The self-made metal cored wires with Fe-Si-Mn-Ti-B microalloyed series were adopted to directly form a part by gas metal arc welding (GMAW) surfacing rapid prototyping technology. The microstructure and microhardness of the part are both investigated. Its continuous metallographic microstructure along and vertical to the deposition direction shows layered characteristic, due to the special thermal cycles and cooling conditions. The microhardness values of intermediate sections of the part are much higher and stabler than those of surface sections. It is necessary to deposit a wear-resistant metal layer for enhancing the surface abradability. Among the microstructures of the part, the average nanohardness of acicular ferrite is 1.28 times than that of massive ferrite, but their Young’s modulus values are almost equivalent, which indicates acicular ferrite possesses excellent mechanical property. Therefore, achieving acicular ferrite microstructures is an appropriate means to enhance the combination property of the formed parts.