Effect Of Rare Earth Lanthanum On Segregation Of Arsenic And Precipitation Of Inclusions In Steel

The continuous enrichment of the residual element arsenic in steel is one of the important factors affecting the quality of China's steel products.Arsenic is prone to segregation and segregation at the grain boundaries during the solidification and cooling of the molten steel,which seriously harms the hot workability and mechanical properties of the steel.High quality iron ore and molten iron are commonly used in industrial production to dilute arsenic-containing raw materials to reduce the arsenic content in steel products.However,the drastic fluctuation of the price of imported iron ore prompts China to continuously develop and utilize domestic low-grade iron ore,which intensifies the enrichment of residual element arsenic in steel.In the current smelting process,it is difficult to remove it.When the arsenic content is not high,it is a feasible control method to improve its occurrence state in steel by adding inhibitors.Rare earth can form high melting point compounds with the residual element arsenic in steel,and inhibit the segregation of arsenic atoms,thereby improving its occurrence state in steel.This subject is based on the first-principles method of density functional theory,combined with thermodynamic and kinetic calculations,to study the occupational tendency of rare earth and arsenic in austenite and ferrite and its effect on grain boundaries The precipitation behavior of inclusions was verified with laboratory experiments.Based ?3[110](112)ferrite grain boundaries and ?5[100](012)austenite grain boundary models,the effects of rare earth and As atoms on ferrite and austenite grain boundaries were discussed.The results show that the Laand As atoms in ferrite and austenite tend to occupy the grain boundary positions,and show a tendency to segregate for competition.When the two occupy the ferrite grain boundary,the charge density between the iron atoms on both sides of the grain boundary is significantly increased,strengthening the grain boundary;while the lanthanum occupying the position of the austenite grain boundary causes the grain boundary to expand seriously,resulting in inter-atomic The charge density is significantly reduced and the grain boundaries are brittle.The non-aqueous solution electrolysis method was used to successfully extract rare earth inclusions,including La₂O₃?La₂O₂S and La-S-As.The arsenic-containing inclusions LaAs and La-S-As can be generated during the solidification of molten steel,which is consistent with the enrichment rule of Laand As at the grain boundaries.The calculation result of the plane mismatch degree shows that the plane mismatch degree of LaS and LaAs is 4.94%,the former can be used as the effective heterogeneous nucleation core of the latter,and the interface between the two is combined by a covalent bond.The structure of La-S-As inclusions was identified as cubic crystal system,which can be considered as a solid solution formed by LaAs and LaS.The calculation results show that when the molar ratio of LaS to LaAs is 3:1,La-S-As has the lowest energy and the most stable structure,which is similar to the experimental results.