| The manganese in steel is mainly exists as sosoloid and MnS,the rest of the manganese can also form Mn3 C, moreover, there are also a few MnSi,FeMnSi, etc. Manganese is usually used as deoxidizer and desulfurization agent in steelmaking process. MnS formed from the reaction between Mn and S can avoid the hot short phenomenon caused by FeS-Fe2O3 eutecticum.Meanwhile,it can also improve the cutting performance of the free-cutting steel.Generally, MnS inclusions has good deformation performance and prolongs along the rolling direction after rolling easily,becoming large size stripe inclusions, worsening the lateral performance and being the source of crack in steel.Classical thermodynamic calculation shows that MnS inclusions in steel usually formed under the liquidus temperature even under solidus temperature. Furthermore, as the balance distribution coefficient of S and Mn differs a lot, kMn = 0.70, kS = 0.02, so how does MnS inclusions form? Therefore, it is necessary to find out the formation mechanism of MnS and oxide- MnS compound inclusions in steel, in order to get the method of improving sulfide inclusion.First of all, analyzes carbon manganese steel sample about inclusions in it.Uses electrolytic separation and observes from scanning electron microscopy(SEM)shows that white stripe and irregular long fan material is MnS inclusions, the length of part of the long strip MnS inclusions is more than 100 μm, and the distribution of them are clustered serious.And there is also a small amount of composite oxide inclusions, named Al2O3- MnO- SiO2- MnS inclusions.Secondly, the DMol3 package based on the First Principle is used to calculate the structures and thermodynamic properties of all possible clusters of MnxSy, according to the results, MnxSy clusters,(Mn1S2),(Mn1S3) and(Mn3S3), and other 16 kinds of geometric structure are stably exist, their thermodynamic properties with temperature and the changing rule of the atomic number(MnxSy) with CP, H and S were increases with the rise of temperature, and GV decreases with the rise of temperature;the growth trend of CP leveling off with the rise of temperature, and the growth trend of S, H is more steep, the results of above is the same as the relationship between thermodynamics parameters and T in classical thermodynamics. The thermodynamic properties of(MnxSy) changes with x, y obviously, this has to do with the size dependent effect.Finally, based on the above, Fukui function(Mr Fukui function) is used to predict the possible reaction zone of the reaction,Mn and S atoms and(MnxSy)formed on the surface of α- Al2O3 inclusions, further based on the optimization of reaction zone to simulate the change of interface area of α- Al2O3- MnS structure and energy change in the growth process, and compared with interface shape of α- Al2O3-MnS observed by SEM.The results shows that: with the increase of Mn, S atom,the total energy of α- Al2O3- MnS interface is reduced, and the energy of the individual atoms changes(Δ E) is decreased; the atoms are "penetration" in this process, a containing polyatomic(Al, Mn, S, O) region is formed by all atoms joined each other,and the both sides of the interface are Al2O3 and MnS single-phase regions,respectively. |
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