Research on Inclusions in Low Alloy Steel Welds with Nano Alumina Addition

The proper control of oxides, sulfides and other inclusions to become favorable substance is an effective way to refine microstructure and improve mechanical properties. An attempt was made to exploit the traits of Al containing oxides. In order to avoid accurate controlling process of parameter and chemical composite, nano oxide alloying technology were proposed. After the pre-scattered treating process of nano oxides, double-coated electrodes were prepared to study inclusions in low alloy steel weld metal with the addition of nano Al₂O₃. The experimental results showed that Al₂O₃ can well transfer from electrode into molten pool and distribute uniformly without significant aggregation. Moreover, the composite inclusion containing elements, such as Al, Mn, Si, O, S formed in weld metal because the added nano oxides accelerated the precipitation of other oxides and sulfides, which resulted in the cleanness of weld metal. Compare to weld metal without Al₂O₃ addition, the sulfur content decreased by 25%. The complex inclusion in weld metal were mainly spherical and with the size of 0.2∼0.8 μm, which can effectively promoted the formation of acicular ferrite.