Effect Of Rare Earth Ce On TiN Precipitation In Titanium Microalloyed Steel

TiN particles in titanium microalloyed steel are a kind of brittle inclusion.When the size of brittle inclusion reaches a certain level,it will be unfavorable to the mechanical properties of the steel.Therefore,the size and distribution of TiN precipitated in titanium microalloyed steel is an important standard to evaluate the titanium microalloyed steel.However,there are few in-depth studies on the inclusions generated by adding rare earth element Ce to Ti-containing microalloy steels.In this work,the size,shape and mismatched nucleation relationship between the heterogeneous nucleated inclusions and the second phase TiN inclusions precipitated under the action of three gradients of rare earth Ce content and N content were studied respectively.SEM,XRD,non-aqueous solution electrolysis and EBSD phase identification were used for detection and analysis.Research shows with the increase of N content in steel,TiN particles with large size（>10μm）tend to appear,and the increase of N content promotes the precipitation of TiN in the liquid phase.When the rare earth Ce is added into the steel,spherical inclusions will be generated in the steel,and the main components are CeO₂,MgO,Al₂O₃,TiO and TiN.In the sample with lower N content,the outer of Ce-containing composite inclusions is mainly TiO,while in the sample with higher N content,the outer part of Ce-containing inclusion is mainly composed of TiN.When the addition amount of rare earth Ce is 100ppm,the Ce-containing composite inclusion is generated with CeO₂ as the nucleation core,and the composite inclusion is formed in the form of multiple regions interlaced.When the addition amount of rare earth Ce is 100ppm,the inclusion in steel plays a refining and purification role.When the addition amount of Ce is200ppm,it not only plays a role in refining inclusions,but also promotes the precipitation of large inclusions,and promotes the increase of N content in steel,which has a negative effect on the properties of steel.By XRD analysis of the inclusions after electrolysis extraction,the main component of inclusions in steel is TiN,and the main growth crystal planes are（111）,（200）and（220）.Electron microscopy（SEM）was used to contain the Ce composite inclusions EBSD phase identification of each part,and the side-the side matching model is used to calculate the degree of mismatch between the material and identified to the relationship,between different substances have identified according to the results of Mg-O-Al composite inclusion exists in the form of MgO style and Al₂O₃ mix,between different substances in the crystal to<101?>and{111},{200},{220},{311}to better matching relation between,between has a lower crystal and crystal degree of mismatch.When rare earth Ce is added,part of Ce is dissolved in TiN,and its existence is proved to be reasonable by first principles.In this paper,the precipitation law of the second phase containing Ti in steel is obtained by analyzing the precipitation statistics,precipitation thermodynamics and the calculation of the mismatch between different parts of the composite inclusion.In the argon smelting environment,the addition of 100ppm rare earth Ce promotes the refinement of the second phase TiN in the steel,plays a certain role in the purification of molten steel,and promotes the spherical Ce-containing inclusions in the steel.Al₂O₃,MgO and CeO₂ can act as the nucleation core of TiN and play a positive role in the steel.With the increase of N content,the number and size of TiN particles are increased,which is unfavorable to the properties of steel.The textured CeO₂,TiO,MgO and Al₂O₃ are interluded in the central nucleation position.The Ce content of 200ppm can promote the occurrence of TiN clusters and increase the number of large inclusions in steel,which is harmful to the properties of steel.