Modification of Alumina Inclusions in High-Carbon Hard Wire Steel by Rare Earth Yttrium
High-carbon hard wire steel is widely used in production,and its performance is related to the number,size,shape and distribution of inclusions in the steel.Even a single large inclusion can weaken the stretchability of the wire.Therefore,it is necessary to remove or refine the inclusions in the steel to improve the drawing performance of the steel.In the steelmaking process,aluminum strips are often used for deoxidation.In order to modify the inclusions in aluminum deoxidized steel(Al2O3),an experimental program of rare earth yttrium treatment of inclusions in steel was used.Under the same experimental conditions,aluminum strips were added first,and then rare earth yttrium with different contents was added to explore the effect of yttrium on the modification of inclusions.Based on classical thermodynamics and Factsage software,the evolution law of yttrium activity on inclusions was calculated.The re-sults showed that at about 1800 K(melting temperature of molten steel),yttrium was difficult to react with Al2O3 inclusions,but Al2O3 was modification by rare earth yttrium at low temperature(solidification process).Through the modification of Al2O3 inclusions,the brittle inclusions in the steel were modified into tough inclusions,which reduced the harm of inclusions.After the rare earth yttrium was added,it combined with O,S and Al in the molten steel to generate yttrium oxide,yttrium oxysulfide,aluminum oxide,and yttri-um sulfide.It hindered the aggregation and growth of Al2O3 inclusions and played a role in refining the inclusions in steel.According to the change rule of inclusion types during solidification,the modification process of rare earth yttrium to inclusions was discussed.When the content of yttrium was sufficient(yttrium content exceeded 0.065％),the inclusions in the steel were fully modified,and the final inclusions were Y2O3 and Y2S,.The experiment was carried out with an intermediate frequency induction furnace.Pure iron,recar-burizer and Fe-Mn alloy were added to the alumina crucible of the intermediate frequency induction furnace for melting.When the in-termediate frequency induction furnace was heated to 1873 K,the molten steel was stirred to melt completely.After 5 min,the alumi-num bar was added to deoxidize and stirred the molten steel.After 5 min,the rare earth yttrium particles were added and stirred the molten steel.After 5 min,the molten steel was poured into the mold.The cut experimental samples were polished,and then the struc-ture and morphology of the inclusions were analyzed by scanning electron microscopy(SEM).Combined with Image-ProPlus image processing software,various parameters of inclusions in the shooting area were counted.The statistical results were used to calculate the size distribution,number density,degree of homogeneity,minimum inter-surface distance and area density of the inclusions in the steel,and the results showed that yttrium could modify the inclusions to varying degrees.When the amount of yttrium added was 0.032％,the proportion of small-size inclusions(0～2.5 μm)was 36.1％,the average diameter of the inclusions was 2.97 μm,the number of inclusions was 316,the degree of homogeneity was 0.68,the proportion of inclusions with a minimum inter-surface greater than 10 μm was 24.1％,and the area density of inclusions was concentrated at 0.037％.When the addition amount of yttrium was 0.065％,the proportion of small-size inclusions was 56.6％,the average diameter of inclusions was 2.34 μm,the number of inclusions was 274,the degree of homogeneity was 0.76,the proportion of inclusions with a minimum inter-surface greater than 10 μm was 33.7％,and the area density of inclusions was concentrated at 0.024％.When the amount of yttrium added was 0.087％,the proportion of small-size inclusions was 81.6％,the average diameter of the inclusions was 1.71 μm,the number of inclusions was 223,the degree of homogeneity was 1.02,the proportion of inclusions with a minimum inter-surface greater than 10 μm was 46.7％,and the area den-sity of inclusions was concentrated at 0.015％.Theoretical calculations and experimental results basically verified that the best solution in the three groups of experiments was to add 0.087％of yttrium.In addition,after adding rare earth yttrium,the size of inclusions in each experimental steel was reduced,and the distribution of inclusions was more uniform,which improved the performance of steel.The impact of the slab was reduced,but the modification effect was different.Finally,it was speculated that when the yttrium content was between 0.032％and 0.089％,the optimal addition amount of yttrium was 0.089％.Due to limited data,there was no refinement of the yttrium content range,so the optimal content was only for readers'reference.Rare earth had a modified effect on the inclusions,and the two-dimensional morphology of the inclusions was close to circular.However,the three-dimensional morphology of the inclu-sions was not characterized.Two-dimensional could only reflect the three-dimensional effect and could not achieve the visualization ef-fect of the inclusions.Therefore,the three-dimensional view of the inclusions had research value.
high-carbon hard wire steelAl2O3 inclusionsinclusion modificationrare earth yttrium
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