Abstract: In the past few years,weld-metallurgists have paid a good of attention to inclusions and their role in the nucleation of acicular ferrite.In this research the nucleation of acicular ferrite in submerged arc weld metals has been observed by transmission electron microscopy (TEM).Inclusion phase composition and construction have been analyzed by X-ray microanalysis and electron diffraction.These analysis have shown that the inclusions in weld metals are not single phase but contain many different elements and compounds.Following phaseshave been indentified:α-MnS,TiO,Al₂O₃·MnO(Galaxite) and 3MnO·Al₂O₃·3Sio₂(Spessartite) and etc.It is concluded that inclusions nucleate acicularferrite by acting as inert substrates,so that energy barrier to nucleation isreduced.This mechanism successfuly explains multi-nucleation of ferrite grainswhich takes place at most inclusions.