Effect Of Hood Annealing On The Properties Of Cold-rolled High-strength Steel

With the wide application and development of cold rolled high strength steel sheet for automobile,the higher strength and good molding performance are the criteria for evaluating the performance of the sheet,In the mainstream cold rolling sheet of automobile,most of them are put to use continuous annealing,high efficiency and good shape,but because of the long production line and complicated technology,it is suitable for large batch and fewer varieties of sheet metal.For small cold-rolled plants and small batch metal sheets,it is possible to consider the production from a hood annealing process.Based on the chemical composition design of typical steel280 VK and DP590 cold rolled sheet,combined with relevant professional knowledge,the influence of bell annealing process on the mechanical properties,molding properties and microstructure and properties of the cold rolled sheet was studied and analyzed in this paper.The main contents and results are as follows:(1)Through theoretical Analysis and hardness determination to determine the relative heating regime of Bell annealing,draw up annealing process parameters,the heating temperatures were: 620?,640?,660?,680?,holding time: 120 min.(2)The mechanical properties of annealed sheet were tested by static uniaxial tensile test,including elongation after breaking,tensile strength,yield strength,n value and r value.(3)Evaluation of forming properties of steel materials at different annealing temperatures by universal forming tester,using reaming test and cupping test to measure the important index of formability of annealed sheet metal,the reaming rate and the IE value of were measured to evaluate the formability of annealed sheet,study the effect of different annealing temperatures on deep drawing properties of materials.The maximum reaming rate of steel 1# is 140.53% under air cooling,the maximum IE value is 9.94 mm under slow cooling,the reaming rate of steel 2# is144.4% and the maximum IE value is 9.58 mm.(4)By observing the microstructure of the test steel after annealing at different temperatures,the metallographic analysis of the optical microscope can be used in thelaboratory to observe the microstructure and analyze the morphology of different grain structures on the steel.The effect of the overall performance of the structure determines the optimum process parameters.The main structure obtained under hood annealing is ferrite + cementite structure,in which ferrite morphology and grain size affect the performance of the metal sheet.(5)By comparing the comprehensive performance difference between the same steel under hood annealing and continuous annealing,the performance advantages of the same steel under different processes are reasonably analyzed.It can be concluded that the mechanical properties of continuous annealing are slightly stronger than the hood Annealing,but hood annealing has better molding properties.