Due to the increasing growth of nanomaterial science and abundant reported studies on Nano materials and the extensive use of nanomaterials in welding, this study investigates the composition and distribution of cerium nanomaterial in submerged welds, and for this purpose, welded samples with different thicknesses of cerium oxide nanoparticles were tested for investigating microstructure. In this part of experiments, optical microscopic images, scanning electron microscopic images and microstructure of weld metal were studied. The experiments were carried out at the Razi metallurgical research center. As a result, we found that the weld metal with a 0. 5 mm cerium oxide nanocoating had a finer grain structure than that of a weld metal without a nanocoating, and one of the reasons for the presence of oxides and inclusions, is to form the seeds of ferrite grain and needle ferrite.