Abstract: The electrospark deposition technique was applied to deposit hard TiN coatings on 45 steel substrates with TA2 electrode and nitrogen gas as the reacting and shielding atmosphere.The forming mechanism, microstructures and interfacial behavior of the nitrided coatings were investigated by optical microscope, scanning electronic microscope and X-ray diffraction.And the microhardness profile of nitrided coating was measured as well.The results show that a good metallurgical bonding between the coating and the substrate is obtained.The nitrided deposition coatings are mainly composed of TiN and α-Fe phases.They are fully dense, uniform and comparatively continuous with 30 -40 μm thickness.The highest microhardness of the coating reaches to 1 515 HV which is five times more than that of the substrates.The surface performance of the substrate may be effectively improved.