Effect Of Tensile Pre-strain On Surface Morphology And Friction Behavior Of DP590 High Strength Steel Sheet

Advanced high strength steel sheet has become one of the main development directions of lightweight materials for automobiles because of its good impact energy absorption and comprehensive mechanical properties.It is widely used in the field of automobile parts forming and manufacturing.However,with the increase of the strength of advanced high strength steel sheet,its stamping formability becomes worse,and the contact area,especially the die fillet area,is born with large and uneven interface contact pressure,which results in the sheet / die contact state not only has regional differences,but also changes greatly with the punching stroke.Therefore,it is of great significance for us to understand the friction mechanism of stamping deformation with advanced high strength steel sheet and correctly grasp its deformation law to carry out the variation law of surface related properties of sheet metal under different deformation states.In this paper,a DP590 dual-phase high-strength steel sheet is used as the research object,using the uniaxial tensile quantitative pre-strain forming test,friction test and surface inspection technology to study the surface morphology evolution and mechanics of DP590 dual-phase high-strength steel sheet under different tensile pre-strain.The surface plastic roughening mechanism of advanced high-strength steel is systematically clarified.And the tension pre-strain,interface contact pressure,and the friction law and lubrication mechanism of advanced high-strength steel sheet with oil-lubricant are revealed.Finally,the main results are concluded as follows.(1)Tensile pre-strain has a significant effect on the mechanical properties of DP590 dual-phase high-strength steel sheet.The specific manifestation is that as the amount of pre-strain increases,the tensile strength,yield strength,and anisotropy index of the sheet increase,while the elastic modulus decreases.Under the same pre-strain condition,the mechanical properties of the sheet perpendicular to the rolling direction have the largest value,and the sheet with an angle of 45° has the smallest value.(2)Tensile pre-strain induces roughening behavior on the surface of DP590 dual-phase high-strength steel sheet.As the amount of pre-strain increases,the surface roughness parameters Ra and Rz increase,and Rsm decreases.The roughening mechanism of DP590 dual-phase high-strength steel sheet under tensile pre-strain is the unevenness of the surface grain group after slippage,which is manifested in the appearance of more mountains and valleys on the surface of the sheet.(3)Tensile pre-strain has a certain effect on the friction behavior of DP590 dual-phase high-strength steel plate.When the contact load is 100 N,under dry friction conditions,as the amount of pre-strain increases,the friction coefficient increases;under lubrication conditions,as the amount of pre-strain increases,the friction coefficient basically remains unchanged.(4)Under the condition of oil-lubricant with different viscosity,the tensile pre-strain has a great influence on the lubrication mechanism of the friction interface with DP590 dual-phase high-strength steel sheet.As the viscosity of oil-lubricant increases,the roughened surface caused by pre-strain shows a better lubricating effect.Compared with the non-pre-stretched deformed surface,the friction coefficient of the sheet surface after pre-straining under a certain contact load becomes smaller.