Research On Key Annealing Technology Of 600MPa Cold Rolling Dual Phase Steel

Since the beginning of the 21st century,China's automobile industry has been developing rapidly.In 2012,China's auto production and sales double over 19 million,production and sales for four consecutive years,ranking first in the world,the automotive industry has really become a pillar industry of China.With the globalization of nervous energy,energy saving,emission reduction has become the focus of attention,iron and steel as the main material for car manufacturers,from the development of mild steel to high strength steel,promote automobile lightweight and energy conservation,and to adapt to the requirements of the development of the times.Dule phase steel with high strength and high ductility has become a high strength,good formability new stamping steel,successfully used in the automobile industry.In in lightweight automobile research projects at domestic and abroad,the amount of dual phase steel account for a very high level,and indicates that the dual phase steel has a very substantial market prospects.According to the automotive high-strength sheet condition 600MPa cold-rolled dual-phase steel as the application of one of the largest proportion of steels,product development has a strong practical significance.The subject as sub-project of the Handan Iron and Steel Company-Beijing University of Science and Technology 'the automobile steel series development project',focused on the dual-phase steel continuous annealing technology,take the combination of laboratory simulation and pilot test,study thermal simulation machine,continuous annealing simulation machine,sheet metal forming testing machine and a variety of experimental methods and tensile experiments,metallographic analysis,test method,the phase transition of the dual phase steel 600MPa Grade,organization,performance studies.The research works in this paper are presented as follows.1)through the research of dynamic CCT and static CCT experiments,which find out the continuous annealing process in dual phase steels transformation rules and organization:the cooling rate of ferrite + pearlite in 1-5?/s range,and with the increase of cooling rate,ferrite and pearlite transformation temperature decreased to cooling rate;more than 5?/s after bainite transformation;start cooling rate higher than 15?/s after martensitic transformation,with the increase of cooling rate,martensite start temperature increase.2)through simulation studies the key technical parameters of heating and overaging temperature continuous annealing experiments,summarized the influence of continuous annealing process on the microstructure and performance:intercritical heating temperature,ferrite content decreased,the content of the martensite increases,the yield strength increases,the annealing temperature of 820-840 ? range elongation reaches the maximum value;the two-phase region heat preservation time increasing,the yield strength and tensile strength decrease dual phase steel,the elongation increased significantly;as the overaging temperature increased,the yield strength increases slowly,the tensile strength decreases slowly,overaging temperature 230-270?,the elongation decreases with the aging temperature increasing,great value at 290 ?,310? elongation decreased to achieve minimum.3)Effects of the relationship,baking parameters after continuous annealing of the dual phase steel forming performance and related parameters of the bake hardening value was studied by forming and baking experiment.