Abstract: Effect of trace carbon (w(C)＜0.05%) in submerged-arc welding materials on the impact toughness of ultralow carbon hull steel deposited metal has been investigated. It was found that the impact toughness at low temperature was improved significantly with the increase of the content of carbon. The cause of the improvement in impact toughness lies on the inhibition to polygonal ferrite and side-plate ferrite of austenite grain, and the slight increase of the fraction of acicular ferrite.