Effect of Welding Speed on Mechanical Properties and Formability in Nd:YAG Laser Welds of 1000MPa Grade DP Steel

Abstract

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 3.5㎾ 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.

Laser Welding Characteristics of 1.5GPa Grade Hot Stamping Steel for Automobiles

“…한편 레이저 용접은 타 용접법에 비해 용접속도가 빠 르고 입열량이 작아 열변형이 작은 이점이 있고, 비드 외관이 미려할 뿐만 아니라 정밀성, 안정성이 높다. 이 런 특성으로 인해 일본, 독일, 미국 등 자동차 생산기 술의 선진국들은 이미 많은 부분에 레이저용접기술을 도입, 응용하고 있으며 국내에서도 기존 저항 점용접을 대체하기 위한 차세대 생산기술로서 각광받고 있다[4][5][6][7][8] .Nd:YAG 레이저 용접 등에 관한 많은 연구가 진행되 었다[9][10][11][12][13] . 반면 핫스템핑강의 도입은 최근에야 이뤄짐에 따라 관련 레이저 용접기술은 아직까지는 국내에 관 련 연구결과를 거의 찾아볼 수 없다.…”