• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.274-277
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• 2009

There have been a number of works on manufacturing ultrafine grained steels with average ferrite grain sizes of smaller than a few micrometers to develop beneficial high strength steels. Among microstructures in low carbon steels, lath martensite is known to be useful to produce an ultrafine grained ferrite matrix and finely globular cementite particle. Thus, severe plastic deformation and subsequent annealing at lower temperature of lath martensite would become an effective way to produce ultrafine grained steels. However, most ultrafine grained steels exhibited a total elongation of a few per cent in tensile tests. Such a defect is one of the primary factors restricting the potential applications of ultrafine grained steels. Therefore, the improvement of the strength-elongation balance is required for the application of ultrafine grained structural steels. In this study, the effect of deformation temperatures on microstructure, such as ferrite grain size and the distribution of cementite particles, and mechanical property of lath martensite steels, was investigated. Specimens were fabricated through cold rolling or warm rolling and subsequent annealing.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.652-655
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• 2001

Power transformers are increasingly becoming more significant in the advancement of electronic equipment. A high-performance, low-cost core material is necessary in order th come up with power transformers in the smallest and lightest scale possible and with low power requirements. In this study, we added V$_2$O$_{5}$ and CaCo$_3$to Mn-Zn ferrite to produce a high-performance low-cost core material. The compositions used were MnO : ZnO : Fe$_2$O$_3$= 37 : 11 : 52 mol%. The materials were sintered at 125$0^{\circ}C$ for three hours. Initial permeability was measured at 0.1MHz. At 200mT, power loss was measured by changing the temperature at 25KHz, 50KHz, 100KHz. When we added 0.lwt% and 0.1%wt% of V$_2$O$_{5}$와 CaCo$_3$, respectively we obtained 405 405KW/㎥ at 200mT, 100KHz, 6$0^{\circ}C$. We tan reduce eddy current loss as a primary loss of high frequency by adding a small amount of V$_2$O$_{5}$와 CaCo$_3$. This reduces power loss in the power transformersormers

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.131-136
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• 2003

CF8M cast austenitic stainless steel is used for several components such as primary coolant piping, elbow, pump casing, and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. In this study, three kinds of the aged CF8M specimen were prepared using an artificially simulated aging method. The objective of this study is to summarize the method of estimating ferrite contents, Charpy impact energy and J-R curve, and to evaluate the thermal embrittlement of the CF8M cast austenitic stainless steel piping used in the domestic nuclear power plants.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.89-96
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• 1999

The base metal and weld metal of alloy designed austenitic stainless steels were electrochemically tested in artificial sea water. Pitting resistance of 14 different stainless steels was evaluated by measuring pitting potential. The effect of alloy element to pitting potential was evaluated by changing chromium, nickel, sulfur content. The site of pitting initiation was observed by optical microscope. As a result of electrochemical test, pitting resistance of weld metal was higher than base metal, and rapidly cooled weld metal has higher pitting potential than slowly cooled weld metal. In case of primary δ-ferrite solidification, pitting potential was increased, but residual δ-ferrite was detrimental to pitting resistance. Chromium was more effective to pitting resistance than nickel, and sulfur was very detrimental element to pitting resistance.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.96-101
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• 2004

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal embrittlement at the reactor operating temperature. The objective of this study is to summarize the method of estimating ferrite content, Charpy impact energy and J-R curve and to evaluate the thermal embrittlement of the cast austenitic stainless steel piping used in the domestic nuclear power plants. The result of evaluation, two domestic nuclear power plants used CF-8M and CF-8A material has adequate fracture toughness after saturation.

• Journal of Welding and Joining
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• v.30 no.3
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• pp.57-65
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• 2012

The interest of austenitic heat resistant stainless steels containing high Si has increased because they have higher resistance of oxidation and higher strength at high temperature than STS 310. This study carried out Varestraint test for evaluation of solidification cracking sensitivity of 14 different stainless steels. As a result of Varestraint test, all specimens solidified as primary ferrite, and solidification crack sensitivity increased with adding $N_2$ to shielding gas. Nb and W had beneficial effect on solidification crack resistance in case of less than FN 2 containing, but crack sensitivity increased with Nb and W in case of more than FN 2. Ce had beneficial effect on solidification crack resistance but impaired weld bead appearance.

• Journal of the Korean Magnetics Society
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• v.20 no.3
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• pp.94-99
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• 2010

Minor B-H loop measurement for a rectangular high tensile steel was obtained by using Labview. A ferrite cores of high permeance with primary and secondary windings on the steel plate were used to form a closed loop of magnetic flux. To compensate errors due to an extremely small gap between a pair of ferrite core, and between the ferrite core and the rectangular high tensile steel, quadratic function of least square method was used. Also a 3D FEM magnetic analysis tool was used to measure H and B of the steel. B-H loop of the high tensile steel plate can be measured up to 520 A/m of a magnetic field and 0.15 T of a magnetic flux density.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.47-47
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• 2009

용착금속의 미세조직은 크게 Acicular ferrite(AF), Ferrite with aligned second phase(FS), Primary ferrite(=Grain boundary Ferrite) 등으로 나눌 수 있다. 이 중 침상형 페라이트(AF)는 인성과 강도를 동시에 증가시킬 수 있으므로 이를 다량 확보하는 것이 용접산업의 관건이다. 본 연구에서는 침상형 페라이트 발생에 기여한다고 알려진 Ti 함량을 용착금속에서 단계적으로 조절하여 나타나는 미세조직과 특성변화를 관찰하였다. 모재는 HSB-600을 사용하였으며 용접재료는 ER100S-G급의 Ti가 함유되어 있는 것(A)과 미함유된 것(B)을 사용하였다. 모재 성분의 희석을 방지하기 위해 V-Groove 가공 후 Buttering 용접을 실시하였다. 중앙에 가공된 V-그루브에 이들 재료를 적절히 조합하고 용접(입열량 20kJ/cm)하여 Ti함유량을 총 4가지(0.002~0.025% Ti)로 제어하였다. 용접 후 각각의 시편에 대해 미세조직, 충격시험, O/N분석, 성분분석 등의 시험을 진행하였다. 미세조직 관찰결과 Ti함량이 증가할수록 AF는 증가하고 FS는 감소함을 확인할 수 있었으며 충격시험결과 Ti가 많이 함유된 시편일수록 더 낮은 연성취성 천이온도(DBTT)를 나타내었다. EDS와 SEM으로 관찰한 결과 Ti함량 증가에 따라 비금속개재물의 크기는 작아지고 밀도는 높아지는 것을 확인할 수 있었으며 개재물 내에서의 Ti함량도 더 많아지는 것을 확인 할 수 있었다.

• Journal of Welding and Joining
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• v.32 no.2
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• pp.29-36
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• 2014

Recently, in order to enhance the function and usefulness of products, cladding of dissimilar materials that maximizes the performance of the material is being widely used in all areas of industry as an important process. Clad steel plate, produced by cladding stainless steel plate, an anticorrosive material, on carbon steel plate, is being used to produce pressure vessels. Stainless steel plate has good corrosion resistance, and carbon steel plate has good rigidity and strength; clad steel can satisfy all of these qualities at once. This study aims to find the ${\delta}$-ferrite behavior, mechanical properties, structure change, integrity and reliability of clad steel weld on hot rolled steel plates. For this purpose, multi-layer welding, repair welding and post weld heat treatment were implemented according to welding procedure specifications (WPS). In order to observe the mechanical properties and toughness of clad steel weld zone, post weld heat treatment was carried out according to ASME Sec. VIII Div.1 UW-40 procedure for post weld heat treatment. With heat treatment at $625^{\circ}C$, the hold time was used as the process variable, increased by intervals that were doubled each time, from 80 to 1,280 min. The structure of weld part was typical cast structure; localized primary austenite areas appeared near central vermicular ferrite and fusion line. The heat affected zone showed rough austenite structure created by the weld heat input. Due to annealing effects of heat treatment, the mechanical properties (tensile strength, hardness, impact value) of the heat affected area tended to decrease. From the results of this study, it is possible to conclude the integrity of clad steel welds is not affected much in field welding, repair welding, multi-layer welding, post weld heat treatment, etc.

• Journal of Power Electronics
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• v.16 no.1
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• pp.111-120
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• 2016

Generally, a single phase H-bridge converter feeding a single primary track is employed in conventional inductive power transfer systems. However, these systems may not be suitable for some high power applications due to the constraints of the semiconductor switches and the cost. To resolve this problem, a novel dual coupled primary tracks IPT system consisting of two high frequency resonant inverters feeding the tracks is presented in this paper. The primary tracks are wound around an E-shape ferrite core in parallel which enhances the magnetic flux around the tracks. The mutual inductance of the coupled tracks is utilized to achieve adjustable power sharing between the inverters by configuring the additional resonant capacitors. The total transfer power can be continuously regulated by altering the pulse width of the inverters' output voltage with the phase shift control approach. In addition, the system's efficiency and the control strategy are provided to analyze the characteristic of the proposed IPT system. An experimental setup with total power of 1.4kW is employed to verify the proposed system under power ratios of 1:1 and 1:2 with a transfer efficiency up to 88.7%. The results verify the performance of the proposed system.