Effect Of Annealing Process On Hot-Dip Galvanizing Of IF Steel

IF steel possesses high strength and excellent drawability,it's widely used in the automotive industry.Its property and finished product rate will improve effectively after annealing process.In order to meet the demand of corrosion prevention,IF steel is usually treated by hot-dip galvanizing.Hot-dip galvanizing is the most widely used technology to protect the steels from corrosion.The influence factors of coating quality consist of galvanizing temperature,immersing time,liquid zinc and elements in the basic steel.Annealing process effects the formation and distribution of microstructure.In order to investigate the effect of technological paraments of annealing process on the coating of IF steel,annealing and hot-dip galvanizing experiment of IF steel was conducted.The material used in the experiment is IF steel,reduction rate and thickness of IF steel are 75% and 0.75 mm respectively.Steel is annealed at 810? and 870? for 90 s,120s and 300 s,then the steel is immersed in the liquid zinc for 90 s,120,180 s,galvanizing temperature is from 450?,470?,490? and 510?.After the galvanizing process,metallographic and electron backscatter diffraction(EBSD)analysis were conducted to investigate the change of microstructure of steel and coating.The results show that:(1)Grain is characterized by {111} texture after annealing process,and {111} texture is enhanced with the increase of both annealing temperature and annealing time.(2)The size of isometric crystals is smaller when steel is annealed at 810? for 120 s,percentage composition of two kinds of Secondary texture,{111} <112> and {111}<110>,is approximately the same,the uniform of texture is better than the rest.(3)Coating is consisted of ? phase,? phase and ? phase,? phase is presented for two morphologies: columnar and granuliform,pure zinc is existed in the interspace of ? phase,pure zinc will contact and erosion the ? phase directly.(4)Annealing time has some effect on the formation of the coating.Coating of the sample annealed at 810?for 120 s is more coherent with less defects and high coating quality.Stripe defects appear at the surface of samples for less annealing time,punctate defects will appear when the annealing time increases to 870?.(5)Coating of steel annealed at 810? is of high quality then those annealed at 870?,with less defects while the technological paraments of hot-dip galvanizing are the same.(6)Stripe defects exist on the coatings surface when the galvanizing temperature is low,and cracks appear at high temperature.The increase of immersing time will accelerate the growth of ? phase,and then it will rupture,increasing fissuring between ? phase,leading the decrease of coherence of coating,which is harmful for the coating.