Microstructure and properties of laser-MIG hybrid welded X80 and X100 steel dissimilar joint

X80 and X100 pipeline steels were welded together by laser-MIG hybrid welding method. The effects of laser power on weld geometry, microstructures, hardness, tensile strength and impact toughness of the hybrid welded joints were investigated. Results show that, when laser power is elevated from 2.0 kW to 3.5 kW, both weld bead width and penetration of cap weld increase with a pronounced rise in laser zone penetration. Increasing acicular ferrite content and decreasing lath bainite content is obtained in the laser zone weld. The contents of lath bainite in coarse grained heat affected zone and fine grained heat affected zone of X100 steel side decrease. The contents of quasi-polygonal ferrite in coarse grained heat affected zone and fine grained heat affected zone of X80 steel side increase. Hardness distribution is asymmetrical with the maximum hardness occurs in the fusion zone. Tensile strength of the hybrid welded joints barely changes with varying laser powers, and all the tensile specimens fractured at base metal of X80 steel side. Maximum hardness and impact toughness of the hybrid welded joint decrease with increasing laser power.