Research Of P Precipitation Behavior Of Rare Earth Microalloyed High Strength IF Steel During Hot Rolling

High strength IF steel is a kind of common IF steel,which adds P,Si and Mn elements,solid solution strengthening and fine grain strengthening to improve the deep drawing property,strength and toughness of the steel.Among them,P is the most economical element with the strongest solid solution strengthening effect and the smallest damage to deep drawing property.The precipitation of P during metallurgy and hot rolling will affect the strengthening effect.Adding trace B element to prevent P element segregation to grain boundary can improve the secondary cold working brittleness of high strength IF steel,thus affecting the deep drawing property of high strength IF steel.The precipitation of P during continuous casting and hot rolling ultimately affects the mechanical properties of high strength IF steel.Most studies only show the precipitation type of P,but no studies show the solid solution precipitation content of quantitative P element.Therefore,the precipitation behavior of P during hot rolling of high strength IF Steel Microalloyed with rare earth is studied,and the solid solution precipitation content of P in each step of hot rolling process is further mastered,which has certain theoretical guidance for controlling the solid solution content of P in the actual hot rolling process of high strength IF steel in thefuture.This paper mainly focuses on the heating and hot rolling process of rare earth microalloyed high strength IF steel slab in a domestic plant.The simulation experiments of billet heating temperature,holding time and hot rolling were carried out in the laboratory.Inductively Coupled Plasma Mass Spectrometer ICP-MS,scanning electron microscopy,transmission electron microscopy,X-ray diffractometer and Zeiss metallographic microscope were used.The solid solution precipitation content of P was calculated by measuring the concentration of P,the type of P precipitation phase was determined,and the structure of hot rolled plate was observed.The results of system analysis showthat:The higher the billet heating temperature is,the more the insoluble matter of Fe-P is dissolved back,and the smaller the precipitation percentage of P is.The longer the cooling time is,the more P precipitates and the larger the percentage of P precipitates.The final pass deformation of rough rolling has no obvious effect on the precipitation percentage of P in the initial pass of finishing rolling.Whenthe coiling temperature is 650?,600?and 550?,the precipitation percentage of P in IF steel increases with the decrease of coiling temperature.FeTiP is the main precipitate of P when coiling temperature is 700?.Abnormal precipitation and growth occur,and the precipitation percentage of P in IF steel is the highest.Under the conditions of 20%,40% and 60% reduction at 920 ?,the size of precipitated second phase particles increases with the increase of reduction rate.The precipitation percentage of P in IF steel decreases first and then remains unchanged when coiling temperature is600?.With the decrease of coiling temperature,the size of precipitated second phase particles decreases,and the precipitation percentage of P in IF steel increases when the temperature is reduced by 20%.The precipitation percentage of P in IF steel did not change significantly when 40% and60% of IF steel were pressed at 920 ?.With the decrease of finishing rolling temperature and coiling temperature,the solid solution percentage of P increases.The structure is refined,a large number of elongated and recrystallized ferrite grains appear,the tensile strength and yield strength decrease,and theelongation increases afterfracture.