Study On Morphology Control Of B-type Inclusions In High Carbon Hard Wire Steel By Calcium And Magnesium Treatment

Theoretical calculation and laboratory study on the process of treating B-type inclusions in high-carbon hard wire steel with calcium,magnesium and calcium-magnesium compound were carried out.The irregular alumina inclusions are transformed into spherical calcium aluminate inclusions by calcium treatment.With the increase of Ca/Al mass ratio in molten steel,the liquid effect of inclusions is better,and the segregation area of inclusions is reduced,which is beneficial to the control of inclusion distribution uniformity.According to the unreacted core model,the kinetics of calcium treatment of class B inclusions was studied.With the increase of Ca content in molten steel,the complete denaturation time of inclusions decreases significantly.When different types of inclusions are transformed,the time required for the transformation rate of inclusions from 57.8%to 100%is about 6 times that of the transformation rate from 0 to 57.8%.With the increase of the radius of inclusions,the complete denaturation time is gradually prolonged.Through verification,the calculated results of the model are basically consistent with the experimental results.When Mg content is less than 0.002%,alumina inclusions are denatured into magnesia-alumina spinel.When the content is higher than 0.0020%,the alumina inclusions are denatured into magnesia,which is smaller than the magnesia-alumina spinel inclusions.The kinetic calculation results show that the diffusion of magnesium in magnesium aluminate layer is the limiting link in the process of inclusion denaturation.With the increase of magnesium content in molten steel,the denaturation time of inclusions is significantly shortened.The time required for the conversion rate of inclusions from 50%to complete denaturation is 8 times that of the conversion rate from 0-50%.After calcium-magnesium composite treatment,the size of inclusions decreased from 3.2?m to 1.41?m,and the modification effect was better than that of single element treatment.When magnesium content in molten steel is lower than calcium content,the segregation of inclusions is obvious,and high magnesium content is beneficial to fine dispersion of inclusions in high carbon hard wire steel.Thermodynamics of formation of calcium aluminate inclusions and spinel inclusions in experimental steel were calculated.The calculation results show that with the increase of calcium addition,the alumina inclusions gradually change into liquid calcium aluminate inclusions when the aluminum addition in steel is 0.0050%.When a Al activity is greater than 0.0018%,the type of inclusions mainly depends on magnesium activity in steel.With the increase of magnesium activity,the inclusions gradually change as follows:Al₂O₃?MgO·Al₂O₃?MgO.