Effect of beam oscillating behavior on pore inhibition and microstructure evolution mechanisms of laser welded Q235 steel

Abstract

To study the effect of beam oscillating behavior on pore inhibition and microstructure evolution, laser oscillating welding of Q235 steel was carried out. The pore formation, microstructure evolution and mechanical properties were investigated. The pore formation was inhibited at frequency lower than 75 Hz and radius larger than 0.75 mm. The weld microstructure was mainly composed of blocky martensite (MB), lath martensite (ML), and ferrite. Under given radius of 0.75 mm, the fraction of the ML first increases and then decreases with the frequency increasing. Under given frequency of 75 Hz, the fusion zone is almost composed of MB while the ML disappears with the radius increasing to 1.25 mm. The weld microstructure was well accordance with the mechanical properties. The larger the fraction of the MB, the higher the micro-hardness and the tensile strength. The oscillating parameters were optimized as radius of 0.75 mm and frequency of 50 Hz. In this case, the weld is mainly composed of ML free of pores, with the elongation rate 15.5% higher than that without beam oscillation. Finally, the pore formation and inhibition mechanisms were illustrated by the Reynolds model basing on the melt stirring theory, and the microstructure evolution was discussed basing on the solidification theory.

Keywords

• Laser oscillating welding
• Carbon steel
• Pore formation
• Microstructure
• Mechanical property