Role of non-metallic inclusions in formation of acicular ferrite in low alloy weld metals

Abstract

AbstractA critical investigation into the role of non-metallic inclusions in the nucleation of acicular ferrite in low alloy C–Mn–Ni weld metals was carried out using rapid in situ quenching, transmission electron microscopy, energy dispersive X-ray spectroscopy analysis, and dilatometric techniques. The relationship between the transformed acicular ferrite, the inclusions, and the chemical nature of the inclusions which had actually nucleated ferrite laths was examined in detail. By employing weld metals with either intermediate (200–350 ppm) or low (15–30 ppm) oxygen levels, the inclusion chemistry and nucleation behaviour of acicular ferrite in welds with different oxygen contents were compared. In addition, the influence of the [Al]/[O] ratio in lower oxygen content weld metals was also examined. It was found that the first acicular ferrite laths nucleated from the inclusions at both oxygen levels, and the chemical composition of the active inclusions varied considerably. The inclusions nucleated acic...