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페라이트계 스테인리스강 / 용융아연도금강 이종 저항 점용접부의 특성
김정길,우인수,정보영,이종봉,Kim, Jeong-Kil,Woo, In-Su,Jeong, Bo-Young,Lee, Jong-Bong 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.6
A ferritic stainless steel, STS430, and a galvanized steel for case and frame of electronic goods are welded by resistance spot welding and resistance projection welding methods. In this study, resistance spot welding has been performed to investigate the weldability of dissimilar materials such as a ferritic stainless steel and a galvanized steel. Tensile load of the spot weld without heat treatment was 196 kN and brittle fracture occurred at interface between STS430 and nugget due to the high hardness, 380 Hv, in nugget. It was found that the hardness of as-welded nugget increased with higher cooling rate during resistance spot welding by comparing with GTA weld of same materials. Heat treatment by applying second current made nugget softened. Tensile load of heat treated weld increased and reached to 303 kN and fracture occurred at base metal, a galvanized steel.
확산접합기술을 이용한 H2 Station용 PCHE형 Compact 열교환기 개발
김정길(Jeong Kil Kim),심덕남(Deog Nam Shim),선칠령(Chil Yeong Seon),양기훈(Ki Hoon Yang),박해지(Hae Ji Park),김동진(Dong Jin Kim) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.5
Diffusion bonding was performed on STS316L plate with micro channels to understand the relationship between bonding conditions and mechanical properties of the joints. Various defects such as spot and line defects developed along the joints bonded at various bonding conditions. As the bonding temperature increased, these defects had a tendency to decrease. With experimental results, it was revealed that bonding temperature was the most critical for formation of defects along the joints. Additionally, the sound joint showed coalescence of grains along the joint by migration of the grain boundaries. Tensile test result showed that the sound joint had better mechanical properties than STS316L base metal, and that crack initiated at spot and line defects followed by fracture. Based on experimental results, PCHE was manufactured and it passed hydraulic test under 1200 bar.
HSC발전소 터빈용 초내열합금 Alloy 617 및 263 용접부의 미세조직에 미치는 후열처리의 영향
김정길(Jeong Kil Kim),심덕남(Deog Nam Shim),박혜지(Hae Ji Park) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.3
Recently nickel based superalloys are extensively being regarded as the materials for the steam turbine parts for hyper super critical (HSC) power plants working at the temperature over 700℃, since the materials have excellent strength and corrosion resistance in high temperature. In this paper, alloy 617 of solution strengthened material and alloy 263 of γ-precipitation strengthened material were prepared as the testing materials for HSC plants each other. Post weld heat treatment (PWHT) was conducted with the gas tungsten arc (GTA) welded specimens. The microstructure of the base metals and weld metals were investigated with Electron Probe Micro-Analysis (EPMA) and Scanning Transmission Electron Microscope (STEM). The experimental results revealed that Ti-Mo carbides were formed in both of the base metals and segregation of Co and Mo in both of the weld metals before PWHT and PWHT leaded to precipitation of various carbides such as Mo carbides in the specimens. Furthermore, fine γparticles, that were not precipitated in the specimens before PWHT, were observed in base metal as well as in the weld metal of alloy 263 after PWHT.
김정길(Jeong Kil Kim),박해지(Hae Ji Park),심덕남(Deog Nam Shim) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.3
Transient liquid phase (TLP) bonding is essential technology to repair micro-cracking on the airfoil of blades and vanes for gas turbines. Understanding of the characteristics of TLP bonding of the superalloys is necessary in the application of the technology for repairing these components. In this study, the focus was on investigating TLP bonding characteristics of γ′ precipitation strengthened Ni based superalloy. TLP bonding was carried out with an amorphous filler metal in various bonding conditions, and the microstructural characterization wasinvestigated through optical microscopy (OM) and electron probe micro-analysis (EPMA). The experimantal results explained clearly that bonding temperatures had critical effects on the TLP bonding behaviors, and that isothermal solidication of the joints made at higher temperatures than 1170 ℃ was controlled by Ti diffusion instead of B.
김정길(Jeong Kil Kim),남철우(Chul Woo Nam),김석중(Seok Joong Kim),송판섭(Pan Seob Song),한광래(Kwang Lae Han),최도성(Do Sung Choi),문두석(Doo Seok Moon) 한국초등과학교육학회 2001 초등과학교육 Vol.20 No.1
The purpose of this study is to guide and apply gettable and accessible materials around everyday life into classroom instruction, and to find out their effects on student academic achievement. In order to achieve it, this study was tried to develop and guide available materials around life in learning activities, to provide a preliminary assignment that could apply the available materials, and to compare its academic achievement to one from field trip learning. For the hypothesis testing, first, the experimental and comparing classes were selected based on the results of basic learning diagnostic evaluation, which conducted by the researcher being served as a full-time science teacher of the third and sixth grade of K elementary school in Kwangju for 2 years. Secondly, the instructional use of the available materials around life was applied to the experimental class. Also, the instructional use of the existing materials was applied to the comparing class. Finally, for the testing of the effects on academic achievement, the posterio test was implemented after conducting the experimental instruction in knowledge·understanding, inquiry process, and attitude domains classified by the unit characteristics. Using SPSS/WIN program the t-test was performed in order to compare the differences between the two groups. Major findings were as follows: 1) In the achievement test of knowledge·understanding domain, there were no significant differences at the 5% level between the experimental and comparing classes. It could be difficult to say, therefore, that the instructional use of the available materials around life was more effective than the instructional use of the existing materials. However, it had some effects on differences between the third grade final achievement test and sixth grade experimental class. 2) In the achievement test of inquiry process domain, there were some significant differences in that the sixth grade experimental class was higher than the third grade out-of classroom experience unit. It was indicated that the instructional use of the available materials around life had some effects on improving the students` inquiry ability. 3) In achievement test of attitude domain, there were some significant differences. It was shown that the self-evaluation test of the sixth grade experimental class unit was higher than that of the third grade out-of classroom experience unit; Especially, the learning activities in the experimental class were more active, and the experimental practice ability was improved. It was presented that the instructional use of the available materials around life had some effects on the students` academic achievement in attitude domain. It was concluded from this study that the instructional use of the available materials around life was less effective on knowledge·understanding domain, but was effective on improving their scientific inquiry ability and interest on science education.