| At present,the domestic demand for shipbuilding steels of high heat input welding to improve the strength and toughness of the heat-affected zone is becoming more and more urgent,and oxide metallurgy technology has received attention in the field of metallurgy,the method of grain refinement by uniformly distributed fine particles in steel has become a consensus,and the nanoscopic explanation of the mechanism of microalloying elements to refine intragranular ferrite grains is still unclear.In order to reveal the strengthening mechanism of NbC and NbN particles in steel,from a nanoscopic perspective,ab initio molecular dynamics simulation method was used to theoretically study the properties of NbC/α-Fe and NbN/α-Fe low-index interfaces.The thermodynamic calculation of the precipitation of carbide and nitride particles in steel shows that NbC particles are mainly precipitated in the phase transformation zone,which can effectively hinder the growth of intragranular ferrite.The Leica metallographic microscope was used to observe the microstructure of the test steel,and the results indicated that the addition of element Nbcould effectively refine the steel structure.The first-principles method of density functional theory was used to calculate and analyze the surface properties such as surface configuration,surface energy,electronic structure and density of states of NbC,NbN andα-Fe low-index surfaces.The results show that the surface energy of the NbC(001)surface is the lowest,which is 1.311 J/m~2;under the condition of low N chemical potential,the surface energy of the NbN(001)surface is the lowest,which is 1.308 J/m~2.The C-terminated(111)surface and the N-terminated(111)surface have the most effective charge transfer between the adjacent Nb-4d and C-2p,N-2p orbitals,and the orbital hybridization is more intense,forming polar covalent bonds,resulting in larger relaxation amplitudes.The low-index surface stability ofα-Fe is(110)>(001)>(111).First-principles and ab initio molecular dynamics methods were used to calculate and analyze the interface properties such as NbC/α-Fe,NbN/α-Fe low-index interface configuration,interface energy,electronic structure and density of states.The results show that the Fe atoms on the interface are easier to move to the top of the C and N atoms,accompanied by a large number of charge transfer;there are strong orbital resonances between adjacent Fe-3d orbital and Nb-4d,C-2p and N-2p orbitals,resulting in strong metal bonds and polar covalent bonds,C and N atoms are the most stable bonding atoms of Fe atom.After the interface configuration relaxation,the NbC(001)/α-Fe(001)and NbN(001)/α-Fe(001)interfaces are the most stable structures with the smallest relaxation amplitude,the smallest interface energy and the smallest misfit degree,theα-Fe(001)surface has an optimal orientation relationship with the NbC(001)and NbN(001)surfaces.Clarify the combination mode of the inclusion particles NbC and NbN in the steel with the steel matrixα-Fe,pin the ferrite grain boundaries to the NbC and NbN particles,refine the ferrite grains,improve the structure,and improve the HAZ toughness of shipbuilding steels of high heat input welding has certain theoretical guiding significance.Figure 33;Table 34;Reference 84... |
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