Microstructure—Mechanical Property Relationships in High-Strength 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 (31 March 2024) | Viewed by 9678

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Guest Editor
School of Science and Technology, Department of Mechanical Systems Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
Interests: steel; microstructure; mechanical property; micromechanics; heat treatment; thermo-mechanical process; metal forming; surface treatment
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Guest Editor
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8557, Japan
Interests: microstructure; plasticity; high-strength steel; heat treatment; mechanical property; materials processing; fracture mechanics; hydrogen embrittlement
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

A variety of high-strength steels have been under development for application in automobiles, industrial machinery, power plant, construction machinery, robots, ships, aircraft, buildings, etc. Recently, high-strength steels have received a great deal of attention from both academic and industrial sectors. To properly apply these high-strength steels to machines and parts, there is a requirement for a deep understanding of the microstructure and mechanical properties of the steels subjected to various manufacturing processes, such as casting process, rolling process, additive manufacturing process, heat-treatment, thermo-mechanical process, hot/cold stamping and forging, welding process, machining process, surface modification process, etc. In addition, understanding the microstructure–mechanical property relationships is essential for developing novel high-strength steels since the developed microstructures, obtained by a variety of processes, greatly affect the mechanical properties of the high-strength steels.

This Special Issue of Metals has as its focus the microstructure–mechanical property relationships in (1) traditional high-strength steels such as ferritic/pearlitic steels, precipitation-hardening steels, bainitic/martensitic steels, maraging steels, stainless steels, bearing steels, spring steels, rail steels, etc. Additionally, we intend to highlight (2) advanced high-strength steels such as dual-phase steels, complex phase steels, low-alloy TRIP-aided steels with a different matrix structure, medium-/high- Mn steels, medium-/high- entropy steels, low-density steels, etc. In addition to inviting submissions on these topics, we also welcome research articles on mechanical properties such as tensile properties, formability, toughness, fatigue properties, delayed fracture strength, wear properties, and so on, tested in several conditions such as elevated and cryogenic temperatures, corrosive atmosphere, etc.

Prof. Dr. Koh-ichi Sugimoto
Dr. Tomohiko Hojo
Guest Editors

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Keywords

  • physical metallurgy
  • microstructure
  • mechanical property
  • high-strength steel
  • heat treatment
  • manufacturing process

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Related Special Issue

Published Papers (5 papers)

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Research

12 pages, 3423 KiB  
Article
Impact Toughness Dependent on Annealing Temperatures in 0.16C-6.5Mn Forged Steel for Flywheel Rotors
by Tinghui Man, Jun Wang, Hongshan Zhao and Han Dong
Metals 2024, 14(5), 501; https://doi.org/10.3390/met14050501 - 25 Apr 2024
Viewed by 1006
Abstract
For the application of forged medium-Mn steels on flywheel rotors, the effect of annealing temperatures from 300 °C to 650 °C on the impact toughness of 0.16C-6.5Mn forged steel was investigated to demonstrate the microstructural characteristics and austenite reverse transformation determining the impact [...] Read more.
For the application of forged medium-Mn steels on flywheel rotors, the effect of annealing temperatures from 300 °C to 650 °C on the impact toughness of 0.16C-6.5Mn forged steel was investigated to demonstrate the microstructural characteristics and austenite reverse transformation determining the impact toughness. The results obtained through standard Charpy V-notch impact tests at ambient temperature show that the impact absorbed energy holds at lower than 10 J almost constantly at annealing temperatures of 300 °C to 500 °C, and a representative intergranular fracture is presented. At an annealing temperature of 600 °C, the impact absorbed energy increases to 147 J, with the ductile fracture characteristics showing plenty of fine dimples, and the high impact toughness is attributed to the high volume fraction above 30% and the moderate stability of reverted austenite. Subsequently, the annealing temperature rises higher than 600 °C, the impact absorbed energy decreases, and the fracture morphology shows brittleness characterized by more flat facets of intergranular fractures and small quasi-cleavage facets, presumably corresponding to the insufficient transformation and twinning-induced plasticity effect due to weakening the Mn partitioning from quenched martensite to reverted austenite, which results in lower austenitic stability. Furthermore, the ductile-to-brittle transition temperature (DBTT) of the 0.16C-6.5Mn forged steel annealed at 600 °C, which holds the highest impact absorbed energy, and is explored for the possibility of flywheel rotor application in a service environment. The DBTT reaches −21 °C, obtained through the Boltzmann function, and the impact absorbed energy is approximately 72 J. Full article
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15 pages, 8383 KiB  
Article
Microstructural Evolution in a 0.09% Niobium Low Carbon Steel during Controlled Hot Deformation
by E. Pineda Martínez and E. J. Palmiere
Metals 2024, 14(3), 283; https://doi.org/10.3390/met14030283 - 28 Feb 2024
Viewed by 982
Abstract
A series of plane strain compression tests were carried out in order to simulate the thermomechanical controlled processing of a 0.09wt% Nb low carbon steel, in a scheme of multipass finish rolling at 950 °C with interpass times of 10 s. It was [...] Read more.
A series of plane strain compression tests were carried out in order to simulate the thermomechanical controlled processing of a 0.09wt% Nb low carbon steel, in a scheme of multipass finish rolling at 950 °C with interpass times of 10 s. It was observed that after the first two finishing passes a remarkable grain refinement can be achieved, since the recrystallisation was fully suppressed and abundant ultrafine ferrite was transformed dynamically during the deformation. The addition of a third finishing pass however, led to partial recrystallisation. A deep characterisation of the dynamic ferrite was carried out by diverse methods conducting to relevant findings that contribute to a better elucidation of the dynamic transformation. The results obtained indicated that the dynamic formation of a colony of Widmanstätten ferrite plates during deformation, initiates with the formation of a pair of self-accommodating plates followed by face-to-face sympathetic nucleation of new plates at one of the faces of the pairs of plates already formed. Furthermore, the crystal orientation within the dynamic ferrite phase was analysed with EBSD, it was observed that during the coalescence of plates, prior to the full polygonisation of grains, the ferrite adopts a transitory morphology which possesses particular crystallographic characteristics. Full article
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13 pages, 4010 KiB  
Article
Heat Treatment Process, Microstructure, and Mechanical Properties of Spring Steel with Ultra-High Strength and Toughness
by Fang Shi, Jian Zheng, Jie Zhang, Yang Zhao and Liqing Chen
Metals 2024, 14(2), 180; https://doi.org/10.3390/met14020180 - 1 Feb 2024
Cited by 3 | Viewed by 2518
Abstract
In this research, a new type of spring steel with ultra-high strength and toughness was designed, and its mechanical properties and microstructure under different heat treatment processes were studied. The results show that the optimal heat treatment process for the steel is oil [...] Read more.
In this research, a new type of spring steel with ultra-high strength and toughness was designed, and its mechanical properties and microstructure under different heat treatment processes were studied. The results show that the optimal heat treatment process for the steel is oil quenching at 890 °C for 40 min, followed by tempering at 400 °C for 1 h. Its mechanical properties have an optimal combination of 1865MPa tensile strength, a yield strength of 1662 MPa, an elongation of 11.5%, a cross-sectional shrinkage of 51.5%, and a Charpy impact energy of 43.7 J at room temperature. With increasing austenitizing temperature, the austenite grain size increases, the martensite lath becomes thicker, and the strength decreases. With increasing tempering temperature, the lath boundary of martensite becomes blurred, the strength decreases, and the plasticity improves. In addition, it was found that during tempering at higher temperature (450 °C), large particle inclusions and secondary cracks appeared in the fractured surface, and a large number of carbides precipitated, leading to the brittleness of tempered martensite. Full article
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16 pages, 7503 KiB  
Article
Optimizing Heat Treatment to Improve the Microstructures and Mechanical Properties of 5CrNiMoV Steel
by Wanhui Huang, Liping Lei and Gang Fang
Metals 2023, 13(7), 1263; https://doi.org/10.3390/met13071263 - 13 Jul 2023
Cited by 3 | Viewed by 2613
Abstract
A strategy combining intercritical quenching, pre-tempering, and tempering processes was implemented to optimize the microstructures and mechanical properties of 5CrNiMoV steel. By intercritically quenching at 1050 °C, pr-tempering at 600 °C, and tempering at 550 °C, the steel exhibited a comprehensive performance with [...] Read more.
A strategy combining intercritical quenching, pre-tempering, and tempering processes was implemented to optimize the microstructures and mechanical properties of 5CrNiMoV steel. By intercritically quenching at 1050 °C, pr-tempering at 600 °C, and tempering at 550 °C, the steel exhibited a comprehensive performance with a yield strength of 1120 MPa, an ultimate tensile strength of 1230 MPa, and an elongation of 8.2%. The high strength of the steel is attributed to the presence of tempered martensite and abundant secondary carbides. The favorable ductility is mainly provided by the pearlite inherited from intercritical quenching and tempering. Additionally, the precipitation of secondary carbides not only enhances precipitation strengthening, but also reduces the dislocation density and lattice strain of the matrix, thereby enhancing strength and ductility. This study offers a scheme for producing strong and ductile 5CrNiMoV steel. Full article
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19 pages, 8173 KiB  
Article
Effects of Partial Replacement of Si by Al on Impact Toughness of 0.2%C-Si-Mn-Cr-B TRIP-Aided Martensitic Steel
by Koh-ichi Sugimoto, Yumenori Nakashima, Junya Kobayashi and Tomohiko Hojo
Metals 2023, 13(7), 1206; https://doi.org/10.3390/met13071206 - 29 Jun 2023
Viewed by 1792
Abstract
The effects of partial replacement of Si by Al on the microstructure, tensile properties, and Charpy impact toughness were investigated using 0.2%C-Si/Al-Mn-Cr-B TRIP-aided martensitic steels to promote the application of galvanized third-generation ultrahigh- and high-strength steels. The impact toughness was related to the [...] Read more.
The effects of partial replacement of Si by Al on the microstructure, tensile properties, and Charpy impact toughness were investigated using 0.2%C-Si/Al-Mn-Cr-B TRIP-aided martensitic steels to promote the application of galvanized third-generation ultrahigh- and high-strength steels. The impact toughness was related to the microstructural and mechanical properties. The partial replacement decreased the volume fraction of retained austenite and increased the mechanical stability, accompanied by softening and an increase in the volume fraction of the primary martensite. Resultantly, the partial replacement decreased strength and ductility. The impact absorbed energy (value) at 25 °C was slightly increased by the partial replacement. The increased impact absorbed energy was mainly caused by high crack/void propagation energy due to the softened primary martensite and a small contribution of the stabilized retained austenite. The 50% shear fracture ductile-to-brittle transition temperature was marginally raised by the partial replacement. The raised transition temperature was mainly associated with an increase in a unit crack path of quasi-cleavage/cleavage fracture. Full article
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