• Journal of the Korean Society for Heat Treatment
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• v.25 no.4
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• pp.181-189
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• 2012

The demand on quantitative measurement of the heat flux is motivated in making higher-quality steel product through a water quenching process of plate mill. To improve a spatial degree of heat flux measurement, the multi-point heat flux measurement was carried out by a unique experimental technique that has a combination of the existing single-point heat flux gauge. The corresponding heat flux can be easily determined by Fourier's law in a conventional way. The multi-point heat flux gauge developed in this study can be applicable to measure the surface heat flux, the surface heat transfer coefficient during a water quenching applications of steelmaking process. The results exhibit different heat transfer regimes; such as single-phase forced convection, nucleate boiling, and film boiling, that are occurred in close proximity on the multi-point heat flux gauge quenched by water impinging jet.

• Interaction and multiscale mechanics
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• v.4 no.2
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• pp.155-164
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• 2011

The lattice strain evolution within polycrystalline solids is influenced by the crystal orientation and grain interaction. For multi-phase polycrystals, due to potential large differences in properties of each phase, lattice strains are even more strongly influenced by grain interaction compared with single phase polycrystals. In this research, the effects of the grain interaction and crystal orientation on the lattice strain evolution in a two-phase polycrystals are investigated. Duplex steel of austenite and ferrite phases with equal volume fraction is selected for the analysis, of which grain arrangement sensitivity is confirmed in the literature through both experiment and simulation (Hedstr$\ddot{o}$m et al. 2010). Analysis on the grain interaction is performed using the results obtained from the finite element calculation based on the model of restricted slip within crystallographic planes. The dependence of lattice strain on grain interactions as well as crystal orientation is confirmed and motivated the need for more in-depth analysis.

• Steel and Composite Structures
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• v.38 no.2
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• pp.213-221
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• 2021

The objective of this paper is to study the deformation in a homogeneous isotropic thermoelastic solid using modified couple stress theory subjected to ramp-type thermal source with two temperature. The advantage of this theory is the involvement of only one material length scale parameter which can determine the size effects. Laplace and Fourier transform technique is applied to obtain the solutions of the governing equations. The components of displacement, conductive temperature, stress components and couple stress are obtained in the transformed domain. A numerical inversion technique has been used to obtain the solutions in the physical domain. The effect of two temperature is depicted graphically on the resulted quantities. Numerical results show that the proposed model can capture the size effects of microstructures.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.284-288
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• 2012

A study on microstructure control of multi-phase steel have been implemented to higher strength with improved formability. However, it is well known that the high strength of steel are susceptible to hydrogen embrittlement. The mechanisms of hydrogen embrittlement is caused by complex interactions. In this paper, the test specimens were fabricated to 5 type of 590DP steels at different levels of volume faction. The hydrogen charging was conducted by electrochemical hydrogen-charge method with varying charging time. The relationship between hydrogen concentration and volume fraction of 590DP steel was established by SP test and SEM-fractography. It was shown that the hydrogen amounts charged in 590DP steels increased with increasing the volume faction of austenite. The maximum loads of the 590DP steels in SP test were sharply decreased with increasing hydrogen charging time. The results of SEM-fractography investigation showed typical brittle-fracture surfaces for hydrogen-charged 590DP steels.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.113-120
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• 2024

An attempt was made to apply digital image correlation (DIC) strain analysis to in-situ scanning electron microscopy (SEM) observations of bending deformation to quantify local strain distribution inside a ZnMgAl-alloy coating in deformation. Interstitial-free steel sheets were hot-dipped in a Zn-3Mg-6Al (mass%) alloy melt at 400 ℃ for 2 s. The specimens were deformed using a miniature-sized 4-point bending test machine inside the SEM chamber. The observed in situ SEM images were used for DIC strain analysis. The hot-dip ZnMgAl-alloy coating exhibited a solidification microstructure composed of a three-phase eutectic of fine Al (fcc), Zn (hcp), and Zn2Mg phases surrounding the primary solidified Al phases. The relatively coarsened Zn₂Mg phases were locally observed inside the ZnMgAl-alloy coating. The DIC strain analysis revealed that the strain was localized in the primary solidified Al phases and fine eutectic microstructure around the Zn₂Mg phase. The results indicated high deformability of the multi-phase microstructure of the ZnMgAl-alloy coating.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.678-683
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• 2003

Ultrasonic method using SH(shear horizontal) wave has been developed to determine the surface damage in fatigued material. Fatigue damages based on propagation energy were analyzed by multiregression analysis and phase measurement in interrupted fatigue test specimen including CrMoV and 12Cr alloy steel. From the test results, as the fatigue damage increased the propagation time of the launched waves increased and amplitude of wavelet decreased. Also, analysis for the waveform modulation showed a reliable estimation, with confidence limit of 97% for 12Cr steel and 95% for CrMoV steel, respectively. Therefore, It is thought that SH ultrasonic wave technique can be applied to determine fatigue damage of in-service component nondestructively.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.3-11
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• 2005

Using various thermo-mechanical schedules characterized by varying reheating temperature, deformation temperature and strain, the austenite recrystallization and ferrite refinement of a Nb bearing low carbon steel(0.15C-0.25Si-1.11Mn-0.04Nb) were investigated. For single pass heavy deformations at $800^{\circ}C$, the 40% deformed austenite was not recrystallized while the 80% deformed one was fully recrystallized. Ferrite grains formed in the 80% deformed specimen was not very small compared with those in the 40% deformed specimen, which implied the recrystallized austenite was not more beneficial to ferrite refinement than the non-recrystallized one. In case of deformation in low temperature austenite region, a multi-pass deformation made finer ferrites than a single-pass deformation, as the total reduction was the same, due to more ferrite nucleation sites in the non-recrystallization of austenite for multi-pass deformation. When specimen was deformed at $775^{\circ}C$ that was $10^{\circ}C$ higher than $Ar_3$, the ferrite of about $1{\mu}m$ was formed through deformation induced ferrite transformation(DIFT), and the amount of ferrite was increased with increasing reduction. Dislocation density was very high and no carbides were observed in DIFT ferrites, presumably due to supersaturated carbon solution. By deformation in two phase(50% austenite+50% ferrite) region the very refined ferrite grains of less than $1{\mu}m$ were formed certainly by recovery and recrystallization of deformed ferrites and, a large portion of ferrites were divided by subgrain boundaries with misorientation angles smaller than 10 degrees.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.4 s.33
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• pp.1-5
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• 2004

A multi-layer flexible substrate is composed of copper(Cu)/polyimide that are known as good electrical conductivity, and low dielectric constant, respectively. In this study. conductor line of $5{\mu}m$-pitch was successfully fabricated without non-uniform pattern shape by electroplating copper and coating polyimide on patterned stainless steel. For multi-layer flexible substrate, via holes were drilled by UV laser and filled with electroplating copper and tin. And then, the PI layer with vias and conductor lines was stripped from stainless steel substrate. The PI layers were laminated at once with careful alignment between layers. Solid state reaction between tin and copper during lamination formed the intermetallic compounds of $Cu_6Sn_5$($\eta$-phase) and $Cu_3Sn$($\epsilon$-Phase) and achieved a complete inter-connection by vertically positioning the plugged via holes on via pad. The via formation process has several advantages; such as better electrical property and lower cost than V type via and paste via.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.71-71
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• 2010

SBD (Strain-based design) of pipe lines have gained world-wide attention in recent years. The present research aims to evaluate the fracture characteristics of API (America Petroleum Institute) SBD X100 girth weldment that typically applied for cold climate and deep water offshore, with the focus on the influence of heat input changing with 6kJ/cm and 10kJ/cm from GMAW (Gas Metal Arc Welding). At a low heat input at 6kJ/cm, the weld metal had Multi-phase matrix (Acicular ferrite + Banite + Martensite) that could fill up both fracture toughness and strength as reported previously. Also, the weld metal exhibited 859MPa YS (Yield strength), 108J impact toughness at $-40^{\circ}C$ and 0.52mm CTOD (Crack Tip Open Displacement) at $-10^{\circ}C$. These results can be satisfied with the requirement of API SBD X100 girth weldment and Alaska pipe line project.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.25-30
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• 2009

SBD (Strain-based design) of pipe lines have gained world-wide attention in recent years. The present research aims to evaluate the fracture characteristics of API (America Petroleum Institute) SBD X100 girth weldment that typically applied for cold climate and deep water offshore, with the focus on the influence of heat input changing with 6kJ/cm and 10kJ/cm from GMAW (Gas Metal Arc Welding). At a low heat input at 6kJ/cm, the weld metal had Multi-phase matrix (Acicular ferrite + Banite + Martensite) that could fill up both fracture toughness and strength as reported previously. Also, the weld metal exhibited 859MPa YS (Yield strength), 108J impact toughness at $-40^{\circ}C$ and 0.52mm CTOD (Crack Tip Open Displacement) at $-10^{\circ}C$. These results can be satisfied with the requirement of API SBD X100 girth weldment and Alaska pipe line project.