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

Jang, Jin-Young; Choi, Woo-Nam; Jung, Byung-Hun; Kang, Chung-Yun

JWJ > Volume 27(2); 2009 > Article

Journal of KWJS 2009 April;27(2) :69-75.
Published online May 18, 2009.

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

Jin-Young Jang, Woo-Nam Choi, Byung-Hun Jung, Chung-Yun Kang

Correspondence: Published online May 18, 2009

ABSTRACT

The effects of welding speed were investigated on penetration characteristics, defects and mechanical properties including formability test in Nd:YAG laser welded 1000㎫ 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.

Keywords: Nd:YAG Laser welding;DP Steel;Welding speed;Hardness;Mechanical property