Effect Of CaF₂-MgF₂ On The Removal Of Inclusions In Steel

Inclusions in steel not only affect the mechanical properties of steel,such as strength,toughness and fatigue life,but also destroy the surface quality of steel,and caused the nozzle clogging during the casting process.Inclusion modification is a kind of method used to reduce the harm of inclusions in steel commonly,many different methods have been put forward for inclusion modification by metallurgical workers,which have their own advantages and disadvantages.In this paper,fluorine-containing compounds was been modifiers,the modification and removal of inclusions in steel were studied.Firstly,the oxygen content in steel was increased by Fe₂O₃ and then molten steel was treated by different amounts of CaF₂,MgF₂,Na₃AlF₆ and CaF₂ and MgF₂ mixture after pure aluminum deoxidation.The effects of different fluorine based modifiers on the content of oxygen and the removal of inclusions were studied in the tube furnace.On this basis,the experiment was carried out by the vacuum medium frequency induction furnace,and finally preliminary industrial test in the industrial field.The study found that:?1?the total oxygen content can been reduced after adding fluorine-containing modifiers in the tube furnace,the lowest oxygen content was modified by CaF₂/MgF₂ mixture,while the use of CaF₂ treatment alone is relatively higher.?2?when using the same fluorine series compounds on the liquid steel processing,with the dosage of modifier was increased from 0 to 1%,the total oxygen content in steel was reduced,but further increase of the amount of modifier,the total oxygen content will increase,so the amount of modifier need in a suitable range;?3?MnS and Al₂O₃ compound type inclusions appeared in the steel after modification agent,the middle position of which with more Al₂O₃ and less MnS,and in the edge MnS will increase,even showing a composite layer shape of MnS wrapped Al₂O₃,In this way,there is a plastic easily deformed MnS as a buffer layer between the Al₂O₃ and the steel matrix,which can reduce the harm of Al₂O₃;There are some complex inclusions,MnS appears in between two or more Al₂O₃,play a connecting role,Al₂O₃ inclusions were connected by MnS,it is beneficial to the Al₂O₃ inclusions aggregation and floating to the slag layer.