Abstract
The microstructure and mechanical properties of 600 MPa grade high strength steel welds made by CO2 laser welding and CO2 laser-MAG hybrid welding have been investigated. The microstructures of weld metals and heat-affected zone (HAZ) were observed by optical microscope and scanning electron microscope (SEM). The distribution of alloying element in weld metal was identified by electron probe microanalysis (EPMA). Microstructure and chemical composition were different between the locations of the hybrid weld metal. There was more ferrite and bainite in the nail head part than nail part (bottom part) in the hybrid weld metal. Tensile tests of the laser welded joints and the hybrid welded joints were performed according to JIS-Z-2201 and JIS-Z-2202. The notch toughness of the weld metals were also measured using half-size Charpy V-notch impact test specinen. The hybrid weld metals showed higher toughness than the laser weld metal at the testing temperature range of -60°C to +15°C.
