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Cu-Si 삽입금속을 이용한 DP강의 MIG 아크 브레이징 접합부의 미세조직과 기계적 성질
조욱제(Wook-Je Cho),윤태진(Tae-Jin Yoon),곽승윤(Sung-Yun Kwak),이재형(Jae-Hyeong Lee),강정윤(Chung-Yun Kang) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
In this study, Microstructure and tensile properties in arc brazed joints of 1000MPa grade DP steel using Cu-Si insert metal were investigated. The fusion zone was composed of Cu phase which solidified a little Fe and Si. The former phase formed due to dilute the edge of base material by arc, although Fe was not solid solution in Cu at the room temperature. Cu3Si particles formed by crystallization at 1100℃during faster cooling. After the tensile shear test, there are no differences between the brazed joint efficiencies. The maximum joint efficient was about 37% compared to strength of base metal. It is better than that of arc brazed joint of DP steel using Cu-Sn filler metal. Fracture position of all brazing conditions was in the fusion zone. Crack initiation occurred at three junction point which was a stress singularity point of upper sheet, lower sheet and the fusion zone. And then crack propagated across the fusion zone. The reason why the fracture occurred at fusion zone was that the hardness of fusion zone was lower than that of base material and heat affected zone. The correlation among maximum load and hardness of fusion zone and EST at fractured position was R²=0.9338. Therefore, this means that hardness and EST can have great impact on maximum load.
1000MPa급 DP강 MIG 아크 브레이징 접합부의 기계적 성질에 미치는 브레이징 전류의 영향
조욱제(Wook-Je Cho),윤태진(Tae-Jin Yoon),곽승윤(Sung-Yun Kwak),이재형(Jae-Hyeong Lee),강정윤(Chung-Yun Kang) 대한용접·접합학회 2017 대한용접·접합학회지 Vol.35 No.2
Mechanical properties and hardness distributions in arc brazed joints of Dual phase steel using Cu-Al insert metal were investigated. The maximum tensile shear load was 10.4kN at the highest brazing current. It was about 54% compared to tensile load of base metal. This joint efficiency is higher than that of joint of DP steel using Cu-based filler metals which are Cu-Si, Cu-Sn. Fracture positions can be divided into two types. Crack initiation commonly occurred at three point junction among upper sheet, lower sheet and the fusion zone. However crack propagations were different with increasing the brazing current. In case of the lower current, it instantaneously propagated along with the interface between fusion zone and upper base material. On the other hand, in case of higher current, a crack propagation occurred through fusion zone. When the brazing current is low (60, 70A), the interface shape is flat type. However the interface shape is rough type, when the brazing current is high (80A). It is thought that the interface shapes were the reason why the crack propagations were different with brazing current. The interface was the intermetallic compounds which consisted of (Fe,Al)0.85Cu0.15 IMC formed by crystallization at 1200℃during cooling. Therefore the maximum tensile shear load and the fracture behavior were determined by a interface shape and effective sheet thickness of the fracture position.