Research Of SFG IF Steel Continuous Annealing Process And Formation Mechanism Of PFZ

With the energy crisis and environmental pollution problems intensified, theautomotive industry for lightweight requirements are also increasing, automotive highstrength steel is also growing rapidly. As the third generation of automotive deepdrawing steel, IF steel has been widely used in automobile manufacturing, research ofhigh strength IF steel deep drawing properties and microstruvtures of high strengthcold rolled automobile has the great significance.In this paper, SFG IF steel as the object of study, the control of different coldrolling reduction rate of cold rolling experiments. At different annealing temperaturesto simulate steel continuous annealing experiments, observe the microstructure andmechanical properties of the test. and using TEM on the experimental steel PFZ tostudy law, the main results are as follows:1. SFG IF steel grain size decreases with the increase of the cold rollingratio. The cold rolling ratio is79%, the highest tensile strength is426MPa, coldrolling reduction ratio is75%, the yield strength and yield ratio and thelowest, respectively239and0.58MPa, and the elongation rate was the highest is38.9%. As the pressure increases, the r value and n value are increased and thendecreased, the cold rolling ratio is75%, the maximum r value is1.9, the maximum nvalue is0.29.2. SFG IF steel grain size increases with increasing annealing temperaturedecreases, the pie ferrite increased, and more uniform distribution. Increasingannealing temperature, SFG IF steel fine grain tensile strength and elongation areimproved, yield strength and yield strength decreased. Annealing temperature of880℃, the tensile strength up to432MPa, elongation up to37.8%, yield strength andyield strength than the minimum224MPa and0.519respectively. With the increase ofannealing temperature, the r value increased first and then decreased, when theannealing temperature is850℃, r values of up to1.9. n values are increased withincreasing annealing temperature rising, when the annealing temperature is880℃,the maximum n value is0.27.3. When the annealing temperature is low, SFG IF steel of second phase particleprecipitation number is large, small size, dispersion and distribution. With theincrease of annealing temperature, the second phase particles constantly gathersolution to grow up and larger size, the uneven distribution of the number reduced. Inthe direction of the grain boundary migration dispersed second phase particles, grainboundary migration rear fewer two-phase particles, pinning in the second phaseparticle size of the largest grain boundaries.4. The average width of the SFG IF steel precipitate free zone (PFZ) increaseswith annealing temperature and PFZ more wide, the lower the yield strength, tensile strength rose slightly. When the experiment was severely deformed steel, the impactof the presence of PFZ of dislocation generation and accumulation decreases.5. SFG IF steel consumption and space consumption solute simultaneouslyprecipitate free zone (PFZ) formation work, high temperature soluteconsumption-based, low consumption in space-based. According to Ostwald ripeningtheory, annealing temperature so that the two-phase particle coarsening, reducing thetwo-phase particle pinning force, improving the driving force of the grain boundary,the grain boundary migration process, the driving force of the grain boundarymigration is greater than the two-phase particles of grain boundary pinning force,while the second phase and solution coarsening of particles occurs along with themigration of grain boundaries, grain boundary through the "sweep" effect caused by aregional matter little precipitation (PFZ).