• Korean Journal of Materials Research
• /
• v.33 no.3
• /
• pp.106-114
• /
• 2023

The carbon concentration in the carburized steels was measured by electron probe microanalysis (EPMA) for a range of soluted carbon content in austenite from 0.1 to 1.2 wt%. This study demonstrates the problems in carbon quantitative analysis using the existing calibration curve derived from pure iron (0.008 wt%C) and graphite (99.98 wt%C) as standard specimens. In order to derive an improved calibration curve, carbon homogenization treatment was performed to produce a uniform Kα intensity in selected standard samples (AISI 8620, AISI 4140, AISI 1065, AISI 52100 steel). The trend of detection intensity was identified according to the analysis condition, such as accelerating voltage (10, 15, 30 keV), and beam current (20, 50 nA). The appropriate analysis conditions (15 keV, 20 nA) were derived. When the carbon concentration depth profile of the carburized specimen was measured for a short carburizing time using the improved calibration curve, it proved to be a more reliable and accurate analysis method compared to the conventional analysis method.

• Design & Manufacturing
• /
• v.17 no.2
• /
• pp.55-61
• /
• 2023

With femtosecond (fs) laser pulse irradiation on metals, various types of nano- and micro-scale structures can be naturally induced at the surface through laser-matter interaction. Two notable structures are laser-induced periodic surface structures (LIPSSs) and cone/spike structures, which are known to significantly modify the optical and physical properties of metal surfaces. In this work, we irradiate fs laser pulses onto various types of metals, cold-rolled steel, pickled & oiled steel, Fe-18Cr-8Ni alloy, Zn-Mg-Al alloy coated steel, and pure Cu which can be useful for precise molding and imprinting processes, and adjust the morphological profiles of LIPSSs and cone/spike structures for clear structural coloration and a larger range of surface wettability control, respectively, by changing the fluence of laser and the speed of raster scan. The periods of LIPSSs on metals used in our experiments are nearly independent of laser fluence. Accordingly, the structural coloration of the surface with LIPSSs can be optimized with the morphological profile of LIPSSs, controlled only by the speed of the raster scan once the laser fluence is determined for each metal sample. However, different from LIPSSs, we demonstrate that the morphological profiles of the cone/spike structures, including their size, shape, and density, can be manipulated with both the laser fluence and the raster scan speed to increase a change in the contact angle. By injection molding and imprinting processes, it is expected that fs laser-induced surface structures on metals can be replicated to the plastic surfaces and potentially beneficial to control the optical and wetting properties of the surface of injection molded and imprinted products.

• Journal of the Korean Society for Heat Treatment
• /
• v.36 no.6
• /
• pp.402-411
• /
• 2023

In order to examine the effect of cementite precipitated on the steel surface on the carburizing rate, the carburizing process was carried out at various boost times to measure the mass gain and carbon flux, phase analysis and carbon concentration analysis were performed on the surface of the carburized specimen. In the case of the only boost type, the longer the boost time, the more the mass gain by the diffused carbon follows the parabolic law and tends to increase. In particular, as the boost time increased, the depth of cementite precipitation and the average size of cementite on the steel surface increased. At a boost time of 7 min, the fraction of cementite precipitated on the surface is 7.32 vol.%, and the carburizing rate of carbon into the surface (surface-carbon flux) is about 17.4% compared to the calculated value because the area of the chemical (catalyst) where the carburization reaction takes place is reduced. The measured carbon concentration profile of the carburized specimen tended to be generally lower than the carbon concentration calculated by the model without considering precipitated cementite. On the other hand, in the pulse type, the mass gain by the diffused carbon increased according to the boost time following a linear law. At a boost time of 7 min, the fraction of cementite precipitated on the surface was 3.62 vol.%, and the surface-carbon flux decreased by about 4.1% compared to the calculated value. As a result, a model for predicting the actual carbon flux was presented by applying the carburization resistace coefficient derived from the surface cementite fraction as a variable.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.81.2-81.2
• /
• 2012

To fabricate a metal mold for injection molding, hot-embossing and imprinting process, mechanical machining, electro discharge machining (EDM), electrochemical machining (ECM), laser process and wet etching ($FeCl_3$ process) have been widely used. However it is hard to get precise structure with these processes. Electrochemical etching has been also employed to fabricate a micro structure in metal mold. A through mask electrochemical micro machining (TMEMM) is one of the electrochemical etching processes which can obtain finely precise structure. In this process, many parameters such as current density, process time, temperature of electrolyte and distance between electrodes should be controlled. Therefore, it is difficult to predict the result because it has low reliability and reproducibility. To improve it, we investigated this process numerically and experimentally. To search the relation between processing parameters and the results, we used finite element simulation and the commercial finite element method (FEM) software ANSYS was used to analyze the electric field. In this study, it was supposed that the anodic dissolution process is predicted depending on the current density which is one of major parameters with finite element method. In experiment, we used stainless steel (SS304) substrate with various sized square and circular array patterns as an anode and copper (Cu) plate as a cathode. A mixture of $H_2SO_4$, $H_3PO_4$ and DIW was used as an electrolyte. After electrochemical etching process, we compared the results of experiment and simulation. As a result, we got the current distribution in the electrolyte and line profile of current density of the patterns from simulation. And etching profile and surface morphologies were characterized by 3D-profiler(${\mu}$-surf, Nanofocus, Germany) and FE-SEM(S-4800, Hitachi, Japan) measurement. From comparison of these data, it was confirmed that current distribution and line profile of the patterns from simulation are similar to surface morphology and etching profile of the sample from the process, respectively. Then we concluded that current density is more concentrated at the edge of pattern and the depth of etched area is proportional to current density.

• Restorative Dentistry and Endodontics
• /
• v.24 no.3
• /
• pp.503-510
• /
• 1999

The purpose of this study was to evaluate the amount of transportation of original canal, zip formation, permanent deformation and fracture of instruments after canal enlargement. In this study, the 60 resin blocks that have curved canals were randomly divided into 3 experimental groups with 20 teeth each according to instrument types and filling methods for canal enlargement. The curved canals of each experimental groups were enlarged to No 40 ISO size with the K-flexo stainless steel file (Group 1), Engine-driven Ni-Ti Profile new series(Group 2) and Engine-driven Ni-Ti Quantec 2000 series(Group 3) according to the manufacturer's recommendation. Pre- and postoperative X-rays were taken at same position and the films were scanned and the canal images were traced to determine the canal curvature according to the method of Schneider. The amount of reduction in canal curvature were calculated between pre- and postoperative X-rays. In addition to zip formation, permanent deformation and fracture of instruments were examined after canal enlargement. The results were as follows : 1. All experimental groups showed some loss of canal curvature after instrumentation. There was a significant change in curvature between before and after instrumentation in each group(p<0.001). 2. Engine-driven Ni-Ti instrumentations resulted in an average loss of curvature of 2.36 degrees for Profile new series, 3.43 degrees for Quantec series, and hand instrumentation showed an average loss of curvature of 6.48 degrees for K-flexo file. There was a statistical significant difference between hand instrumentation and engine-driven Ni-Ti instrumentations(p<0.05). But there was no statistical difference between Profile new series and Quantec series. 3. There were many apical zip formations in group 1(Hand instrumentation). But there were no apical zip formations in group 2,3(Engine-driven Ni-Ti instrumentation). 4. The instrument deformation occured 9 cases in group 1(K-flexo file), 2 cases in group 2(Profile new series) and 3 cases in group 3(Quantec) after instrumentation. And the instrument fracture occured 1 case in each group. The results showed that the engine-driven Ni-Ti instruments, if we use carefully according to manufacturer's recommendations, can be use effectively for instrumenting the curved root canals in case of the MAF was over size 40.

• Advances in concrete construction
• /
• v.2 no.1
• /
• pp.57-75
• /
• 2014

This paper presents an analysis of the results of an experimental program on the performance of a novel configuration of a hybrid FRP-concrete beam. The beam section consists of a GFRP pultruded profile, a CFRP laminate, and a concrete block all wrapped up using filament winding. It was found that the thickness of the concrete block and the confinement by the filament-wound wrapping had a profound effect on the energy dissipation behaviour of the beam. Using a shear punching model, and comparing the predicted results with the experimental ones, it was found that beyond a given value of the concrete block thickness, the deformational behaviour of the beam shifts from brittle to ductile. It was also found that the filament-wound wrap had many benefits such as providing a composite action between the concrete block and the GFRP box, improving the stiffness of the beam, and most importantly, enhancing the load carrying ability through induced confinement of the concrete.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1996.04a
• /
• pp.93-98
• /
• 1996

Friction and wear characteristics of metals in dry and boundary lubricated sliding conditions are observed experimentally using pin-on-disk and pin-on-plate type tribotesters. The motivation of this research is to investigate the effect of sliding history on the tribological behavior of metals. Cu and SM45C steel materials were used for the experiment. The results show that in dry condition the fictional behavior as well as wear of the specimens differed between uni-directional and bi-directional sliding conditions. The friction coefficient values, wear profile and optical micrograph of the wear track are presented.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2001.10a
• /
• pp.181-185
• /
• 2001

Three-dimensional finite-element-based numerical model of turbulent flow, heat transfer, macroscopic solidification and inclusion trajectory in a continuos steel slab caster was developed Turbulence was incorporated using the Improved Low-Re turbulence model with positive preserving approach. The mushy region was modeled as the porous media with average effective viscosity. A series of simulations was carried out to investigate the effects of the casting speed, the slab size, the delivered superheat the immersion depth of the SEN on the transport phenomena. In the absence of any known experimental data related to velocity profiles, the numerical predictions of the solidified profile on a caster was compared with breakouts data and a good agreement was found.

• The korean journal of orthodontics
• /
• v.43 no.4
• /
• pp.201-206
• /
• 2013

This article describes the orthodontic treatment of a 25-year-old Korean female patient with anterior crowding, including palatally displaced lateral incisors. Her facial profile was satisfactory, but 3.5 mm of maxillary anterior crowding was observed. To correct this crowding, we decided to minimize the use of the conventional fixed orthodontic appliances and employed a less bulky and more aesthetic appliance for applying light continuous force. We determined the final positions of the maxillary teeth via a working model for diagnostic set up and achieved space gaining and alignment with simple Ni-Ti spring and stainless steel round tubes. Tooth alignment was achieved efficiently and aesthetically without the conventional brackets.

• 한국신재생에너지학회:학술대회논문집
• /
• 2005.06a
• /
• pp.17-20
• /
• 2005

This paper presents an overview analysis on the observed wind shear at Pohang Steel Works, focusing on diurnal patterns and the frequency of high nighttime shear at the site in case of land breeze. In addition, this paper discusses the importance of accurate shear estimates for reliable evaluation of wind energy density. In order for a long-term correlation of the site, three Measure-Correlate-Predict methods were tested with Pohang wind data and it was shown that the linear MCP gives poor estimation due to the geographic characteristics of complex terrain where the severe transformation of wind direction was accompanied.