Effect Of Mg-treatment On The Distribution And Polymerization Of Inclusions In Steel

The morphology control of non-metallic inclusions(including composition,quantity,size,distribution,etc.)is one of the important tasks in the production of clean steel.The non-metallic inclusions not only have a great influence on the strength,toughness,plasticity and other mechanical properties of the final steel,but also affect the molten steel casting seriously.Mg-treatment has the function of controlling the composition and size of non-metallic inclusions.Therefore,study on the polymerization behavior of inclusions in steel with Mg-treatment,not only has important scientific significance for analysising the mechanism of the dispersive distribution of inclusions,but also can promote the application of Mg-treatment and the development of theory.In this paper,the evolution of inclusion chemical composition,quantity and size in Al,Mg and Al-Mg killed steel was analysised respectively,and the dynamic behavior of non-metallic inclusions in the molten steel was observed by high temperature simulation experiment.The results show that,the inclusions in Al killed steel existed as singular Al2O3 whose morphology was irregularly agminage.And the average size of the inclusions in Mg killed steel was greater than 2?m.,the inclusions as spherical MgO whose average size was about 1?m and constant with time.In Al-Mg killed steel,Mg treatment could make Al2O3 inclusions transform to MgO-Al2O3 inclusions.The proportion of small size inclusions increased significantly after Mg treatment.The results of non-metallic inclusion dynamic observation show that the polymerization phenomenon of Al2O3 inclusions was obvious,the single Al2O3 inclusion grows into clusters by movement,collision and aggregation gradually.The most of MgO inclusions were all nearly spherical,with small size and dispersive distribution,and had no tendency to aggregate.The morphology of MgO·Al2O3 inclusions was irregular,and the size was larger than that of the MgO inclusions,and no obvious aggregation tendency was found.The behavior of nucleation and growth of inclusions was calculated and analysised by using classical nucleation theory,diffusional growing theory,Brownian motion and Ostwald ripening theory.The results show that,the critical nucleation radius of MgO was smaller than that of Al2O3,while the nucleation rate of MgO was larger than that of Al2O3.Ostwald ripening theory was more suitable for descripting the growth behavior of inclusions in molten steel.The growth rate of MgO was smaller than that of Al2O3.The characteristics of MgO nucleation and growth determined their small size and dispersibe distribution in the steel.