Microstructure and mechanical properties of laser beam welded 10 mm-thick Q345 steel joints

Abstract

The present study systematically investigated the effects of a laser welding speed and a defocusing amount on the microstructure and mechanical properties of low alloy high strength Q345 steel joints. The macro-morphology, microstructure, Vickers microhardness, and tensile properties of as-welded joints were analyzed. The results indicated a significant correlation between the laser welding speed and the size of individual zones within the welded joint. As the laser welding speed increased, the size of each zone decreased noticeably. The microstructure of the fusion zone was composed of proeutectoid ferrite, ferrite side-plate, and acicular ferrite. An increase in welding speed and defocusing amount facilitated microstructural changes towards formation of ferrite side-plate and acicular ferrite. Maximum tensile strength and maximum elongation of as welded joints were measured to be 669 MPa and 21.8%, respectively. The joints with maximum tensile strength tended to fracture within the fusion zone. The increase in welding speed and defocusing amount caused a significant decrease in normalized enthalpy and volumetric energy density.

Keywords:

• Q345 steel
• laser welding speed
• defocusing amount
• microstructure
• mechanical properties

Acknowledgements

The authors acknowledge funding from the Natural Science Foundation of Jilin Province (No. 20220101250JC), China.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.