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1 Journal of Achievements in Materials and Manufacturing Engineering

1 2010

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A study on the CO2 laser welding characteristics of high strength steel up to 1500 MPa for automotive application

Kim C.-H., Choi J.-K., Kang M.-J., Park Y.-D.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 39, nr 1

79-86

Purpose: This paper presents the mechanical and metallurgical characteristics of laser weldments for automotive steels with high strength ranging from 370 MPa to 1500 MPa. Design/methodology/approach: Butt joint welding was conducted on high strength steel sheets by using a CO2 laser with 6 kW output power. For sound welds with full penetration, the proper welding conditions were chosen and the cross-sectional bead shape, tensile strength, hardness profile and micro-structure were evaluated for each case. Findings: Laser welding is known to be a low heat input process because of its high heat density and welding speed. But for laser welding of ultra high strength steel with strength over 780 MPa, micro-structural softening was observed in the HAZ (heat affected zone), resulting from dissolved martensite. Practical implications: The tensile strength reduction in laser welding of ultra high strength steed should be considered in the design of car body structures. The HAZ softening that occurs in butt joint welding can reduce the tensile shear strength for overlap joint welds, which are predominantly mostly used in the BIW (body-in-white) structure. Originality/value: This paper quantitatively demonstrates the occurrence of HAZ softening and a tensile strength reduction in laser welding of automotive steel with 780 MPa strength and more.