Effect Of Pulse Current Parameters On Microstructure Of 304 Stainless Steel

In recent years,pulse current processing technology has been widely used in material development and improvement,and has become the focus of many researchers.However,pulse current technology has a long way to industrial applications.Researchers generally apply pulse currents in the solidified state.At present,the mechanism of applying pulse current treatment directly to the molten state of stainless steel is still unclear.The mechanism on the properties of metals in the molten state is also inconclusive.Moreover,there is still a lack of systematic and in-depth research on the influence of pulse current processing technology on the microstructure of materials,especially on the texture and inclusions of the material by pulse current.Therefore,in this experiment,304 stainless steel are used as this experimental material.The influence of the pulse current on the microstructure and inclusions of 304 stainless steel in the molten state was systematically studied by changing the frequency of the pulse current,the intensity of the pulse current and the time of pulse current.In this paper,metallographic analysis,scanning electron microscopy and backscattered electrons(SEM-EBSD),X-ray diffractometer,and microhardness test analysis are used to analyze the influencing factors of pulse current.Further improve and deepen people's understanding of the nature of pulse current processing,and promote the development of pulse current processing.(1)The effect of low frequency pulse current on grain size is not obvious.The microstructure is uniform and uniform under the action of high-frequency pulse current,and the crystal grain diameter is reduced and the number is increased.After the low-intensity pulse current,the microstructure is uniform and the crystal grain diameter is reduced and the number is increased.High-intensity pulse currents,as well as long-term pulse currents,can cause grain growth.(2)When a pulse current is applied,the pulse current flows along the path of the lowest resistance to maximize the system conductivity,resulting in a change in material orientation.Due to the different pulse currents given,the rate of movement of the atoms inside the material and the moving distance are different,resulting in a change in the orientation of the sample.(3)The application of the pulse current can refine the inclusions,increase the number of inclusions,and reduce the size.Due to the pulse current,the free energy of the molten steel containing inclusions is higher than that of the molten steel without inclusions.And as the continuous pulse current increases,the free energy difference is expanded.In order to minimize the system free energy,the inclusions are refined to reduce the free energy in the system.(4)The hardness of the sample to which the pulse current is applied is increased.On the one hand,according to the classical Hall-Petch effect,the smaller the crystal grains,the higher the hardness of the sample,and thus the hardness of the sample to which the pulse current is applied is increased.On the other hand,the pulse current increases the number of sample inclusions and reduces the size.The effect of dispersion strengthening on the sample also increases the hardness of the sample.