An Investigation of Casting Defects Revealed in Forming Process of USD7 Steel

USD7 is one of the steel products of Isfahan Steel Company. It is cast in continuous casting moulds and rolled up to a rod of 5 mm diameter. Finally, it is wire drawn up to 3 mm and used as welding electrodes. This steel contains 0.05 to 0.09 wt. % carbon. The acceptable limit of the aluminium in this class of steel is less than 0.003 wt%. Therefore, it is categorized as rimmed steel. During forming process, there are some defects such as tearing and laminating that stop the forming process. The aim of this research is to evaluate the factors causing the aforementioned defects. It was found that there were many porosities in the cast ingot. The area around these porosities was analyzed with EDS method, and inclusions with MnO and (Fe, Mn)O chemical composition were observed. It was found that they were external inclusions (slag inclusions caused by reoxidation and entrapment phenomena). Because of the presence of these inclusions, these porosities are not welded together during rolling process. Therefore, in the next steps of the forming process, these defects are revealed.