Acicular ferrite nucleation mechanism in laser-MAG hybrid welds of X100 pipeline steel

Abstract Acicular ferrite nucleation mechanism in laser-MAG hybrid welding of X100 pipeline steel is studied in this paper. The experimental results show that the inclusions are mainly composed of Ti2O3 and Al2O3 in the weld, which induce the nucleation of acicular ferrite. There is Mn-depleted zone (MDZ) near the inclusions. Therefore, MDZ mechanism is responsible for the acicular ferrite nucleation in the laser-MAG hybrid weld of X100 pipeline steel. In addition, inclusions should contain a high mole fraction of Ti2O3 in order to form MDZ and consequentially induce acicular ferrite nucleation.