| It has become an inevitable trend for the structural steel of automobiles to develop towards high strength,which was to ensure the improvement of energy saving and safety,and the reduction of the weight has become the research direction of the new generation of automobiles.The vanadium?V?was added to hot stamping steel-22MnB5.The V-microalloyed steel was taken as the research object and combined with theory and production processes.The deformation resistance model was established,and the microstructure and properties of microalloyed steel after hot forming were studied.The evolution of microstructure and mechanical properties of hot stamped steel sheets during production and hot-stamping forming process was systematically studied.Through thermal simulation experiment and calculations,shown that the peak and steady state activation energy were 312.4 kJ/mol and 297.8 kJ/mol.From the data,the CCT curve were plotted,which concluded that Ac1=728?and Ac3=817?.The austenite grain diameter increased slightly with increasing the temperature below 900?.The grain diameter increased rapidly with the increasing temperature above 900?.Through the production,stamping forming and welding of V-microalloy steel,shown that the anti-collision beam of the door the Rm=1561MPa,YS=1209MPa,and the elongation was 8.7%at 910?.The properties meet the requirements.The impact toughness of the room temperature laminate was 70 J/cm2,and the low temperature impact toughness of the temperature of-40°C reached 65 J/cm2.The three-point bending angle of the sample without decarbonizing layer was bigger than 75°,and that of the sample without decarbonizing layer was bigger than 60°.After stamping for welding test,the electrode pressure was 8 kN,the welding time was 20 cyc,the optimum welding current range was 10.5 kA to 12 kA,the maximum tensile shear force was 39 kN,and the cross tensile force was 10.6 kN.It was found that the original austenite grains of the V-containing hot stamped parts were significantly refined,and the grain refinement was about 5?m when the heating temperature was 910°C and 930°C.Figure 48;Table 20;Reference 41. |
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