Research

14 pages, 11711 KiB

Open AccessArticle

Effect of Friction Stir Welding and Tempering on the Microstructure and Strength of a Tempformed Low-Alloy Steel

by Anastasiia S. Dolzhenko, Anna S. Lugovskaya, Sergey Malopheyev, Valeriy Dudko, Marina Tikhonova, Rustam Kaibyshev and Andrey Belyakov

Metals 2024, 14(1), 114; https://doi.org/10.3390/met14010114 - 17 Jan 2024

Viewed by 734

Abstract

The microstructure developed in a low-alloy steel during friction stir welding and post-weld tempering was studied. The quenched steel samples were subjected to tempering at 650 °C for 1 h, followed by warm rolling to a total strain of 1.5 at the same [...] Read more.

The microstructure developed in a low-alloy steel during friction stir welding and post-weld tempering was studied. The quenched steel samples were subjected to tempering at 650 °C for 1 h, followed by warm rolling to a total strain of 1.5 at the same temperature. The processed steel samples were characterized by an ultrafine-grained microstructure of the lamellar type with a transverse grain size of 360 nm and exhibited an yield strength of about 1200 MPa and a total elongation of 13%. Then, the steel plates were joined by friction stir welding. The yield strength of the weld joint was about 1170 MPa, although the total elongation decreased to 1.5%. The martensite microstructure, with a high-angle grain boundary spacing of about 800 nm, was developed in the stir zone. This martensite in the stir zone originated from the ultrafine-grained prior austenite, resulting in an almost two-fold increase in hardness as compared to the base material. Tempering of the welded sample at 650 °C for 1 h resulted in a decrease in the hardness of the weld joint to the level of the base material. Nevertheless, the fracture of the welded and tempered sample occurred in the base material. The yield strength of the welded sample after tempering was 930 MPa, with a total elongation of 13%. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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22 pages, 12175 KiB

Open AccessArticle

Effect of Fe-Bearing Phases on the Mechanical Properties and Fracture Mechanism of Al–2wt.%Cu–1.5wt.%Mn (Mg,Zn) Non-Heat Treatable Sheet Alloy

by Nikolay Belov, Torgom Akopyan, Kirill Tsydenov, Stanislav Cherkasov and Natalia Avxentieva

Metals 2023, 13(11), 1911; https://doi.org/10.3390/met13111911 - 20 Nov 2023

Cited by 1 | Viewed by 890

Abstract

The effects of Fe-bearing phases on the structure, mechanical properties, and fracture mechanism of a non-heat-treatable model sheet alloy (wt.%: Al–2%Cu–1.5%Mn(-Mg,Zn)), designed for Al₂₀Cu₂Mn₃ dispersoids, was investigated. This involved a combination of thermodynamic modeling in the Thermo-Calc program [...] Read more.

The effects of Fe-bearing phases on the structure, mechanical properties, and fracture mechanism of a non-heat-treatable model sheet alloy (wt.%: Al–2%Cu–1.5%Mn(-Mg,Zn)), designed for Al₂₀Cu₂Mn₃ dispersoids, was investigated. This involved a combination of thermodynamic modeling in the Thermo-Calc program and experimental studies of structure and mechanical properties. It has been shown that the addition of 0.5 and 0.4% iron and silicon leads to the formation of eutectic inclusions in the Al₁₅(Mn,Fe)₃Si₂ phase. In addition to the Fe- bearing inclusions, the formation of the eutectic Al₂Cu and Al₂CuMg phases can be expected in the as-cast structure of the experimental alloys. Despite their relatively high fraction of eutectic particles, non-homogenized alloy ingots demonstrated sufficiently high deformation processability during the hot (400 °C) and cold rolling, which made it possible to obtain high-quality sheet alloys (with reduction degrees of 80 and 75%, respectively). The results of the tensile tests revealed that, after cold rolling, the addition of 1% Mg significantly increased the tensile and yield strengths, whereas the effect of 1% Zn was negligible. At the same time, the uniform distribution of Fe-bearing phases in the structure of the cold-rolled sheets contributes to the preservation of the dimple mechanism of the fracture toughness. This helps to maintain the same level of ductility for the cold-rolled sheet Fe-containing alloys as for Fe-free alloys. It has been shown, based on the data obtained, that adding Fe, Si, Mg, and Zn to the base Al–2%Cu–1.5%Mn alloy in a total amount of more than 3% makes it possible to retain the ductile fracture patterns of the base alloy and obtain a fairly higher level of mechanical properties. This suggests the fundamental possibility of using a variety of secondary raw materials (containing the main elements present in aluminum alloys of different alloying systems) to prepare a base alloy that does not require homogenization or thermal hardening. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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13 pages, 7060 KiB

Open AccessArticle

Failure of Elliptical Tubes with Different Long–Short Axis Ratios under Cyclic Bending in Different Directions

by Min-Cheng Yu and Wen-Fung Pan

Metals 2023, 13(11), 1891; https://doi.org/10.3390/met13111891 - 14 Nov 2023

Viewed by 597

Abstract

Although elliptical tubes are stronger and more stable than circular tubes, few studies have fully considered the behavior of elliptical tubes under cyclic bending loads. This study experimentally investigated the response and failure of SUS304 stainless steel elliptical tubes with four different ratios [...] Read more.

Although elliptical tubes are stronger and more stable than circular tubes, few studies have fully considered the behavior of elliptical tubes under cyclic bending loads. This study experimentally investigated the response and failure of SUS304 stainless steel elliptical tubes with four different ratios of long and short axes (1.5, 2.0, 2.5, and 3.0) under cyclic bending along four different orientation angles (0°, 30°, 60°, and 90°). The wall thickness was 0.7 mm, and cyclic bending was applied until buckling failure occurred. The moment–curvature curves exhibited cyclic hardening, and stable loops were formed for all long–short axis ratios and orientation angles. Increasing the long–short axis ratio slightly decreased the peak bending moment while increasing the orientation angle increased the peak bending moment. For a given orientation angle, the curves relating the short-axis variation (i.e., change in length divided by the original length of the short axis) and curvature demonstrated symmetry, serrations, and a growth pattern as the number of cycles increased regardless of the long–short axis ratio. At long–short axis ratios of 2.0, 2.5, and 3.0, these curves even exhibited a butterfly-like trend. Increasing the long–short axis ratio increased the short-axis variation, while increasing the orientation angle decreased the short-axis variation. Regarding the curves relating the curvature and number of cycles required to initiate buckling, for each orientation angle, the four long–short axis ratios corresponded to four straight lines when plotted on double-logarithmic co-ordinates. Based on the experimental results, empirical equations are proposed to describe the above relationships. The empirical equations were applied to predicting experimental data and showed close agreement. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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17 pages, 15964 KiB

Open AccessArticle

Effect of Rotary Swaging on Microstructure and Properties of Cr-Ni-Ti Austenitic Stainless Steel

by Olga Rybalchenko, Vladimir Torganchuk, Georgy Rybalchenko, Natalia Martynenko, Elena Lukyanova, Alexey Tokar, Dmitry Prosvirnin, Vladimir Yusupov and Sergey Dobatkin

Metals 2023, 13(10), 1760; https://doi.org/10.3390/met13101760 - 17 Oct 2023

Viewed by 796

Abstract

In this study, Cr-Ni-Ti austenitic stainless steel was subjected to rotary swaging in various modes, followed by annealing. The effect of processing conditions on the resulting microstructure and, therefore, on the mechanical properties under static and cyclic loading was studied. After RS the [...] Read more.

In this study, Cr-Ni-Ti austenitic stainless steel was subjected to rotary swaging in various modes, followed by annealing. The effect of processing conditions on the resulting microstructure and, therefore, on the mechanical properties under static and cyclic loading was studied. After RS the formation of an ultrafine-grained predominantly twinned structure, with structural elements sized between 100–250 nm in Cr-Ni-Ti stainless steel, was observed. The stepwise temperature reduction during rotary swaging allows the manipulation of the microstructure transformations, which eventually leads to the desired properties of the steel. As a result, the ultimate tensile strength increased from 610 MPa to 1304 MPa when the elongation decreased from 40% to 10.5%, and the fatigue limit increased from 425 MPa to 700 MPa. The Cr-Ni-Ti steel is strengthened through the formation of an ultrafine-grained structure, twinning in austenite, and martensitic transformation. Subsequent annealing at a temperature 475 °C triggers the active precipitation of nanosized TiC carbides in the deformed steel. On one hand, the presence of these carbides increases the tensile strength up to 1938 Mpa, while on the other hand, slows down crack propagation with a slight decrease in ductility (ε = 8%) of the deformed sample. At the same time, dispersion hardening does not affect the fatigue limit of steel. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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10 pages, 3673 KiB

Open AccessCommunication

Contact Fatigue Behavior Evolution of 18CrNiMo7-6 Gear Steel Based on Surface Integrity

by Luji Wu, Yongxin Lv, Yalong Zhang, Anhu Li and Vincent Ji

Metals 2023, 13(9), 1605; https://doi.org/10.3390/met13091605 - 17 Sep 2023

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Abstract

In this work, the surface integrity (surface morphology, microstructure, microhardness, residual stress) of contact fatigue (CF) samples with different numbers of running cycles was comprehensively studied. Based on typical working conditions, a fatigue life evaluation method was proposed based on the evolution law [...] Read more.

In this work, the surface integrity (surface morphology, microstructure, microhardness, residual stress) of contact fatigue (CF) samples with different numbers of running cycles was comprehensively studied. Based on typical working conditions, a fatigue life evaluation method was proposed based on the evolution law of surface integrity. The CF with different numbers of running cycles revealed that the average grain size decreased with the increase in the number of running cycles, and the surface microhardness, residual stress and surface roughness Ra increased first and then decreased. In addition, the relationships between different surface integrity parameters and fatigue life were plotted. Moreover, based on the fatigue life profiles, the running state and remaining life of gear samples can be evaluated. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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18 pages, 10535 KiB

Open AccessArticle

A Molecular Dynamics Simulation to Shed Light on the Mechanical Alloying of an Al-Zr Alloy Induced by Severe Plastic Deformation

by Alina Y. Morkina, Rita I. Babicheva, Elena A. Korznikova, Nariman A. Enikeev, Kaveh Edalati and Sergey V. Dmitriev

Metals 2023, 13(9), 1595; https://doi.org/10.3390/met13091595 - 14 Sep 2023

Cited by 3 | Viewed by 944

Abstract

In a recent experimental work, as a result of severe plastic deformation, a non-equilibrium solid solution was obtained despite the very limited solubility of zirconium (Zr) in aluminum (Al). This opens up a new path in the development of heat-treatable alloys with improved [...] Read more.

In a recent experimental work, as a result of severe plastic deformation, a non-equilibrium solid solution was obtained despite the very limited solubility of zirconium (Zr) in aluminum (Al). This opens up a new path in the development of heat-treatable alloys with improved electrical and mechanical properties, where mechanically dissolved elements can form intermetallic particles that contribute to precipitation strengthening. In the present study, molecular dynamics simulations were performed to better understand the process of mechanical dissolution of Zr within an Al model, with Zr atoms segregated along its grain boundaries. Stress–strain curves, radial distribution functions, and mechanisms of plastic deformation and dissolution of Zr in Al were analyzed. It is revealed that orientation of the grain boundary with segregation normal to the shear direction promotes more efficient mixing of alloy components compared to its parallel arrangement. This happens because in the second case, grain boundary sliding is the main deformation mechanism, and Zr tends to remain within the interfaces. In contrast, the involvement of dislocations in the case of normal orientation of grain boundaries with Zr segregation significantly contributes to deformation and facilitates better dissolution of Zr in the Al matrix. The findings obtained can provide new insights considering the role of texture during mechanical alloying of strongly dissimilar metals. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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22 pages, 9986 KiB

Open AccessArticle

Influence of Quenching and Subsequent Artificial Aging on Tensile Strength of Laser-Welded Joints of Al–Cu–Li Alloy

by Alexandr Malikov, Evgeniy Karpov, Konstantin Kuper and Alexandr Shmakov

Metals 2023, 13(8), 1393; https://doi.org/10.3390/met13081393 - 03 Aug 2023

Viewed by 932

Abstract

The research aim was to optimize post-weld heat-treatment (PWHT) modes for a laser-welded joint of the Al–Cu–Li alloy and improve their respective strength properties. As a result, the ultimate tensile strength, yield point, and elongation of the joint were enhanced up to 95%, [...] Read more.

The research aim was to optimize post-weld heat-treatment (PWHT) modes for a laser-welded joint of the Al–Cu–Li alloy and improve their respective strength properties. As a result, the ultimate tensile strength, yield point, and elongation of the joint were enhanced up to 95%, 94%, and 38%, respectively, of those inherent in the base metal. Before and after PWHT, both microstructures and phase compositions have been examined by optical and scanning electron microscopy, as well as synchrotron X-ray diffractometry. In the as-welded metal, the α-Al and T₁(Al₂CuLi) phases were found, along with the θ′(Al₂Cu) and S′(Al₂CuMg) phases localized at the grain boundaries, significantly reducing the mechanical properties of the joint. Upon quenching, the agglomerates dissolved at the grain boundaries, the solid solution was homogenized, and both Guinier–Preston zones and precipitates of the intermediate metastable θ″ phase were formed. After subsequent optimal artificial aging, the (predominant) hardening θ′ and (partial) T₁(Al₂CuLi) phases were observed in the weld metal, which contributed to the improvement of the strength properties of the joint. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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15 pages, 4192 KiB

Open AccessArticle

Tempering Behavior of Novel Low-Alloy High-Strength Steel

by Valeriy Dudko, Diana Yuzbekova, Sergey Gaidar, Sofia Vetrova and Rustam Kaibyshev

Metals 2022, 12(12), 2177; https://doi.org/10.3390/met12122177 - 17 Dec 2022

Cited by 10 | Viewed by 1569

Abstract

The effect of tempering on the mechanical properties, structure, and dispersion of secondary phase particles is studied in 0.4%C-2%Si-1%Cr-1%Mo-VNb steel. This steel austenitized at 900 °C with subsequent water quenching exhibits a yield stress of 1445 MPa and a lath martensite structure with [...] Read more.

The effect of tempering on the mechanical properties, structure, and dispersion of secondary phase particles is studied in 0.4%C-2%Si-1%Cr-1%Mo-VNb steel. This steel austenitized at 900 °C with subsequent water quenching exhibits a yield stress of 1445 MPa and a lath martensite structure with MX particles of ~40 nm located in matrix and boundary M₆C carbides of ~210 nm. Tempering in the temperature interval of 200–400 °C provides a yield stress of 1625 MPa due to the precipitation of ε-carbide and cementite within laths. The yield stress decreases to 1415 and 1310 MPa after tempering at 500 and 650 °C, respectively, due to the replacement of matrix carbides by boundary M₂₃C₆ carbide. A Charpy V-notch impact energy of ~12 J/cm² is almost independent from tempering temperatures of up to 400 °C and increases up to ~33 J/cm² after tempering at 650 °C due to decreased yield stresses and increased plasticity. Full article

(This article belongs to the Special Issue Feature Papers in Metal Failure Analysis)

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