Forming Process And Microstructure Evolution Of Tailor Rolled Blanks Hot Stamping

The high-strength steel hot stamping technology can realize the weight reduction under the premise of ensuring the safety of the vehicle body,and thetailor rolled blanks technology can design the thickness of the sheet according to the load distribution of different positions of the workpiece,and also has obvious weight reducing effect.By combining the two technologies,it is possible to prepare a hot stamping part with a relatively small thickness to better realize the weight reduction of the vehicle body.The hot stamping technology of the tailor rolled blanks has not been applied in the domestic independent models,one of the reasons is that the process feasibility verification has not been carried out.In this paper,1.6mm thick 22MnB5 sheet is used as raw material,and thickness plates of 1.4mm,1.2mm,1.0mm and 0.8mm are obtained by cold rolling test to characterize different thickness regions of the tailor rolled blanks.Through the experimental research on phase transformation,quenching and tempering of these tailor rolled blanks,the feasibility of the hot plate stamping technology is verified.(1)The quenching experiments and phase transformation experiments under cold stamping conditions were carried out on cold-rolled samples of different thicknesses.The results show that the austenitizing starting temperature of cold-rolled samples with different thickness is about 745?.The martensite transformation starting temperature is the same at different speeds of cooling,both at 390?,and the termination temperature sheet is slightly higher than the thick plate.The higher the cooling rate,the higher the hardness value of the obtained sample,but the hardness values of the samples obtained at the same cooling rate of different thicknesses did not differ.(2)It can be confirmed by the high temperature tensile test and the normal temperature tensile test of the normalized sample after quenching that the difference in mechanical properties after cold-rolled sheet of different thickness has been eliminated,whether it is high temperature deformation or quenching or normalizing After the normal temperature stretching,the plates of different thicknesses have the same tensile strength under the same process conditions.The results of this experiment show that the cold-rolled sheet to be hot stamped does not need to be annealed.(3)The tempering properties of the different thickness plates after quenching were studied.The results show that the boron steel material used in the experiment can obtain better comprehensive mechanical properties after tempering at 180? for 30min.High temperature tempering can significantly improve the material elongation and make the material obtain a higher strong plastic product,but back.Excessive heat preservation time will lead to high temperature temper brittleness,and the tempering temperature is 700?.(4)The tailor rolled blanks U-shaped member having a thickness of 1.4mm,1.2mm,1.0mm,and 0.8mm and a thickness of 1.6mm in thickness was prepared,and an equal thickness U-shaped member was prepared from the original sheet.The five kinds of U-shaped specimens were quenched and tempered at 180? for 30 min,and then subjected to zone high temperature tempering experiments.Research indicates:Compared with the U-shaped specimens of the equal-thickness plate after quenching and 180? holding for.30min,the U-shaped specimens of the tailor rolled blanks are obviously delayed in the crushing process;after quenching,180? insulation The U-shaped test piece of the low-thickness tempering in 30min low-temperature tempering and thin-zone 700? holding for 10min high-temperature tempering process showed good toughness.No crack occurred from the beginning of loading to the end of loading,and the maximum bearing capacity was 180?.Low temperature tempering specimens kept for 30min are similar or even higher.