A method for smelting low-manganese and low-phosphorus molten steel in a converter

Abstract

The present invention relates to a method for smelting low-manganese and low-phosphorus molten steel in a converter. By slagging multiple times in the converter, the temperature, molten steel composition, and slag composition during the smelting process are strictly controlled. The converter is smelted with an empty furnace. During the first blowing, the molten bath temperature is controlled below 1400 °C, and light-burned dolomite + lime + ore are used for slagging. During the second blowing, the process temperature is strictly controlled, and at the end of the second blowing, the molten bath temperature ≤ 1550 °C and the carbon content ≤ 0.20%. During the third blowing, the temperature is raised again, and the molten bath temperature is controlled at 1580 - 1620 °C. When smelting in this way, when the manganese content in the hot metal is about 0.45% + ordinary scrap steel, the manganese content at the end of the converter ≤ 0.03% and the phosphorus content ≤ 0.005%.

Description

Technical Field

[0001] The present invention relates to a method for smelting low-manganese and low-phosphorus molten steel in a converter, belonging to the field of metallurgical technology. Background Art

[0002] Industrial pure iron is a metal material with a very low carbon content. Its chemical composition is mainly iron, and the lower the content of other alloying elements, the better. The room-temperature structure of industrial pure iron is mainly ferrite, which has the characteristics of soft texture, high toughness, good ductility, and excellent electromagnetic properties. The manganese content requirement of the industrial pure iron involved in the present invention is ≤0.03%. However, due to the problem of ore sources in a certain company, the manganese content in the hot metal is relatively high, ranging from 0.40% to 0.60%, with an average of 0.50%. When smelting with this hot metal + ordinary scrap steel and using the ordinary single slag method, the average manganese content at the end of the converter is 0.15%. When using the ordinary double slag method, the average manganese content at the end of the converter is 0.08%. It is difficult to achieve a stable de-manganese target.

[0003] CN115261564A Non-aluminum deoxidized raw material pure iron for amorphous soft magnetic thin strip and its preparation method uses desulfurized and de-manganese hot metal, without adding scrap steel, and requires the manganese content in the de-manganese hot metal to be controlled within 0.25%. Combined with the double slag method in the converter, the manganese content at the end of the converter can be stably controlled within 0.05%. For higher manganese content in the hot metal and lower manganese content at the end of the converter, this control method cannot achieve the manganese control target.

[0004] CN110453032A A method for smelting ultra-low manganese steel using high-manganese hot metal provides a method for smelting ultra-low manganese steel using high-manganese hot metal. In the converter process, the double slag method is used to remove most of the manganese elements in the hot metal, and the low-temperature tapping of the converter and the LF refining deep de-manganese process are used for further de-manganese. When the manganese content in the hot metal is higher than 0.40%, the manganese content in the molten steel can be stably controlled below 0.02%. Compared with this patent, the manganese content in the hot metal of the present invention is higher, and the de-manganese task can be completed in the converter, without the need for further de-manganese and slag skimming operations in refining, and the production is more stable without increasing the difficulty of production organization.

[0005] CN113774277A A super-low carbon and ultra-low manganese industrial pure iron and its preparation method obtain low-sulfur hot metal through KR desulfurization of hot metal and then pour it into the converter; in the converter smelting, through one-time slag pouring and a series of technical measures such as controlling the addition amount of solvents, the temperature of molten steel, the lance position of the oxygen lance, and the free oxygen content in the molten steel, low-manganese tapping is achieved. Subsequently, through LF refining de-manganese and RH oxygen blowing de-manganese, the manganese content in the molten steel is finally ≤0.035%. Compared with it, the manganese content at the end of the converter of the present invention is lower, and the production target of ≤0.03% manganese in the molten steel can be achieved without refining de-manganese, and the operation is more concise.

[0006] It can be seen that it is difficult to complete the expected dephosphorization and demanganization tasks in the converter at present. Therefore, how to ensure the completion of dephosphorization and demanganization in the converter, improve the castability of molten steel and the coordinated production arrangement is the technical problem to be solved by the present invention. Summary of the Invention

[0007] To solve the above problems, the present invention provides a method for smelting low-manganese and low-phosphorus molten steel in a converter. By using converter smelting, through controlling the temperature, slag composition and molten steel composition in the smelting process, slag-making is carried out multiple times. In the converter, the manganese content in hot metal can be reduced from 0.5% to below 0.03%, and the demanganization rate can reach over 90%.

[0008] The specific method steps and the controlled method parameters are as follows:

[0009] Adding scrap steel and charging hot metal → primary blowing → primary slag tapping → secondary blowing → secondary slag tapping → tertiary blowing → tapping. The specific operation steps are as follows:

[0010] Step 1: Adding scrap steel and charging hot metal, with the hot metal ratio being 75 - 85% and the scrap steel ratio being 15 - 25%.

[0011] Step 2: Primary blowing. After lowering the lance, the top-blowing oxygen supply intensity is controlled at 3.5 - 4.0 Nm 3 / t / min, the lance position of the oxygen lance is controlled at 1.7 - 2.0 m, the oxygen blowing time is controlled at about 6 - 8 min. Using calcined dolomite, lime and ore for slag-making, where the addition amount of calcined dolomite is 15 - 25 kg / t, the addition amount of lime is 3 - 7 kg / t, and the addition amount of ore is 15 - 30 kg / t. At the end of the primary blowing, the molten bath temperature ≤ 1400 °C.

[0012] Step 3: Primary slag tapping, with the primary slag tapping amount ≥ 80%.

[0013] Step 4: Secondary blowing. The top-blowing oxygen supply intensity is controlled at 4.0 - 4.5 Nm 3 / t / min, the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; for secondary blowing, a combination of calcined dolomite and lime is used for slag-making, and a combination of ore + raw dolomite is used for temperature control; at the end of the secondary blowing, the molten bath temperature is controlled within 1550 °C, and at the same time, the carbon content in the molten steel is 0.10 - 0.20%; the addition amount of calcined dolomite is controlled at 5 - 12 kg / t, the addition amount of lime is controlled at 7.5 kg / t - 15 kg / t; the addition amount of ore is controlled at 5 - 15 kg / t, and the addition amount of raw dolomite is controlled at 5 - 15 kg / t.

[0014] Step 5: Secondary slag tapping, with the secondary slag tapping amount ≥ 80%.

[0015] Step 6: Tertiary blowing. The top-blowing oxygen supply intensity is controlled at 4.0 - 4.5 Nm 3 / t / min, the lance position is controlled at 1.3 - 1.6 m; 3 - 8 kg / t of light burned dolomite is added. The tapping temperature is controlled at 1580 - 1620 °C, and the tapping carbon content is ≤0.05%.

[0016] Further, as a preference, in step one, before charging hot metal and scrap, after slag splashing for the previous heat, all the slag is poured out, and it is required that the converter is empty without remaining slag; the manganese content in the hot metal is 0.4 - 0.6%, and the manganese content in the scrap is 0.3 - 0.6%.

[0017] Further, as a preference, in step two, the chemical composition of the molten steel at the end of the first blowing is: [C] 3.0 - 3.5%, [Mn] 0.1 - 0.2%, [P] 0.03 - 0.06%; the chemical composition of the slag is CaO: 20% - 35%, MgO: 10% - 15%, SiO2: 15% - 25%, FeO: 20% - 25%, MnO: 10% - 20%, and some inevitable impurities, and the slag basicity is 1.0 - 1.5.

[0018] Further, as a preference, in step four, the chemical composition of the molten steel at the end of the second blowing is: [C] 0.10 - 0.20%, [Mn] 0.03 - 0.06%, [P] 0.002 - 0.005%; the chemical composition of the slag is CaO: 25% - 35%, MgO: 10% - 20%, SiO2: 5% - 15%, FeO: 15% - 30%, MnO: 5% - 10%, and some inevitable impurities, and the slag basicity is 2.5 - 3.0.

[0019] Further, as a preference, in step six, the chemical composition of the molten steel at the end of the third blowing is: [C] ≤0.05%, [Mn] 0.01 - 0.03%, [P] 0.002 - 0.005%; the chemical composition of the slag is CaO: 20% - 35%, MgO: 15% - 25%, SiO2: 5% - 15%, FeO: 20% - 35%, MnO: 2% - 8%, and some inevitable impurities, and the slag basicity is 2.5 - 3.5.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The present invention studies the phase of the slag under the conventional process (such as Figure 1 ), and it is obtained from the phase analysis under the conventional process that Mn in the slag mainly exists in the form of FeO - MgO - MnO solid solution, and CaO will consume FeO in the slag. Therefore, by increasing the contents of FeO and MgO and reducing the slag basicity, the de - manganese effect can be effectively improved.

[0022] 2. In the converter's empty furnace smelting, since the MnO content in the slag of the previous furnace is high and the slag basicity is high, it is not conducive to de-manganese. Since this process creates a low basicity slag during the first blowing process of the converter and uses ore to control the temperature, it is prone to splashing. By using empty furnace smelting, the slag volume can be reduced, the splashing phenomenon can be avoided, and the first blowing time can be guaranteed to meet the requirements.

[0023] 3. Strictly control the process temperature and slag composition. Especially when the molten steel temperature at the end of the second blowing ≤ 1550 °C, the carbon content of the molten steel is 0.10 - 0.20%; the manganese content in the first blowing can be controlled at 0.1 - 0.2%, the manganese content in the second blowing can be controlled at 0.03 - 0.06%, the manganese content at the blowing end can be controlled within 0.03%, the de-manganese rate reaches over 95%, and the end phosphorus content can be stably controlled within 0.005%. Description of the Drawings

[0024] Figure 1 It is the phase analysis diagram of the converter's end slag under the conventional process. Detailed Implementation Modes

[0025] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with the preferred embodiments and the drawings. Those skilled in the art should understand that the specific content described below is illustrative rather than restrictive, and should not limit the protection scope of the present invention accordingly.

[0026] Figure 1 It is the phase analysis diagram of the converter's end slag under the conventional process, and the dot analysis of the phase components is shown in Table 1 and Table 2.

[0027] Table 1 Figure 1 Dotting of the phase components in a

[0028]

[0029] Table 2 Figure 1 Dotting of the phase components in b

[0030]

[0031] Example 1:

[0032] Adopt empty furnace smelting, charge 115t of hot metal + 30t of scrap steel. The silicon content of the hot metal in the converter is 0.28%, the manganese content of the hot metal is 0.42%, the manganese content of the scrap steel is 0.45%, and the phosphorus content of the hot metal is 0.152%.

[0033] For the first blowing, the oxygen supply flow rate is controlled at 28000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; during smelting, light-burned dolomite, lime, and ore are added for slag formation. 2500 kg of light-burned dolomite, 500 kg of lime, and 2500 kg of ore are added; the lance is lifted after blowing oxygen for 6.3 min. The temperature of the molten steel is 1338 °C, and the slag composition is CaO: 23.5%, MgO: 13.2%, SiO2: 18.5%, FeO: 23.2%, MnO: 13.2%, and some inevitable impurities. The basicity of the slag is 1.27; the composition of the molten steel is [C] 3.3%, [Mn] 0.12%, [P] 0.045%.

[0034] The first slag tapping is carried out, and the amount of the first slag tapping is 90%.

[0035] The second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; during smelting, lime, light-burned dolomite, ore, and raw dolomite are added for slag formation. The addition amount of light-burned dolomite is 1200 kg, the addition amount of lime is 1500 kg, the addition amount of ore is 1500 kg, and the addition amount of raw dolomite is 1200 kg. After the second blowing is completed, the temperature of the molten steel is 1543 °C, and the slag composition is CaO: 30.2%, MgO: 15.2%, SiO2: 11.5%, FeO: 26%, MnO: 8.9%, and some inevitable impurities. The basicity of the slag is 2.63; the composition of the molten steel is [C] 0.12%, [Mn] 0.03%, [P] 0.003%.

[0036] The second slag tapping is carried out, and the amount of the second slag tapping is 85%.

[0037] The third blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 500 kg of light-burned dolomite is added. After the third blowing is completed, the temperature of the molten steel is 1612 °C, and the slag composition is CaO: 30.0%, MgO: 17.3%, SiO2: 10.2%, FeO: 28%, MnO: 7.6%, and some inevitable impurities, and some inevitable impurities. The basicity of the slag is 2.94; the composition of the molten steel is [C] 0.04%, [Mn] 0.012%, [P] 0.003%.

[0038] The temperature of the molten steel at the end point of converter smelting is 1612 °C, the manganese in the molten steel is 0.012%, the phosphorus in the molten steel is 0.003%, the de-manganese rate is 97.3%, and the de-phosphorization rate is 98.0%.

[0039] Example 2:

[0040] The empty furnace smelting is adopted, and 115t of hot metal + 30t of scrap steel are charged. The silicon content of the hot metal in the converter is 0.41%, the manganese content of the hot metal is 0.51%, the manganese content of the scrap steel is 0.48%, and the phosphorus content of the hot metal is 0.147%.

[0041] For the first blowing, the oxygen supply flow rate is controlled at 28000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; During the smelting process, light-burned dolomite, lime and ore are added to make slag. 2800 kg of light-burned dolomite, 700 kg of lime and 3200 kg of ore are added; The lance is lifted after blowing oxygen for 6.7 min. The molten steel temperature is 1380 °C, and the slag composition is CaO: 24.3%, MgO: 14.1%, SiO2: 17.5%, FeO: 23.2%, MnO: 12.3%, and some inevitable impurities. The slag basicity is 1.39; The molten steel composition is [C] 3.4%, [Mn] 0.14%, [P] 0.042%.

[0042] For the first slag tapping, the first slag tapping amount is 88%.

[0043] For the second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; During the smelting process, lime, light-burned dolomite, ore and raw dolomite are added to make slag. The addition amount of light-burned dolomite is 1300 kg, the addition amount of lime is 1600 kg, the addition amount of ore is 1500 kg, and the addition amount of raw dolomite is 1200 kg. At the end of the second blowing, the molten steel temperature is 1537 °C, and the slag composition is CaO: 29.5%, MgO: 16.3%, SiO2: 10.6%, FeO: 27.0%, MnO: 9.2%, and some inevitable impurities. The slag basicity is 2.78; The molten steel composition is [C] 0.10%, [Mn] 0.041%, [P] 0.0036%.

[0044] For the second slag tapping, the second slag tapping amount is 86%.

[0045] For the third blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 500 kg of light-burned dolomite is added.. At the end of the third blowing, the molten steel temperature is 1607 °C, and the slag composition is CaO: 28.8%, MgO: 16.6%, SiO2: 9.9%, FeO: 29.1%, MnO: 7.6%, and some inevitable impurities. The slag basicity is 2.91; The molten steel composition is [C] 0.04%, [Mn] 0.022%, [P] 0.0033%.

[0046] The molten steel temperature at the end of converter smelting is 1607 °C, the manganese content in the molten steel is 0.022%, the phosphorus content in the molten steel is 0.0033%, the de-manganese rate is 95.7%, and the de-phosphorus rate is 97.8%.

[0047] Example 3:

[0048] Empty furnace smelting is adopted, and 115t of hot metal + 30t of scrap steel are charged. The silicon content in the converter hot metal is 0.55%, the manganese content in the hot metal is 0.59%, the manganese content in the scrap steel is 0.50%, and the phosphorus content in the hot metal is 0.151%.

[0049] For the first blowing, the oxygen supply flow rate is controlled at 28000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; during the smelting process, light burned dolomite, lime and ore are added to make slag. 3000 kg of light burned dolomite, 800 kg of lime and 3500 kg of ore are added; the lance is lifted after blowing oxygen for 7.2 min. The molten steel temperature is 1352 °C, and the slag composition is CaO: 20.6%, MgO: 13.9%, SiO2: 17.7%, FeO: 24.3%, MnO: 15.5%, and some inevitable impurities. The slag basicity is 1.16; the molten steel composition is [C] 3.3%, [Mn] 0.11%, [P] 0.051%.

[0050] For the first slag tapping, the first slag tapping amount is 92%.

[0051] For the second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; during the smelting process, lime, light burned dolomite, ore and raw dolomite are added to make slag. The addition amount of light burned dolomite is 1500 kg, the addition amount of lime is 1800 kg, the addition amount of ore is 1800 kg, and the addition amount of raw dolomite is 1300 kg. At the end of the second blowing, the molten steel temperature is 1528 °C, and the slag composition is CaO: 32.5%, MgO: 14.7%, SiO2: 12.5%, FeO: 26.7%, MnO: 8.8%, and some inevitable impurities. The slag basicity is 2.60; the molten steel composition is [C] 0.11%, [Mn] 0.032%, [P] 0.0041%.

[0052] For the second slag tapping, the second slag tapping amount is 92%.

[0053] For the third blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 600 kg of lightly burned dolomite is added. After the third blowing, the molten steel temperature is 1587 °C, the slag composition is CaO: 30.1%, MgO: 21.3%, SiO2: 9.3%, FeO: 29.6%, MnO: 7.7%, and some inevitable impurities, and the slag basicity is 3.24; the molten steel composition is [C] 0.036%, [Mn] 0.017%, [P] 0.0036%.

[0054] At the end of the converter smelting, the molten steel temperature is 1587 °C, the manganese content in the molten steel is 0.017%, the phosphorus content in the molten steel is 0.0036%, the de-manganese rate is 97.1%, and the de-phosphorization rate is 97.6%.

[0055] Comparative Example 1: Compared with Example 1, when using the conventional single slag method for smelting and controlling the same converter end point, the manganese content and phosphorus content in the molten steel cannot meet the requirements.

[0056] The converter is smelted with an empty furnace, and 115 t of hot metal + 30 t of scrap steel are charged. The silicon content in the hot metal of the converter is 0.28%, the manganese content in the hot metal is 0.41%, the manganese content in the scrap steel is 0.45%, and the phosphorus content in the hot metal is 0.149%. After the blowing, the molten steel temperature is 1612 °C, the slag composition is CaO: 35.3%, MgO: 17.3%, SiO2: 11.5%, FeO: 28%, MnO: 6.5%, and some inevitable impurities, and the slag basicity is 3.07; the molten steel composition is [C] 0.04%, [Mn] 0.15%, [P] 0.012%.

[0057] At the end of the converter smelting, the molten steel temperature is 1612 °C, the manganese content in the molten steel is 0.15%, the phosphorus content in the molten steel is 0.012%, the de-manganese rate is 63.4%, and the de-phosphorization rate is 91.9%.

[0058] Comparative Example 2: Compared with Example 1, when using the slag retention operation, splashing occurred during the first blowing, and the lance had to be lifted, so the oxygen blowing time could not meet the requirements. Moreover, due to the relatively high basicity of the end slag, the basicity of the slag in the early stage could not meet the requirements, and the manganese content in the molten steel during the first blowing could not meet the requirements, ultimately resulting in the manganese content in the molten steel at the end point not meeting the requirements.

[0059] For the slag retention operation, the slag retention amount is 5 t, and the slag composition of the retained slag is: CaO: 42.3%, MgO: 7.5%, SiO2: 12.5%, FeO: 14.3%, MnO: 6.3%, and some inevitable impurities, and the slag basicity is 3.38; 115 t of hot metal + 30 t of scrap steel are charged. The silicon content in the hot metal of the converter is 0.29%, the manganese content in the hot metal is 0.42%, the manganese content in the scrap steel is 0.44%, and the phosphorus content in the hot metal is 0.150%.

[0060] During the first blowing, the oxygen supply flow rate is controlled at 28000 Nm3 / h, the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; during smelting, light burned dolomite, lime and ore are added for slag formation. 2500 kg of light burned dolomite, 500 kg of lime and 2500 kg of ore are added; splashing occurs 3.5 minutes after oxygen blowing, and the lance is forced to be lifted. The temperature of the molten steel is 1319 °C, and the slag composition is CaO: 30.2%, MgO: 14.2%, SiO2: 15.1%, FeO: 24.3%, MnO: 8.9%, and some inevitable impurities. The basicity of the slag is 2.0; the composition of the molten steel is [C] 3.7%, [Mn] 0.27%, [P] 0.076%.

[0061] The first slag tapping is carried out, and the amount of the first slag tapping is 90%.

[0062] The second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; during smelting, lime, light burned dolomite, ore and raw dolomite are added for slag formation. The addition amount of light burned dolomite is 1200 kg, the addition amount of lime is 1500 kg, the addition amount of ore is 1500 kg, and the addition amount of raw dolomite is 1200 kg. At the end of the second blowing, the temperature of the molten steel is 1543 °C, and the slag composition is CaO: 32.5%, MgO: 14.7%, SiO2: 12.5%, FeO: 26.7%, MnO: 7.1%, and some inevitable impurities. The basicity of the slag is 2.6; the composition of the molten steel is [C] 0.12%, [Mn] 0.13%, [P] 0.012%.

[0063] The second slag tapping is carried out, and the amount of the second slag tapping is 85%.

[0064] The third blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 500 kg of light burned dolomite is added. At the end of the third blowing, the temperature of the molten steel is 1612 °C, and the slag composition is CaO: 30.1%, MgO: 17.3%, SiO2: 10.3%, FeO: 28.7%, MnO: 5.8%, and some inevitable impurities. The basicity of the slag is 2.92; the composition of the molten steel is [C] 0.04%, [Mn] 0.067%, [P] 0.009%.

[0065] At the end of the converter smelting, the temperature of the molten steel is 1612 °C, the manganese in the molten steel is 0.067%, the phosphorus in the molten steel is 0.009%, the de-manganese rate is 84.0%, and the de-phosphorus rate is 94.0%.

[0066] Comparative Example 3: Compared with Example 1, the MgO content in the slag is controlled by the conventional method (MgO: 6.0 - 10.0%), and the manganese content in the first blowing, the second blowing and the end point is higher than that in Example 1.

[0067] Smelting is carried out with an empty furnace, and 115t of hot metal + 30t of scrap steel are charged. The silicon content of the hot metal in the converter is 0.27%, the manganese content of the hot metal is 0.40%, the manganese content of the scrap steel is 0.45%, and the phosphorus content of the hot metal is 0.153%.

[0068] For the first blowing, the oxygen supply flow rate is controlled at 28000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; During the smelting process, light-burned dolomite, lime and ore are added to make slag. 1200 kg of light-burned dolomite, 500 kg of lime and 2500 kg of ore are added; The lance is lifted after 6.3 minutes of oxygen blowing. The molten steel temperature is 1338 °C, and the slag composition is CaO: 29.5%, MgO: 6.5%, SiO2: 23.5%, FeO: 23.2%, MnO: 9.8%, and some inevitable impurities. The slag basicity is 1.27; The molten steel composition is [C] 3.3%, [Mn] 0.22%, [P] 0.045%.

[0069] For the first slag tapping, the amount of the first slag tapping is 90%.

[0070] For the second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; During the smelting process, lime, light-burned dolomite, ore and raw dolomite are added to make slag. The addition amount of light-burned dolomite is 700 kg, the addition amount of lime is 1500 kg, the addition amount of ore is 1500 kg, and the addition amount of raw dolomite is 1200 kg. At the end of the second blowing, the molten steel temperature is 1543 °C, and the slag composition is CaO: 33.5%, MgO: 7.6%, SiO2: 12.5%, FeO: 26%, MnO: 7.5%, and some inevitable impurities. The slag basicity is 2.68; The molten steel composition is [C] 0.12%, [Mn] 0.067%, [P] 0.0035%.

[0071] For the second slag tapping, the amount of the second slag tapping is 85%.

[0072] For the third blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance is controlled at 1.3 - 1.6 m. At the end of the third blowing, the molten steel temperature is 1612 °C, and the slag composition is CaO: 34.8%, MgO: 8.2%, SiO2: 12.0%, FeO: 28%, MnO: 5.2%, and some inevitable impurities. The slag basicity is 2.90; The molten steel composition is [C] 0.04%, [Mn] 0.052%, [P] 0.0032%.

[0073] At the end point of converter smelting, the molten steel temperature is 1612 °C, the manganese content in the molten steel is 0.052%, the phosphorus content in the molten steel is 0.0032%, the de-manganese rate is 87.0%, and the de-phosphorization rate is 97.9%.

[0074] Comparative Example 4: The carbon content during the secondary blowing was not controlled within 0.10 - 0.20%, and the phosphorus and manganese contents at the end of the secondary blowing were higher than those in Example 1, and the end-point phosphorus and manganese contents did not meet the requirements.

[0075] Empty furnace smelting was adopted, and 115 t of hot metal + 30 t of scrap steel were charged. The silicon content of the hot metal in the converter was 0.28%, the manganese content of the hot metal was 0.423%, the manganese content of the scrap steel was 0.44%, and the phosphorus content of the hot metal was 0.151%.

[0076] For the first blowing, the oxygen supply flow rate was controlled at 28000 Nm 3 / h, and the lance position of the oxygen lance was controlled at 1.7 - 2.0 m; during the smelting process, light-burned dolomite, lime, and ore were added for slag formation. 2500 kg of light-burned dolomite, 500 kg of lime, and 2500 kg of ore were added; the lance was lifted after blowing oxygen for 6.3 min. The molten steel temperature was 1338 °C, and the slag composition was CaO: 24.1%, MgO: 13.2%, SiO2: 19.2%, FeO: 22.9%, MnO: 13.2%, and some inevitable impurities. The slag basicity was 1.26; the molten steel composition was [C] 3.27%, [Mn] 0.123%, [P] 0.044%.

[0077] The first slag tapping was carried out, and the first slag tapping amount was 90%.

[0078] For the secondary blowing, the oxygen supply flow rate was controlled at 32000 Nm 3 / h, and the lance position of the oxygen lance was controlled at 1.6 - 2.0 m; during the smelting process, lime, light-burned dolomite, ore, and raw dolomite were added for slag formation. The addition amount of light-burned dolomite was 1200 kg, the addition amount of lime was 1500 kg, the addition amount of ore was 1500 kg, and the addition amount of raw dolomite was 1200 kg. At the end of the secondary blowing, the molten steel temperature was 1543 °C, and the slag composition was CaO: 30.2%, MgO: 15.6%, SiO2: 11.2%, FeO: 26.2%, MnO: 7.8%, and some inevitable impurities. The slag basicity was 2.70; the molten steel composition was [C] 0.31%, [Mn] 0.10%, [P] 0.021%.

[0079] The second slag tapping was carried out, and the second slag tapping amount was 85%.

[0080] For the third blowing, the oxygen supply flow rate was controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 500 kg of calcined dolomite is added. At the end of the third blowing, the molten steel temperature is 1612 °C, the slag composition is CaO: 29.3%, MgO: 17.3%, SiO2: 10.2%, FeO: 28.3%, MnO: 6.2%, and some inevitable impurities, and the slag basicity is 2.87; the molten steel composition is [C] 0.04%, [Mn] 0.056%, [P] 0.009%.

[0081] At the end of the converter smelting, the molten steel temperature is 1612 °C, the manganese content in the molten steel is 0.056%, the phosphorus content in the molten steel is 0.009%, the de-manganese rate is 86.8%, and the de-phosphorus rate is 94.0%.

[0082] Comparative Example 5: At the end of the second blowing, the molten pool temperature is not controlled within 1550 °C. The phosphorus content and manganese content at the end of the second blowing are higher than those in Example 1, and the end phosphorus content and manganese content do not meet the requirements.

[0083] Empty furnace smelting is adopted, and 115 t of hot metal + 30 t of scrap steel are charged. The silicon content in the converter hot metal is 0.277%, the manganese content in the hot metal is 0.413%, the manganese content in the scrap steel is 0.44%, and the phosphorus content in the hot metal is 0.148%.

[0084] For the first blowing, the oxygen supply flow rate is controlled at 28000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; during the smelting process, calcined dolomite, lime and ore are added to make slag. 2500 kg of calcined dolomite, 500 kg of lime and 2500 kg of ore are added; the lance is lifted after blowing oxygen for 6.3 min. The molten steel temperature is 1338 °C, the slag composition is CaO: 23.5%, MgO: 13.3%, SiO2: 18.5%, FeO: 23.2%, MnO: 13.2%, and some inevitable impurities, and the slag basicity is 1.27; the molten steel composition is [C] 3.3%, [Mn] 0.12%, [P] 0.045%.

[0085] The first slag tapping, and the first slag tapping amount is 90%.

[0086] For the second blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; during the smelting process, lime, lightly burned dolomite, ore and raw dolomite are added for slag formation. The addition amount of lightly burned dolomite is 1200 kg, the addition amount of lime is 1500 kg, the addition amount of ore is 800 kg, and the addition amount of raw dolomite is 700 kg. At the end of the secondary blowing, the molten steel temperature is 1585 °C, and the slag composition is CaO: 31.3%, MgO: 15.2%, SiO2: 11.6%, FeO: 26.3%, MnO: 7.5%, and some inevitable impurities. The slag basicity is 2.70. The molten steel composition is [C] 0.12%, [Mn] 0.092%, [P] 0.012%.

[0087] Secondary slag tapping, and the secondary slag tapping amount is 85%.

[0088] Tertiary blowing, the oxygen supply flow rate is controlled at 32000 Nm 3 / h, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m, and 500 kg of lightly burned dolomite is added. At the end of the tertiary blowing, the molten steel temperature is 1612 °C, and the slag composition is CaO: 31.5%, MgO: 18.2%, SiO2: 10.7%, FeO: 28%, MnO: 5.8%, and some inevitable impurities. The slag basicity is 2.94; the molten steel composition is [C] 0.04%, [Mn] 0.061%, [P] 0.008%.

[0089] At the end point of converter smelting, the molten steel temperature is 1612 °C, the manganese in the molten steel is 0.061%, the phosphorus in the molten steel is 0.008%, the de-manganese rate is 85.2%, and the de-phosphorus rate is 94.6%.

[0090] As mentioned above, it is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered within the protection scope of the present invention.

Claims

1. A method for smelting low-manganese and low-phosphorus molten steel in a converter, characterized in that: The process flow is adding scrap steel, charging hot metal → primary blowing → primary slag tapping → secondary blowing → secondary slag tapping → tertiary blowing → tapping. The specific operation steps are as follows: Step 1: Add scrap steel and charge hot metal. The ratio of hot metal is 75 - 85%, and the ratio of scrap steel is 15 - 25%. Step 2: Primary blowing. After lowering the lance, the top-blowing oxygen supply intensity is controlled at 3.5 - 4.0 Nm 3 / t / min, the oxygen blowing time is controlled at 6 - 8 min for slag making. The slag composition is CaO: 20% - 35%, MgO: 10% - 15%, SiO2: 15% - 25%, FeO: 20% - 25%, MnO: 10% - 20%, and some inevitable impurities. The slag basicity is 1.0 - 1.5; at the end of the primary blowing, the molten pool temperature ≤ 1400 °C; Step 3: Primary slag tapping, and the primary slag tapping amount ≥ 80%. Step 4: Secondary blowing, with the top blowing oxygen supply intensity controlled at 4.0 - 4.5 Nm 3 / t / min; During secondary blowing for slag formation, the slag composition is as follows: CaO: 25% - 35%, MgO: 10% - 20%, SiO2: 5% - 15%, FeO: 15% - 30%, MnO: 5% - 10%, and some inevitable impurities. The slag basicity is 2.5 - 3.0, and the temperature is controlled using a combination of ore and raw dolomite. At the end of secondary blowing, the molten bath temperature is controlled within 1550°C, and at the same time, the carbon content of the molten steel is 0.10 - 0.20%; Step 5: Secondary slag tapping, and the secondary slag tapping amount ≥ 80%. Step 6: Three - stage blowing, with the top - blowing oxygen supply intensity controlled at 4.0 - 4.5 Nm 3 / t / min, the tapping temperature is controlled at 1580 - 1620 °C, and the tapping carbon content ≤ 0.05%.

2. The method for smelting low-manganese and low-phosphorus molten steel in a converter according to claim 1, characterized in that: In Step 1, before charging hot metal and adding scrap steel, after slag splashing for the previous heat, all the slag is poured out. It is required that the converter is empty without remaining slag. The manganese content in hot metal is 0.4 - 0.6%, and the manganese content in scrap steel is 0.3 - 0.6%.

3. The method for smelting low-manganese and low-phosphorus molten steel in a converter according to claim 1, characterized in that: In Step 2, after the primary blowing, the chemical composition of the molten steel meets: [C] 3.0 - 3.5%, [Mn] 0.1 - 0.2%, [P] 0.03 - 0.06%. Light burned dolomite, lime and ore are used for slag making.

4. The method for smelting low-manganese and low-phosphorus molten steel in a converter according to claim 1, characterized in that: In Step 4, after the secondary blowing, the chemical composition of the molten steel meets: [C] 0.10 - 0.20%, [Mn] 0.03 - 0.06%, [P] 0.002 - 0.005%. The secondary blowing uses a combination of light burned dolomite and lime for slag making.

5. The method for smelting low-manganese and low-phosphorus molten steel in a converter according to claim 1, characterized in that: In Step 6, after the tertiary blowing, the chemical composition of the molten steel meets: [C] ≤ 0.05%, [Mn] 0.01 - 0.03%, [P] 0.002 - 0.005%. The slag composition is CaO: 20% - 35%, MgO: 15% - 25%, SiO2: 5% - 15%, FeO: 20% - 35%, MnO: 2% - 8%, and some inevitable impurities. The slag basicity is 2.5 - 3.

5.

6. The method for smelting low-manganese and low-phosphorus molten steel in a converter according to claim 1, characterized in that: During the primary blowing, the lance position of the oxygen lance is controlled at 1.7 - 2.0 m; during the secondary blowing, the lance position of the oxygen lance is controlled at 1.6 - 2.0 m; during the tertiary blowing, the lance position of the oxygen lance is controlled at 1.3 - 1.6 m.

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