Study On Damage Characteristics Of Metal Under Long Continuing Current

Metallic material is an indispensable material for industrial production,and the ablation damage of metal is mainly caused by the long continuing current after the return stroke in lightning components.The existing studies mostly focus on the simulated lightning current test with high-amplitude,and the study on the lightning current component of long continuing current after the return stroke,which can cause obvious electro-thermal damage to the metal,is still insufficient.Due to the strong light effect caused by the lightning striking,studies on experiments mostly use high-precision infrared thermometer to measure the temperature rise of the backside of the lightning metal plate,leading to the lack of the metal temperature rise data near the lightning striking point.Therefore,the study on the temperature rise characteristics of the lightning current metal also stays in the qualitative analysis stage.The existing studies pay more attention to the macro damage characteristics of the metal and lack the microscopic analysis of the damage characteristics.Therefore,it is difficult to conduct a deeper analysis of the damage characteristics of the metal under the simulated lightning current.In this paper,firstly,according to SAE and IEC standards,the definition of four simulated lightning current components in laboratory is defined,and the current parameters of the experiment in this paper are confirmed.Secondly,the test scheme and measurement method under long continuing current are determined through the experiment method,and the experiment of steel Q235 under long continuing current is carried out accordingly.Thirdly,based on the control volume finite element method and the finite difference method,a numerical model of the temperature rise of metal plate and the node temperature control equations of each classification node group are established,which are suitable for the analysis of temperature rise characteristics of metal plate under long continuing current after the return stroke.The temperature rise distribution of steel Q235 plate at different time under long continuing current is calculated.The damage characteristic of steel Q235 is analyzed according to the temperature distribution chart.The rationality of the model and numerical calculation method is further verified based on the metal damage test results under simulated lightning current.Finally,the microstructure analysis of steel Q235 under long continuing current is performed by using the method of metallographic analysis.The results show that under the long continuing current,the microstructure of the cross section of the sample show obvious stratification,which are the oxide layer,the damage zone mainly composed of Martensite,the transition zone mainly composed of the mixed microstructure of Martensite and Ferrite,the matrix composed of the mixed microstructure of Ferrite and Pearlite.The micro-hardness value of the damage zone increases 150% relative to the matrix.Under the action of electric stress,cracks germinate on the edge of the ablation zone,around the pores in the damaged zone of the sample and in the uneven distribution of the elements.The numerical calculation model is verified according to the relationship between the change of the microstructure and the temperature.