Strengthening And Toughing Performance And First Principle Characterization Of“Expanded”?Phase On Stainless Steel

Martensite stainless steel possesses a good comprehensive performance,so it is widely used in the key parts of aeronautics and aerospace as well as marine engineering equipments.With the development of the manufacturing industry,the requirement of martensitie stainless steel performance is stricter.The low temperature plasma carburizing technology is a new surface modification technology of stainless steel in modern times,which can efficiently improve the performance of the stainless steel surface without affecting its corrosion resistance.In the present paper,1Cr17Ni2 stainless steel is treated by low temperature plasma carburizing to prepare the carbon‘expanded'?layer,the surface performance is improved.And studied the dynamics of layer thickening,organization evolution,change regular of microhardness.Then a structural model of carbon containing"expanded"phase is designed and optimized,and calculated with the stability,electronic structure and relevant mechanical properties.Finally,base on the rationality of the calculation results,forcast analysis the electronic structure and properties of contain lanthanum‘expanded'?phase.Experimental test results show that 1Cr17Ni2 steel has uniform organize after plasma carburizing treatment at 430?.The sample treated by 4h and 16h is mainly contains‘expanded'?phase and a small amount of Fe₃C.And 16h treatment sample contains tiny amount of Cr₃C₂ by transmission electron microscope test.There is a single‘expanded'?phase in the layer of 8h treatment sample.In addition,the thickness of carburizing layer increases with carburizing time has a growth of parabola law.The surface hardness of sample is above800Hv,wearability is greatly improved.The electronic structure,energy and properties of the carbon‘expanded'?phase of the nominal molecular formula of Fe₁₃Cr₃C_x?x=0,2,4,6?are calculated by the first principle.The calculation results show that The C atom tends to occupy the eight-hedral gap that does not contain Cr..Adding C atom expand the lattice and increase crystal volume.Body-centered cubic lattice structure transform into body-centered tetragonal.With the increasing of carbon content,structure stability decreased,hardness increased first and then decreased,the toughness increased.The calculation results are in agreement with the experimental results.In addition,it is found that the activation energy of carbon atoms in?phase is lower than that in the expansion phase,and the C atoms are easier todiffuse inthe?phase.The calculation results of the La containing‘expanded'?phase with nominal molecular formula Fe12Cr3LaCx?x=0,2,4,6?indicate that La atoms tend to occupy the peak angle position.The addition of La atoms makes the stability of the"expanded"?phase decrease,the hardness increases,and the toughness decreases slightly.In the result of activation energy of diffusion calculation,it is found that C atom diffusion activation energy in La containing?phase is lower than that of in La containing‘expanded'?phases.Adding La atoms decreased the diffusion activation energy of C atom in‘expanded'phase and?phase,it shows that the rare earth La can promote the diffusion of carbon atoms inlayer.