Effect Of Performance On Boron And Phosphorus Grain Boundaries Segregation In High Strength Interstitial-free Steel Sheets

High strength interstitial-free steel sheets are widely used for automobile panels forboth of excellent drawing properties and high strength, The phosphorus bearing highstrength IF steels make it possible for automobiles to reduce weight and save energy.The effect of boron and phosphorus segregation behavior at grain boundary, texture andmechanical properties in high strength IF steel with different boron and phosphoruscontents with different annealing parameters was studied by optical microscope(OM),electron back scattered diffraction(EBSD) technology, universal testing machine andauger electron spectroscopy(AES). The results were as following:Both boron and phosphorus segregation at grain boundaries in both hot rolled andannealing boron added high strength IF steels. The low-angle boundaries and thecoincidence site lattice (CSL) grain boundaries increased and random high angle grainboundaries decreased in the boron added high strength IF steels. On the other hand, thediffuse coefficient of boron in-Fe was larger than phosphorus. Boron could diffuse tograin boundaries faster than phosphorus and it could inhibit phosphorus segregation atgrain boundaries. The different of grain boundaries structure and diffuse coefficient ofboron in boron added IF steels led to the segregation content of phosphorus at grainboundaries decreased greatly in boron added high strength IF steels. Strong γ fibertextures were attained and the main texture component were {111}<110> and{111}<112>. With the increased of annealing temperature from750℃to840℃, the{111} plane texture content increased initially and decreases afterwards. The grain sizeand boron and phosphorus segregation contents were different with and without boronadded hot rolled IF steel, which caused the different of dislocation cell structure,deformation band for the cold rolled IF steels. The dislocation cell structure,deformation band affected the new grain nucleation and growth when the steels wererecrystallization annealed. The different of boron and phosphorus segregated at grain boundaries and grain boundary structure affected grain boundary migration and theevolution of {111} plane texture. The strength and plastic strain ratio r changed greatlywith the different contents of boron and phosphorus in IF steels, and the higher strengthand lower value of r were obtained when the steel had a higher phosphorus content andlower boron content. When the content of phosphorus and boron appropriate, highstrength steel IF could have better mechanical properties...