Large-diameter hot induction bends are mainly made by hot induction bending of longitudinal-seam submerge arc welded (LSAW) steel pipes. The effects of the bending process on microstructure and properties of welding HAZ of hot induction bends are important factors to affect the quality of bends. In this paper, the Gleeble-3500 thermal simulator was adopted to study the effects of welding thermal cycle on the microstructure and mechanical properties of welding HAZ for hot bends. Furthermore, the influences of the hot bending process on the microstructure and mechanical properties of the HAZ were also analyzed. The results show that the strength of the welding HAZ decreases with the increase of the welding heat input; however, the strength is still far higher than the value specified in the technical specification. The welding HAZ strength increases along with both the heating temperature and the cooling rate adopted in bending; the impact toughness bears apparent relation to the variation in the heating temperature, the cooling rate and the tempering temperature.

hot induction bends, X80 steel, HAZ, heat treatment, microstructure.