| It is very important to control inclusions in steel for improving steel performance.First-principles calculation is a popular computational simulation method in the field of materials science.It can predict and explain the relationship and mechanism between the structure and properties of materials from the microscopic perspective.The first-principles calculation methods have been applied in the study of inclusions properties.In the study of inclusions control in steel,the basic properties of different inclusions and their difference with steel matrix can be analyzed to provide theoretical support for the control of inclusions in steel.Firstly,based on density functional theory of first-principles calculation,the common non-metallic inclusions generated in the process of steelmaking are studied.The structural properties such as formation energy and binding energy,electronic properties such as energy band density and work function,mechanical properties such as elastic modulus,Poisson’s ratio,Vickers hardness,thermal expansion coefficient,were calculated.The formation trend,structural stability and influence of inclusions on mechanical properties and corrosion properties of steel are summarized from the microscopic perspectivew,which provides a basis for controlling inclusions in steel.All the six non-metallic inclusions have a tendency of spontaneous formation,among which the formation energy of Al2O3 is the smallest and the easiest.The formation energy of Mn S and Ti N is the largest and relatively difficult to form.Ti N has the highest bulk modulus,shear modulus and Young’s modulus.The average work function of inclusions is Ti N>Fe>Mg O>Ca O>Ca S>Mn S,indicating that Ti N and Mn S have great influence on pitting corrosion.Secondly,the modification of inclusions in J5 stainless steel by rare earth element Ceand its induced corrosion mechanism were studied from the microscopic point of view by in-situ corrosion observation and first-principles calculation based on density functional theory.The composition and type of inclusions modified by rare earth element Cewere analyzed by SEM-EDS.The typical inclusions are CeAlO3-Ce2O2S,Ce2O3-Ce2O2S,Mn S,etc.According to the formation energy calculation,the stable inclusions Ce2O3,Ce2O2S and CeAlO3 were formed after Cetreatment.The stability of crystal plane can be judged by the surface energy.The surface energy of the Fe（100）-2 plane is 2.4374 J/m2,and the work function is 4.7352 e V.By comparing the work function and the calculated potential difference between inclusions and steel matrix,the trend of pitting corrosion induced by different Ce-containing inclusions was analyzed,and the effects of different atomic positions,atomic numbers and different slab models on the work function were discussed.The results show that the potential difference of Mn S,CeS,Ce2O3 and Ce2O2S is mostly less than 0,and the potential difference of CeAlO3 is about 0 e V,compared with the electron work function of Fe（100）-2 surface.The work function is greatly affected by the difference of inclusions crystal face.The average value of the work function of the crystal plane with morenon-metallic atoms such as O and S is higher.The addition of rare earth element Cecan effectively reduce the work function of crystal plane.The order of the average work function of the five inclusions and steel matrix is CeAlO3>Fe>Mn S>CeS>Ce2O2S>Ce2O3.Combined with the experimental results of composite inclusions in stainless steel,it can be seen that as the highest probability of pitting corrosion,and CeAlO3 can effectively improve the corrosion resistance of steel. |
