Microstructure and mechanical properties of a thick-section high-strength steel welded joint by novel double-sided hybrid fibre laser-arc welding

In this paper, a novel double-sided hybrid fibre laser-arc welding procedure was developed to join 30 mm thick, high-strength steel, and this procedure was compared with conventional double-sided arc welding. The welded joint was divided into two zones, the laser zone and the arc zone, and the microstructure and mechanical properties of the welded joint in these zones were investigated in detail. The results indicated that the laser zone and arc zone predominately consisted of lath martensite with a high dislocation density. The average grain sizes of the laser zone and the arc zone were smaller than that of the base metal. The results also indicated that the laser zone and the arc zone possessed higher strength when compared with the base metal because of the fine lath martensite. Meanwhile, the strength observed in the laser zone was slightly higher than that of the arc zone due to the small average effective grain size. On the contrary, the toughness of the base metal was higher than the toughness in the laser zone and the arc zone because of massive polygonal ferrites. Meanwhile, a significant increase in the toughness of the laser zone when compared with the arc zone occurred due to an increase in the prevalence of grain boundaries with large misorientation angles.