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Al-Si 도금된 보론강과 Zn 도금된 DP강 TWB 레이저 용접부내의 Al-편석부 미세조직에 미치는 핫스탬핑 열처리의 영향
정병훈 ( Byung Hun Jung ),공종판 ( Jong Pan Kong ),강정윤 ( Chung Yun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.6
Al-Si coated boron steel and Zn coated DP steel plates were laser-welded to manufacture a Tailor Welded Blank (TWB) for a car body frame. Hot-stamping heat treatment (900℃, 5 min) was applied to the TWB weld, and the microstructural change and transformation mechanism were investigated in the Al-rich area near the bond line of the Al-Si coated steel side. There was Al-rich area with a single phase, Fe3(Al,Si), which was transformed to α-Fe (Ferrite) after the heat treatment. It could be explained that the Fe3(Al,Si) phase was transformed to α-Fe during heat treatment at 900℃ for 5 min and the resultant α-Fe phase was not transformed by rapid cooling. Before the heat treatment, the microstructures around the Fe3(Al,Si) phase consisted of martensite, bainite and α-Fe while they were transformed to martensite and δ-Fe after the heat treatment. Due to the heat treatment, Al was diffused to the Fe3(Al,Si) and this resulted in an increase of Al content to 0.7 wt% around the Al-rich area. If the weld was held at 900℃ for 5 min it was transformed to a mixture of austenite (γ) and δ-Fe, and only γ was transformed to the martensite by water cooling while the δ-Fe was remained unchanged.
600MPa급 자동차용 석출경화형 고장력강판 Nd:YAG 레이저 용접부의 특성에 미치는 용접속도의 영향
한태교,정병훈,강정윤,Han, Tae-Kyo,Jung, Byung-Hun,Kang, Chung-Yun 한국레이저가공학회 2007 한국레이저가공학회지 Vol.10 No.3
The effect of welding speed on the weldability, microstructures, hardness, tensile property of Nd:YAG laser welding joint in 600MPa grade precipitation hardening high strength steel was investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5kW. Porosity in the joints occurred at 1.8m/min, but were not observed over the welding speed of 2.1m/min. However, spatter occurred over the welding speed of 6.6m/min. The hardness was the highest at heat affected zone(HAZ) near fusion zone(FZ), and was decreased on approaching to the base metal. The maximum hardness increased with increasing welding speed. The microstructure of FZ was composed of coarse grain boundary ferrite and bainite(upper) but the HAZ near the FZ contained bainite(Lower) and fine ferrite at a low welding speed. With increasing welding speed, ferrite at the FZ and the HAZ became finely and upper binite changed to lower bainite. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal, and the tensile strength and the yield strength of joints was equal to those of raw material. Elongation was found to be lower than that of the raw material.
1000MPa급 DP강의 Nd:YAG 레이저 용접부의 기계적 성질과 성형성에 미치는 용접 속도의 영향
장진영,최우남,정병훈,강정윤,Jang, Jin-Young,Choi, Woo-Nam,Jung, Byung-Hun,Kang, Chung-Yun 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.2
The effects of welding speed were investigated on penetration characteristics, defects and mechanical properties including formability test in Nd:YAG laser welded 1000MPa grade DP steels. A shielding gas was not used and bead-on-plate welding was performed with various welding speeds at 3.5kW laser power. Defects of surface and inner beads were not observed in all welding speeds. As the welding speed increased, the weld cross-section varied from the trapezoid having wider bottom bead, through X type, finally to V type in partial penetration range of welding speeds. The characteristic of hardness distribution was also investigated. The center of HAZ had maximum hardness, followed by a slight decrease of hardness as approaching to FZ. Significant softening occurred at the HAZ near BM. Regardless of the welding speed, the weld showed approximately the same hardness distribution. In the perpendicular tensile test with respect to the weld direction, all specimens were fractured at the softening zone. In the parallel tensile test to the weld direction, the first crack occurred at weld center and then propagated into the weld. Good formability over 80% was taken for all welding conditions.
600㎫급 자동차용 석출경화형 고장력강판 Nd:YAG 레이저 용접부의 특성에 미치는 용접속도의 영향
한태교(Tae-Kyo Han),정병훈(Byung-Hun Jung),강정윤(Chung-Yun Kang) 한국레이저가공학회 2007 한국레이저가공학회지 Vol.10 No.3
The effect of welding speed on the weldability, microstructures, hardness, tensile property of Nd:YAG laser welding joint in 600㎫ grade precipitation hardening high strength steel was investigated. A shielding gas was not used, and bead-on-plate welding was performed using various welding speeds at a power of 3.5㎾.<BR> Porosity in the joints occurred at 1.8m/min, but were not observed over the welding speed of 2.1m/min. However, spatter occurred over the welding speed of 6.6m/min. The hardness was the highest at heat affected zone(HAZ) near fusion zone(FZ), and was decreased on approaching to the base metal. The maximum hardness increased with increasing welding speed. The microstructure of FZ was composed of coarse grain boundary ferrite and bainite(upper) but the HAZ near the FZ contained bainite(Lower) and fine ferrite at a low welding speed. With increasing welding speed, ferrite at the FZ and the HAZ became finely and upper binite changed to lower bainite. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal, and the tensile strength and the yield strength of joints was equal to those of raw material. Elongation was found to be lower than that of the raw material.