Crystals

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10 pages, 3530 KiB

Open AccessArticle

First-Principle Investigation of the Interface Properties of the Core-Shelled L1₂-Al₃M (M = Sc, Zr, Er, Y) Phase

by Yu Song, Songtao Zhan, Baohua Nie, Shuai Liu, Haiying Qi, Fangjun Liu, Touwen Fan and Dongchu Chen

Crystals 2023, 13(3), 420; https://doi.org/10.3390/cryst13030420 - 28 Feb 2023

Cited by 4 | Viewed by 1742

Abstract

The interface structure and segregation behavior of L1₂-Al₃M (M = Sc, Zr, Er, Y) phases were investigated based on first-principles calculations. The results showed that the order of the thermodynamically stable interface was Al₃Zr/Al > Al₃ [...] Read more.

The interface structure and segregation behavior of L1₂-Al₃M (M = Sc, Zr, Er, Y) phases were investigated based on first-principles calculations. The results showed that the order of the thermodynamically stable interface was Al₃Zr/Al > Al₃Sc/Al > Al₃Er/ Al > Al₃Y/Al. The interfaces of Al₃Sc/Al₃Zr, Al₃Er/Al₃Zr, and Al₃Y/Al₃Er obtained negative interfacial energies and low coherent strain energies and were favorable to form a clear interface. Zr atom tended to segregate to the first atomic layer on the Al side of the Al/Al₃Sc, Al/Al₃Er, and Al/Al₃Y interfaces. The driving effect of the Zr atom segregation to the Al₃Y shows was stronger than that to Sc and Er atoms, whereas the high coherent strain energy hindered the formation of Al₃Y/Al₃Zr interface. Er atom tended to segregate at the Al/Al₃Y interface and accelerated the formation of core-shelled Al₃Y/Al₃Er. Furthermore, the formation of the double core-shelled Al₃Y/Al₃Er/Al₃Zr was discussed. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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12 pages, 1774 KiB

Open AccessArticle

First-Principles Study of the Structural, Mechanical and Thermodynamic Properties of Al₁₁RE₃ in Aluminum Alloys

by Touwen Fan, Lan Lin, Houjiang Liang, Yuhong Ma, Yuwei Tang, Te Hu, Zixiong Ruan, Dongchu Chen and Yuanzhi Wu

Crystals 2023, 13(2), 347; https://doi.org/10.3390/cryst13020347 - 17 Feb 2023

Cited by 6 | Viewed by 2296

Abstract

The stability and mechanical and thermodynamic properties of Al₁₁RE₃ intermetallics (RE = Sc, Y and lanthanide La-Lu) have been investigated by combining first-principles and Debye model calculations. It was found that the formation enthalpies of the Al₁₁RE₃ [...] Read more.

The stability and mechanical and thermodynamic properties of Al₁₁RE₃ intermetallics (RE = Sc, Y and lanthanide La-Lu) have been investigated by combining first-principles and Debye model calculations. It was found that the formation enthalpies of the Al₁₁RE₃ intermetallics are all negative, indicating that they are stable; moreover, the experimental values of Al₁₁La₃ and Al₁₁Ce₃ are in good agreement with the predicted values, which are −0.40 kJ/mol and −0.38 kJ/mol, respectively. The calculated results of the mechanical properties reveal that the Young’s modulus E and shear modulus G of Al₁₁RE₃ (RE = La, Ce, Pr, Nd and Sm) intermetallics are obviously greater than that of Al, implying that the stiffness, toughness, and tensile strength of them are significantly greater than those of aluminum, and that they, as strengthen phases, can effectively improve the mechanical property of aluminum alloys. The Poisson’s ratio v of Al₁₁Sc₃ (0.37) is the largest, and the heterogeneity is obvious. All the Al₁₁RE₃ intermetallics can enhance the thermostability of the aluminum because of their lower Gibbs free energy F in the range of −5.002~−4.137 eV/atom and thermal expansion coefficient α of Al in the range of 2.34~2.89 × 10⁻⁵/K at 300K, as well as higher entropy and constant volume-specific heat than aluminum at finite temperatures. With an increase in the atomic number, different change trends were observed for the formation enthalpy ΔH_f, bulk modulus B, Young’s modulus E, and shear modulus G. This paper can provide ideas and help for designing a high-performance, heat-resistant aluminum alloy. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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10 pages, 4528 KiB

Open AccessArticle

980 MPa Grade Low-Alloy Carbide-Free Bainitic Steel Obtained by Dynamic Continuous Cooling Transformation

by Pengfei Wang, Peng Chen, Dapeng Yang, Tao Wang and Hongliang Yi

Crystals 2023, 13(2), 213; https://doi.org/10.3390/cryst13020213 - 24 Jan 2023

Viewed by 1967

Abstract

The addition of high-content alloying elements and the unbefitting process make carbide-free bainite steel difficult in industrial production. Thus, we adopted a dynamic continuous cooling process for developing the high-strength cold-rolled low-alloy carbide-free bainitic steels in this study. The influence of cooling rates [...] Read more.

The addition of high-content alloying elements and the unbefitting process make carbide-free bainite steel difficult in industrial production. Thus, we adopted a dynamic continuous cooling process for developing the high-strength cold-rolled low-alloy carbide-free bainitic steels in this study. The influence of cooling rates on the microstructure and mechanical properties was investigated by dilatometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and tensile tests. The results show that the bainitic ferrite plates were refined by decreasing the cooling rate, and more austenite was retained in the steel with a medium cooling rate. Both the TRIP effect and the refined bainitic ferrite plate contribute to the good strength–ductility match. Consequently, the propitious microstructure adjustment is critical for developing 980 MPa carbide-free bainitic steel. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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11 pages, 5359 KiB

Open AccessArticle

Very High Cycle Fatigue Damage of TC21 Titanium Alloy under High/Low Two-Step Stress Loading

by Baohua Nie, Shuai Liu, Yue Wu, Yu Song, Haiying Qi, Binqing Shi, Zihua Zhao and Dongchu Chen

Crystals 2023, 13(1), 139; https://doi.org/10.3390/cryst13010139 - 13 Jan 2023

Cited by 4 | Viewed by 1949

Abstract

Very high cycle fatigue (VHCF) tests were carried out under variable amplitude loading for TC21 titanium alloy. The first level of high amplitude loading was set as 950 MPa close to yield strength, and the second level of low amplitude loading was determined [...] Read more.

Very high cycle fatigue (VHCF) tests were carried out under variable amplitude loading for TC21 titanium alloy. The first level of high amplitude loading was set as 950 MPa close to yield strength, and the second level of low amplitude loading was determined between 435 MPa and 500 MPa where fatigue cracks initiated at the specimen subsurface under constant amplitude. The results indicate that the high/low stress block significantly reduced the cumulative fatigue life of low stress amplitude, and the fatigue crack initiation site changed from the specimen subsurface under constant loading to the specimen surface under stress block. Based on continuum damage mechanics, the fatigue damage model of two-step stress block was established to estimate the fatigue damage process. The prediction of cumulative fatigue life generally agreed with the experimental data. The cumulative fatigue damage of the stress block was related to the stress amplitude and the cycle ratio, which determined the stress fatigue damage and its interaction damage. The surface crack initiation in the stress block accelerated fatigue damage of low stress amplitude, reducing the cumulative life. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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11 pages, 5644 KiB

Open AccessArticle

Effects of Nitrogen Content and Strain Rate on the Tensile Behavior of High-Nitrogen and Nickel-Free Austenitic Stainless Steel

by Feng Shi, Xinyue Zhang, Tianzeng Li, Xianjun Guan, Xiaowu Li and Chunming Liu

Crystals 2023, 13(1), 129; https://doi.org/10.3390/cryst13010129 - 11 Jan 2023

Cited by 7 | Viewed by 2109

Abstract

The uniaxial tensile behaviors of Fe-19Cr-16Mn-2Mo-0.49N and Fe-18Cr-16Mn-2Mo-0.85N high-nitrogen and nickel-free austenitic stainless steels at two strain rates of 10⁻² s⁻¹ and 10⁻⁴ s⁻¹ were comparatively investigated. The related deformation microstructure was characterized and fracture mechanism was analyzed. The [...] Read more.

The uniaxial tensile behaviors of Fe-19Cr-16Mn-2Mo-0.49N and Fe-18Cr-16Mn-2Mo-0.85N high-nitrogen and nickel-free austenitic stainless steels at two strain rates of 10⁻² s⁻¹ and 10⁻⁴ s⁻¹ were comparatively investigated. The related deformation microstructure was characterized and fracture mechanism was analyzed. The results show that the nitrogen content and strain rate both have significant effects on the tensile properties of the tested steels. As the strain rate is the same, the tested steel containing a higher nitrogen content has higher R_m and R_p_0.2. However, R_m is higher at a lower strain rate and R_p_0.2 is higher at a higher strain rate in the case of the same nitrogen content. The tested steel with a lower nitrogen content (0.49 wt.%N) tensioned at a lower strain rate of 10⁻⁴ s⁻¹ obtains the highest elongation, while the tested steel with a higher nitrogen content (0.85 wt.%N) tensioned at a higher strain rate of 10⁻² s⁻¹ has the lowest elongation. The tensile plastic deformation is mainly governed by slip and twinning, affected jointly by stacking fault energy and short-range order. Dislocation slip featured by planar slip bands and twin-like bands is the main deformation structure in the tested steel containing a higher nitrogen content (0.85 wt.%N) tensioned at a lower strain rate of 10⁻⁴ s⁻¹, whereas twinning deformation becomes more prominent with decreasing nitrogen content and increasing strain rate. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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12 pages, 3326 KiB

Open AccessArticle

Effects of Compositional Inhomogeneity on the Microstructures and Mechanical Properties of a Low Carbon Steel Processed by Quenching-Partitioning-Tempering Treatment

by Ning Zhong, Songpu Yang, Tao Liu, Yuantao Zhao, Wenge Li, Wei Li and Xiaodong Wang

Crystals 2023, 13(1), 23; https://doi.org/10.3390/cryst13010023 - 23 Dec 2022

Cited by 1 | Viewed by 1921

Abstract

Quenching-partitioning-tempering (Q-P-T) heat treatment is a relatively novel approach to attain excellent ductility in high-strength steels. In the present work, the microstructural evolution and the mechanical properties of a low carbon microalloyed advanced steel were systematically investigated after the Q-P-T process. The microstructural [...] Read more.

Quenching-partitioning-tempering (Q-P-T) heat treatment is a relatively novel approach to attain excellent ductility in high-strength steels. In the present work, the microstructural evolution and the mechanical properties of a low carbon microalloyed advanced steel were systematically investigated after the Q-P-T process. The microstructural evolution was explored by employing X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results indicate that the multiphase microstructures strongly depend on both the initial microstructure and the processing parameters of the quenching and partitioning process, especially the quenching temperature. Compositional inhomogeneity during the Q-P-T process results in multiphase microstructures, in which the mechanical properties of the quenching and partitioning steels may be strongly impacted by the distribution of heterogeneous austenite phase in the steel matrix. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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11 pages, 7277 KiB

Open AccessArticle

Effect of Secondary α Phase on Stress Corrosion Cracking of a Novel Metastable β Titanium Alloy in 3.5% NaCl Solution

by Haoyu Zhang, Chuan Wang, Shuai Zhang, Xiaoling Yu, Ge Zhou, Zhiqiang Zhang and Lijia Chen

Crystals 2022, 12(12), 1849; https://doi.org/10.3390/cryst12121849 - 19 Dec 2022

Cited by 1 | Viewed by 1843

Abstract

The effect of the secondary α phase on stress corrosion cracking of a novel metastable β titanium alloy, Ti-6Mo-5V-3Al-2Fe, in 3.5% NaCl solution was investigated by slow strain rate testing. Fine acicular secondary α phase was obtained by aging at the low temperature [...] Read more.

The effect of the secondary α phase on stress corrosion cracking of a novel metastable β titanium alloy, Ti-6Mo-5V-3Al-2Fe, in 3.5% NaCl solution was investigated by slow strain rate testing. Fine acicular secondary α phase was obtained by aging at the low temperature of 520 °C, and coarsened rod-like secondary α phase was obtained by aging at the high temperature of 680 °C. The electrochemical measurement results and slow strain rate testing results show that the microstructure contained with fine acicular secondary α phase exhibits better corrosion resistance and less stress corrosion cracking susceptibility. The fracture morphology exhibits a mixed fracture characteristic with shallow and small dimples, as well as tear ridges and flat facets with undulating surfaces. The combination of Absorption Induced Dislocation Emission and Hydrogen Enhanced Localized Plasticity is the main mechanism for stress corrosion cracking. Fine acicular secondary α phase with narrow spacing leads to less accumulated dislocations and smaller localized stress, so that has a beneficial effect on stress corrosion performance. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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10 pages, 13758 KiB

Open AccessArticle

Effect of Short-Range Ordering on the Grain Boundary Character Distribution Optimization of FCC Metals with High Stacking Fault Energy: A Case Study on Ni-Cr Alloys

by Yifan Liu, Xianjun Guan, Yanjie Zhang, Zipeng Jia, Simin Liang and Xiaowu Li

Crystals 2022, 12(12), 1822; https://doi.org/10.3390/cryst12121822 - 14 Dec 2022

Viewed by 1822

Abstract

The critical roles of short-range ordering (SRO) in the grain boundary character distribution (GBCD) optimization of Ni-Cr alloys with high stacking fault energies were experimentally studied by thermomechanical treatments. It is found that, with the enhancement of the SRO degree (or the increase [...] Read more.

The critical roles of short-range ordering (SRO) in the grain boundary character distribution (GBCD) optimization of Ni-Cr alloys with high stacking fault energies were experimentally studied by thermomechanical treatments. It is found that, with the enhancement of the SRO degree (or the increase in Cr content), the dislocation slip mode changes from wavy slip to planar slip, and even deformation twins (DTs) appear in the cold-rolled Ni-40at.%Cr alloy. Within the lower level of Cr content (≤20 at.%), the optimized result of GBCD is conspicuous with the increase in Cr content. As the Cr content is higher than 20 at.%, the GBCD optimization of Ni-Cr alloys cannot be further enhanced, since the cold rolling induced DTs would hinder the growth of twin related domains during subsequent annealing. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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12 pages, 4855 KiB

Open AccessArticle

Cumulative Damage in Very High/Low Cycle Combined Fatigue for TC21 Titanium Alloy

by Baohua Nie, Shuai Liu, Yue Wu, Yu Song, Haiying Qi, Binqing Shi, Zihua Zhao and Dongchu Chen

Crystals 2022, 12(12), 1702; https://doi.org/10.3390/cryst12121702 - 24 Nov 2022

Cited by 2 | Viewed by 1499

Abstract

The effect of low cycle fatigue (LCF) predamage with no precracks on very high cycle fatigue (VHCF) properties, and crack initiation characteristics for TC21 titanium alloy, was investigated. The results showed that LCF predamage with less than 5% of fatigue life had little [...] Read more.

The effect of low cycle fatigue (LCF) predamage with no precracks on very high cycle fatigue (VHCF) properties, and crack initiation characteristics for TC21 titanium alloy, was investigated. The results showed that LCF predamage with less than 5% of fatigue life had little influence on fatigue limit, but reduced its fatigue life. Fatigue cracks were initiated on the surface of the specimen at high stress amplitude, whereas fatigue cracks were initiated on the subsurface of the specimens at low stress amplitude. Based on Lemaitre damage theory, a very high/low cycle combined fatigue damage model was established to analyze the fatigue damage process, which was consistent with the experimental data. It was indicated that 5% LCF predamage value was the equivalent damage value, which was close to the critical value of VHCF crack initiation. The fatigue crack initiation of the specimens with LCF predamage less than 5% took up the major components of fatigue life. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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18 pages, 4108 KiB

Open AccessArticle

Mechanical and Microstructural Behavior of Tempered CPM^® 3V High-Density Sintered Tool Steel

by Stephen A. C. Hanson and Sudhakar Vadiraja

Crystals 2022, 12(11), 1670; https://doi.org/10.3390/cryst12111670 - 19 Nov 2022

Cited by 3 | Viewed by 2594

Abstract

The tempering response of CPM^® 3V tool steel was investigated via a hardening and tempering heat treatment, tensile testing, fractography, and microstructural evaluation. CPM^® 3V tool steel is manufactured using Crucible Particle Metallurgy (CPM^®), a proprietary high-density sintering technique [...] Read more.

The tempering response of CPM^® 3V tool steel was investigated via a hardening and tempering heat treatment, tensile testing, fractography, and microstructural evaluation. CPM^® 3V tool steel is manufactured using Crucible Particle Metallurgy (CPM^®), a proprietary high-density sintering technique developed by Crucible Industries. The hardening and tempering heat treatments were applied to ASTM E8 standard test specimens. Tempering temperature was the experimental variable. The following samples were prepared: As-Hardened (no tempering); tempered at 450 °C, 550 °C, 650 °C, and 700 °C; and As-Received (annealed). Ultimate tensile strength and the yield strength of each treatment was determined using the ASTM E8 standard tensile test. The failed specimens were examined for mode of fracture at macro- and microscopic scales. Reflected light microscopy and a scanning electron microscope (SEM) was used for microstructural characterization. Testing and analysis established the samples tempered at <550 °C were dominated by brittle failure while samples tempered at >550 °C experienced ductile failure. The 550 °C treatment showed mixed ductile and brittle fracture features. This study found that CPM^® 3V can be optimized for strength, with good tensile toughness, at a 550 °C tempering temperature. This is consistent with Crucible Industries’ recommended tempering temperature for good wear resistance and toughness. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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10 pages, 2961 KiB

Open AccessArticle

Improving Strength-Ductility via Short Austenitization in a Low-Carbon Carbide-Free Bainitic Steel

by Jianhua Li, Peng Chen, Dapeng Yang, Hongshuang Di and Hongliang Yi

Crystals 2022, 12(11), 1636; https://doi.org/10.3390/cryst12111636 - 14 Nov 2022

Cited by 3 | Viewed by 1696

Abstract

The strength and ductility of low-carbon carbide-free bainitic (CFB) automotive steel are not good enough. In this study, a short austenitization (SA) process in conjunction with isothermal bainitic transformation was adopted to refine the bainitic ferrite lath, thus improving the mechanical properties of [...] Read more.

The strength and ductility of low-carbon carbide-free bainitic (CFB) automotive steel are not good enough. In this study, a short austenitization (SA) process in conjunction with isothermal bainitic transformation was adopted to refine the bainitic ferrite lath, thus improving the mechanical properties of low-carbon CFB steel. The microstructure evolution was traced by dilatometric measurements and microstructure characterization, which revealed the refined microstructure by SA process. Besides, the deformation behaviors of the studied steels were analyzed, indicating that the improved work hardening capability by refined bainitic ferrite lath and more stable austenite were responsible for the better strength-ductility match. The CFB steel treated by SA process exhibits a high tensile strength of ~1180 MPa, and its elongation of 22.6% is comparable with commercial QP980 steel. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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11 pages, 4112 KiB

Open AccessArticle

The Microstructure Evolution during Divorced Eutectoid Transformation in a κ-Carbide Reinforced High Specific Young’s Modulus Steel

by Fuming Yang, Peng Chen and Xiaowu Li

Crystals 2022, 12(10), 1372; https://doi.org/10.3390/cryst12101372 - 27 Sep 2022

Cited by 2 | Viewed by 2372

Abstract

High specific Young’s modulus steel reinforced by κ-carbides has the characteristics of high strength and low density, which introduces potential applications of this material in automotive parts with a stiffness requirement. In this work, a 780 MPa grade Fe-Al-C high specific Young’s [...] Read more.

High specific Young’s modulus steel reinforced by κ-carbides has the characteristics of high strength and low density, which introduces potential applications of this material in automotive parts with a stiffness requirement. In this work, a 780 MPa grade Fe-Al-C high specific Young’s modulus steel was developed, and the addition of high contents of carbon and aluminum introduced a large fraction of κ-carbides into the steel matrix. To improve the ductility of this steel, a divorced eutectoid transformation (DET) treatment was adopted to regulate the microstructure of κ-carbides. A detailed evolution of κ-carbide during DET was investigated by staged quenching and microstructure characterization. It has been found for the first time that the κ-pearlite transformation and κ-carbides precipitation were mainly completed in the early stage during slow cooling, and the spheroidization of κ-carbides was mainly completed in the later stage. In addition, the effect of DET parameters on the microstructure evolution was analyzed, and it was found that a better spheroidization effect of carbides can be obtained at a lower cooling rate. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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14 pages, 6934 KiB

Open AccessArticle

Low Cycle Fatigue Crack Damage Behavior of TC21 Titanium Alloy with Basketweave Microstructure

by Baohua Nie, Shuai Liu, Xianyi Huang, Haiying Qi, Binqing Shi, Zihua Zhao and Dongchu Chen

Crystals 2022, 12(9), 1211; https://doi.org/10.3390/cryst12091211 - 28 Aug 2022

Cited by 6 | Viewed by 1961

Abstract

Low cycle fatigue (LCF) crack initiation, propagation and damage behaviors of TC21 alloy with basketweave microstructure were investigated. The process of LCF damage was observed by a long-focus optical microscopic imaging system, and fatigue crack propagation was analyzed through in-situ SEM fatigue. The [...] Read more.

Low cycle fatigue (LCF) crack initiation, propagation and damage behaviors of TC21 alloy with basketweave microstructure were investigated. The process of LCF damage was observed by a long-focus optical microscopic imaging system, and fatigue crack propagation was analyzed through in-situ SEM fatigue. The results indicated that LCF crack damage displayed different sensitivity to cyclic stress. LCF microcracks initiated from slip bands and propagated through the microcrack coalescences at high stress, while LCF cracks tended to initiate at the α_L/β interface and connect with these interface microcracks. Furthermore, the LCF damage model was established on the basis of Lemaitre damage theory. When the maximum stress exceeded yield stress, LCF damage increased sharply and fatigue life decreased significantly, which agreed with experiment data. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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13 pages, 5876 KiB

Open AccessArticle

Effect of Austempering on Mechanical Properties of Nb/V Microalloyed Bainitic Bearing Steel

by Yanhui Wang, Baisong Liu, Qiang Pan, Jing Zhao, Xiaojia Zhao, Huaqiang Sun, Dong Xu and Zhinan Yang

Crystals 2022, 12(7), 1001; https://doi.org/10.3390/cryst12071001 - 19 Jul 2022

Cited by 8 | Viewed by 2228

Abstract

In this study, a multi-element microalloyed GCr15Si1MoNbV bainitic bearing steel was designed by adding trace amounts of Nb and V. The bainite/martensite/retained austenite/undissolved carbide multiphase bearing steel with a short heat-treated cycle and remarkable comprehensive mechanical properties was prepared via low-temperature austempering, which [...] Read more.

In this study, a multi-element microalloyed GCr15Si1MoNbV bainitic bearing steel was designed by adding trace amounts of Nb and V. The bainite/martensite/retained austenite/undissolved carbide multiphase bearing steel with a short heat-treated cycle and remarkable comprehensive mechanical properties was prepared via low-temperature austempering, which was compared with a traditional quenched and tempered martensitic microstructure. The results showed that the comprehensive mechanical properties of the low-temperature bainitic microstructure of the Nb/V microalloyed bearing steel were better than those of a traditional tempered martensitic microstructure. In addition, as the isothermal temperature increased, the impact toughness of experimental steel was significantly improved, and the hardness decreased slightly. The tensile strength was improved with the increase in isothermal time. As the isothermal temperature increased, the bainite content of the experimental steel rose, and the stability of the retained austenite enhanced due to more carbon atoms being partitioned into it. The research work in this paper made a preliminary exploration for the application of Nb/V microalloyed bainitic bearing steel in the bearing field and provided some basic data for reference. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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18 pages, 12031 KiB

Open AccessArticle

Effects of Microstructural Properties on Damage Evolution and Edge Crack Sensitivity of DP1000 Steels

by Niloufar Habibi, Santhosh Mathi, Thorsten Beier, Markus Könemann and Sebastian Münstermann

Crystals 2022, 12(6), 845; https://doi.org/10.3390/cryst12060845 - 15 Jun 2022

Cited by 5 | Viewed by 2895

Abstract

In the present work, the microstructural damage behavior of two DP1000 steel test subjects through various stress states was studied to thoroughly learn the interaction between microstructure, damage evolution, and edge stretchability. In addition, microstructural changes at the fracture sites and fracture surfaces [...] Read more.

In the present work, the microstructural damage behavior of two DP1000 steel test subjects through various stress states was studied to thoroughly learn the interaction between microstructure, damage evolution, and edge stretchability. In addition, microstructural changes at the fracture sites and fracture surfaces were observed using a scanning electron microscope. The distinctive mechanical and damage behaviors of the materials were revealed. However, the steels were slightly different in chemical composition, microstructural characteristics, and yield stress. The results showed that when microstructural and mechanical properties of phases were more similar, i.e., the microstructure was more homogenous, the damage was initiated by cracking at ferrite-martensite interfaces, and it propagated along the loading direction. This allowed the material to represent high local formability and significant necking. In contrast, by increasing the dissimilarity between ferrite and martensite phases, damage propagated by the shear linking of the voids hindered local deformation of the material and led it to sudden fracture after negligible necking. These distinct damage evolutions noticeably influenced the materials’ edge stretchability. Since higher local formability favors the edges with higher resistance to cracking, the hole expansion ratio increases, as clearly observed throughout the current study. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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19 pages, 11739 KiB

Open AccessArticle

Effective Case Depth and Wear Resistance of Pack Carburized SCM 420 Steel Processed Using Different Concentrations of Natural Shell Waste Powders and Carburizing Duration

by Ramli and Chung-Chun Wu

Crystals 2022, 12(2), 296; https://doi.org/10.3390/cryst12020296 - 19 Feb 2022

Cited by 3 | Viewed by 3868

Abstract

The efficacy of using coconut shell powder (CSP) and dog conch shell powder (DCSP) as an alternative carburizing media for SCM 420 steel pack carburization was investigated. The effective case depth and wear resistance of quenched specimens prepared using various CSP–DCSP ratios and [...] Read more.

The efficacy of using coconut shell powder (CSP) and dog conch shell powder (DCSP) as an alternative carburizing media for SCM 420 steel pack carburization was investigated. The effective case depth and wear resistance of quenched specimens prepared using various CSP–DCSP ratios and carburizing times were determined and compared. The effective case depth was measured from the microhardness profile obtained using a Vickers hardness testing machine. A CSP–DCSP ratio of 60%:40% and carburization time of 12 h were found to increase the effective case depth of SCM 420 quenched specimens to 2340 µm. The results clearly showed that the effective case depth increased by increasing carburization time and DCSP concentrations from 0% to 40% as a carburizing media and decreased by further increasing DCSP concentrations to 50%. Moreover, the wear resistance of quenched specimens increased approximately two times as DCSP concentrations were increased from 0% to 40% for a carburization time of 12 h. Full article

(This article belongs to the Special Issue Advances in High Strength Steels)

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