Effect Of Continuous Annealing Process On Microstructure Evolution Behavior Of Rare Earth High Strength IF Steel

With the progress of science and technology and the development of society,the demand for human automobiles is increasing,and the problems of environmental pollution and energy consumption follow.Therefore,it is imperative to reduce weight,save energy,protect environment,prevent corrosion,improve safety and comfort of automobiles.As a solution-strengthening steel,high strength IF steel is used more and more in automobile industry because of its composition characteristics and the reasons of no interstitial atoms,which makes it have good deep drawing performance,no aging and high strength.Rare earth elements play an important role in controlling and improving inclusions,purifying molten steel,refining grains and producing microalloying in steels.Rare earth elements can be used reasonably in automobile production,and some properties of automobile plates can be improved.Annealing is one of the key links in the industrial production of high strength IF steel.It is very important to control annealing process properly to obtain the best performance.Continuous annealing has been widely used and developed for its advantages of short annealing time,high production efficiency and good surface quality of finished strip.The microstructure and texture of high strength IF steel will change during continuous annealing,which determines the properties of high strength IF steel.In this paper,the continuous annealing process of rare earth high strength IF steel cold-hardened plate produced in batches in a domestic iron and steel plant is simulated by Gleeble-1500 thermal simulator according to the specific parameters and requirements of continuous annealing equipment.The soaking temperature and strip steel in the process of continuous annealing are studied.The effect of operating speed on annealing structure,the evolution of structure and texture during continuous annealing,and the effect of overaging temperature on precipitation behavior of RE high strength IF steel during continuous annealing were studied.The results show that:The effect of soaking temperature on annealing structure is obvious,but the speed of strip operation has little effect on annealing structure.In the continuous annealing process with soaking temperature of 790 ? and running speed of 120 m/min,the recovery stage is when the heating temperature is lower than 740 ?,the recrystallization stage is between 740 ? and 790 ? for 105 s,the recrystallization time is 129 s,and the grain growth stage is after 105 s.In the continuous annealing process with soaking temperature of 800 ? and running speed of 150 m/min,the recovery stage is when soaking temperature is lower than 690 ?,recrystallization stage is between 690 ? and 800 ? for 56 s,recrystallization time is 97 s,and grain growth stage is after 56 s.The texture evolution law of the annealing process with soaking temperature 800 ? is similar to that of the annealing process with soaking temperature 790 ?.With the recrystallization process,the texture strength of {001} < 110 >,{112} < 110 > decreases gradually,while the texture strength of {111} < 110 >,{111} < 112 > increases gradually,and the texture strength of {111} < 112 > is obviously higher than that of {111} < 110 >.The hardness and precipitate surface density of RE high strength IF steel increase with the increase of overaging temperature,and the hardness and precipitate surface density will gradually increase with the increase of overaging temperature.