Study On The Hot Stamping Process Of High Strength Steel And The Crashworthiness Of Anti-collision Beam With Tailored Properties

Safety,energy saving,environmental protection and comfort is the general trend of the development of the automotive industry,Automotive lightweight technology is the most important means to achieve these goals.One of the most effective measures to realize the lightweight goal is to design and manufacture with tailored properties parts,different regions have different strength components can meet the goal of energy saving and environmental protection,and meet the safety standards.Nowadays the steel with tailored properties has a wide application in the automotive industry.Traditional furnace heating has the disadvantages of low heating speed and high energy consumption,Because the temperature field in the furnace is uniform,the temperature distribution of the sheet is uniform,which is not conducive to the production of tailored properties parts.Self-resistance heating technology relies on the resistance of the sheet itself to convert electric energy into heat energy,this method has the advantages of high heating rate and high energy utilization rate.With the development of the selfresistance heating technology,this heating method is becoming more and more popular.The main content of this paper is to study the effect of process parameters on the properties of 22MnB5 steel in the process of heating and tempering.Tailored properties samples were prepared by partition heating and local tempering,and their comprehensive properties were analyzed by means of experiments.The experimental data are introduced into the FEA model,and the safety performance of the tailored properties door impact beam is analyzed by comparing with the uniform door impact beam.The main research results are as following:(1)When the heating time is 30 seconds,the tensile strength of 22MnB5 steel is 1534 MPa,the elongation is 11%.In the process of increasing the temperature from 710 to 910 Celsius,The hardness and strength of the material increases and the elongation decreases,the microstructure of the material changed from ferrite and pearlite to ferrite and high carbon martensite,finally turn into lath martensite structure.(2)With increasing tempering temperature,the tensile strength decreases,the elongation can be improved.Martensite recovery and carbides precipitation is found with 420 Celsius tempering,martensite disappear and carbides begin to grow at 620 Celsius tempering.Mixed-rupture characteristics of cleavage and dimples is found in the steel tempered at 420 Celsius,small and uniform dimples is found in the steel tempered at 620 Celsius.The grain size of the steel are refined after quenching,the grain size increases with increasing tempering temperature.(3)Develop a electrical heating device.Different regions of the steel can rise to different temperatures through three different ways.Stamping U shape specimens with tailored properties.High strength region is about 500 HV.The hardness of the low strength region is within 200-460 HV.The transition zone is about 12 mm wide.(4)Through local electrical heating,the tailored properties of high strength steel sheet have been achieved.High strength region is about 500 HV.The hardness of the low strength region is within 200-260 HV.The microstructure of the high strength side is mainly martensite,and the bainite structure appears gradually during the transition to the low strength zone.The low strength region is mainly composed of ferrite and carbide.(5)In the static and rigid cylinder collision simulation,compare tailored properties anti-collision beam with raw materials and quenched materials anti-collision beam,the interface force,energy absorption and acceleration of the anti-collision beam with tailored properties are in the middle position,the anti-collision beam with tailored properties has the best comprehensive performance.