Applied sciences

Archives of Metallurgy and Materials

Content

Archives of Metallurgy and Materials | 2021 | vol. 66 | No 2

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Abstract

The results of tests and examinations of the microstructure and mechanical properties of cast steel used for large-size slag ladles are presented. Castings of this type (especially large-size ladles with a capacity of up to 16 m3) operate under very demanding conditions resulting from the repeated cycles of filling and emptying the ladle with liquid slag at a temperature exceeding even 1600°C. The changes in operating temperature cause faster degradation and wear of slag ladle castings, mainly due to thermal fatigue.
The tests carried out on samples taken from different parts/areas of the ladle (flange, bottom and half-height) showed significant differences in the microstructure of the flange and bottom part as compared to the microstructure obtained at half-height of the ladle wall. The flange and bottom were characterized by a ferritic-pearlitic microstructure, while the microstructure at the ladle half-height consisted of a ferritic matrix, cementite and graphite precipitates. Changes in microstructure affected the mechanical properties. Based on the test results it was found that both the flange and the bottom of the ladle had higher mechanical properties, i.e. UTS, YS, hardness, and impact energy than the centre of the ladle wall. Fractography showed the mixed character of fractures with the predominance of brittle fracture. Microporosity and clusters of non-metallic inclusions were also found in the fractures of samples characterized by low properties.
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Authors and Affiliations

Barbara Kalandyk
ORCID: ORCID
R. Zapała
1
ORCID: ORCID
S. Sobula
1
ORCID: ORCID
Grzegorz Tęcza
ORCID: ORCID
K. Piotrowski
2
ORCID: ORCID

  1. AGH University of Science and Technology, Department of Cast Alloys and Composite Engineering, Faculty of Foundry Engineering, 23 Reymonta Str., 30-059 Krakow, Poland
  2. Krakodlew S.A., 1 Ujastek Str., 30-969 Krakow, Poland
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Abstract

Aurivillius Bi5Ti3FeO15 (BTF) and Bi5-xNdxTi3FeO15 (BNTF) ceramics were successfully synthesized by a simple solid state reaction method. Ceramics were prepared from simple oxide powders Bi2O3, TiO­2, Nd2O3 and Fe2O3. The microstructure, structure, chemical composition and dielectric properties of the obtained materials were examined. Dielectric properties were investigated in a wide range of temperatures (T = 25ºC-550ºC) and frequencies (20Hz-1MHz).
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Authors and Affiliations

N. Kocoń
1
J. Dzik
ORCID: ORCID
D. Szalbot
1
ORCID: ORCID
T. Pikula
2
ORCID: ORCID
M. Adamczyk-Habrajska
1
ORCID: ORCID
B. Wodecka-Duś
1
ORCID: ORCID

  1. University of Silesia, Institute of Materials Science, 12 Zytnia Str., 41-200 Sosnowiec, Poland
  2. Lublin University of Technology, Institute of Electronics and Information Technology, 38A Nadbystrzycka Str., 20-618 Lublin, Poland
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Abstract

A source of pure silicon was added into an alloy refining system during a refining process with the application of a direct electric current. The effect of the temperature difference between the graphite electrodes and the alloy was decreased. The temperature increase value (ΔT) of the Al-28.51wt.%Si alloy sample caused by Joule heating was calculated by weighing the mass of primary silicon. When the current density was 5.0×105 A/m2, the overall temperature increase in the alloy was about 90°C regardless of the alloy composition. Adequate silicon atoms recorded the footprint of the electric current in the alloy melt. The flow convection generated by the electric current in the melt during the solidification process resulted in the refinement of primary silicon. The Fe impurity content in alloy refining without the electric current density was 2.16 ppm. However, it decreased to 1.27 ppmw with the application of an electric current density of 5.0×105 A/m2.
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Authors and Affiliations

Jiayan Li
1 2
Benson Kihono Njuguna
1 2
Ping Ni
1 2
Liang Wang
2 1
ORCID: ORCID
Yi Tan
1 2

  1. Dalian University of Technology, School of Materials Science and Engineering, No. 2 Linggong Road, Ganjingzi District, Dalian 116023, China
  2. Dalian University of Technology, Key Laboratory for Solar Energy Photovoltaic System of Liaoning Province, Dalian 116024, China
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Abstract

In this study, the effects of heat treatment on aluminum/steel structural transition joint (STJ) strength were analyzed with ram tensile tests to find the right welding conditions. Before ram tensile tests, the specimens were subjected to different heat treatments to simulate possible thermal conditions, which may occur during the welding of STJ to the steel side of ship construction. Temperatures were varied from 100°C to 500°C, and durations were changed between 5-25 minutes in the heat treatments. The results of the ram tensile tests indicated that tensile strength decreased above 300°C. Micro-hardness test and microstructure examination were conducted to understand behavior change during ram tensile tests. The investigation showed that precipitation of the secondary hard phases with aging at interface above 300°C, reduced the bonding between aluminum and steel materials, which lead to a decrease of strength, and also changed the mechanical behavior of the STJ during ram test from ductile to brittle fracture. If the temperature is below 500°C and the duration is under 15 minutes, the STJ strength value meets the standard requirement. Short and rapid welding could be suggested to reduce heat buildup during welding.
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Authors and Affiliations

Y. Palaci
1
ORCID: ORCID
M. Olgun
1

  1. Yildiz Technical University, Naval Arch. and Marine Eng. Dept, Besiktas , Istanbul, Turkey
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Abstract

This study focused on the fatigue and corrosion fatigue of maraging steel 18Ni (250). The 18Ni (250) samples were tested for axial fatigue in air and 3.5% NaCl solution. The effects of loading frequency and stress ratio on the fatigue strength of 18Ni (250) were studied. In air, the loading frequency was 10 Hz, and the stress ratio was 0.5. However, three loading methods were used in the 3.5% NaCl solution: (i) the loading frequency of 1 Hz and stress ratio of 0.5; (ii) the loading frequency of 1 Hz and stress ratio 0.1, and (iii) the loading frequency 5 Hz and stress ratio 0.5. The corrosion fatigue strength of samples in the 3.5% NaCl solution was 63.3% lower than that of the samples in air. The fractures in the samples were observed after the test.
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Authors and Affiliations

Zhu Yongmei
1
Chen Junjie
1
Tang Wenxian
1
Cui Weicheng
2 3
Wang Xiaorong
1
Wang Fang
2
Yin Baoji
1

  1. Jiangsu University of Science and Technology, College of Mechanical Engineering, Zhenjiang 212003, China
  2. College of Engineering Science and Technology, Shanghai Ocean University, Shanghai 201306, China
  3. Westlake University, School of Engineering, Hangzhou 310024, China
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Abstract

The paper studied the tribological behaviour of electro discharge deposited ZE41A magnesium alloy using wear map. The wear experiments are conducted using pin on disc technique for different parameters such as applied load (1.5 kg-3.5 kg), sliding speed (100 rpm-200 rpm) and sliding time (3 min-7 min). Wear mechanism map is constructed by taking the applied load on y-axis and sliding speed on x-axis. The wear mechanism map is utilized to study the dominance of particular wear mechanism that dominates particular wear regimes such as mild wear, severe wear and ultra severe wear. It is observed that the wear rate increased with increased the applied load and sliding speed. Various mechanisms such as abrasion, oxidation, delamination and melting are identified through scanning electron microscope (SEM).
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Authors and Affiliations

U. Elaiyarasan
1
ORCID: ORCID
V. Satheeshkumar
2
ORCID: ORCID
C. Senthilkumar
3
ORCID: ORCID

  1. Department of Automobile Engineering, Easwari Engineering College, Chennai, India-600089
  2. Department of Mechanical Engineering, Government College of Engineering, Salem, India-636011
  3. Department of Mechanical Engineering, University College of Engineering, Panruti-607106, India
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Abstract

Tensile strength of aluminum castings has been improved by employing surge and filter in a conventional non-pressurizing gating system. For this purpose, three non-pressurizing bottom-gating systems were designed where the first design was a simple design with no filter and no surge, in the second design filter and in the third one surge was added to the end of runner. Tensile strength, Weibull module, scanning electron microscopy, chemical analysis, and melt pattern during the mold filling were thoroughly analyzed to compare these three designs. It was observed that employing filter and surge in the gating system reduces flow kinetic energy and consequently avoid surface turbulence and air entrainment, which leads to castings with fewer defects and higher reliabilities. Finally, it found that appropriate use of surge in the running system can be as effective as employing a filter in reducing melt front velocity.
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Authors and Affiliations

Amir Baghani