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16 pages, 4449 KiB

Open AccessArticle

The Cooling Phase Transition Behavior of 30MnNbRE Steel Studied Based on TMCP

by Shimin Guo, Hui Ma, Xirong Bao, Jia Sun, Xuejiao Tang and Xiaodong Wang

Crystals 2025, 15(4), 327; https://doi.org/10.3390/cryst15040327 - 28 Mar 2025

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Abstract

The continuous cooling transformation (CCT) curves of undercooled austenite serve as crucial references for obtaining desired microstructures and properties in metallic materials (particularly deformed metals) through heat treatment. In this study, static and dynamic CCT curves were constructed for experimental steels micro-doped with [...] Read more.

The continuous cooling transformation (CCT) curves of undercooled austenite serve as crucial references for obtaining desired microstructures and properties in metallic materials (particularly deformed metals) through heat treatment. In this study, static and dynamic CCT curves were constructed for experimental steels micro-doped with rare earth element Ce by combining temperature-dilatometric curves recorded after austenitization at 900 °C with microstructural characterization and microhardness measurements. Comparative analyses were conducted on the microstructures and microhardness of three experimental steels with varying Ce contents subjected to sizing (reducing) diameter deformation at 850 °C and 950 °C. The CCT experimental results revealed that the microhardness of the tested steels increased with cooling rates. Notably, dynamic CCT specimens cooled at 50 °C/s to room temperature following superheated deformation exhibited 56.7 HV5 higher microhardness than static CCT specimens, accompanied by increased martensite content. The reduction of deformation temperature from 950 °C to 850 °C resulted in the expansion of the bainitic phase region. The incorporation of trace Ce elements demonstrated a significant enhancement in the microhardness of 30MnNbRE steel. This research proposes an effective processing route for improving strength-toughness combination in microalloyed oil well tubes: introducing trace Ce additions followed by sizing (reducing) diameter deformation at 950 °C and subsequent ultra-fast cooling at 50 °C/s to room temperature. This methodology facilitates the production of high-strength/toughness steels containing abundant martensitic microstructures. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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21 pages, 22532 KiB

Open AccessArticle

Influence of Rotational Speed on the Microstructure and Mechanical Properties of Refill Friction Stir Spot Welded Pure Copper

by Xiaole Ge, I. N. Kolupaev, Di Jiang, Weiwei Song and Hongfeng Wang

Crystals 2025, 15(3), 268; https://doi.org/10.3390/cryst15030268 - 13 Mar 2025

Viewed by 352

Abstract

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited [...] Read more.

Refill friction stir spot welding (RFSSW) is an effective technique for achieving high-quality joints in metallic materials, with rotational speed being a critical parameter influencing joint quality. Current research on RFSSW has primarily focused on low-melting-point materials such as aluminum alloys, while limited attention has been given to pure copper, a material characterized by its high-melting-point and high-thermal-conductivity. This study aims to investigate the effects of rotational speed on the microstructure and mechanical properties of RFSSW joints in pure copper. To achieve this goal, welding experiments were conducted at five rotational speeds. The welding defects, microstructure, and hook morphology of the welded joints were analyzed, while the variations in axial force and torque during welding were studied. The influence of rotational speed on the microhardness and tensile-shear failure load of the welded joints was explored, and the fracture modes of the welded joints at different rotational speeds were discussed. The results indicated that the primary welding defects were incomplete refill and surface unevenness. Higher rotational speeds resulted in coarser microstructures in the stir zones. As the rotational speed increased, the hook height progressively rose, the peak axial force showed an increasing trend, and the peak torque continuously decreased. The high microhardness points in the welded joints were predominantly located at the top of the sleeve stir zone (S-Zone), while the low microhardness points were observed at the center of the pin stir zone (P-Zone) and in the heat-affected zone (HAZ). The tensile-shear failure load of the welded joints initially increased and then decreased on the whole with the rising rotational speed, peaking at 5229 N at a rotational speed of 1200 rpm. At lower rotational speeds, the fracture type of the welded joints was characterized as plug fracture. Within the rotational speed range of 1200 rpm to 1600 rpm, the fracture type transitioned to upper sheet fracture. The initial fractures under different rotational speeds exhibited ductile fracture. This study contributes to advancing the understanding of RFSSW characteristics in high-melting-point and high-thermal-conductivity materials. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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17 pages, 3345 KiB

Open AccessArticle

Data-Driven ANN-Based Predictive Modeling of Mechanical Properties of 5Cr-0.5Mo Steel: Impact of Composition and Service Temperature

by Muhammad Ishtiaq, Saurabh Tiwari, Molakatala Nagamani, Sung-Gyu Kang and Nagireddy Gari Subba Reddy

Crystals 2025, 15(3), 213; https://doi.org/10.3390/cryst15030213 - 24 Feb 2025

Cited by 1 | Viewed by 483

Abstract

The mechanical properties of steel are intricately connected to their composition and service temperature. Predicting these properties across different work temperatures using traditional statistical methods, algorithms, and equations is highly challenging due to these complex interdependencies. To address this, we developed an artificial-neural-network [...] Read more.

The mechanical properties of steel are intricately connected to their composition and service temperature. Predicting these properties across different work temperatures using traditional statistical methods, algorithms, and equations is highly challenging due to these complex interdependencies. To address this, we developed an artificial-neural-network (ANN) model to elucidate the relationships between composition, temperature, and mechanical properties of 5Cr-0.5Mo steels. Our model demonstrated high accuracy, with minimal percentage errors in predicting YS, UTS, and El (%)—3.5%, 0.97%, and 1.9%, respectively. The ANN predictions are realistic and closely match the experimental results. We propose an easy-to-use model’s GUI to predict steel composition to achieve desired properties at any temperature. The ANN model’s findings offer valuable insights for researchers and designers, aiding in developing steel components with optimized properties. This technique is expected to significantly enhance the planning of practical experiments and improve material performance overall. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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17 pages, 10341 KiB

Open AccessArticle

Unveiling the Strengthening and Ductility Mechanisms of a CoCr₀.₄NiSi₀.₃ Medium-Entropy Alloy at Cryogenic Temperatures

by Li Zhang, Lingwei Zhang and Xiang Chen

Crystals 2025, 15(2), 170; https://doi.org/10.3390/cryst15020170 - 10 Feb 2025

Viewed by 565

Abstract

Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. [...] Read more.

Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. This study investigates the quasi-static mechanical properties of a CoCr₀.₄NiSi₀.₃ medium-entropy alloy (MEA) at room temperature, −75 °C, and −150 °C. The deformation behavior and mechanisms responsible for strengthening and toughening at reduced cryogenic temperatures are analyzed, revealing that decreasing cryogenic temperature enhances the strength of the as-cast MEA. Specifically, both the yield strength (YS) and ultimate tensile strength (UTS) of the MEA increase significantly with decreasing temperature during cryogenic tensile testing. Under tensile testing at −150 °C, the YS reaches 617.5 MPa, the UTS is 1055.0 MPa, and the elongation to fracture remains approximately 21.0% at both −150 °C and −75 °C. After cryogenic temperature tensile deformation, the matrix exhibits a dispersed distribution of nanoscaled tetragonal and orthorhombic phases, a coherent hexagonal close-packed phase, L1₂ phase and layered long-period stacking ordered (LPSO) structures, which are rarely observed in the cryogenic deformation of metals and alloys. The metastable phase evolution path of this MEA at cryogenic temperatures is closely associated with the decomposition of perfect dislocations into a/6<112> Shockley partial dislocations and their subsequent evolution at reduced cryogenic temperatures. At −75 °C, the a/6<112> Shockley partial dislocation interacts with the L1₂ phase to form antiphase boundaries (APBs) approximately 3 nm thick. At −150 °C, two phase transition paths from stacking faults (SFs) to nanotwins and LPSO occur, leading to the formation of layered LPSO structures and deformation-induced nanotwins. The dispersion of these coherent nanophases and nanotwins induced by the reduced stacking fault energy under cryogenic temperatures is the key factor contributing to the excellent balance of strength and plasticity in the as-cast MEA, providing an important basis for research on the cryogenic mechanical properties of CoCrNi-based MEAs. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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12 pages, 29110 KiB

Open AccessArticle

Study on Pitting Behavior of Welding Joint of Bimetal Composite Pipes in Suspended Sulfur Solution

by Yuwei Sun, Sirong Yu, Bingying Wang, Lin Liu, Enyang Liu and Tao Feng

Crystals 2025, 15(2), 165; https://doi.org/10.3390/cryst15020165 - 8 Feb 2025

Viewed by 383

Abstract

Due to the severe corrosion environment, corrosion problems caused by sulfur deposition are one important reason for the failure of composite pipes in the long-term service process when Incoloy825/X65 bimetallic composite pipes are used in high-sulfur oil and gas transportation. In this paper, [...] Read more.

Due to the severe corrosion environment, corrosion problems caused by sulfur deposition are one important reason for the failure of composite pipes in the long-term service process when Incoloy825/X65 bimetallic composite pipes are used in high-sulfur oil and gas transportation. In this paper, an Incoloy825/X65 bimetallic composite pipe was subjected to an immersion corrosion test in suspended sulfur solution to observe the corrosion morphology and characterize the corrosion products using a SEM, EDS, and XRD. The adsorption behavior of the Incoloy825 alloy in terms of sulfur elements was investigated. The results show that the heat-affected zone (HAZ) of the welding joint is the preferred region for pitting corrosion. The film of corrosion product on the Incoloy825 was mainly composed of NiS, FeS, and Cr₂S₃, and its thickness was 7–13 μm. With prolongation of the immersion time, the pitting resistance of the surface product film of nickel-based alloys is weakened and then enhanced, and the corrosion product film can act as a barrier to anion transfer and inhibit the occurrence of pitting. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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10 pages, 5242 KiB

Open AccessArticle

Morphology and Formation of Chrysanthemum-like Pearlite in 100Mn13 Steel During Aging Treatment

by Bo Liang, Jiaoyang Sun, Zhimin Ding, Rujin Tian and Feng Yan

Crystals 2025, 15(1), 65; https://doi.org/10.3390/cryst15010065 - 11 Jan 2025

Viewed by 546

Abstract

The morphology and microstructure of pearlite formed in 100Mn13 high-carbon high-manganese steel aged, respectively, at 525 °C and 650 °C after 1050 °C water toughening treatment were observed and analyzed by a scanning electron microscope (SEM) and transmission electron microscope (TEM). The results [...] Read more.

The morphology and microstructure of pearlite formed in 100Mn13 high-carbon high-manganese steel aged, respectively, at 525 °C and 650 °C after 1050 °C water toughening treatment were observed and analyzed by a scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that some pearlite colonies are chrysanthemum-like and are composed of M₇C₃ lamellae and ferrite lamellae, maintaining an orientation relationship (OR) of (

\bar{3}

3

12

)_M7C3‖(

0 \bar{2} 4

)_α, [

4 0 1

]_M7C3‖[

5 2 1

]_α. Moreover, the lamellae in pearlite colonies with chrysanthemum-like morphology are distributed in an emanative way, where there are protrusions and branches at the growth frontier. A growth physical model describing the growth process of chrysanthemum-like pearlite is proposed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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21 pages, 8730 KiB

Open AccessArticle

Numerical Simulation of Surface Thermal Analysis and Cooling Optimization of Continuous Casting Rolls

by Guangwei Cheng, Ningxia Yin, Qiaoxin Zheng, Yuming Qiu and Junqi Chen

Crystals 2025, 15(1), 41; https://doi.org/10.3390/cryst15010041 - 30 Dec 2024

Viewed by 704

Abstract

In many steel mills, the working life of continuous casting machine rollers is relatively short, requiring frequent replacement and negatively impacting production efficiency. To effectively extend the service life of these rollers, this study focuses on a continuous casting machine at a steel [...] Read more.

In many steel mills, the working life of continuous casting machine rollers is relatively short, requiring frequent replacement and negatively impacting production efficiency. To effectively extend the service life of these rollers, this study focuses on a continuous casting machine at a steel mill in China. A numerical simulation was conducted, revealing that the rollers in contact with the high-temperature casting billet experience significant thermal and stress impacts. The traditional cooling channel struggles to sufficiently reduce both the surface temperature and stress, resulting in severe thermal fatigue damage to the roller surfaces. Observations of roller surface wear showed signs of adhesive wear, fatigue cracks, and spalling occurring in various regions of the roller, which aligned with the stress distribution predicted by the simulation. In response, the cooling channel structure was modified to enhance the cooling effect of the water. Optimization of both the cooling channel structure and its parameters was carried out using a coupled flow-heat-force numerical simulation method. The optimized cooling channel effectively improved the working condition of the continuous casting roll, as the maximum temperature of the roll surface was reduced from 810 K to 591 K, the circumferential temperature difference was reduced by 38%, and the maximum equivalent stress decreased from 791 MPa to 558 MPa. This adjustment also resulted in a more uniform surface temperature distribution, mitigating the sudden fluctuations in normal stress that are typical of conventional rollers. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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Review

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29 pages, 8842 KiB

Open AccessEditor’s ChoiceReview

Development and Research Status of Wear-Resistant Coatings on Copper and Its Alloys: Review

by Fei Meng, Yifan Zhou, Hongliang Zhang, Zhilan Wang, Dehao Liu, Shuhe Cao, Xue Cui, Zhisheng Nong, Tiannan Man and Teng Liu

Crystals 2025, 15(3), 204; https://doi.org/10.3390/cryst15030204 - 20 Feb 2025

Viewed by 752

Abstract

Wear-resistant coatings applied to the surface of copper and copper alloys through diverse advanced technologies can substantially enhance their wear resistance and broaden their application spectrum. This paper provides a comprehensive review of the development and current research status of wear-resistant coatings fabricated [...] Read more.

Wear-resistant coatings applied to the surface of copper and copper alloys through diverse advanced technologies can substantially enhance their wear resistance and broaden their application spectrum. This paper provides a comprehensive review of the development and current research status of wear-resistant coatings fabricated on copper and its alloys. It presents the research findings on the preparation of wear-resistant coatings using both one-step methods (such as laser cladding, electroplating, thermal spraying, cold spraying, electro-spark deposition, etc.) and two-step methods (chemical plating and heat treatment, electrodeposition and laser cladding, laser cladding and in situ synthesis, etc.). This paper provides an in-depth examination of the characteristics, operating principles, and effects of various coating techniques on enhancing the wear resistance of copper and copper alloys. The advantages and disadvantages of different coating preparation methods are compared and analyzed; meanwhile, a prospective outlook on the future development trends is also offered. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Behaviour of Structural Materials: 2nd Edition)

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