Effect Of Rare Earth On Batch Annealing Microstructure And P Precipitation Behavior Of 440MPa High Strength IF Steel

Rare earth is an indispensable resource for the development of a country,As a large country in the storage of rare earth resources,China has been using rare earth resources in military,steel and metallurgy,aerospace,glass and other fields.Recent studies on rare earths in steel have shown that rare earth can purify steel,refine structure and improve properties.However,the effects of rare earth on the microstructure,texture,precipitation phase and mechanical properties of high strength IF steel during annealing process are lack of systematic and integrated research.In the batch annealing process,the P element is easily precipitated and forms a P-containing harmful phase FeTi(Nb)P,which causes the ? texture strength to decrease and impairs the final mechanical properties,and reports that the rare earth has little effect on the P element and the P-containing precipitation phase.China's Bayan Obo mine is rich in rare earth resources,and there are rare earth residues in the steel produced from the mine.Therefore,this paper draws lessons from the positive influence of rare earth on steel products,Based on the problem of residual rare earth in high value-added iron and steel materials of Bayan Obo mine,In order to obtain better structure and texture of high strength IF steel and reduce the precipitation of P element and P phase in steel,The subject of “The effect of rare earth on batch annealing microstructure and P precipitation behavior of 440 MPa high strength IF steel” was proposed.In this paper,the box furnace is used to simulate the batch annealing,Comparative tests were carried out with or without rare earth samples.Metallographic microscope to observe the evolution of the microstructure of the recrystallization process and the change of the hardness value of the annealing process,To analyze the effect of rare earth Lanthanum on the recrystallization process.Tensile tests were carried out on the finished products of the two samples,and the effect of rare earth La on mechanical properties was analyzed.The effect of rare earth Lanthanum on the evolution of macro-texture and micro-orientation during annealing was studied by XRD and EBSD orientation analysis.TEM observed the precipitates in different states,and confirmed the species of precipitates by EDS,The effect of rare earth Lanthanum on precipitates,especially FeNb(Ti)P phase,was investigated.Two samples of different states were subjected to second phase electrolysis and the concentration of P element in the second phase of the electrolysis was measured by ICP-MS,The ratio of the precipitation of the sample to the solid solution phosphorus in different states can be calculated by calculation.The amount of P precipitated indirectly reflects the amount of FeNb(Ti)P precipitated.The effect of rare earth Lanthanum on the precipitation of P and the precipitation phase containing phosphorus can be studied.The results show that rare earth Lanthanum increases the recrystallization starting temperature during the bell annealing processandPostponing the recrystallization process,Grain refinement and tensile strength increase,but the elongation is lowered.The rare earth Lanthanum makes the ? texture strength decreases and the ?-{111} texture uniformity deteriorates.The recrystallization nucleation mechanism of the two samples is the same as the directional nucleation and selective growth,directional nucleation dominates.Rare earth Lanthanum inhibits the precipitation of P during Solidification of molten steel,hot rolling coiling and annealing,which increases the solid solution content of P.The precipitation and solid solution ratio of P element in both samples were about 50%.Rare earth Lanthanum inhibits precipitation of composite phase Fe(Nb+Ti)P phase during hot rolling coiling and annealing.