• Corrosion Science and Technology
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• v.11 no.1
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• pp.1-8
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• 2012

The development of martensitic grades which can be processed in continuous galvanizing lines requires the reduction of the oxides formed on the steel during the hot dip process. This reduction mechanism was investigated in detail by means of High Resolution Transmission Electron Microscopy (HR-TEM) of cross-sectional samples. Annealing of a martensitic steel in a 10% $H_2+N_2$ atmosphere with the dew point of $-35^{\circ}C$ resulted in the formation of a thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film and amorphous $_{a-X}MnO.SiO_{2}$ oxide particles on the surface. During the hot dip galvanizing in Zn-0.13%Al, the thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was reduced by the Al. The $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides however remained embedded in the Zn coating close to the steel/coating interface. No $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formation was observed. During hot dip galvanizing in Zn-0.20%Al, the $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was also reduced and the amorphous $_{a-X}MnO.SiO_{2}$ and $a-SiO_{2}$ particles were embedded in the $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formed at the steel/coating interface during hot dipping. The results clearly show that Al in the liquid Zn bath can reduce the crystalline $_{C-X}MnO.SiO_{2}$ (x>1) oxides but not the amorphous $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides. These oxides remain embedded in the Zn layer or in the inhibition layer, making it possible to apply a Zn or Zn-alloy coating on martensitic steel by hot dipping. The hot dipping process was also found to deteriorate the mechanical properties, independently of the Zn bath composition.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.31-34
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• 2015

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of $1200^{\circ}C$ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

• Journal of Power System Engineering
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• v.8 no.4
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• pp.31-37
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• 2004

The damping capacity and strength of Fe-2Al-26Mn alloys have been studied for the development of new materials with high strength and damping capacity. Particularly, the effect of ${\alpha}'\;and\;{\varepsilon}$ martensite phase, which constitutes the microstructure of cold rolled Fe-Al-Mn alloys, has been investigated in terms of the strength and damping capacity of the alloys. The damping capacity rises with increasing the degree of cold rolling and reveals the maximum value at 25% reduction. The damping capacity is strongly affected by the volume fraction of ${\varepsilon}$ martensite, while the other phases, such as ${\alpha}'$ martensite and austenite phase, actually exhibit little effect on damping capacity. Considering that tensile strength increases and elongation decreases with increasing the volume fraction of ${\alpha}'$ martensite, it is proved that tensile strength is mainly affected by the amount of ${\alpha}'$ martensite.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.259-262
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• 2009

The influence of pre-strain in low-cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the strain amplitudes in the range of ${\pm}0.4{\sim}{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negilgible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been devised adding a correction term of ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.2
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• pp.99-107
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• 1999

The graphitization is affected by the addition of small amount of the elements(such as Si, Al, Ni, B, Cr and Mn etc.) and the pre-treatment(such as cold rolling). Boron is well known element to accelerate the graphitization of cementite in high carbon steels. Also, cold rolling is known to accelerate the graphitization. But the graphitization nucleation mechanism by cold rolling is few reported. Therefore the effect of cold rolling in Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel on the graphitization is investigated quantitatively using hardness test, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The nucleation of graphite in cold-rolled Fe-0.5%C-1.0%Si-0.47%Mn-0.005%B steel is formed at void which is formed at pearlite/pearlite boundary by cold rolling. But the effect of cold rolling on graphitization in boron addition steel is more effective than that of no boron addition steel due to segregation of BN at void in boron addition steel.

• Journal of the Korean Vacuum Society
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• v.1 no.2
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• pp.259-268
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• 1992

냉연강판의 성능은 그 표면 상태에 의해서 많은 영향을 받는다. Temper-color(T/C)층은 tempering 과정 중 형성되는 다양한 색깔의 얇은 산화층으로서, 우 수한 표면 품질을 갖기 위해서는 방지 또는 제어되어져야 한다. T/C 현상을 이해하기 위하 여 여러 가지 표면 분석방법이 동원되었다. 유백색 T/C층의 표면은 1$mu extrm{m}$ 크기의 구형의 미 세구조로 구성되어 있었다. thens과정 중 C, Si, Mn과 Al이 표면으로 농화됨을 알았고, Mn 과 C은 정상시료에서 보다 T/C 시료에서 농화가 심하였다. T/C 시료에서의 산화층 두께는 정상시료의 60-$\AA$ 보다 매우 두꺼웠으나, 발생 정도에 따라 변화하였다. T/C층 내의 각 원소 산화 상태는, Si은 SiO2의 상태로, Mn은 MnO나 MnO2의 상태로 Fe는 극표면층의 Fe2O3 상태를 제외하고는 metallic 상태로 분석되었다.

• Corrosion Science and Technology
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• v.10 no.1
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• pp.6-12
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• 2011

The selective surface oxidation of a transformation-induced-plasticity (TRIP) steel containing 1.6 wt.% Mn and 1.5 wt.% Si during annealing at $800^{\circ}C$ was investigated for its influence on the formation of an inhibition layer during hot-dip galvanizing. The selective oxidation of the alloying elements and the oxide morphology were significantly influenced by the annealing atmosphere. The pure $N_{2}$ atmosphere with a dew point $-40^{\circ}C$ promoted the selective oxidation of Mn as a crystalline $Mn_{2}SiO_{4}$ phase, whereas the $N_{2}$ + 10% $H_{2}$ atmosphere with the same dew point $-40^{\circ}C$ promoted the selective oxidation of Si as an amorphous Si-rich oxide phase. During hot-dip galvanizing, the $Mn_{2}SiO_{4}$ phase was reduced more readily by Al in the Zn bath than the Si-rich oxide phase. Consequently, the pure $N_{2}$ atmosphere resulted in a higher formation rate of $Fe_{2}Al_{5}$ particles at the Zn/steel interface and better galvanizability than the $N_{2}$ + 10% $H_{2}$ atmosphere.

• Korean Journal of Materials Research
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• v.30 no.1
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• pp.44-49
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• 2020

The effect of intercritical annealing temperature on the microstructure and mechanical properties of Fe-9Mn-0.2C-3Al-0.5Si medium manganese steels containing Cu and Ni is investigated in this study. Six kinds of medium manganese steels are fabricated by varying the chemical composition and intercritical annealing temperature. Hardness and tensile tests are performed to examine the correlation of microstructure and mechanical properties for the intercritical annealed medium manganese steels containing Cu and Ni. The microstructures of all the steels are composed mostly of lath ferrite, reverted austenite and cementite, regardless of annealing temperature. The room-temperature tensile test results show that the yield and tensile strengths decrease with increasing intercritical annealing temperature due to higher volume fraction and larger thickness of reverted austenite. On the other hand, total and uniform elongations, and strain hardening exponent increase due to higher dislocation density because transformation-induced plasticity is promoted with increasing annealing temperature by reduction in reverted austenite stability.

• Journal of Welding and Joining
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• v.35 no.1
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• pp.9-15
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• 2017

IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of $1150^{\circ}C$ and $1250^{\circ}C$. Microstructures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests. The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (${\kappa}-carbide$) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in $1150^{\circ}C$ peak temperature was higher as compared to the base steel due to the formation of ${\kappa}-carbide$, while the yield strength of the HAZ samples (HAZ 2) simulated in $1250^{\circ}C$ decreased as compared to HAZ 1 due to the excessive grain growth.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.627-633
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• 2008

The austenitic Fe-Mn alloys have received considerable attention as a possible candidate for the automotive structural materials due to their high strength and high formability with high elongation. This research investigates the effect of alloying elements on the phase transformation, deformation behavior and mechanical properties in high Mn steels for the development of a high strength high ductility steel. The mechanical stability of austenitic phases is very important for high ductility and it depends largely on the composition of carbon, manganese and aluminum. The dominant deformation mode shifts from TRIP to TWIP mode as the amount of C, Mn and Al is increased. Especially, even a small amount of Al addition facilitates significantly TWIP deformation due to the increase of stacking fault energy in Fe-Mn alloys, this leads to increase the ductility and also decrease the crack sensitivity.