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.

Profiling inclusion characteristics in submerged arc welded metals of EH36 shipbuilding steel treated by CaF2–TiO2 fluxes

“…It has been documented that phase constituents of Ti-containing inclusions may shift as a function of Ti level in the WM and their relative proportions of the major elements could vary with the inclusions [24, 32]. It has also been confirmed that as the Ti content in the WM increases, more Ti-containing phases are expected to be generated with O being consumed, while fractions of phases containing other major alloying elements are reduced [6, 32-34].…”

“…Thus, these inclusions are formed in the “cold zone” of the weld pool, and their sizes are generally smaller than 1 μm [7]. The growth time of inclusions during solidification in the weld pool is controlled by the retention time, which, in turn, depends on the heat input in SAW process [8, 34]. Consequently, for any flux treated sample, the final size distribution of inclusions remains essentially unchanged due to the nearly identical time available for inclusion growth [19].…”

Investigations on microstructural and mechanical properties of BSK 46 steel weldments

“…56 Zhang et al 49 reported that acicular ferrite exhibiting different orientations with the surrounding microstructural phases results in high-angle grain boundaries. 57 High-angle grain boundaries resist crack propagation and promote impact toughness. 58,59 The impact toughness increases with the proportion of acicular ferrite.…”