A converter sulfur control smelting process

Abstract

The present invention belongs to the technical field of converter steelmaking, and specifically relates to a converter sulfur control smelting process, which includes subjecting hot metal to KR pretreatment, converter smelting, and RH vacuum treatment in sequence. The converter smelting process includes three slag-making smelts, and makes full use of the characteristics of different periods of the converter for desulfurization. Specifically, in the early stage of converter smelting, due to the relatively low temperature of the molten steel and the relatively high oxidizability of the slag, the desulfurization conditions are relatively poor; in the middle stage of converter smelting, a relatively high molten steel temperature, a large slag amount, a high slag basicity, and a relatively high temperature and a reduced oxygen blowing flow rate during the slag drying period are used to obtain a relatively low oxidizability, providing good thermodynamic conditions for converter desulfurization, thereby realizing efficient converter desulfurization; in the late stage of converter smelting, the sulfur content in the steel is relatively low and the desulfurization rate decreases. During this period, the converter slag with a large slag amount is mainly used for desulfurization, so that the sulfur content at the end point of the converter is controlled below 0.0015%, realizing sulfur control in the converter desulfurization process.

Description

Technical Field

[0001] The invention belongs to the technical field of converter steelmaking, and in particular relates to a converter sulfur-controlled smelting process. Background Art

[0002] Sulfur is a harmful element for most steel grades. In its solid state, sulfur is insoluble in iron and exists as FeS. FeS forms a low-melting-point eutectic with Fe, causing intergranular cracking in the steel—hot brittleness. This reduces the steel's ductility and toughness, and easily causes cracks during forging and rolling. Sulfur also negatively impacts weldability, causing hot cracking in welds and generating SO2 gas during welding, which can lead to porosity and looseness in the weld. Furthermore, sulfur reduces the corrosion resistance of steel. Therefore, desulfurization is necessary during the steelmaking process.

[0003] Currently, the desulfurization processes widely used by steel companies both domestically and internationally mainly include the following three steps: the first is pretreatment of molten iron desulfurization, which involves a variety of methods, including pre-desulfurization in the molten iron ditch or ladle, KR pre-desulfurization, and magnesium powder spraying. The second is LF refining desulfurization; and the third is desulfurization by spraying or adding a desulfurizer during the RH vacuum refining process. For example, Chinese patent document CN110218839A discloses a method for deep desulfurization during the bearing steel smelting process. This method addresses the problem of flocculation at the water outlet during the bearing steel casting process. By adjusting various operating procedures and the composition of the refining slag, this method achieves deep desulfurization during the bearing steel smelting process without increasing the refining time of the molten steel outside the furnace, stabilizing the sulfur content of the finished bearing steel to below 0.0015%. For example, Chinese patent document CN111893242A discloses a smelting method for deep desulfurization of low-aluminum steel. This method achieves deep desulfurization of low-aluminum steel by fully pretreating molten iron, advancing deoxidation in the converter, deep desulfurization using diffusion deoxidation in the refining furnace, and calcium treatment in the vacuum furnace. However, desulfurization treatment using the converter process is rarely used in the prior art. This is because the primary function of converter smelting is to decarburize molten iron to produce molten steel, a process that often requires oxygen blowing. High oxidizing properties are detrimental to desulfurization, and therefore desulfurization is not considered in the prior art. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a converter sulfur-controlled smelting process that utilizes the converter process to achieve deep desulfurization.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] According to an embodiment of the present invention, in a first aspect, the present invention provides a converter sulfur-controlled smelting process, comprising the following steps:

[0007] The hot metal is subjected to KR pretreatment, converter smelting, and RH vacuum treatment in sequence; among them, the converter smelting process includes three slag-making smelting steps:

[0008] The first slag-making smelting: Charge the KR desulfurized hot metal and scrap steel into the converter, add the first slag-making agent and conduct the first-stage blowing. When the first-stage blowing ends, the slag basicity is 2.0 - 3.0, and the T.Fe content is 13 - 17%. Then, pour out the slag;

[0009] The second slag-making smelting: Add the second slag-making agent to the molten steel after the first slag-making smelting. The mass ratio of the second slag-making agent to the molten steel after the first slag-making smelting is 0.038 - 0.053:1. Conduct the second-stage blowing with a low lance position. When the slag shows signs of drying out, reduce the oxygen supply flow rate and simultaneously increase the bottom blowing flow rate. When the second-stage blowing ends, the slag basicity ≥ 6.0, and the T.Fe content is 7 - 10%. Then, pour out the slag;

[0010] The third slag-making smelting: Add the third slag-making agent to the molten steel after the second slag-making smelting and conduct the third-stage blowing. The mass ratio of the third slag-making agent to the molten steel after the second slag-making smelting is 0.023 - 0.032:1. When the third-stage blowing ends, the slag basicity ≥ 4.5, and the T.Fe content is 8 - 13%.

[0011] According to the embodiment of the present invention, the raw material composition of the first slag-making agent includes: 4 - 8 kg / t of lime, 3 - 6 kg / t of lightly burned dolomite, and 5 - 7 kg / t of pellets; the lime accounts for 38 - 50% of the total mass of the first slag-making agent.

[0012] According to the embodiment of the present invention, the raw material composition of the second slag-making agent includes: 20 - 26 kg / t of lime, 8 - 12 kg / t of pellets, and 10 - 15 kg / t of lightly burned dolomite; the lime accounts for 43 - 59% of the total mass of the second slag-making agent.

[0013] According to the embodiment of the present invention, the raw material composition of the third slag-making agent includes: 14 - 18 kg / t of lime, 4 - 6 kg / t of pellets, and 5 - 8 kg / t of lightly burned dolomite; the lime accounts for 50 - 67% of the total mass of the third slag-making agent.

[0014] According to the embodiment of the present invention, after the KR pretreatment process ends, the desulfurization slag is removed to obtain hot metal with a temperature ≥ 1300°C, a sulfur content ≤ 0.0005%, and a Si content of 0.25 - 0.55%, that is, the KR desulfurized hot metal. This is beneficial for controlling the S content of the hot metal entering the furnace.

[0015] According to the embodiment of the present invention, the scrap steel is clean scrap steel, and the sulfur content in the clean scrap steel ≤ 0.003%, and the scrap steel ratio ≤ 10%. This is beneficial for controlling the S content of the scrap steel entering the furnace.

[0016] According to an embodiment of the present invention, the mass ratio of the first slag-forming agent to the sum of the masses of the KR desulfurized hot metal and the scrap steel is 0.013 to 0.022:1. In the first stage, the bottom blowing flow rate is controlled at 400 to 600 NL / min. After blowing for 4 to 6 minutes, more than 80% of the slag is poured out. Pouring out the early-stage desulfurization slag can effectively reduce the total S content.

[0017] According to an embodiment of the present invention, during the blowing process in the second stage, when the slag shows signs of drying back, the oxygen supply flow rate is reduced by 20 to 40%. The bottom blowing flow rate is increased from 300 to 500 NL / min to 800 to 1000 NL / min. After stirring for 1 to 2.5 minutes, the blowing in the second stage ends, and 75 to 85% of the slag is poured out. Pouring out the mid-stage desulfurization slag can effectively reduce the total S content.

[0018] According to an embodiment of the present invention, in the third stage, the bottom blowing flow rate is controlled at 300 to 500 NL / min. After blowing for 3 to 5 minutes, the steel is tapped without pouring out the slag. The tapping temperature of the converter is controlled to be ≥1640 °C. The C content of the molten steel is 0.05 to 0.12%, the P content is ≥0.025%, and the S content is ≤0.0015%. Controlling a relatively high carbon content is beneficial to reducing oxidation, and combined with controlling a relatively high temperature, it is beneficial to further desulfurization.

[0019] According to an embodiment of the present invention, the converter smelting process is controlled within 40 minutes.

[0020] According to an embodiment of the present invention, during the tapping process of the converter sulfur control smelting process, if it is a silicon-manganese deoxidized steel, ferrosilicon and silicomanganese are added to the ladle for deoxidation alloying according to the target composition of the steel grade. At the end of tapping, 2 to 4 kg / t of lime is added to form a desulfurization slag with an alkalinity of 2.0 to 3.0.

[0021] According to an embodiment of the present invention, if it is an aluminum deoxidized steel, aluminum blocks and ferrosilicon are added to the ladle for deoxidation alloying according to the target composition of the steel grade. At the end of tapping, 2 to 4 kg / t of lime is added to form a desulfurization slag with a mass ratio of CaO / Al2O3 of 1.7 to 2.1 and an alkalinity ≥4.0. Further desulfurization is achieved during the tapping process to avoid sulfur reversion.

[0022] According to an embodiment of the present invention, during the tapping process of the converter smelting process, a slag stopper rod is used to block the tapping hole in the early stage, and a slag dam is used to block the slag in the later stage of tapping, and the slag entrainment per ton of steel is controlled within 1.2 kg / t. By controlling the slag entrainment amount during converter tapping, sulfur reversion from the converter slag to the molten steel is avoided.

[0023] It should be noted that the term "scrap ratio" refers to the ratio of the mass of scrap to the sum of the masses of scrap and hot metal. The term "kg / t lime" refers to the number of kilograms of lime added per ton of hot metal or molten steel; the term "kg / t calcined dolomite" refers to the number of kilograms of calcined dolomite added per ton of hot metal or molten steel; the term "kg / t pellets" refers to the number of kilograms of pellets added per ton of hot metal or molten steel.

[0024] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0025] 1. The converter sulfur control smelting process provided by the embodiment of the present invention includes subjecting hot metal to KR pretreatment, converter smelting, and RH vacuum treatment in sequence. The converter smelting process includes three slag-making smelts, and makes full use of the characteristics of different periods of the converter for desulfurization. Specifically, in the early stage of converter smelting, since the molten steel temperature is relatively low and the slag oxidation is relatively high, the desulfurization conditions are relatively poor. To effectively save slag-making materials, a small amount of slag-making agent can be added, and the slag basicity control is relatively low; in the middle stage of converter smelting, a relatively high molten steel temperature, a large slag volume, a high slag basicity, and a relatively high temperature and reduced oxygen blowing flow rate during the slag drying period are used to obtain a relatively low oxidation, providing good thermodynamic conditions for converter desulfurization. Moreover, during this period, the converter is blown with a relatively large bottom blowing flow rate, providing good kinetic conditions for desulfurization. In addition, since the desulfurization slag needs to be poured out after the early and middle stages of converter smelting, the sulfur content in the molten steel can be effectively reduced, thus realizing efficient desulfurization of the converter; in the late stage of converter smelting, the sulfur content in the steel is relatively low and the desulfurization rate decreases. During this period, the converter slag with a large slag volume is mainly used for desulfurization, so that the sulfur content at the end of the converter is controlled below 0.0015%, realizing sulfur control in the converter.

[0026] Moreover, the converter smelting process of the converter sulfur control smelting process provided by the embodiment of the present invention is controlled within 40 minutes, with the characteristics of low cost and strong operability. The converter process of the present invention focuses on desulfurization during the process, and the controlled end temperature is relatively high. High temperature is not conducive to converter dephosphorization. However, compared with the phosphorus content of 0.08 - 0.10% in hot metal, the converter still has a certain dephosphorization ability. Therefore, compared with the phosphorus content of 0.012 - 0.018% in the molten steel of other normal furnace charges, the phosphorus content at the end of the converter of the present invention is relatively high, above 0.025%.

[0027] 2. For the converter sulfur control smelting process provided by the embodiment of the present invention, considering that the sulfur content in the converter slag is relatively high during the converter tapping process and it is easy to resulfurize into the molten steel, the converter tapping is controlled to have a relatively high carbon content (0.05 - 0.12%) to facilitate reducing oxidation. At the same time, in cooperation with a relatively high tapping temperature (≥1640°C) and the tapping desulfurization step, further desulfurization can be achieved.

[0028] 3. The converter sulfur control smelting process provided by the embodiments of the present invention uses a slag blocking rod to block the tapping hole in the early stage of tapping during the converter smelting process, and uses a slag blocking cone to block the slag in the later stage of tapping, and controls the slag entrainment per ton of steel within 1.2 kg / t. Through the above-mentioned steel retention operation during converter tapping, the converter slag is strictly controlled, and the re-sulfurization of the molten steel caused by the converter slag is reduced. On the premise of not affecting the production efficiency of the converter, the purpose of smelting ultra-low sulfur steel in the converter can be achieved, and at the same time, the desulfurization pressure of the subsequent process is reduced. Detailed implementation manners

[0029] The following embodiments are provided to better further understand the present invention, which is not limited to the described optimal implementation manner, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other prior arts falls within the protection scope of the present invention.

[0030] For those not specifying specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0031] Embodiment 1

[0032] The converter sulfur control smelting process provided by this embodiment includes the following steps:

[0033] KR pretreatment: The hot metal before entering the furnace is subjected to KR hot metal desulfurization treatment. After the desulfurization is completed, the desulfurization slag is thoroughly removed, and there is no obvious floating slag on the surface, obtaining hot metal with a temperature of 1300 °C, a sulfur content of 0.0005%, and a Si content of 0.55%, that is, the desulfurized hot metal;

[0034] The converter blowing process includes three slag-making smelts:

[0035] The first slag-making smelt: 161 t of desulfurized hot metal and 17.9 t of clean scrap steel are charged into the converter. Before blowing, 8 kg / t of lime, 6 kg / t of light-burned dolomite, and 7 kg / t of pellets are added, and oxygen is blown for dephosphorization and desiliconization. The molten steel temperature is 1440 °C, the oxygen supply amount is 40000 Nm 3 / h, the bottom blowing flow rate is 600 NL / min. After blowing for 4 min, slag is poured out. The slag basicity is 3.0, the T.Fe content is 17%, and 80% of the slag is poured out; among them, the sulfur content in the clean scrap steel is 0.0025%, and the scrap ratio is 10%;

[0036] The second slag-making smelt: 20 kg / t of lime, 10 kg / t of light-burned dolomite, and 3 12 kg / t of pellets are added to the molten steel after the first slag-making smelt. Low lance position is adopted for dephosphorization, decarburization and desulfurization. The molten steel temperature is 1510 °C, the oxygen supply amount is 40000 Nm3 At a bottom blowing flow rate of 500 NL / min and an oxygen supply rate of 40000 Nm³ / h, after 6 minutes of blowing, the slag became dry. The oxygen supply rate was reduced by 30%, and the bottom blowing flow rate of the converter was increased to 1000 NL / min. After strong stirring for 1 minute, the basicity of the slag was 6.0, the T.Fe content was 10%, and 85% of the slag was poured out.

[0037] Third slag-making smelting: 18 kg / t of lime, 8 kg / t of lightly burned dolomite, and 6 kg / t of pellets were added to the molten steel after the second slag-making smelting. The bottom blowing flow rate was 500 NL / min. After 3 minutes of blowing, the steel was tapped without pouring out the slag. The basicity of the slag was 5.7, the T.Fe content was 8%. During the tapping process, aluminum blocks and ferrosilicon were added to the ladle for deoxidation and alloying. After the tapping was completed, 3.1 kg / t of lime was added to form a desulfurization slag with a CaO / Al₂O₃ mass ratio of 2.1 and a basicity of 5.5. The tapping temperature was controlled at 1670 °C. At the early stage of tapping, a slag stopper was used to block the tapping hole, and at the later stage of tapping, a slag cone was used to block the slag, and the slag entrainment per ton of steel was controlled at about 1.2 kg / t. The C content of the molten steel was 0.05%, the P content was 0.028%, the end-point S content was 0.0010%, and the converter smelting cycle was controlled within 37 minutes.

[0038] RH vacuum treatment: Conducted according to normal operating procedures.

[0039] The P content in the final product was 0.025%, and the end-point S content was 0.0010%.

[0040] Example 2

[0041] The converter sulfur control smelting process provided in this example includes the following steps:

[0042] KR pretreatment: The hot metal before entering the furnace was subjected to KR hot metal desulfurization treatment. After desulfurization, the desulfurization slag was thoroughly removed without obvious floating slag on the surface, obtaining hot metal with a temperature of 1340 °C, a sulfur content of 0.0004%, and a Si content of 0.25%, namely the desulfurized hot metal.

[0043] The converter blowing process includes three slag-making smelting steps:

[0044] First slag-making smelting: 165 t of desulfurized hot metal and 14.3 t of clean scrap were charged into the converter. Before blowing, 8 kg / t of lime, 3 kg / t of lightly burned dolomite, and 5 kg / t of pellets were added, and oxygen was blown for dephosphorization and de-siliconization. The temperature of the molten steel was 1451 °C, and the oxygen supply amount was 40000 Nm³ / h. 3 At a bottom blowing flow rate of 400 NL / min, after 6 minutes of blowing, the slag was poured out. The basicity of the slag was 3.0, the T.Fe content was 17%, and 85% of the slag was poured out. Among them, the sulfur content in the clean scrap was 0.0030%, and the scrap ratio was 8%.

[0045] Second slag-making smelting: Add 26 kg / t of lime, 15 kg / t of calcined dolomite and 8 kg / t of pellets to the molten steel after the first slag-making smelting. Carry out dephosphorization, decarburization and desulfurization with a low lance position. The temperature of the molten steel is 1525 °C, and the oxygen supply is 40000 Nm 3 / h. The bottom blowing flow rate is 400 NL / min. After blowing for 4 min, the slag becomes dry. Reduce the oxygen supply flow rate by 30%, and increase the bottom blowing flow rate of the converter to 800 NL / min. After strong stirring for 2.5 min, the basicity of the slag is 6.5, and the T.Fe content is 7%. Pour out 75% of the slag;

[0046] Third slag-making smelting: Add 14 kg / t of lime, 5 kg / t of calcined dolomite and 4 kg / t of pellets to the molten steel after the second slag-making smelting. The bottom blowing flow rate is 300 NL / min. After blowing for 5 min, tap the steel without pouring out the slag. The basicity of the slag is 4.5, and the T.Fe content is 8%. During tapping, add aluminum blocks and ferrosilicon to the ladle for deoxidation alloying. After tapping, add 2.5 kg / t of lime to form a desulfurization slag with a CaO / Al2O3 mass ratio of 1.8 and a basicity of 4.3. Control the tapping temperature at 1640 °C. Use a slag stopper to block the tapping hole in the early stage of tapping, and use a slag cone to block the slag in the later stage of tapping, and control the slag entrainment per ton of steel at about 1.0 kg / t. The C content of the molten steel is 0.12%, the P content is 0.030%, and the end-point S content is 0.0015%. Control the converter smelting cycle within 40 min;

[0047] RH vacuum treatment: Carry out according to the normal operating procedures.

[0048] The P content in the final product is 0.029%, and the end-point S content is 0.0014%.

[0049] Example 3

[0050] The converter sulfur control smelting process provided by this example includes the following steps:

[0051] KR pretreatment: Carry out KR hot metal desulfurization treatment on the hot metal before entering the furnace. After desulfurization, thoroughly remove the desulfurization slag so that there is no obvious floating slag on the surface, and obtain hot metal with a temperature of 1353 °C, a sulfur content of 0.0003%, and a Si content of 0.40%, that is, the desulfurized hot metal;

[0052] The converter blowing process includes three slag-making smelting processes:

[0053] First slag-making smelting: Charge 163 t of desulfurized hot metal and 16.1 t of clean scrap steel into the converter. Before blowing, add 4 kg / t of lime, 4 kg / t of calcined dolomite and 6 kg / t of pellets, and blow oxygen for dephosphorization and desiliconization. The temperature of the molten steel is 1463 °C, and the oxygen supply is 40000 Nm 3 / h, bottom blowing flow rate 500 NL / min, slag tapping is carried out after blowing for 5 min, the basicity of the slag is 2.6, the content of T.Fe is 15%, and 82% of the slag is poured out; among them, the sulfur content in the clean scrap is 0.0025%, and the scrap ratio is 9%;

[0054] The second slag-making smelting: Add 23 kg / t of lime, 12 kg / t of light-burned dolomite and 10 kg / t of pellet stone to the molten steel after the first slag-making smelting, and carry out dephosphorization and decarburization with a low lance position. The temperature of the molten steel is 1510 °C, and the oxygen supply amount is 40000 Nm 3 / h, the bottom blowing flow rate is 300 NL / min. After blowing for 5 min, the slag becomes dry. The oxygen supply flow rate is reduced by 20%, the bottom blowing flow rate of the converter is increased to 900 NL / min, and after strong stirring for 2 min, the basicity of the slag at the end of blowing is 6.3, the content of T.Fe is 8%, and 80% of the slag is poured out;

[0055] The third slag-making smelting: Add 16 kg / t of lime, 6 kg / t of light-burned dolomite and 5 kg / t of pellet to the molten steel after the second slag-making smelting. The bottom blowing flow rate is 400 NL / min. After blowing for 4 min, the steel is tapped without slag pouring. The basicity of the slag is 5.3, the content of T.Fe is 10%. During the tapping process, ferrosilicon and silicomanganese are added to the ladle for deoxidation alloying. After the tapping is completed, 2 kg / t of lime is added to form a desulfurization slag with a basicity of 2.2, and the tapping temperature is controlled at 1662 °C. At the early stage of tapping, the tapping hole is blocked by a slag stopper, and at the later stage of tapping, a slag dam is used to block the slag, and the slag entrainment per ton of steel is controlled at about 1.1 kg / t. The C content of the molten steel is 0.08%, the P content is 0.025%, the end-point S content is 0.0010%, and the smelting cycle of the converter is controlled within 35 min.

[0056] RH vacuum treatment: Refer to the normal operating procedures.

[0057] The P content in the final product is 0.023%, and the end-point S content is 0.0008%.

[0058] Comparative Example 1

[0059] Except for the following content, the rest is the same as Example 1.

[0060] In the converter blowing process, one-time slag-making smelting is adopted, specifically:

[0061] The KR desulfurized hot metal and clean scrap (sulfur content 0.0025%, scrap ratio 10%) are charged into the converter, 48 kg / t of lime, 23 kg / t of light-burned dolomite and 25 kg / t of pellet are added, and dephosphorization, decarburization and desulfurization are carried out with a low lance position. The temperature of the molten steel is 1449 °C, and the oxygen supply amount is 40000 Nm 3 / h, the bottom blowing flow rate is 500 NL / min. After blowing for 6 min, the slag becomes dry. The oxygen supply flow rate is reduced by 30%, and the bottom blowing flow rate of the converter is increased to 1000 NL / min. After strong stirring for 1 min, the blowing ends with a slag basicity of 4.5 and a T.Fe content of 17%. 85% of the slag is poured out.

[0062] The C content in the molten steel tapped from the converter is 0.07%, the P content is 0.018%, and the S content is 0.0032%.

[0063] The P content in the final product is 0.022%, and the end-point S content is 0.0040%.

[0064] Comparative Example 2

[0065] Except for the following content, the rest is the same as in Example 1.

[0066] After the third slag-making smelting in the converter blowing process, there is no steel left in the furnace. The steel is directly tapped, and the slag entrainment amount is 2.4 kg / t.

[0067] The C content in the molten steel tapped from the converter is 0.06%, the P content is 0.028%, and the S content is 0.0015%.

[0068] The P content in the final product is 0.032%, and the end-point S content is 0.0023%. Because the slag entrainment amount in this comparative example is large, the sulfur return amount is large in the subsequent production process.

[0069] Comparative Example 3

[0070] The converter sulfur control smelting process method provided in this comparative example includes the following steps:

[0071] KR hot metal desulfurization treatment: The hot metal before entering the furnace is subjected to KR hot metal desulfurization treatment. After desulfurization, slag skimming is carried out to obtain hot metal with a sulfur content of 0.0012%, a temperature of 1327 °C, and a Si content of 0.45%;

[0072] Converter blowing: 158 t of KR desulfurized hot metal and 25.7 t of clean scrap steel are charged into the converter for blowing. Among them, the sulfur content in the clean scrap steel is 0.0033%, and the scrap ratio is 14%; 38 kg / t of lime, 24 kg / t of light burned dolomite, and 22 kg / t of pellets are added during the smelting process. The oxygen supply amount is 40000 Nm 3 / h, the bottom blowing flow rate is 400 - 600 NL / min. After blowing, the slag basicity is 4.2, the T.Fe content is 18%, the tapping temperature is controlled at 1,656 °C, and a slag dam cone is used for slag blocking during the tapping process of the converter. The slag entrainment per ton of steel is 2.58 kg / t. The C content in the molten steel is 0.04%, the S content is 0.0042%, and the P content is 0.023%. The converter smelting cycle is 42 min.

[0073] The P content in the final product is 0.028%, and the S content at the end point is 0.0055%.

[0074] Obviously, the above embodiments are merely examples given for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A converter sulfur control smelting process, characterized in that, It includes the following steps: Carry out KR pretreatment, converter smelting, and RH vacuum treatment on hot metal in sequence; wherein, the converter smelting process includes three slag-making smelts: The first slag-making smelt: Charge the KR desulfurized hot metal and scrap steel into the converter, add the first slag-making agent and conduct the first-stage blowing. When the first-stage blowing ends, the basicity of the slag is 2.0 - 3.0, and the T.Fe content is 13 - 17%. Then, pour out the slag; The second slag-making smelt: Add the second slag-making agent to the molten steel after the first slag-making smelt. The mass ratio of the second slag-making agent to the molten steel after the first slag-making smelt is 0.038 - 0.053:

1. Conduct the second-stage blowing with a low lance position. When the slag shows drying back, reduce the oxygen supply flow rate and simultaneously increase the bottom blowing flow rate. When the second-stage blowing ends, the basicity of the slag ≥ 6.0, and the T.Fe content is 7 - 10%. Then, pour out the slag; The third slag-making smelt: Add the third slag-making agent to the molten steel after the second slag-making smelt and conduct the third-stage blowing. The mass ratio of the third slag-making agent to the molten steel after the second slag-making smelt is 0.023 - 0.032:

1. When the third-stage blowing ends, the basicity of the slag ≥ 4.5, and the T.Fe content is 8 - 13%; The raw material composition of the first slag-making agent includes: 4 - 8 kg / t of lime, 3 - 6 kg / t of light-burned dolomite, 5 - 7 kg / t of pellets, and lime accounts for 38 - 50% of the total mass of the first slag-making agent; The raw material composition of the second slag-making agent includes: 20 - 26 kg / t of lime, 8 - 12 kg / t of pellets, 10 - 15 kg / t of light-burned dolomite, and lime accounts for 43 - 59% of the total mass of the second slag-making agent; The raw material composition of the third slag-making agent includes: 14 - 18 kg / t of lime, 4 - 6 kg / t of pellets, and 5 - 8 kg / t of light-burned dolomite, and lime accounts for 50 - 67% of the total mass of the third slag-making agent.

2. The converter sulfur control smelting process method according to claim 1, characterized in that, After the KR pretreatment process ends, remove the desulfurized slag to obtain hot metal with a temperature ≥ 1300°C, a sulfur content ≤ 0.0005%, and an Si content of 0.25 - 0.55%, which is the KR desulfurized hot metal.

3. The converter sulfur control smelting process according to claim 1, characterized in that, The scrap steel is clean scrap steel, and the sulfur content in the clean scrap steel ≤ 0.003%, and the scrap steel ratio ≤ 10%.

4. The converter sulfur control smelting process according to claim 1, characterized in that, During the first-stage blowing process, the mass ratio of the first slag-making agent to the sum of the masses of the KR desulfurized hot metal and the scrap steel is 0.013 - 0.022:

1. Control the bottom blowing flow rate at 400 - 600 NL / min. After blowing for 4 - 6 min, pour out more than 80% of the slag.

5. The converter sulfur control smelting process according to claim 1, characterized in that, During the second-stage blowing process, when the slag shows drying back, reduce the oxygen supply flow rate by 20 - 40%, increase the bottom blowing flow rate from 300 - 500 NL / min to 800 - 1000 NL / min. After stirring for 1 - 2.5 min, the second-stage blowing ends, and pour out 75 - 85% of the slag.

6. The converter sulfur control smelting process according to claim 1, characterized in that, During the third-stage blowing process, control the bottom blowing flow rate at 300 - 500 NL / min. After blowing for 3 - 5 minutes, tap the steel without slagging. Control the tapping temperature of the converter to be ≥1640 °C, with the C content of the molten steel being 0.05 - 0.12%, the P content ≥0.025%, and the S content ≤0.0015%.

7. The converter sulfur control smelting process according to claim 1, characterized in that, Control the converter smelting process within 40 minutes.

8. The converter sulfur control smelting process according to claim 1, characterized in that, During the tapping process of the converter sulfur control smelting process, if it is a silicomanganese deoxidized steel, add ferrosilicon and silicomanganese to the ladle for deoxidation alloying according to the target composition of the steel grade. Add 2 - 4 kg / t of lime at the end of tapping to form a desulfurization slag with an alkalinity of 2.0 - 3.0; or if it is an aluminum deoxidized steel, add aluminum blocks and ferrosilicon to the ladle for deoxidation alloying according to the target composition of the steel grade. Add 2 - 4 kg / t of lime at the end of tapping to form a desulfurization slag with a CaO / Al2O3 mass ratio of 1.7 - 2.1 and an alkalinity ≥4.

0.

9. The converter sulfur control smelting process according to claim 8, characterized in that, During the early stage of tapping in the converter smelting process, block the tapping hole with a slag stopper. During the later stage of tapping, use a slag dam to block the slag, and control the slag entrainment per ton of steel within 1.2 kg / t.