Abstract: Bead welding process was conducted by shielded metal arc welding process on 45 steel substrate using electrode D172.When single layer metal was deposited on the substrate,the thickness of deposited metals is about 3 mm,and the 3rd deposited metal was put on the pre-deposited metals,the total thickness of deposited metals is about 8 mm.The microstructure was observed,and the hardness and ES analysis were made.The microstructure and hardness of heat-affected zone and transition zone in different weld conditions,and migration of carbon in the vicinity of fusion area were analyzed.The results show that the higher the heat input,the less the austenite and the more the ferrite in fusion area,the smaller the pearlite and ferrite of base material in the vicinity of fusion area,the coarser the martensite and the lower the hardness value of deposited metals in the vicinity of fusion area.If the three layer metals were deposited on the substrate,the carbides of deposited metals in the vicinity of fusion area were precipitated and gathered,and relatively coarse martensite was formed.