Mechanism investigation on inclusion evolution in Nb-Ti micro-alloyed steel with Mg treatment
Under industrial conditions,the Mg treatment test of Nb-Ti micro-alloyed steel was carried out.The evolution of nonmetallic inclusions in micro-alloyed steel treated with Mg was analyzed.The results show that,Al2O3 inclusion is the main product of aluminum deoxidation in micro-alloyed steel.After Ca treatment,Al2O3 inclusions are reduced and transformed into CaO-Al2O3 inclusions,and part of MnS inclusions are transformed into CaS inclusions.After Ca treatment is changed to Mg treatment in the refining stage,Al2O3 inclusions of aluminum deoxidation product can be denatalized to MgO-Al2O3 inclusions.Before Mg treatment,the inclusions in LF are mainly Al2O3 inclusions.After Mg treatment and Ti alloying,the main inclusions in steel become MgO-Al2O3 inclusions,MgO inclusions and TiN inclusions.The final inclusions in the billet are MgO-Al2O3 coated with CaS/MnS and(Nb,Ti)N complex inclusions.The size of inclusions treated with Ca and Mg was compared,and the size of inclusions mainly distributed within 5 μm.The proportion of inclusions within 2 μm formed by Mg treatment is higher than that by Ca treatment,which indicates that magnesium treatment can fine inclusions better.The formation of a large number of dispersed small inclusions is helpful to improve the comprehensive mechanical properties of steel.
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