The aim of this study is to determine the effect of depth of fusion on the behavior of tempered martensite and thermomechanically rolled steel welded joints. To obtain the effect of depth of fusion on the stress and displacements, three different welded sample welded to each other by metal active gas welding method applied in PB position were prepared in accordance with the related standard. According to the welding procedure specification EN ISO 15614-1 which clarifies how samples should be welded, different current, voltage, travel speed and wire feed speed were selected for each sample. After the welding process, welded samples were subjected to visual and magnetic testing to evaluate quality of the weld seams. After the non-destructive tests, samples were cut into small pieces to measure the depth of fusion and three samples having different depth of fusion were obtained. The finite element models of these samples were created in ANSYS to evaluate the stresses and displacements of samples. The models of samples were subjected to the loads which range from 1000N to 45000N and the results were obtained under lineer- static analysis. The results of finite element analyses of samples such as stresses and displacements are compared with each other in terms of depth of fusion for each sample. It is seen that depth of fusion has remarkable effect on the behavior of welded joints.