Quantitative Evaluation of Nucleation Potency of Ti-containing Inclusions for Acicular Ferrite

Abstract

The nucleation potency of different types of inclusions for acicular ferrite (AF) plates was quantitatively evaluated for Ti-containing welds. The objective of this investigation was to determine the relative efficiency of AF nucleation among the inclusions and to understand the effect of nucleation potency on the AF content. A series of bead-in-groove welds having Ti concentrations in the range of 0.002 to 0.091 wt.% were used in this study. The nucleation event of the inclusions was examined using scanning electron microscopy for a large number of inclusions of various sizes. Then, the nucleation probability curves were constructed as a function of inclusion size for each weld. The experimental results demonstrated that the nucleation probability increased with the inclusion size for all welds. However, this size effect varied with the Ti content of the welds substantially. By employing two different parameters to represent the difference of nucleation potency in a quantitative manner, it was found that the Ti effect on AF content resulted from the corresponding change in nucleation potency.