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발전용 저탄소 ASTM A356 CA6NM 마르텐사이트계 스테인리스 주강의 용접성
방국수 ( Kook Soo Bang ),박찬 ( Chan Park ),이주영 ( Jong Young Lee ),이경운 ( Kyong Woon Lee ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
Weldability, especially HAZ cold cracking, weld metal solidification cracking, and HAZ liquation cracking susceptibilities, of ASTM A356 CA6NM martensitic stainless steel casting was investigated and compared with that of 9-12% Cr ferritic steel castings. Irrespective of the Cr and Ni content in the castings, the HAZ maximum hardness increased with an increase of carbon content. CA6NM steel, which has the lowest carbon content, had the lowest HAZ hardness and showed no cold cracking in y-slit cracking tests. CA6NM steel, meanwhile, showed the largest weld metal solidification cracking susceptibility in varestraint tests because of its higher amount of impurity elements, phosphorus, and sulfur. All castings investigated had good high temperature ductility in hot ductility tests and showed little difference in liquation cracking susceptibility.
셀프실드아크 용접금속의 확산성수소량에 미치는 용접변수의 영향
방국수(Kook-Soo Bang),박찬(Chan Park) 한국해양공학회 2013 韓國海洋工學會誌 Vol.27 No.5
The effects of the welding parameters, contact tip-to-workpiece distance (CIWD), current, and voltage on the diffusibel hydrogen content in weld metal deposited by self-shielded flux, cored are welding were investigated and rationalized by comparing the amount of heat generated in the extension length of the wire. This showed that as CTWD increased from 15mm to 25mm, the amount of heat generated was increased from 71.7J to 174.8J, and the hydrogen content was decreased from 11.3mL/100g to 5.9mL/100 g. Even if little difference was observed in the amount of heat generated, the hydrogen content was increased with an increase in voltage because of the longer arc length. A regression analysis showed that the regression coefficient of voltage in self-shielded flux cored arc welding is greater than that in CO₂ arc welding. This implies that voltage control is more important in self-shielded flux cored arc welding than in CO₂ arc welding.
다층용접한 저합금 용접금속의 강도와 인성에 미치는 입열량 및 예열/패스간 온도의 영향
방국수(Kook-soo Bang),정호신(Ho-shin Jung),박찬(Chan Park) 한국해양공학회 2015 韓國海洋工學會誌 Vol.29 No.6
The effects of the heat input and preheat/interpass temperatures on the tensile strength and impact toughness of multipass welded weld metal were investigated and interpreted in terms of the recovery of the alloying elements and microstructure. Increases in both the heat input and preheat/interpass temperatures decreased the tensile strength of the weld metal. A lower recovery of alloying elements, especially Mn and Si, and smaller area fraction of acicular ferrite in the weld metal were observed in higher heat input welding, resulting in a lower tensile strength. In contrast, only a microstructure difference was observed at a higher preheat/interpass temperature. The impact toughness of the weld metal gradually increased with an increase in the heat input because of the lower tensile strength. However, it decreased again when the heat input was larger than 45 kJ/cm because of the much smaller area fraction of acicular ferrite. No effect of the preheat/interpass temperature on the impact toughness was observed. The formation of a weld metal heat-affect zone showed little effect on the impact toughness of the weld metal in this experiment.
셀프실드용접 와이어의 Al 첨가량에 따른 용접금속 인성 및 기공형성 변화
방국수,박찬,길웅,장웅성,Bang, Kook-Soo,Park, Chan,Woong, Kil,Chang, Woong-Seong 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.1
Three different welding wires were used to study the effects of Al content on weld metal toughness and porosity formation in self-shielded arc welding. Weld metal microstructure showed that while wire with 1.3% Al content contains coarse $\delta$-ferrite, wires with less than 0.5% Al content showed no such phase. In addition to the microstructural differences, cleanliness in weld metal was also different among wires. It showed that weld metal toughness was influenced by the $\delta$-ferrite formation, cleanliness and Ni addition. Even though wires with less than 0.5% Al content showed higher weld metal toughness, they showed relatively poor workability, forming porosities in weld bead in lower arc voltages.
FCAW에서 용접변수에 따른 용접금속 강도 및 와이어 합금원소의 회수율 변화
정동희,방국수,박찬,장웅성,박철규,Jung, Dong-Hee,Bang, Kook-Soo,Park, Chan,Chang, Woong-Sung,Park, Chul-Gyu 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.2
590MPa grade weldable steels were gas metal arc welded with flux cored wires. Welding parameters such as current, voltage, and speed were varied independently. Effects of each parameter on the strength and chemical composition of weld metal were investigated. Increase of voltage caused decrease of weld metal tensile strength due to the low recovery of alloying elements such as carbon and manganese. On the contrary, increase of current and speed resulted in increase of weld metal strength because of higher recovery of the alloying elements.
회주철의 마찰용접 특성에 관한 연구 - 입열량 이론식을 중심으로 -
정호신,방국수,Jeong, Ho-Shin,Bang, Kook-Soo 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.3
Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).
FCAW에서 용접금속 확산성수소량에 미치는 용접변수 영향의 정량적 해석
한동우,방국수,정홍철,이종봉,Han, Dong-Woo,Bang, Kook-Soo,Jeong, Hong-Chul,Lee, Jong-Bong 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.2
The effects of welding parameters such as contact tip-to-work distance (CTWD), voltage, and current on the weld metal diffusible hydrogen contents (HD) were investigated and rationalized by the calculation of heating time and amount of heat generated in the extension length of flux cored wire. As CTWD increased from 15 to 25mm, HD decreased from 8.46 to 5.45mL/100g deposited metal. Calculations showed that, with an increase of CTWD, the amount of heat generated increased from 46 to 92J in addition to an increase of heating time. Increase of current from 250 to 320A, however, gave little variation of HD. It showed that no significant change in the amount of heat generated was found, and heating time was decreased with an increase of current. It also showed that CTWD is more influential than voltage in relatively lower heat input ranges, while voltage is more in higher input ranges
570MPa급 용접구조용강 다층 용접금속의 강도 및 충격인성에 미치는 입열 및 패스간 온도의 영향
변지철,방국수,장웅성,박철규,정우현,Byun, Ji-Chul,Bang, Kook-Soo,Chang, Woong-Sung,Park, Chul-Gyu,Chung, Woo-Hyun 대한용접접합학회 2006 대한용접·접합학회지 Vol.24 No.1
570MPa grade weldable steels were gas metal arc welded with various heat inputs and interpass temperatures using flux cored wires. Effects of heat input and interpass temperature on the strength and impact toughness of weld metal were investigated in terms of microstructural change, recovery of alloying elements, and the amount of reheated weld metal. Increase of heat input and interpass temperature resulted in decrease of weld metal strength. This is because of the small amount of acicular ferrite, large columnar size and low recovery of alloying elements such as manganese and silicon. In addition to the microstructural change, weld metal toughness was also influenced by the deposition sequence. It increased with an increase of the amount of reheated weld metal.
AZ61 필러 와이어를 첨가한 AZ31B-H24 마그네슘 합금의 레이저 용접
류충선,방국수,이목영,장웅성,Ryu, Chung-Sun,Bang, Kook-Soo,Lee, Mok-Young,Chang, Woong-Sung 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.6
Laser welding with AZ61 filler wire was carried out to improve formability though reduction of porosity and formation of under fill bead. Optimum welding condition and mechanical properties of butt joint for $400{\times}500{\times}1.3mm$ magnesium sheets were studied. Optimal welding conditions of laser power, welding speed, and defocusing length are 1000W, 3m/min, and 2mm, respectively. Results of tensile test indicated that both tensile strength and elongation of specimens welded with filler wire were improved at room temperature because of reduction of porosity and under-filled bead formation in addition to the precipitation hardening and microstructure refinement by Al-Mn and Mg-Al-Zn precipitates. At elevated temperature of $200{\sim}350^{\circ}C$, fracture location of tensile specimen was shifted from weld metal to base metal, indicating less softening of weld metal than base metal.
에어로졸 증착법에 의한 압전 PZT 후막의 전기적 특성
김기훈,방국수,박동수,박찬,Kim, Ki-Hoon,Bang, Kook-Soo,Park, Dong-Soo,Park, Chan 한국결정성장학회 2015 韓國結晶成長學會誌 Vol.25 No.6
에어로졸 증착법에 의해 실리콘 기판위에 $10{\sim}20{\mu}m$의 두께를 가진 PZT 후막을 제조한 후 $700^{\circ}C$에서 어닐링처리하였다. PZT 분말에 의해 제조된 막은 임피던스 분석기(impedance analyzer)와 쇼여-타워 서킷(Sawyer-Tower circuit)으로 분석하였다. PZT 분말은 통상적인 고상반응법 및 솔-젤 법으로 준비되었다. 고상반응법으로 만들어진 분말을 사용한 $10{\mu}m$ 두께 PZT 막의 잔류분극, 항전계 및 유전상수는 각각 $20{\mu}C/cm^2$, 30 kV/cm 그리고 1320이었다. 한편 솔-젤 법으로 제조된 분말을 사용한 경우의 유전상수는 635로 비교적 낮은 값을 나타낸다. 이는 어닐링시 생기는 발생하는 유기물에 의한 기공의 존재 때문이다. Lead zirconate titanate (PZT) thick films with thickness of $10{\sim}20{\mu}m$ were fabricated on silicon substrate by aerosol deposition method. As-deposited films on silicon were annealed at the temperatures of $700^{\circ}C$. The electrical properties of films deposited by PZT powders were characterized using impedance analyzer and Sawyer-Tower circuit. The PZT powder was prepared by both conventional solid reaction process and sol-gel process. The remanent polarization, coercive field, and dielectric constant of the $10{\mu}m$ thick film with solid reaction process were $20{\mu}C/cm^2$, 30 kV/cm and 1320, respectively. On the other hand, the PZT films by sol-gel process showed a poor dielectric constant of 635. The reason was probably due to the presence of pores produced from organic residue during annealing.