• Title/Summary/Keyword: Spheroidization

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Study on the Cold Formability of Drawn Dual-Phase Steels (신선 가공된 이상 조직강의 냉간 성형성에 대한 연구)

  • 박경수;최상우;이덕락;이종수
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.10a
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    • pp.269-273
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    • 2003
  • There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

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Microstructural Evolution of Aluminum Nitride - Yttrium Aluminum Garnet Composite Coatings by Plasma Spraying from Different Feedstock Powders (Aluminum Nitride - Yttrium Aluminum Garnet 분말 특성과 플라즈마 용사 코팅층의 미세조직)

  • So, Woong-Sub;Baik, Kyeong-Ho
    • Korean Journal of Materials Research
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    • v.21 no.2
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    • pp.106-110
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    • 2011
  • A high thermal conductive AlN composite coating is attractive in thermal management applications. In this study, AlN-YAG composite coatings were manufactured by atmospheric plasma spraying from two different powders: spray-dried and plasma-treated. The mixture of both AlN and YAG was first mechanically alloyed and then spray-dried to obtain an agglomerated powder. The spray-dried powder was primarily spherical in shape and composed of an agglomerate of primary particles. The decomposition of AlN was pronounced at elevated temperatures due to the porous nature of the spray-dried powder, and was completely eliminated in nitrogen environment. A highly spherical, dense AlN-YAG composite powder was synthesized by plasma alloying and spheroidization (PAS) in an inert gas environment. The AlN-YAG coatings consisted of irregular-shaped, crystalline AlN particles embedded in amorphous YAG phase, indicating solid deposition of AlN and liquid deposition of YAG. The PAS-processed powder produced a lower-porosity and higher-hardness AlN-YAG coating due to a greater degree of melting in the plasma jet, compared to that of the spray-dried powder. The amorphization of the YAG matrix was evidence of melting degree of feedstock powder in flight because a fully molten YAG droplet formed an amorphous phase during splat quenching.

Study on the Cold Formability of Drawn Non-heat Treated Steels (신선 가공된 열처리 생략강의 냉간 성형성에 대한 연구)

  • 박경수;박용규;이덕락;이종수
    • Transactions of Materials Processing
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    • v.12 no.4
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    • pp.364-369
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    • 2003
  • Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to study their mechanical properties and the cold formability. The cold formability of three steels was investigated by estimating the deformation resistance and the forming limit. The deformation resistance was estimated by calculating the deformation energy, and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strains of ultra low carbon bainitic steel and low-Si steel were higher than that of commercial SWRCH45F steel.

Effect of Ball milling Time on Graphite Dispersion and Mechanical Properties in Rapidly Solidified 6061 Al Composite (급속응고 6061Al/Graphite 복합재료의 볼밀링 시간에 따른 흑연 분산거동 및 기계적 특성)

  • Son, Hyeon-Taek;Lee, Jae-Seol;Hong, Soon-Jik;Chun, Byong-Sun
    • Journal of Powder Materials
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    • v.16 no.3
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    • pp.209-216
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    • 2009
  • A composite of rapidly solidified Al-6061 alloy powder with graphite particle reinforcements was prepared by ball milling and subsequent hot extrusion. The microstructure and mechanical properties of these composites were investigated as a function of milling time. With increasing milling time, the gas atomized initially and spherical powders became elongated with a maximum aspect ratio after milling for 30 h. Then, refinement and spheroidization were achieved by further milling to 70 h with a homogeneous and fine dispersion of graphite particles forming between the matrix alloy layers. The best compression and wear properties were obtained in the powder milled for 70 h, associated with the increased fine and homogeneous distribution of graphite particles in the aluminum alloy matrix.

Behavior of Eutectic Si and Mechanical Properties of Sr Modified Al-7Si-0.35Mg alloy with Solid Solution Treatment for Sand Casting (Sr 개량처리된 사형주조 Al-7Si-0.35Mg 합금의 열처리에 따른 공정 Si상 변화거동 및 특성평가)

  • Kim, Myoung-Gyun;Hwang, Seok-Min
    • Journal of Korea Foundry Society
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    • v.38 no.1
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    • pp.1-8
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    • 2018
  • In this study, we focused on the correlation between the solidification structure, heat treatment and mechanical properties of the A356 alloy according to the conditions of Sr modification. The microstructural evolution of the eutectic Si and ${\alpha}-Al$ phase in the A356 alloy castings depending on the amount of Sr were investigated during solid solution heat treatment using an optical microscope, a scanning electron microscope and an image analyzer. In addition, tensile tests on the heat treated materials examined the relationship between the microstructure and the fracture surface. The as-cast A356 alloys under 40 ppm Sr showed an undermodified microstructure, but that of the added 60-80 ppm Sr had well modified structure of fine fibrous silicon. After solid solution treatment, the microstructure of the undermodified A356 alloy exhibited a partially spheroidized morphology, but the remainder showed the fragmentation of fibrous shaped silicon. The spheroidization of the eutectic silicon in the modified A356 alloys was completed during heat treatment, which was very effective in increasing the elongation. This is supported by the fracture surface in the tensile test.

The Effect of Si Content on Important Properties of A Mo and V Free Low Alloy Cast Steel for The Insert of Cold Pressing Die (냉간 인서트 금형용 Mo, V 무첨가 저합금 주강의 주요 성질에 미치는 Si함량의 영향)

  • Shin, Je-Sik;Kim, Bong-Whan;Moon, Byung-Moon
    • Journal of Korea Foundry Society
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    • v.29 no.2
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    • pp.70-77
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    • 2009
  • The aim of this study was to develop a Mo and V free low alloy cast steel materials, enabling the significant cost- and time-savings in manufacturing and maintaining the insert of cold pressing die without impairment of the important properties. For this purpose, the effects of Si content on combinations of important properties such as hardness, hardenability, and weldability, and strength were systematically investigated. In order to evaluate the applicability as the insert of cold pressing die, the mechanical properties were measured after spheroidization annealing, quenching and tempering, and flame hardening heat treatments, respectively. After the Q/T and F.H. treatments, the developed 0.8${\sim}$1.6%Si containing Mo and V free low alloy cast steels showed excellent matrix strengthening effect, hardenability, and weldability, fulfilling the industrial criterion of the mechanical properties for automobile cold pressing die insert.

A Study on the Cold Formability of Drawn Dual-Phase Steels (신선 가공된 이상 조직강의 냉간 성형성에 대한 연구)

  • 박경수;최상우;이덕락;이종수
    • Transactions of Materials Processing
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    • v.13 no.1
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    • pp.84-89
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    • 2004
  • There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

The Effect of Cementite Morphology and Matrix-ferrite Microstructure on the Sliding Wear Behavior in Spheroidized High Carbon Steel (구상화 열처리된 고탄소강의 미끄럼 마멸 거동에 미치는 시멘타이트 형상과 페라이트 기지조직의 영향)

  • Hur, H.L.;Gwon, H.;Gu, B.;Kim, Y.-S.
    • Transactions of Materials Processing
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    • v.25 no.2
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    • pp.96-101
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    • 2016
  • The current study was conducted to elucidate the effect of cementite morphology and matrix-ferrite microstructure on sliding wear behavior in spheroidized high carbon (1wt. % C) steel. The high carbon steel was initially heat treated to obtain a full pearlite or a martensite microstructure before the spheroidization. The spheroidizing heat treatment was performed on the full pearlitic steel for 100 hours at 700℃ and tempering was performed on the martensitic steel for 3 hours at 650℃. A spheroidized cementite phase in a ferrite matrix was obtained for both the full pearlite and the martensite microstructures. Sliding wear tests were conducted using a pin-on-disk wear tester with the heat treated steel as the disk specimen. An alumina(Al2O3) ball was used as the pin counterpart during the test. After the spheroidizing heat treatment and the tempering, both pearlite and martensite exhibited similar microstructures of spheroidized cementite in a ferrite matrix. The spheroidized pearlite specimens had lower hardness than the tempered martensite; however, the wear resistance of the spheroidized pearlite was superior to that of the tempered martensite.

Effect of Austenitizing Temperature on Mechanical Properties in the Spheroidized Cr-Mo Steel (구상화 열처리한 Cr-Mo강의 오스테나이트화 온도가 기계적 성질에 미치는 영향)

  • Kou, D.H.;Yoon, J.H.;Park, S.J.;Kim, J.M.;Kang, H.J.;Sung, J.H.
    • Journal of the Korean Society for Heat Treatment
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    • v.24 no.4
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    • pp.187-192
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    • 2011
  • Effect of austenitizing temperatures on the impact value of the AISI 4140 steel after repetition of spheroidization and cold deep drawing treatment has been studied. Sufficient dissolution of carbide was shown after austenitizing at the high temperature of $950^{\circ}C$. Accordingly, the impact value was remarkably increased by tempering of this high temperature austenitized steel at the tempering temperature ranges between $570^{\circ}C$ and $630^{\circ}C$. On the other hand, remarkable decrease in the impact values and elongations were shown by tempering the low temperature-austenitized ($870^{\circ}C$) steel due to the coarsening of undissolved-carbide existed at the austenitizing temperature.

The Effect of Uni-nanoadditive Manufactured Using RF Plasma Processing on Core-shell Structure in MLCC

  • Song, Soon-Mo;Kim, Hyo-Sub;Park, Kum-Jin;Sohn, Sung-Bum;Kim, Young-Tae;Hur, Kang-Heon
    • Journal of the Korean Ceramic Society
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    • v.46 no.2
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    • pp.131-136
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    • 2009
  • Radio frequency (RF) plasma treatment is studied for the size reduction and the spheroidization of coarse particles to change them into nano-sized powders of spherical shape in MLCC fields. The uni-nanoadditives manufactured by RF plasma processing for high dispersion have been investigated for the effect on core-shell structure in dielectrics of MLCC. Microstructures have been characterized using scanning electron microscope (SEM), transmission electron microscope (TEM) and Electron Probe Micro Analyzer (EPMA). We compared the distribution of core-shell grains between specimens manufactured using uni-nanoadditive and using mixed additive. In addition, the uniformity of rare earth elements in the core-shell structured grains was analyzed. It was shown, from TEM observations, that the sintered specimen manufactured using uni-nanoadditives had more dense small grains with well-developed core-shell structure than the specimen using mixed additives, which had a homogeneous microstructure without abnormal grain growth and shows broad temperature coefficient of capacitance (TCC) curves in all temperature ranges because of well dispersed additives.