Effect of refining slag w(CaO)/w(Al2O3)on removal of inclusions in aluminum deoxidized high-strength steel
Non-metallic inclusions in steel have an important effect on the properties of steel,and large size inclusions have great destructive effects on the properties of steel.In order to study the effect of w(CaO)/w(Al2O3)on re-moval of non-metallic inclusions in aluminum deoxidized high-strength steel in LF refining process,the industrial test of refining slag with different w(CaO)/w(Al2O3)was carried out with Q690 high-strength steel as the research object,and the quantitative analysis was carried out by thermodynamic calculation.The w(CaO)/w(Al2O3)of the three furnaces were 1.58,1.77 and 2.22,respectively,and the refining slag with w(CaO)/w(Al2O3)of 2.22 had the best effect on the removal of inclusions.In the LF refining stage,the number density of inclusions decreased from 13.89/mm2 to 6.56/mm2 with a change rate of 53％,the area fraction decreased from 0.012 2％to 0.003 4％,the change rate was 72％,and the average diameter decreased from 4.82 μm to 3.44 μm with a change rate of 29％.By introducing the inclusion capacity Zh of the refining slag and applying it to the thermodynamic calculation of refi-ning slag with certain solid phase composition,the Zh numbers of refining slag in 3 furnaces were 0.001 940,0.000 307 and 0.000 320,respectively.Because the w(CaO)/w(Al2O3)of 2.22 refining slag had the largest Zh number,it had the best effect on the removal of inclusions.According to the prediction diagram of inclusion capacity,Zh num-ber reached the maximum in the liquid phase line of slag with CaO mass fraction greater than 55％.In order to en-sure the removal effect of inclusions,when the SiO2 mass fraction in the refining slag was 15％,the w(CaO)/w(Al2O3)in refining slag was 2.04-3.05,when the SiO2 mass fraction in the refining slag was 10％,the w(CaO)/w(Al2O3)in refining slag was 1.73-2.22,and when the SiO2 mass fraction in refining slag was 5％,the w(CaO)/w(Al2O3)in refining slag was 1.51-1.55.With the SiO2 content decreases in the refining slag,the suitable refining slag w(CaO)/w(Al2O3)gradually decreases and the range becomes smaller.By adjusting the refining slag w(CaO)/w(Al2O3),the production guidance for aluminum deoxidized high-strength steel is provided.
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