heuristic Design of Advanced Martensitic Steels That Are Highly Resistant to Hydrogen Embrittlement by ε-Carbide
by Michio Shimotomai
Metals 2021, 11(2), 370; https://doi.org/10.3390/met11020370 - 23 Feb 2021
Cited by 5 | Viewed by 2047
Abstract
Many advanced steels are based on tempered martensitic microstructures. Their mechanical strength is characterized by fine sub-grain structures with a high density of free dislocations and metallic carbides and/or nitrides. However, the strength for practical use has been limited mostly to below 1400 [...] Read more.
Many advanced steels are based on tempered martensitic microstructures. Their mechanical strength is characterized by fine sub-grain structures with a high density of free dislocations and metallic carbides and/or nitrides. However, the strength for practical use has been limited mostly to below 1400 MPa, owing to delayed fractures that are caused by hydrogen. A literature survey suggests that ε-carbide in the tempered martensite is effective for strengthening. A preliminary experimental survey of the hydrogen absorption and hydrogen embrittlement of a tempered martensitic steel with ε-carbide precipitates suggested that the proper use of carbides in steels can promote a high resistance to hydrogen embrittlement. Based on the surveys, martensitic steels that are highly resistant to hydrogen embrittlement and that have high strength and toughness are proposed. The heuristic design of the steels includes alloying elements necessary to stabilize the ε-carbide and procedures to introduce inoculants for the controlled nucleation of ε-carbide. Full article
(This article belongs to the Special Issue Heat Treatment of Steels)
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