Formation of Mn-depleted zone in Ti-containing weld metals

Characteristics of non-metallic inclusions are studied using three shielded metal arc (SMA) weld metals which differ greatly in Ti content and are correlated with the acicular ferrite contents measured in the as-deposited weld microstructure. Correlation is found between the inclusion phases present and the amount of acicular ferrite formed in each weld. In the 5 ppm Ti weld, the weld microstructure is extremely low in acicular ferrite content and this microstructure can be correlated with the amorphous Mn-silicate phase that formed abundantly in the inclusions of this weld. At 410 and 580 ppm Ti, the weld microstructure contains very high amount of acicular ferrite, and this microstructure can be explained by the presence of a Mn-depleted zone (MDZ), likely formed associating with the formation of inclusions dominant with Ti2O3 and MnTiO3. The possible mechanisms for MDZ formation are discussed.