Converter smelting method for improving demanganization rate in early stage of blowing

Abstract

The invention relates to the technical field of converter smelting, in particular to a converter smelting method for improving the demanganization rate in the early stage of blowing, and the converter smelting method comprises the following steps: (1) charging; (2) blowing; (3) slagging; (4) blowing stopping control; and (5) deslagging: by accurately mastering the blowing stopping time, the slag is completely melted, the metallurgical functions of dissolving MnO and adsorbing other impurities of the slag are fully played, the foaming degree of the slag is controlled, deslagging operation is facilitated, and conditions are created for pouring out early-stage slag rich in MnO as much as possible. By means of the application of the demanganizing technology, the demanganizing rate in the early stage reaches 92%-95%, the manganese content in molten metal can be reduced to 0.030% or below in the early stage, and therefore a guarantee is provided for smelting of the extremely-low-manganese steel with the manganese content being smaller than or equal to 0.010% under the condition that molten iron pre-demanganizing and RH oxygen blowing demanganizing are not adopted.

Description

Technical Field

[0001] The invention relates to the technical field of converter smelting, and in particular to a converter smelting method for improving the demanganese rate in the early stage of blowing. Background Art

[0002] Manganese has the function of enhancing the strength, wear resistance and hardenability of steel. It is a beneficial element for most types of steel. However, for ultra-low manganese steel, in order to improve its toughness, ductility and electromagnetic properties, the lower the manganese content, the better. Some high-end products of this type require a manganese content of no more than 0.010%.

[0003] As the key process of demanganeseization, the converter undertakes the main task of demanganeseization. The molten iron, scrap steel and iron blocks, which are the main raw materials for converter steelmaking, all contain a certain amount of manganese steel. After the converter smelting is completed, part of the manganese brought into these main raw materials is oxidized to form manganese oxide and enters the slag, and the other part remains in the molten steel as a residue.

[0004] When smelting ultra-low manganese steel, in order to improve the demanganese rate, the converter generally adopts the method of multiple slag pouring in the middle of smelting, so that the generated MnO is discharged from the furnace with the slag, and then artificial slag is added to re-slag. According to the change of decarburization speed, converter smelting can be divided into three stages: early, middle and late stages of blowing. The early stage of converter smelting refers to the period from the start of the converter blowing to the first stop of blowing and slag pouring. During this period, the temperature of the molten metal in the furnace is low, the affinity of manganese to oxygen is greater than the affinity of carbon to oxygen, and manganese is easily oxidized. Therefore, the early stage of blowing is the golden opportunity for demanganese, and the demanganese rate during this period is the key to determining the success of ultra-low manganese steel smelting. In order to ensure that the manganese content of molten steel at the end of the converter is ≤0.010%, the manganese in the molten metal needs to be removed to less than 0.030% in the early stage. When conventional steelmaking is adopted, the demanganese rate in the early stage of converter blowing is generally 70%-80%, and the residual manganese content in the molten metal at the end of this period is 0.06%-0.10%, which cannot meet the manganese content requirements of ultra-low manganese steel.

[0005] As the application of ultra-low manganese steel becomes more and more extensive, its output is also increasing. At present, when producing ultra-low manganese steel, the molten iron pre-demanganese process and the RH oxygen blowing deep demanganese process are generally used. The molten iron pre-demanganese process not only requires a special blowing device, but also the silicon in the water must be removed before the demanganese process is completed. The low silicon content of the molten iron will be unfavorable for converter smelting. The RH oxygen blowing deep demanganese operation not only prolongs the RH treatment time, but also increases the oxygen content in the steel, thereby increasing the inclusion content in the steel; in addition, the continuous vacuum blowing of a large amount of oxygen has a greater thermal shock on the bottom refractory material, increasing the risk of leakage at the bottom of the vacuum chamber. How to achieve efficient and safe production of ultra-low manganese steel and stable quality control has become the key to mass production of this product.

[0006] Application No. CN20120429316 discloses a process for smelting low manganese steel in a converter, which requires that the manganese content of molten iron is not higher than 0.27%, and the manganese content of the final molten steel is not higher than 0.08%, which is far from the requirements of not higher than 0.27% for ultra-low manganese steel, not higher than 0.08% for the final molten steel, and not higher than 0.010% for ultra-low manganese steel. Summary of the invention

[0007] In view of the technical problem of low demanganese rate in the early stage of converter smelting in the prior art, the present invention provides a converter smelting method for improving the demanganese rate in the early stage of blowing, and the demanganese rate in the early stage is achieved by accurately grasping the timing of stopping blowing, so that the manganese content in the molten metal can be removed to below 0.030% in the early stage, thereby providing a guarantee for the smelting of extremely low manganese steel with a manganese content of ≤0.010% without using molten iron pre-demanganese and RH oxygen blowing demanganese.

[0008] A converter smelting method for improving the demanganese rate in the early stage of blowing, the converter smelting comprises the following steps: (1) Charging: During the charging stage, the converter charging system is optimized, including controlling the weight percentage of molten iron, scrap steel, and iron blocks to 78.0%-82.0%: 3.0%-5.0%: 15.0%-17.0%; that is, while the amount of molten iron remains unchanged, the ratio of scrap steel and iron blocks is adjusted from 4:1 to 1:4.

[0009] (2) Blowing: After charging, blowing is carried out to optimize the ratio of silicon and manganese content in the molten iron during the blowing process; (3) Slag making: Slag making is carried out after blowing. The slag making process includes controlling the slag basicity and the slag content; (4) Stop blowing control, including control of stop blowing temperature and control of stop blowing timing; (5) Slag pouring: After the slag pouring conditions are met, the slag pouring operation should be carried out and the amount of slag pouring should be controlled.

[0010] Furthermore, in step (1), the initial blowing time is controlled to be 7.5 min to 8.5 min in the optimization of the converter charging system. The optimization of the converter charging system provides a guarantee for controlling and extending the initial blowing time.

[0011] Furthermore, in step (2), optimizing the silicon-manganese ratio in the molten iron includes controlling the [%Si]: [%Mn] in the molten iron to be between 2.0 and 2.5. If this condition is not met, the silicon content in the molten iron is supplemented by adding ferrosilicon, and the amount of ferrosilicon added is calculated according to the following formula: ; Wherein, w is the amount of ferrosilicon added, the unit is t, δ is the silicon content in ferrosilicon, 1000 is the conversion rate between tons and kilograms, [%Si] is the original silicon content in the molten iron, [%Mn] is the original manganese content in the molten iron, a is the target ratio of silicon content to manganese content in the molten iron, and the value range is 2.0 to 2.5. The manganese content in the molten iron is bounded by 0.25%. When the manganese content in the molten iron is ≤0.25%, a is taken according to the lower and middle limits, and the value range is 2.0-2.25; when the manganese content in the molten iron is ≥0.25%, a is taken according to the upper and middle limits, and the value range is 2.25-2.5.

[0012] Furthermore, in step (3), controlling the slag basicity includes controlling the slag basicity at 1.1-1.3. MnO is a weakly alkaline oxide. In order to increase the solubility of MnO in the early slag, the slag basicity should not be too high when the converter is stopped for the first time.

[0013] Furthermore, in step (3), controlling the slag content includes controlling the MgO content in the previous slag to be between 3.0% and 5.0%. The main function of MgO in the slag is to reduce the corrosion of the slag on the furnace lining. MgO is an alkaline oxide. If the MgO content in the slag is too high, it will have an adverse effect on the dissolution of MnO.

[0014] Furthermore, in step (4), controlling the stop-blowing temperature includes controlling the temperature at the first stop-blowing to be between 1350° C. and 1380° C.

[0015] Furthermore, in step (4), the timing of stopping blowing is controlled to be when the carbon-oxygen reaction in the furnace begins. At this time, the degree of slag foaming is just enough to make slag discharge from the furnace mouth when the converter is shaken to 60°, which facilitates the slag pouring operation. If the blowing is stopped too early, the slag is not fully melted and the metallurgical effect is not fully exerted; if the blowing is stopped too late, the slag foams seriously and causes the converter to discharge slag too early during slag pouring, which may cause splashing in severe cases, bringing adverse effects on the slag pouring operation.

[0016] Furthermore, step (5) of controlling the amount of slag discharge includes discharging slag when the converter stops blowing for the first time, and the amount of slag discharge is not less than 3 / 4 of the total slag amount.

[0017] The beneficial effects of the present invention are: The present invention increases the ratio of iron blocks and prolongs the early blowing time, thus creating conditions for the deep oxidation of manganese in molten iron. The present invention increases the amount of slag by optimizing the ratio of silicon and manganese content in molten iron, thus providing a slag amount guarantee for increasing the amount of MnO dissolved. (3) The present invention accurately grasps the timing of stopping blowing, so that the slag is completely melted, giving full play to the metallurgical function of the slag in dissolving MnO and absorbing other impurities, and the foaming degree of the slag is controlled, which facilitates the slag pouring operation and creates conditions for pouring out as much of the early slag rich in MnO as possible.

[0018] (4) The application of the demanganeseization technology of the present invention enables the early demanganeseization rate to reach 92% to 95%, and the manganese content in the molten metal can be removed to below 0.030% in the early stage, thereby providing a guarantee for the smelting of extremely low manganese steel with a manganese content of ≤0.010% without using molten iron pre-demanganeseization and RH oxygen blowing demanganeseization. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0020] Example 1 A converter smelting method for improving the demanganese rate in the early stage of blowing, the converter smelting comprises the following steps: (1) Charging: During the charging stage, the charging system was optimized, including controlling the weight percentage of molten iron, scrap steel, and iron blocks to 78.0%-82.0%: 3.0%-5.0%: 15.0%-17.0%; that is, while the amount of molten iron remained unchanged, the ratio of scrap steel and iron blocks was adjusted from 4:1 to 1:4. By optimizing the charging system, a guarantee was provided for controlling the initial blowing time to 7.5 min-8.5 min.

[0021] (2) Blowing: After charging, blowing is carried out to optimize the ratio of silicon and manganese content in the molten iron during the blowing process; (3) Slag making: Slag making is carried out after blowing. The slag making process includes controlling the slag basicity and the slag content; (4) Stop blowing control, including control of stop blowing temperature and control of stop blowing timing; (5) Slag pouring: After the slag pouring conditions are met, the slag pouring operation should be carried out and the amount of slag pouring should be controlled.

[0022] The main metal materials for converter steelmaking include molten iron, scrap steel and iron blocks, among which scrap steel and iron blocks play a cooling role. The melting point of scrap steel is generally 1500-1530℃, and the melting point of iron blocks is generally 1100-1200℃. The melting point of iron blocks is relatively low, and they are mainly melted in the early stage of smelting, and their cooling effect is also mainly reflected in the early stage; the melting point of scrap steel is relatively high, and they are mainly melted in the middle and late stages of smelting, and their cooling effect is also mainly reflected in the middle and late stages. The demanganese reaction in the converter mainly occurs in the early stage of smelting. In order to enhance the cooling effect of converter smelting and extend the duration of low temperature in the early stage, the demanganeseization should be fully grasped in the early stage of smelting.

[0023] The ratio of the mass percentage of silicon to the mass percentage of manganese in the molten iron is controlled to be 2.0-2.5. If this condition is not met, the silicon content in the molten iron is supplemented by adding ferrosilicon. The amount of ferrosilicon added is calculated according to the following formula: a.

[0024] Where: w—amount of ferrosilicon added, unit is t δ—Silicon content in ferrosilicon 1000 - Conversion rate between tons and kilograms [%Si]—Original silicon content in molten iron [%Mn]—Original manganese content in molten iron a—The target ratio of silicon content to manganese content in molten iron, with a value range of 2.0 to 2.5. The manganese content in molten iron is limited to 0.25%. When the manganese content in molten iron is ≤0.25%, a is taken according to the lower and middle limits, with a value range of 2.0-2.25; when the manganese content in molten iron is ≥0.25%, a is taken according to the upper and middle limits, with a value range of 2.25-2.5.

[0025] It can be seen from the above formula that, under the condition of constant slag basicity, the amount of lime added per ton of iron depends on the silicon content in the molten iron. As the silicon content in the molten iron increases, the amount of lime added also increases accordingly, and the amount of slag also increases accordingly. In order to have sufficient slag for demanganization, the [%Si]: [%Mn] in the molten iron needs to be controlled at 2.0-2.5. If the ratio of the original silicon and manganese content in the molten iron is less than this ratio, a certain amount of ferrosilicon needs to be added. The amount of ferrosilicon added per ton of iron is calculated according to the following formula:

[0026] Where: w—amount of ferrosilicon added, unit is t δ—Silicon content in ferrosilicon 1000 - Conversion rate between tons and kilograms [%Si]—Original silicon content in molten iron [%Mn]—Original manganese content in molten iron a—The target ratio of silicon content to manganese content in molten iron, with a value range of 2.0 to 2.5. The manganese content in molten iron is limited to 0.25%. When the manganese content in molten iron is ≤0.25%, a is taken according to the lower and middle limits, with a value range of 2.0-2.25; when the manganese content in molten iron is ≥0.25%, a is taken according to the upper and middle limits, with a value range of 2.25-2.5.

[0027] Optimizing the slag making system includes controlling the slag basicity, controlling the slag content, controlling the stop blowing temperature, controlling the stop blowing timing, and controlling the slag pouring amount; including controlling the slag basicity at 1.1-1.3 in the early stage, controlling the MgO content in the slag at 3.0%-5.0%, controlling the temperature at 1350°C-1380°C when the blowing is stopped for the first time, controlling the stop blowing timing to stop blowing when the carbon-oxygen reaction in the furnace begins, controlling the slag foaming degree at a good level means that when the converter is poured for the first time, the converter starts to discharge the slag when it is shaken to about 60°, and when the converter is stopped for the first time to pour the slag, the slag pouring amount is not less than 3 / 4 of the total slag amount. The present invention does not adopt the molten iron pre-demanganese process and the LF and RH demanganese process, and completes the demanganese operation of the ultra-low manganese steel in the converter process, the demanganese rate in the early stage is increased to 92%-95%, and the manganese content in the molten metal after the early stage can be controlled below 0.030%, and finally the finished product has a manganese content of no more than 0.010%.

[0028] Example 2 The loading amount of molten iron, scrap steel and iron blocks as well as the silicon and manganese contents of molten iron are shown in Table 1 Table 1 Main raw material addition and silicon and manganese content in molten iron in Example 2

[0029] When the manganese content of molten iron is ≥0.25%, a is taken as the upper limit, the silicon-manganese ratio is in the range of 2.25-2.5, the silicon content of ferrosilicon is 75.0%, and the amount added is 735kg.

[0030] The first blowing stop time was 7'50", the slag basicity was 1.15, the MgO content in the slag was 3.8%, the temperature was 1352℃, and the residual manganese content in the molten metal was 0.023%.

[0031] Example 3 The loading amount of molten iron, scrap steel and iron blocks as well as the silicon and manganese contents of molten iron are shown in Table 2 Table 2 Main raw material addition and silicon and manganese content in molten iron in Example 3

[0032] When the manganese content of molten iron is ≥0.25%, a is taken as the upper limit, the silicon-manganese ratio is in the range of 2.25-2.5, the silicon content of ferrosilicon is 75.0%, and the amount added is 810kg.

[0033] The first blowing stop time was 8'02", the slag basicity was 1.22, the MgO content in the slag was 3.5%, the temperature was 1363℃, and the residual manganese content in the molten metal was 0.025%.

[0034] Example 4 The loading amount of molten iron, scrap steel and iron blocks, as well as the silicon and manganese contents of molten iron are shown in Table 3 Table 3 Main raw material addition and silicon and manganese content in molten iron in Example 4

[0035] When the manganese content of molten iron is ≥0.25%, a is taken as the upper limit, the silicon-manganese ratio is in the range of 2.25-2.5, the silicon content of ferrosilicon is 75.0%, and the amount added is 1880kg.

[0036] The first blowing stop time was 7'45", the slag basicity was 1.182, the MgO content in the slag was 4.1%, the temperature was 1357℃, and the residual manganese content in the molten metal was 0.027%.

[0037] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A converter smelting method for improving the demanganese rate in the early stage of blowing, characterized in that: Converter smelting includes the following steps: (1) Charging: Optimize the converter charging system during the charging stage, including controlling the weight percentage of molten iron, scrap steel, and iron blocks to 78.0% to 82.0%: 3.0% to 5.0%: 15.0% to 17.0%; (2) Blowing: After charging, blowing is carried out to optimize the ratio of silicon and manganese content in the molten iron during the blowing process; (3) Slag making: Slag making is carried out after blowing. The slag making process includes controlling the slag basicity and the slag content; (4) Stop blowing control, including control of stop blowing temperature and control of stop blowing timing; (5) Slag pouring: After the slag pouring conditions are met, the slag pouring operation should be carried out and the amount of slag pouring should be controlled.

2. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (1), the converter charging system is optimized to control the initial blowing time to 7.5 min to 8.5 min.

3. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (2), the silicon-manganese ratio in the molten iron is optimized, including controlling the [%Si]: [%Mn] in the molten iron to be between 2.0 and 2.

5. If this condition is not met, the silicon content in the molten iron is supplemented by adding ferrosilicon, and the amount of ferrosilicon added is calculated according to the following formula: ; Wherein, w is the amount of ferrosilicon added, the unit is t, δ is the silicon content in ferrosilicon, 1000 is the conversion rate between tons and kilograms, [%Si] is the original silicon content in the molten iron, [%Mn] is the original manganese content in the molten iron, a is the target ratio of silicon content to manganese content in the molten iron, and the value range is 2.0 to 2.

5. The manganese content in the molten iron is bounded by 0.25%. When the manganese content in the molten iron is ≤0.25%, a is taken according to the middle and lower limits, and the value range is 2.0-2.25; when the manganese content in the molten iron is ≥0.25%, a is taken according to the middle and upper limits, and the value range is 2.25-2.

5.

4. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (3), controlling the slag basicity includes controlling the slag basicity within a range of 1.1 to 1.

3.

5. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (3), controlling the slag content includes controlling the MgO content in the early slag to 3.0% to 5.0%.

6. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (4), controlling the stop-blowing temperature includes controlling the temperature at the first stop-blowing time to be between 1350° C. and 1380° C.

7. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (4), the timing of stopping blowing is controlled to stop blowing when the carbon-oxygen reaction in the furnace first starts.

8. A converter smelting method for improving the demanganeseization rate in the early stage of blowing as claimed in claim 1, characterized in that: In step (5), controlling the amount of slag discharge includes discharging slag when the converter stops blowing for the first time, and the amount of slag discharge is not less than 3 / 4 of the total slag amount.

Images