Study On The Behavior Of Si-P-Cu Elements At Grain Boundaries In Steel Under Oxidizing Conditions

In this experiment,three experimental materials containing 0.26%Si,0.51%Cu,containing 0.069%P,0.54%Cu and containing 0.56%Cu were smelted by medium frequency induction furnace.After oxidation of 120 min at 1050?,1100?,and 1150 C,the behavior of Si and Cu elements at grain boundary in steel is investigated by scanning electron microscopy and energy spectrum.Auger electron spectroscopy has been used to study the behavior of P and Cu elements in grain boundaries.The effects of temperature and Si and P elements on the behavior of copper-enriched phase were studied by optical microscopy,scanning electron microscopy and energy spectrum.The results show that in the experimental steel containing 0.26%Si and 0.51%Cu elements,there is a slight segregation of Si elements at the grain boundary,and Cu elements segregated at grain boundaries.With the increase of temperature,the segregation of Si and Cu increases with different degrees.The calculation results of the theory of lattice theory show that thedof?100???110???111?surface between Cu and SiO₂ is less than 6%.SiO₂ and Cu precipitate phase have good match,SiO₂ can be used as the heterogeneous nucleation point of Cu element to influence the behavior of Cu at grain boundary.The segregation of P and Cu elements at grain boundaries increases with the increase of temperature in the experimental steels containing 0.069%P and 0.54%Cu elements.The Cu element hinders the segregation of P elements at the grain boundary and the P element weakens the diffusion of Cu elements at the grain boundary.The calculated results show that the free energy of the grain boundary segregation of P and Cu elements decreases with increasing temperature.With the increase of oxidation temperature,the number of copper-enriched phase near the steel matrix oxide increases and the size increases.In the experimental steel containing 0.069%P,the P element hinder the diffusion of Cu elements along the grain boundaries,and reduce the number of copper-enriched phase,which makes the copper-enriched phase become massive from liquid film.The internal oxide with Fe₂SiO₄ mainly in the steel containing 0.26%Si elements inhibits the diffusion of Cu elements along with the grain boundary to the steel-scale interface in the matrix,and make the Cu disperse in the matrix.The number of copper-enriched phase is reduced.It prevents the Cu elements enriching in the interface to permeate the steel matrix along with the grain boundary,thus reducing the number of copper-enriched phase.