Effect of La content on the microstructure and TiN precipitation behavior of high-titanium steel during slow cooling solidification
In this work,the effects of four kinds of La content on the microstructure and TiN precipitation behavior of high-titanium steel are studied by high temperature melting experiment,optical microscope(OM)and scanning electron microscope(SEM).It is intended to give scientific basis and experimental data for La treatment to refine the size of TiN and the microstructure in the center region of cast ingots of high-titanium steel.The results show that the solidification structures of all experimental steels are equiaxed grains when the solidification cooling rate is 0.17℃/s.La shows obvious ability of deoxidization,S and Al at low La content(0.0013wt％),so LaAlO3 and La2O2S are mainly formed in its steel.La just began to show obvious ability of deoxidization,S and Al at high La content(0.0052wt％,0.0223wt％).With the consumption of a large amount of O atoms,the deoxidization and sulfur ability of La increased rapidly.Therefore,La2O2S is the predominant precipitate that forms in the steel,and some La2O2S particles will nucleate and grow on the surface of LaAlO3 particles that have previously precipitated.TiN mainly precipitates in the Liquid+δtwo-phase region in this experimental steel.LaAlO3 and La2O2S precipitate before TiN,and their small lattice misfit with TiN are the primary cause of their propensity to act as the cores of TiN heterogeneous nucleation.When the La content in the steel is 0wt％,0.0013wt％,0.0052wt％,0.0223wt％,the average axial grain size of each experimental steel is 354,223,154,126 µm,respectively.The maximum size of TiN is 19.1,11.7,11.4,10.4 μm,the TiN area density in each experimental steel is 42.2,82.9,86.3,90.7 No./mm2,the maximum size of TiN is 19.1,11.7,11.4,10.4 µm,and the average size of TiN is 7.8,4.6,4.5,4.4 μm.
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