Nucleation Behavior of Acicular Ferrite in 1 GPa Class High Strength Steel Weld Metal

In this study, the nucleation behavior of acicular ferrite in 1 GPa class high strength steel weld metal was investigated. A 1 GPa class as-deposited weld metal specimen was prepared by single-pass welding using a prototype flux-cored wire, and a reheated weld metal specimen was obtained using Gleeble simulation technique. The typical inclusion in both specimens was composed of MnTi2O4 and amorphous. It was found that the inclusion potency for acicular ferrite nucleation was maximized in the as-deposited weld metal because of both the formation of Mn-depleted zone (MDZ) near the MnTi2O4 and the low interfacial energy between the MnTi2O4 and ferrite. In the reheated weld metal specimen, it was observed that the inclusion potency decreased possibly due to the homogenization of Mn in the MDZ that occurred during reheating thermal cycling. Key words: High strength steel, Weld metal, Acicular ferrite, Nucleation