Microstructures and properties of fiber laser-MIG hybrid welded joints for marine corrosion resistant steel DH36

The marine corrosion resistant steel DH36 plates of 12 mm thickness were welded by using fiber laser-MIG hybrid welding process. The effects of wire feeding speeds on the cross section shapes, microstructures, mechanical properties and corrosion resistance of the joints were studied. The results show that with the wire feeding speed increasing from 7.0 m/min to 8.5 m/min, the weld width of arc zone rises from 8.44 mm to 10.03 mm while the weld width of laser zone increases from 1.63 mm to 2.09 mm. The wire feeding speeds have no obvious influence on the phase types of weld microstructures, which consists predominantly of acicular ferrite (AF), pro-eutectoid ferrite (GBF) and a small amount of bainite (B). As the wire feeding speed increases, the morphology and amount of AF were changed. The microstructure of the HAZ of the joint was composed of ferrite (F), pearlite (P) and a small amount of bainite (B). In addition, the increase of wire feeding speeds has little effect on the joint strength, but has an significant effect on the elongation of the joints. Increasing the wire feeding speed reduces the elongation of the joints, and when the wire feeding speed is 7.0 m/min, the elongation is up to 16.5%. The polarization curves of the joints showed that the corrosion tendency was the lowest when the wire feed speed was 7.5 m/min and the corrosion tendency was the highest when the wire feed speed was 7.0 m/min.