In this study effect of creep process on microstructure of carbon steel have been investigated. Shell of the electric arc furnace of Saba Steel Company has special conditions including hot zones which are regions near the electrodes and therefore, in comparison with other parts of the shell they are under higher stress and temperature than other parts of the shell. There are three regions of the shell, which have high temperature and these three regions experience more deformation. Structural changes of creep, including microstructural evolution, and the nucleation and growth of micro-cavities (or micro-fissures), may cause generation of cracks in the structure. Microstructural evolutionis toward reduction of free energy and includes spherodization, formation of alloy carbides and nucleation and growth of new ferritic grains. Formation of crack from micro-cavities is also based on the creep curve. In the second stage (of these curves), due to reduction of strength of segment, nucleation of cavities suddenly arises and this causes the segment to be destroyed. Accordingly optical and electronic microscopes, evaluation of mechanical properties using tensile testing, micro-hardness analysis and impact test were used to compare the effect of creep structure variation with the initial state. Observed structural changes include a continuous ferrite matrix with spherical shape carbides which performed measurements show that obtained structural change, reduces strength and hardness of the sample and since the structure is most flexible structure of steels, therefore, fracture energy is increased. Results of heat treatment presents improvement of mechanical properties and it is due to recovery of structure to initial state. Keywords : Failure Analysis, Electeric Arc Furnace, Evolution of Creep Microstructure, Hot Oxidation, Ferritic–Pearlitic Steel, Cementite Spheroidization.