Effect Of Electropulsing On Tensile Properties And Microstructures Of 316L Stainless Steel

Pulsed current can change the mechanical properties of metallic materials,usually manifested as reduced flow stress and increased elongation.This phenomenon is called the electroplastic effect.However,at present,the mechanism of the effect of current on the materials' performance is still full of controversy.Changes in the type of materials and electrical parameters will change the deformation behavior of the material,which affects the application and promotion of electrically-assisted processing technology.The study of the internal mechanism is inseparable from the microscopic characterization of materials.Due to the wide application of 316 L stainless steel,the research results on it are rich,and the dislocation structure is easy to observe.Therefore,this article selects 316 L stainless steel as the research object,and uses an electric auxiliary device to carry out the tensile tests,and discusses the mechanism of the pulse current.Before the experiments,the samples were solution treated in order to obtain a uniform and sparse dislocation structure.After the heat treatment,the tensile tests with and without application of electricity were carried out respectively.The changes of mechanical properties of 316 L stainless steel with different current parameters and strain rates were studied.The results showed that the pulse current had a significant effect on the ultimate strength and the strain-to-failure of 316 L stainless steel.The greater the voltage and frequency,the more obvious the decrease in ultimate strength and strain-tofailure.The results were different from the electroplastic effect.At the same time,as the voltage and frequency increase,the strain hardening exponent showed a downward trend,indicating that the uniform deformation ability of the material decreases.In both cases of without and with the application of current,the effect of strain rate on the ultimate strength and the strain-to-failure of 316 L stainless steel was very small.At the same time,in both cases,the strain hardening exponent increased first and then decreased as the strain rate increased.When the strain rate was 10-3 s-1,the strain hardening exponent was the largest.After the tensile experiment,the fracture surface observation,metallographic observation and dislocation characterization of the samples were performed respectively.Using scanning electron microscopy,it was found that under the action of pulse current,the surface of the fracture became more undulating,the number of dimples decreased,and a smooth shear surface appeared.The fracture mode changed from ductile fracture to quasi-cleavage fracture.Through metallographic observation,it was found that the grain underwent severe deformation.When the fixed voltage is 30 V and the frequency is above 600 Hz,dynamic recrystallization occurs.When the fixed frequency is 200 Hz,no dynamic recrystallization is found at elevated voltage.Through the observation of transmission electron microscope,it was found that the dislocation density and twinning density of the material gradually increased with the increase of voltage,and thus showed a different rule from that at high temperature.The effect of pulse current promotes the evolution of dislocations.