The main metal material for converter steelmaking is molten iron. The molten iron consumption of 100t converter is 970~1000kg/t steel, accounting for about 90% of the total loading. Scrap steel mainly includes pig iron, rebar cutting heads, and continuous casting billet cutting heads and tails.
The main causes of converter lining erosion are:
(1) Impact of molten iron and scrap steel on the lining;
(2) Mechanical erosion of molten steel, slag and furnace gas on the lining during the smelting process;
(3) Chemical erosion of slag and furnace gas on the lining;
(4) Damage to the lining caused by rapid cooling and heating;
(5) Erosion of the lining by oxygen jet. The capacity of a 100t converter is 92-95t, the top-blown oxygen flow rate is 18000~19500m3/h, and after the first furnace of steel blowing is completed and the molten steel is discharged, the scouring depth of the converter lining is evaluated. The horizontal axis is the height of the converter centerline calculated from the lowest point of the bottom of the converter as 0.
Under different gun positions, the scouring depth of the furnace bottom by the oxygen jet is not much different. The scouring of the lining in the molten pool is the most serious. As the gun position increases, the scouring depth of the lining in the molten pool increases. For the furnace wall above the molten pool, the scouring degree gradually weakens with the increase of the gun position height.
The melting performance of the slag affects the smelting process and the slag splashing protection, and then affects the life of the lining.
1. The influence of V and Ti in molten iron
The existence form of vanadium in vanadium-containing steel slag is determined by thermodynamic calculation as V2O5, and the existence form of titanium is TiO2. The influence of V2O5 on reducing the melting temperature of steel slag is greater than that of FeO. When the V2O5 content is low, the effect of V2O5 on the melting temperature of the CaO-SiO2 slag is very significant, especially when CaO/SiO2≥1.5, the reduction rate is the largest. Therefore, the presence of V2O5 in the slag will have an adverse effect on the lining of the magnesia carbon brick. The foaming amplitude of the basic steelmaking slag system containing TiO2 is the largest when the slag basicity is 2.1 and the TiO2 is 4%~6%. The foaming is serious and the reaction in the furnace is fierce, which enhances the erosion of the metal and slag on the converter lining.
2. Effect of slag components on slag melting temperature
TFe in slag: The basicity of converter final slag is 3.5~4.0, 6%~10% MgO. Experimental measurements show that TFe in slag has a significant effect on the melting temperature of slag, as shown in Figure 2(a). When the TFe content in slag increases, the melting point of slag decreases. According to the empirical formula: Melting temperature = 0.7498×MgO%+4.5017×R-10.5335×TFe+1582, where R is the basicity of slag. When the TFe content reaches more than 20%, the melting temperature ranges from 1320 to 1395℃. (2) TiO2: For every 1% increase in TiO2 content, the hemispherical temperature of the final slag decreases by about 5℃. When the TiO2 content is 3.5%, the hemispherical temperature decreases by 17.5℃. (3) Al2O3: In the absence of Fe2O3, Al2O3 in the slag will not reduce the liquidus temperature of the slag. The Al2O3 content in the slag is 1.25%, which has little effect on the melting temperature of the slag. (4) MnO: MnO has a smaller effect on the melting temperature of the slag than MgO. It can slightly increase the melting temperature of the slag at a basicity of 1.5, which is not only harmless but also beneficial to the furnace lining. (5) MgO: As shown in Figure 2(b), increasing the MgO content can significantly increase the hemispherical temperature of the slag.
3. Factors affecting the melting rate of slag
(1) Low TFe slag. When the converter final slag (FeO) is 10%~15%, when (TiO2) increases from 0.85% to 2%, 4% and 6%, the melting rate index of the slag increases from 1.1 to 5.1, 8.1 and 8.9 respectively, and when Al2O3 increases from 1.8% to 4% and 6%, the melting rate index increases from 1.1 to 5.1 and 4.1 respectively, that is, in low TFe slag, TiO2 and Al2O3 increase the melting rate of the slag. (2) High TFe slag. When the converter final slag (FeO) is 20%-25%, when (TiC)2) increases from 0.85% to 2%, 4% and 6%, the slag melting rate index changes from 8 to 8.1 and 8.7, respectively, with no significant change. When Al2O3 increases from 1.8% to 4% and 6%, the melting rate index increases from 8 to 9 and 9.5, with a small increase. That is, in high TFe slag, TiO2 and Al2O3 do not affect the slag curing rate, because under high TFe conditions, the slag viscosity is low, so the influence of TiO2 and Al2O3 is very small.
Through the discussion of slag melting performance, it is concluded that:
(1) Reducing the TFe content in the slag not only increases the slag melting temperature, but also reduces the adverse effect of MnO on the slag caused by high Fe2O3, improves the slag splashing effect, and achieves the purpose of long furnace life;
(2) Control the early foaming splashing to ensure the dephosphorization effect and slag volume, and reduce the lining erosion caused by splashing;
(3) For high-TFe slag with high Al2O3 content, ensuring a certain MgO content and SiO2 content can reduce the effect of Al2O3 on the slag melting point temperature;
(4) Reducing the FeO content - (FeO) in the converter slag will improve the slag splashing furnace protection effect;
(5) The main factors causing the slag to become thinner during the vanadium-titanium hot metal smelting process are V2O5, TiO2 and Al2O3. V2O5 forms low-melting-point compounds with CaO or MgO to dissolve the lining surface, and TiO2 forms low-melting-point compounds with FeO and MnO to penetrate and peel off the lining. MnO forms a high melting point solid solution with CaO or MgO, which is beneficial to protecting the furnace lining. In the case of low Fe2O3 content, Al2O3 furnace lining is harmless.
