Study On The Effect Of High Energy Peening On Plasma Titanium Infiltration Of ST12 Steel

ST12steel has been widely used in various fields as it has good formability, such as in automobile manufacturing, electrical products, locomotives, aviation, and precision instrument, etc. The mechanical properties limited application scope of ST12steel because low hardness and poor corrosion resistance. In actual use, the material failure usually occurs in the material surface, such as corrosion and wear. So we want to create a surface structure with have good mechanical properties and corrosion resistance by surface treatment, so as to reduce the production cost greatly.The metallic materials are often treated at high temperature for a long time to diffuse the alloying elements into them during the existing surface alloying process of the double glow plasma. This not only has an adverse effect on the microstructure and performance of the metallic materials, but also caused resource and energy wasting. To solve this problem, the surface nanocrystallization (SNC) technology and surface alloying were combined to realize the surface modification of ST12steel in this paper. There were many grain boundaries and defects in the surface nanocrystallinzed layer, which will provide a large number of diffusion channels. Therefore the atoms may diffuse more rapidly in the self-nanocrystallinzed structure than in the coarse structure, which lead the surface alloying of ST12steel at lower temperature in a short time. This paper mainly deals with the content of four aspects:Get nanocrystallinzed layer; Study the characteristics of nanocrystallinzed layer, plasma permeability titanium and the performance of titanized layer.Firstly nanocrystallinzed layers were prepared on the ST12steel samples by means of high energy shot peening (HESP) method, and the microstructure of the self-nanocrystallinzed layers was characterized through optical microscopy, SEM, XRD, AFM. On this basis, obtained titanized layer by double glow plasma permeability Ti on ST12steel surface; to study the influence of temperature and treatment time, and then sums up the reasonable process parameters of permeability Ti. The microhardness and corrosion resistance of titanized layer have been characterized and researched.Results showed that under0.4MPa press,100mm distance from shotting gun to the surface of samples, a nanocrystalline surface layer without oxidation, porosity and contamination was obtained by means of HESP to ST12steel after15min shot with average grain size of57.5nm and a microstrain of0.0586%. Summed up the HESP15min is the best processing time.Titanized processing on ST12steel by plasma method was performed under500℃for3h in a vacuum furnace. The sample surface is composed of titanium layer^middle zone and substrate, the titanium layer thickness of about10.0μm. The microstructure and corrosion properties of the nanocrystal layer and titanized layer were characterized through optical microscopy, SEM, XRD, microhardness tester and electrochemical measurement system. HESP greatly accelerated the diffusion of titanium, resulting in the formation of titanized layer on ST12steel at a relatively low temperature. The microhardness and corrosion resistance of ST12steel was improved after plasma permeability titanium.