Smelting method for low-alkalinity and low-total-iron converter dephosphorization

Abstract

The invention discloses a smelting method for low-alkalinity and low-total-iron converter dephosphorization, and belongs to the technical field of steel smelting. Ore, lime, dolomite and light-burned dolomite are added for slagging in the early stage and the middle stage of converter smelting; after TSC measurement in the later period of smelting, high-lance-position oxygen supply blowing is adopted, ore is added in the period to promote slagging and dephosphorization, then low-lance-position oxygen supply blowing is adopted, DRI is added into the converter in the period, bottom blowing is reasonably controlled to reduce the total iron content of the steel slag, generation of MgO solid particles and C2S-C3P solid solution is promoted, and therefore the purposes of low alkalinity and low total iron dephosphorization at the end point of the converter are achieved. The alkalinity R of the final slag of the converter is controlled to be 2.4-2.8, the content of MgO is controlled to be 8.0-11.0%, the content of total iron is controlled to be 10.0-15.0%, and the content of P in the final molten steel is smaller than or equal to 0.02 wt%.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method for low-basicity and low-total-iron converter dephosphorization. Background Art

[0002] Society is paying more and more attention to environmental protection, and is asking the metallurgical industry to take the path of green development. Converter-less slag can significantly reduce the emission of waste slag. In addition, by adopting converter-less slag smelting, the amount of waste slag generated can be significantly reduced, thereby effectively reducing the negative impact on the environment. Reducing the low basicity and total iron content of converter slag can effectively reduce the amount of converter steelmaking slag, which helps promote the development of metallurgical converter steelmaking in a green and sustainable direction.

[0003] Generally, dephosphorization requires thermodynamic conditions of low temperature, high basicity, high oxidizability, and large slag volume, as well as good slag formation and molten pool stirring dynamic conditions to meet the converter dephosphorization requirements. x In the liquid phase, it reacts with CaO to form 3CaO·P2O5, and then 3CaO·P2O5 forms a solid solution 3CaO·P2O5-2CaO·SiO2 (C2S-C3P) with 2CaO·SiO2 in the slag to achieve dephosphorization and solidification. Theoretical basis of low-slag smelting: Phosphorus in steel slag is mainly enriched in the C2S-C3P solid solution phase, and low basicity is conducive to the formation of C2S phase in the slag. Therefore, the dephosphorization process technology of converter smelting develops towards low-basicity and multi-phase slag dephosphorization. However, this research mainly focuses on the double slag method. In the early stage of converter smelting, low temperature is conducive to low basicity dephosphorization and slag pouring, and then slag smelting is carried out again. However, due to the increase in temperature at the end of the converter, in order to achieve dephosphorization, the basicity is usually increased and the total iron content in the slag is increased. Even if the basicity is reduced, in order to achieve the purpose of dephosphorization, it is necessary to increase the FeO in the slag. x To increase the oxidizability, this will inevitably lead to an increase in the total iron content of the final slag. In addition, studies have shown that increasing the basicity and FeO x It will cause the phosphorus-rich phase C2S to decrease, which is not conducive to the solidification of P. Some scholars pointed out that after the end of converter smelting, extending or strengthening the bottom blowing will promote the FeO in the slag x The total iron content of the final slag can be reduced by continuing to react with the molten steel [C]. However, this method has limited effects on the reduction of total iron and the speed thereof. Meanwhile, enhanced bottom blowing will cause the molten steel to further corrode the refractory materials at the furnace bottom and shorten the life of the furnace bottom. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a smelting method for low-basicity, low-total iron converter dephosphorization, which solves the problem of high basicity by reasonably controlling the basicity to increase the C2S phase content in the final slag, and solves the problems of final slag overoxidation and high total iron by optimizing the endpoint control, thereby achieving the purpose of low-basicity, low-total iron and low-slag smelting.

[0005] The technical principle of the present invention is to promote the formation of C2S phase in the final slag of converter smelting by controlling the basicity, total iron content and MgO content, thereby improving the dephosphorization effect. (1) Thermodynamic simulation calculations found that reducing total iron is conducive to the precipitation of MgO high melting point phase, as well as the formation of 3CaO·P2O5 and 2CaO·SiO2 phases, thereby promoting the solidification of phosphorus (see Figure 1 ). The present invention reduces the gun position at the end of converter blowing, adds hydrogen-based reduced iron balls DRI, and utilizes the C in DRI and FeO in slag to x reaction, quickly reducing the total iron content of the final slag. (2) MgO in the slag is beneficial to the precipitation and refinement of C2S, see Figure 2 . The test found that the P content in fine and dispersed C2S is higher, and the phosphorus fixation effect is better. (3) High basicity leads to a decrease in the proportion of C2S phase in the slag. At the same time, high basicity leads to an increase in the total iron content of the final slag; when the basicity is high, increasing MgO leads to an increase in the total iron content, but increasing the MgO content in the lower basicity area will not cause an increase in the total iron content (see Figure 3 ). Therefore, moderately reducing basicity is beneficial to reducing total iron. Increasing MgO content in low basicity areas can promote the formation and refinement of phosphorus-rich phase C2S without causing an increase in total iron. This is the theoretical basis for the low basicity and low total iron converter dephosphorization smelting method.

[0006] Based on the above principles, the smelting method of low basicity and low total iron converter dephosphorization of the present invention adopts the following technical solution: lightly burned dolomite is added immediately after the TSC determination is completed to increase the MgO content in the slag. After the TSC determination, high-lance oxygen blowing is adopted, during which ore is added to promote slag dephosphorization. Then, low-lance oxygen blowing is adopted, during which DRI is added to the converter, and the bottom blowing is reasonably controlled to reduce the total iron content of the slag, promote the formation of MgO solid phase particles and C2S-C3P solid solution, thereby achieving the purpose of low basicity and low total iron dephosphorization at the converter end. Specifically, the following steps are included: Step 1: Ore, lime, dolomite and light-burned dolomite are added to make slag in the early and middle stages of converter smelting. No more lime is added after TSC determination. The purpose is to achieve low slag total iron control and increase MgO content by utilizing low basicity.

[0007] Step 2: TSC measurement is carried out in the later stage of smelting. After TSC measurement, the first process parameter adjustment is carried out: the bottom blowing flow rate is controlled at 0.08±0.01m 3 / (min·t), the top gun position is raised to between 1.60 and 1.80m and blowing is continued for 0.5 to 1.5min, during which light-burned dolomite and ore are added; the purpose is to increase the MgO content in the later slag.

[0008] Step 3: After TSC determination, adjust the process parameters for the second time: lower the top gun position to 1.25-1.45m, continue blowing for 0.5-1.5min, then stop blowing. After adding hydrogen-based reduced iron DRI, control the bottom blowing flow rate at 0.06±0.01m 3 / (min·t); the purpose is to use DRI to reduce FeO in slag x Reduce total iron content and promote the formation of C2S-C3P solid solution.

[0009] Step 4: After the TSO determination at the converter smelting end point, DRI is added for bottom blowing and steel is tapped; the relationship between the amount of DRI added and the bottom blowing time and the oxygen [O] content w[O] of the molten steel determined by TSO is: When 350ppm≤w[O]<450ppm, do not add DRI and tap steel after 1-2min of bottom blowing; When 450ppm≤w[O]<550ppm, add 500-800kg of DRI and tap after 2-3min of bottom blowing; When 550ppm≤w[O] ≤650ppm, add 800-1000kg of DRI and tap the steel after bottom blowing for 3-5min.

[0010] Furthermore, in step 1, the gun position in the early stage of smelting is controlled at 1.65±0.1m, and the bottom blowing flow rate is 0.06±0.01m 3 / (min·t); the gun position in the middle stage of smelting is controlled at 1.55±0.1m, and the bottom blowing flow rate is 0.04±0.01m 3 / (min·t).

[0011] Furthermore, in the step 2, the C weight content w(C) of the molten steel is controlled at 0.20-0.40% by TSC, and the temperature of the molten steel is controlled at 1570±10°C.

[0012] Furthermore, in the step 2, 500-1500 kg of light-burned dolomite and 500-1000 kg of ore are added in sequence.

[0013] Furthermore, in the step 2, when 0.2%≤w(C)<0.3%, 500-800kg of ore and 500-1000kg of light-burned dolomite are added, and the top gun is continuously blown for 0.5-1.0min; When 0.3%≤w(C)≤0.4%, add 800-1000kg of ore and 1000-1500kg of light-burned dolomite, and continue blowing with the top gun for 1.0-1.5min.

[0014] Furthermore, in the step three, if 0.5≤top gun continued blowing time<1.0min, 300-400kg of DRI is added; if 1.0≤top gun continued blowing time≤1.5min, 400-500kg of DRI is added.

[0015] Furthermore, in step 4, the temperature of the molten steel at the end of converter smelting is controlled at 1600-1640° C., the weight content of C is controlled at 0.03-0.08%, and the weight content of [O] is controlled at 350-650 ppm.

[0016] Furthermore, the basicity R of the final slag from converter smelting is 2.4-2.8, the weight content of MgO is 8.0-11.0%, and the weight content of total iron is 10.0-15.0%.

[0017] Furthermore, the particle size of the DRI is controlled at 6.0-10.0 mm, and its components include C: 2.0-6.0%, P: 0.007-0.012%, S: 0.02-0.030%, and TFe: 85-95% in terms of mass percentage.

[0018] Furthermore, the P weight content in the molten steel at the end of converter smelting is ≤0.02%.

[0019] The beneficial effects of adopting the above technical solution are as follows: (1) The present invention can effectively reduce the consumption of lime and steel materials in the converter, thereby reducing the smelting cost. (2) The hydrogen-based reduced iron content of the converter is increased, slag-less smelting is achieved, slag discharge and preheating losses are reduced, and the green development of metallurgy is promoted. (3) The final oxidation of the converter is reduced, the consumption of deoxidized alloy is reduced, and the metal recovery rate is increased. (4) The content of high-melting-point phases MgO and C2S in the slag is increased, the splashing slag protection effect is improved, and the life of the converter refractory is extended.

[0020] By adopting the smelting method of the present invention, the basicity R of the final converter slag is controlled at 2.4-2.8, the MgO content is controlled at 8.0-11.0%, the total iron content is controlled at 10.0-15.0%, and the P content in the final molten steel is ≤0.02wt%, thereby achieving the purpose of low basicity, low total iron and low slag dephosphorization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the relationship between the total iron (T.Fe) content and C2S in converter slag; Figure 2 This is the metallographic image of MgO in converter slag promoting the refinement of C2S phase; Figure 3 This is a relationship diagram between the basicity R of converter slag and the MgO and total iron (T.Fe) content in the slag. DETAILED DESCRIPTION

[0022] A smelting method for low basicity and low iron converter dephosphorization is applied to a top and bottom double-blown converter, with a converter loading of 150±5t and a steel output of 140±10t. The specific steps are as follows: Step 1: In the early and middle stages of converter smelting, ore, lime, dolomite and light-burned dolomite are added to make slag. After TSC determination, no lime is added. In the early stage of smelting, the gun position is controlled at 1.65±0.1m, and the bottom blowing flow rate is 0.06±0.01m 3 / (min·t); the gun position in the middle stage of smelting is controlled at 1.55±0.1m, and the bottom blowing flow rate is 0.04±0.01m 3 / (min·t).

[0023] Step 2: TSC determination is carried out in the later stage of smelting, and the C weight content w(C) of molten steel is controlled at 0.20-0.40%, and the temperature of molten steel is controlled at 1570±10℃; After TSC measurement, the first process parameter adjustment was carried out: the bottom blowing flow rate was controlled at 0.08±0.01m 3 / (min·t), the top gun position is raised to between 1.60 and 1.80m and the blowing is continued for 0.5 to 1.5min, during which light-burned dolomite and ore are added; When 0.2%≤w(C)<0.3%, add 500-800kg of ore and 500-1000kg of light-burned dolomite, and continue blowing with the top gun for 0.5-1.0min; When 0.3%≤w(C)≤0.4%, add 800-1000kg of ore and 1000-1500kg of light-burned dolomite, and continue blowing with the top gun for 1.0-1.5min.

[0024] Step 3: After TSC determination, adjust the process parameters for the second time: lower the top gun position to 1.25-1.45m, continue blowing for 0.5-1.5min, then stop blowing. After adding hydrogen-based reduced iron DRI, control the bottom blowing flow rate at 0.06±0.01m 3 / (min·t); If 0.5≤top gun continuous blowing time<1.0min, add 300~400kg of DRI; If 1.0≤top gun continuing blowing time≤1.5min, add 400-500kg of DRI.

[0025] Step 4: Determine TSO. The temperature of the molten steel at the end of converter smelting is controlled at 1600-1640°C, the C weight content is controlled at 0.03-0.08%, and the [O] weight content is controlled at 350-650ppm. The relationship between the amount of DRI added and the bottom blowing time and the oxygen [O] content w[O] of the molten steel determined by TSO is: When 350ppm≤w[O]<450ppm, do not add DRI and tap steel after 1-2min of bottom blowing; When 450ppm≤w[O]<550ppm, add 500-800kg of DRI and tap after 2-3min of bottom blowing; When 550ppm≤w[O] ≤650ppm, add 800-1000kg of DRI and tap the steel after bottom blowing for 3-5min.

[0026] The particle size of DRI is controlled at 6.0-10.0 mm. Calculated by mass percentage, its components include C: 2.0-6.0%, P: 0.007-0.012%, S: 0.02-0.030%, and TFe: 85-95%.

[0027] By adopting the above-mentioned smelting method, the basicity R of the final slag of converter smelting is 2.4-2.8, the weight content of MgO is 8.0-11.0%, the weight content of total iron is 10.0-15.0%; the weight content of P in the molten steel is ≤0.02%.

[0028] The process parameters of each embodiment are shown in Table 1, and the final slag composition and P content of molten steel are shown in Table 2.

[0029] Table 1. Smelting process parameters of Examples 1-8

[0030] Table 2: Final slag composition and P content of molten steel in Examples 1-8 .

Claims

1. A smelting method for low basicity and low total iron converter dephosphorization, characterized in that: The following steps are involved: Step 1: In the early and middle stages of converter smelting, ore, lime, dolomite and light-burned dolomite are added to make slag. After TSC determination, no lime is added. Step 2: TSC measurement is carried out in the later stage of smelting. After TSC measurement, the first process parameter adjustment is carried out: the bottom blowing flow rate is controlled at 0.08±0.01m 3 / (min·t), the top gun position is raised to between 1.60 and 1.80m and the blowing is continued for 0.5 to 1.5min, during which light-burned dolomite and ore are added; Step 3: After TSC determination, adjust the process parameters for the second time: lower the top gun position to 1.25-1.45m, continue blowing for 0.5-1.5min, then stop blowing. After adding hydrogen-based reduced iron DRI, control the bottom blowing flow rate at 0.06±0.01m 3 / (min·t); Step 4: After the TSO determination at the converter smelting end point, DRI is added for bottom blowing and steel is tapped; the relationship between the amount of DRI added and the bottom blowing time and the oxygen [O] content w[O] of the molten steel determined by TSO is: When 350ppm≤w[O]<450ppm, do not add DRI and tap steel after 1-2min of bottom blowing; When 450ppm≤w[O]<550ppm, add 500-800kg of DRI and tap after 2-3min of bottom blowing; When 550ppm≤w[O] ≤650ppm, add 800-1000kg of DRI and tap the steel after bottom blowing for 3-5min.

2. The smelting method of low basicity and low total iron converter dephosphorization according to claim 1, characterized in that: In step 1, the gun position in the early stage of smelting is controlled at 1.65±0.1m, and the bottom blowing flow rate is 0.06±0.01m 3 / (min·t); the gun position in the middle stage of smelting is controlled at 1.55±0.1m, and the bottom blowing flow rate is 0.04±0.01m 3 / (min·t).

3. The smelting method of low basicity and low total iron converter dephosphorization according to claim 2, characterized in that: In the step 2, the C weight content w(C) of the molten steel is controlled at 0.20-0.40% by TSC, and the temperature of the molten steel is controlled at 1570±10°C.

4. The smelting method of low basicity and low total iron converter dephosphorization according to claim 3, characterized in that: In the step 2, 500-1500 kg of light-burned dolomite and 500-1000 kg of ore are added in sequence.

5. The smelting method of low basicity and low total iron converter dephosphorization according to claim 4, characterized in that: In the step 2, when 0.2%≤w(C)<0.3%, 500-800kg of ore and 500-1000kg of light-burned dolomite are added, and the top gun is continuously blown for 0.5-1.0min; When 0.3%≤w(C)≤0.4%, add 800-1000kg of ore and 1000-1500kg of light-burned dolomite, and continue blowing with the top gun for 1.0-1.5min.

6. The smelting method of low basicity and low total iron converter dephosphorization according to claim 5, characterized in that: In the step 3, if 0.5≤top gun continued blowing time<1.0min, 300-400kg of DRI is added; if 1.0≤top gun continued blowing time≤1.5min, 400-500kg of DRI is added.

7. The smelting method of low basicity and low total iron converter dephosphorization according to claim 6, characterized in that: In the step 4, the temperature of the molten steel at the end of converter smelting is controlled at 1600-1640° C., the weight content of C is controlled at 0.03-0.08%, and the weight content of [O] is controlled at 350-650 ppm.

8. The low-basicity, low-total-iron converter dephosphorization smelting method according to any one of claims 1 to 7, characterized in that: The basicity R of the final slag from converter smelting is 2.4-2.8, the weight content of MgO is 8.0-11.0%, and the weight content of total iron is 10.0-15.0%.

9. The smelting method of low basicity and low total iron converter dephosphorization according to claim 8, characterized in that: The P weight content in the molten steel at the end of converter smelting is ≤0.02%.

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