A method for smelting low phosphorus steel in a single slag converter

Abstract

The application provides a method for smelting low-phosphorus steel by a converter single-slag process, and the method is characterized by matching the silicon content of molten iron with the basicity and MgO content of the slag, using a burdening and slagging method with low MgO and strong bottom blowing, and optimizing the process and parameters of each step, so that the raw materials have wide adaptability, the cost is low, and the low-P smelting is realized without using special P-removing agents under the condition that the P mass percentage of the molten iron is less than or equal to 0.13%. The method can not only reduce the combination method of P return, but also reduce the P return of the converter end product to less than 0.0015%, and significantly improve the distribution ratio of P between the slag and the steel, so that the P content of the converter end product is less than 0.0060%, and the P content of the finished product after LF deep desulfurization is less than 0.0070%.

Description

Technical Field

[0001] The invention belongs to the field of steel smelting, relates to a converter smelting process, and in particular to a method for smelting low-phosphorus steel with single converter slag. Background Art

[0002] Phosphorus is a detrimental element for most steels, easily segregating at grain boundaries and causing low-temperature brittleness and temper brittleness. Therefore, dephosphorization is a core issue in steelmaking, a constant throughout its development. Over the past 30 years, with the rapid development of the national economy, the demand for high-grade, high-quality steel has continued to increase, and phosphorus requirements have become increasingly stringent. This is especially true for steel used in low-temperature, marine, natural gas, and oil pipelines, as well as in oil refining equipment, where phosphorus content is required to be less than 0.010% or even below 0.005%. This poses a significant challenge to dephosphorization in converter steelmaking.

[0003] Currently, there are two relatively mature methods for producing low-phosphorus steel in converters. The first involves desiliconizing, desulfurizing, and dephosphorizing molten iron in a torpedo or ladle. However, this method requires extensive equipment, high investment, complex processes, and significant heat loss. The resulting molten iron temperature is low, significantly reducing the amount of scrap added to converter smelting. The second method involves using a converter "double-link" process, where the molten iron is dephosphorized in the converter, then tapped for decarburization. However, this method also involves complex processes, long smelting times, and limited converter efficiency. Furthermore, the frequent tank turnovers increase temperature drop and iron loss.

[0004] The report to the process research of low-phosphorus steel at home and abroad is more, for example, the patent disclosed on November 14, 2012, publication number is CN102776314A, discloses a kind of ultra-low phosphorus steel smelting method, this method adopts double slag and slag retention operation process to smelt low-phosphorus steel, mainly theory and thinking aspect, it does not have clear and feasible concrete steelmaking operation method. The patent disclosed on December 8, 2010, publication number is CN101906504A, discloses a kind of converter production ultra-low phosphorus steel smelting process, this method adopts early stage, mid-term, late stage three times slag pouring and blowing method to dephosphorize molten iron after primary desulfurization, adopts ferrosilicon slag adjustment and temperature control to realize low-phosphorus smelting, and has the problem of poor operability. The disclosed publication number on October 23rd, 2002 is that the patent of CN1375560A discloses a kind of method for controlling phosphorus of producing ultra-low phosphorus steel, this method focuses on the development and utilization of dephosphorizing agent and the control of phosphorus return in the steelmaking back process, namely phosphorus during tapping is controlled at below 0.008% (weight ratio) → molten steel ladle is constantly stirred with argon blowing until 3~5 minutes after tapping, add dephosphorizing agent and quickened lime that molten steel and molten iron are all suitable for simultaneously → after argon blowing and stirring, carry out heating stirring (not deoxidation) in refining furnace → according to steel grade needs, directly carry out deoxidation alloying or carry out deoxidation alloying again after stripping off slag → carry out continuous casting pouring phosphorus return control.It does not disclose the method that does not adopt special dephosphorizing agent to carry out dephosphorization. Summary of the Invention

[0005] The object of the present invention is to provide a method for smelting low-phosphorus steel using single-slag from a converter. The method is low-cost and has a high hit rate. The method has wide raw material adaptability and low cost. Low-phosphorus smelting can be achieved without using a special dephosphorization agent under the condition that the phosphorus mass percentage of molten iron is ≤0.13%.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A method for smelting low-phosphorus steel using single converter slag comprises the following steps:

[0008] 1) Slag adjustment is performed on the first furnace before the first furnace of low-phosphorus steel produced in the converter;

[0009] 2) After the last furnace is tapped, the slag is left, splashed and solidified, and then scrap steel and molten iron are added to smelt the low-phosphorus steel furnace;

[0010] 3) Oxygen supply and slagging in the main blowing stage;

[0011] 4) auxiliary blowing;

[0012] 5) dumping slag;

[0013] 6) After the slag is poured, stir it;

[0014] 7) Steel tapping and slag blocking;

[0015] 8) Alloy is added during the converter tapping process and tapping is completed.

[0016] In step 1), the slag of the first furnace of the converter for producing low-phosphorus steel is adjusted by: using lime and magnesium-containing materials to make slag, wherein the magnesium-containing materials include any one or more of light-burned dolomite, dolomite or magnesium balls; controlling the slag basicity and the MgO content in the slag according to the different silicon contents in the hot metal in the first furnace of the converter for producing low-phosphorus steel; specifically,

[0017] For hot metal with silicon content of 0.1%<Si≤0.2%, the slag basicity should be controlled at 5.0-7.1, and the MgO content in the slag should be 0-5%;

[0018] For hot metal with silicon content of 0.2%<Si≤0.3%, the slag basicity should be controlled at 3.8-5.4, and the MgO content in the slag should be 3-6%;

[0019] For hot metal with silicon content of 0.3%<Si≤0.4%, the slag basicity should be controlled at 3.2-4.4, and the MgO content in the slag should be 4-8%;

[0020] For hot metal with silicon content of 0.4%<Si≤0.5%, the slag basicity should be controlled at 2.8-3.8, and the MgO content in the slag should be 4-8%;

[0021] For hot metal with silicon content of 0.5%<Si≤0.7%, the slag basicity should be controlled at 2.5-3.4, and the MgO content in the slag should be 4-8%;

[0022] In step 1), the adjustment method further includes: the top blowing strength of the first furnace of low-phosphorus steel is 2.8-5.0Nm 3 / (t.min); lance position in the early stage of smelting is 1.15×(32~45)×D throat, lance position in the middle stage is 1.15×(35~50)×D throat, and lance position in the final stage is 1.15×(30~38)×D throat, where D throat is the diameter of the oxygen lance nozzle throat, in mm; bottom blowing intensity is 0.02~0.40Nm 3 / (t.min); converter endpoint temperature>1580℃, endpoint phosphorus mass percentage ≤0.020%;

[0023] In step 2), the slag is retained, and the amount of slag retained is 30-80 kg / t steel;

[0024] In step 2), the molten iron is added, and the molten iron composition and temperature for smelting low-phosphorus steel are required to be: Si 0.10%wt% to 0.70%wt%, P≤0.13wt%, [C]>4.0wt%, and the molten iron entering the furnace temperature is 1200~1450℃.

[0025] In step 3), the main blowing stage refers to the blowing period from the start of blowing to the first temperature measurement and sampling;

[0026] In step 3), before oxygen is supplied for slagging during the main blowing phase, the amounts of lime, magnesium-containing materials, scrap steel, and coolant (including ore, sintered ore, and the like) are calculated based on the charge, the molten iron's carbon and silicon contents, the target alkalinity, the final slag's MgO content, the molten iron temperature, and the target molten steel temperature. This calculation can be performed using conventional methods in the art. The preset coolant addition amount is 5-30 kg / t, and the target molten steel temperature is 1605 ± 25°C. Excess heat is balanced by scrap steel.

[0027] In step 3), the slag basicity and MgO content are controlled according to the silicon content of the molten iron, as follows:

[0028] For hot metal with silicon content of 0.1%≤Si≤0.2%, the slag basicity should be controlled at 6.8±0.3 and the MgO content in the slag should be 0-5%;

[0029] For hot metal with silicon content of 0.2%<Si≤0.3%, the slag basicity should be controlled at 5.1±0.3, and the MgO content in the slag should be 2-5%;

[0030] For hot metal with silicon content of 0.3%<Si≤0.4%, the slag basicity should be controlled at 4.2±0.2, and the MgO content in the slag should be 4-7%;

[0031] For hot metal with silicon content of 0.4%<Si≤0.5%, the slag basicity should be controlled at 3.7±0.2, and the MgO content in the slag should be 4-7%;

[0032] For hot metal with silicon content of 0.5%<Si≤0.7%, the slag basicity should be controlled at 3.2±0.2, and the MgO content in the slag should be 4-7%;

[0033] Step 3) specifically includes the following controls:

[0034] 3-1) Oxygen lance position and flow rate: The converter oxygen supply adopts a staged constant flow and variable lance position operation mode, and the oxygen supply intensity is 2.8~4.5m 3 / (min.t); the lance position in the early stage of smelting is 1.15×(32~45)×Dthroat, the lance position in the middle stage is 1.15×(35~50)×Dthroat, and the lance position in the final stage is 1.15×(30~38)×Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, mm;

[0035] 3-2) Bottom blowing intensity: Bottom blowing intensity in the main blowing stage is 0.03~0.15m 3 / (min.t);

[0036] 3-3) Quantity and timing of converter slag material addition: lime and magnesium-containing materials are used for slag making. The first batch of slag is added within 1.5 minutes of the start of blowing. The amount of lime added is not less than 50% of the total amount, and the amount of magnesium-containing materials is not less than 70% of the total amount. The second batch of slag is added from the time the first batch of slag is added to the time 3.5 minutes after the start of blowing. The cumulative amount of lime added is not less than 70% of the total amount, and all the magnesium-containing materials are added. The remaining amount of lime is added from the time the second batch of slag is added to the time 7 minutes before oxygen blowing. The magnesium-containing materials include light-burned dolomite, dolomite, and magnesium balls. The amount and timing of coolant addition: 0-50% of the total amount of coolant required is added within 1-3 minutes of blowing. After 6 minutes, the remaining coolant is added in batches, with no more than 3 batches.

[0037] In step 3), the gun position is adjusted during the process with reference to the changes in CO concentration, the audio slagging curve, and the changes in the furnace mouth flame. When the CO concentration continues to rise, the audio intensity increases, and the furnace mouth flame hardens, the gun is promptly raised by 100-300 mm or the flow rate is reduced by 5-10%. Conversely, the gun is lowered by 100-300 mm or the flow rate is increased by 5-10%. The CO concentration is the online real-time detection value of the mass spectrometer or laser analyzer of the converter primary dust removal system.

[0038] In particular, when the back-drying is serious, raise the gun until the fire is stopped, and lower the gun in time after the fire is stopped; when splashing occurs, raise the gun position by 100-400mm, reduce the flow rate by 3-8%, and at the same time add 200-700kg of lime or dolomite in batches;

[0039] In step 3), the main blowing target is controlled to be: [C]%: 0.20%-0.70%, temperature T: 1530-1570°C.

[0040] In step 4), after carbon and temperature are measured, if T+[C]%×10000>1610, ore is added to the auxiliary blowing gun to adjust the ore addition amount W O =(T+[C]%×10000-1610)×β×BV÷10, where: [C] is the [C] content, unit wt%; T is the molten steel temperature, unit ℃; W O is the amount of ore added, kg; β is the coefficient, ranging from 1.2 to 3.0; BV is the nominal capacity of the converter, t; when calculating with the formula, substitute the value before the unit into the formula.

[0041] In step 4), the auxiliary blowing is specifically: bottom blowing intensity 0.05~0.30m 3 / (min.t), gun position 1.15×(30~38)×Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, mm; converter end temperature 1580~1630℃, molten steel active oxygen 0.015%~0.080%.

[0042] Step 5) slag pouring: after the auxiliary blowing is completed, the slag is poured by tilting the converter to the slag surface by 85-88 degrees, so that no slag falls from the furnace mouth and the remaining slag amount is not less than 30kg / t steel;

[0043] In step 6), after the slag is poured, the converter is tilted to a vertical position and the bottom blowing intensity is 0.08 to 0.40 m 3 / (min.t) Stir for 1-4 minutes.

[0044] In step 7), a combination of front block + slag dart + slide plate is used to block slag;

[0045] In step 7), the returning ladle is clean and pollution-free, and the molten steel from the previous heat is an aluminum-killed steel ladle with LF-made reducing slag, slag basicity greater than 3.0, and finished product P less than 0.030%; in particular, when tapping, slag should be avoided from entering the ladle at the early furnace mouth to reduce the mixing of steel slag at the tapping mouth, reduce the eddy current slag during the tapping process, improve the success rate of interception at the end of tapping, and the slag discharge amount is less than 3.0 kg / t of molten steel; the front block can be a slide plate or a slag cap, and a slag dart is used during the tapping process to reduce the slag roll-up during the process, and a slag dart or slide plate is used to intercept the flow at the end of tapping.

[0046] In step 8, a low-P alloy is used for the main alloying elements to reduce the P addition of the alloy.

[0047] The present invention provides a method for matching silicon in molten iron with basicity and MgO in slag for low-phosphorus smelting; provides a combined method for reducing P return, with the P return from converter end point to finished product less than 0.0015%; adopts a batching and slag-making method characterized by low MgO and strong bottom blowing, significantly improving the distribution ratio of P between slag and steel, with the P content at converter end point less than 0.0060%, and the P content of the finished product after LF deep desulfurization less than 0.0070%.

[0048] The present invention can be used for, but is not limited to, smelting steel having the following composition: C: 0.06% to 0.10%, Si: 0.25% to 0.35%, Mn: 1.50% to 1.60%, P≤0.007%, S≤0.005%, Ni: 1.00% to 1.10%, V: 0.07% to 0.09%, Als: 0.020% to 0.035%, Cr≤0.50%, Cu≤0.50%, [H]≤1.5ppm, [N]: 50ppm to 80ppm, with the remainder being Fe and unavoidable impurities.

[0049] Compared to existing technologies, the low-cost, high-performance converter slag smelting method for low-phosphorus steel offers broad raw material adaptability and low cost. It achieves low-phosphorus steelmaking without the use of special dephosphorization agents when the molten iron has a phosphorus content of ≤0.13% by mass, significantly reducing the final phosphorus content. Stable control of the final converter phosphorus content to <0.006% and the final product phosphorus content to <0.007% is achieved. This method primarily addresses the prior art's low phosphorus performance, complex dephosphorization procedures, and demanding raw material requirements for converter steelmaking with a final phosphorus content of <0.006% w[P], and achieves low-phosphorus steelmaking in converters. This significantly reduces production costs, shortens post-processing cycles, and ensures an efficient and orderly production process. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] Example 1

[0052] A method for smelting low-phosphorus steel using single-slag converter. In this embodiment, the converter is a 150-ton top-bottom combined-blowing converter. Taking the smelting of low-temperature steel bars for LNG storage tank construction as an example, the converter bottom-blowing gas is argon. The target steel composition is as follows: C: 0.08%, Si: 0.30%, Mn: 1.55%, P≤0.007%, S≤0.005%, Ni: 1.05%, V: 0.08%, Als: 0.028%, Cr≤0.30%, Cu≤0.30%, [H]≤1.5ppm, [N]: 65ppm; the remainder is Fe and unavoidable impurities.

[0053] The specific operations are as follows:

[0054] Slag adjustment and control before S0 smelting:

[0055] The slag adjustment and control were carried out before the first batch of low-phosphorus steel produced by the converter. Specifically, lime and magnesium balls were used for slag making, with a target basicity of R = 3.6 (0.35% Si in the hot metal), MgO = 5.5%; top blowing intensity of 3.4-3.5Nm 3 / (t.min); lance position in the early stage of smelting is 1.15×(32~45)×D throat, lance position in the middle stage is 1.15×(35~50)×D throat, and lance position in the final stage is 1.15×(30~38)×D throat, where D throat is the diameter of the oxygen lance nozzle throat, 39.3mm; bottom blowing intensity is 0.02~0.10Nm 3 / (t.min); the final converter temperature is greater than 1580°C, the mass percentage of final phosphorus is ≤0.020%, and the molten iron composition and process parameters are detailed in Tables 1 and 2.

[0056] After the steel is discharged, 62kg / t of slag is left for splash drying, which is prepared for the production of low-phosphorus steel in the converter.

[0057] Table 1 Slag adjustment and control parameters of Example 1

[0058]

[0059] Table 2 Bottom blowing parameter settings for forehearth smelting in Example 1

[0060]

[0061]

[0062] S1 low phosphorus steel smelting hot metal preparation

[0063] The molten iron composition and temperature for smelting low-phosphorus steel are as follows: Si 0.10% wt% to 0.70% wt%, P ≤ 0.13 wt%, [C] > 4.0 wt%, and the molten iron temperature is 1200 to 1450°C (into the furnace). The main components and temperatures of the molten iron for specific heats are shown in Table 3.

[0064] Table 3 Example 3 Low-phosphorus steel smelting molten iron

[0065] Heat Si% C％ P％ Temperature Heat 1 0.19 4.45 0.118 1345 Heat 2 0.30 4.50 0.115 1351 Heat 3 0.45 4.61 0.123 1408 Heat 4 0.36 4.40 0.125 1401 Heat 5 0.52 4.43 0.128 1342 Heat 6 0.17 4.42 0.116 1335 Heat 7 0.12 4.38 0.108 1330 Heat 8 0.10 4.35 0.112 1329

[0066] S2, the last furnace tapping is completed, the remaining slag is 30-80kg / t steel, splash dry and solidify, then add scrap steel and molten iron;

[0067] Table 4 Slag left in the upper furnace of Example 1

[0068] Heat Slag amount on furnace kg / t steel Remark Heat 1 62 Slag before smelting is adjusted according to S0 Heat 2 55 Heat 3 43 Heat 4 49 Heat 5 35 Heat 6 65 Heat 7 68 Heat 8 70

[0069] S3, based on the charge amount, molten iron carbon and silicon content, target basicity, final slag MgO content, molten iron temperature, and target molten steel temperature, the amounts of lime (main content: CaO content 87.0%, MgO content 0.4%, SiO2 content 1.50%), magnesia slag material (main content: magnesium balls, MgO content 65.0%, SiO2 content 1.10%, CaO content 5.0%), coolant (ore, Fe2O3 content 88.4%, FeO content 0.8%), and scrap steel added were calculated. The results are shown in Table 5;

[0070] Table 5 Calculated amount of slag material and coolant in Example 1

[0071]

[0072]

[0073] Oxygen supply and slagging control in the S4 main blowing stage:

[0074] S4-1 Oxygen lance position and oxygen supply intensity: The converter oxygen supply adopts a staged constant flow and variable lance position operation mode, and the oxygen supply intensity is 2.8~4.5m 3 / (min.t); the lance position in the early stage of smelting is 1.15×(32-45)×Dthroat, the lance position in the middle stage is 1.15×(35-50)×Dthroat, and the lance position in the final stage is 1.15×(30-38)×Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, 39.3 mm; see Table 6 for specific parameters;

[0075] Table 6 Oxygen lance position and oxygen supply intensity of Example 1

[0076]

[0077] S4-2 Bottom blowing intensity: Bottom blowing intensity in the main blowing stage is 0.03~0.15m 3 / (min.t), see Table 7 for details;

[0078] Table 7 Bottom blowing parameter settings for smelting process in Example 1

[0079]

[0080]

[0081] S4-3 Converter slag material addition amount and timing: lime and magnesium balls are used for slag making. The first batch of slag is added within 1.5 minutes of starting blowing. The amount of lime added is not less than 50% of the total amount, and the amount of magnesium-containing materials is not less than 70% of the total amount. The second batch of slag is added from the time the first batch of slag is added to the time 3.5 minutes after blowing starts. The cumulative amount of lime added is not less than 70% of the total amount, and all magnesium-containing materials are added. The remaining amount of lime is added from the time the second batch of slag is added to the time 7 minutes before oxygen blowing. See Table 8 for details. Add 0-50% of the total amount of coolant (ore, sintered ore, etc.) within 1-3 minutes of blowing. Add the remaining amount of ore in batches after 6 minutes. See Table 8 for details.

[0082] Table 8 Example 1 Converter slag material and ore addition amount and timing

[0083]

[0084]

[0085] In step S4, control is performed according to conventional methods. During the refining process, the gun position is adjusted with reference to changes in CO concentration, the audio slagging curve, and the furnace mouth flame. When the CO concentration continues to rise, the audio intensity increases, and the furnace mouth flame hardens, the gun is promptly raised by 100-300 mm or the flow rate is reduced by 5-10%. Conversely, the gun is lowered by 100-300 mm or the flow rate is increased by 5-10%. The CO concentration is the online real-time detection value of the mass spectrometer or laser analyzer of the converter primary dust removal system.

[0086] In particular, when the back-drying is serious, raise the gun until the fire is extinguished, and lower the gun in time after the fire is extinguished; when splashing occurs, raise the gun position by 100-400mm, reduce the flow rate by 3-8%, and add 200-300kg of lime in batches at the same time;

[0087] S5 main blowing target window: main blowing [C]%: 0.20%-0.70%, temperature T: 1530-1570℃.

[0088] Table 9 Main blowing performance of Example 1

[0089]

[0090]

[0091] S6 auxiliary blowing control: bottom blowing intensity 0.05~0.30m 3 / (min.t), lance position 1.15×(30~38)×Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, 39.3 mm; see Table 7 and Table 6 respectively; converter end temperature 1580~1630℃, molten steel active oxygen content 0.015%~0.080%.

[0092] In heat 3, T+[C]%×10000=1560+0.57%×10000=1617, which is greater than 1610. According to the ore addition amount W O =(T+[C]%×10000-1610)×β×BV÷10, where β=1.7, BV=150, and W is calculated. O =178.5, add 179 tons of ore.

[0093] Table 10 Auxiliary blowing control and P content of finished product in Example 1

[0094]

[0095] S7 Slag discharge: After the auxiliary blowing is completed, the slag is discharged by tilting the converter to 85-88 degrees toward the slag surface, with no slag falling from the furnace mouth and the remaining slag amount being no less than 30kg / t steel;

[0096] S8 post-stirring: After the slag is poured, the converter is tilted to a vertical position, and the bottom blowing intensity is 0.08 to 0.40 m 3 / (min.t) stirring for 1.5 minutes, the bottom blowing intensity is shown in Table 7;

[0097] S9 steel tapping and slag blocking: a combination of a slide plate front block + a slag dart + a slide plate rear block is used, the returning ladle is clean and pollution-free, and the molten steel from the previous heat is an aluminum-killed steel ladle made of reducing slag made by LF, with a slag alkalinity greater than 3.0 and a finished product P less than 0.030%; in particular, when tapping, slag should be avoided from entering the ladle at the early furnace mouth to reduce the mixing of steel slag at the tapping mouth, reduce the eddy current slag during the tapping process, and improve the success rate of interception at the end of tapping, with the slag discharge amount less than 3.0kg / t of molten steel; the front block can be a slide plate or a slag blocking cap, and a slag dart is used during the tapping process to reduce the slag curling during the process, and a slag dart or a slide plate is used to intercept the flow at the end of tapping.

[0098] Alloys are added during the tapping process of the S10 converter, with low-P alloys used for the main alloying elements to reduce the amount of P added to the alloy. The main alloying elements in the steel are nickel and manganese, with nickel alloyed in the furnace and phosphorus content requirements being the same as in the molten iron. Manganese is added to the ladle, and low-carbon ferromanganese (P < 0.03%) is used.

[0099] Table 11 Return P amount after steel tapping in Example 1

[0100] Heat End point P% Finished product P% Return P% Heat 1 0.0048 0.0061 0.0013 Heat 2 0.0043 0.0055 0.0012 Heat 3 0.0045 0.0057 0.0012 Heat 4 0.0048 0.0061 0.0013 Heat 5 0.0044 0.0058 0.0014 Heat 6 0.0064 0.0078 0.0014 Heat 7 0.0067 0.0080 0.0013 Heat 8 0.0075 0.0087 0.0012

[0101] The present invention has the following advantages:

[0102] (1) The raw materials have wide adaptability and low cost. When the P content of molten iron is ≤0.13%, low P smelting can be achieved without using special P removal agents, which reduces the cost by more than RMB 10 / ton and the smelting cycle by more than 5 minutes.

[0103] (2) Converter end point - finished product return P < 0.0015%;

[0104] (3) The slag-making method characterized by low MgO and strong bottom blowing is adopted to significantly improve the distribution ratio of P between slag and steel. The P content at the converter end is less than 0.0060%, and the P content of the finished product after LF deep desulfurization is less than 0.0070%.

[0105] The underlined data do not meet the requirements of the present invention.

[0106] The above embodiments are described to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for smelting low-phosphorus steel using single converter slag, characterized in that: The method comprises the following steps: 1) Slag adjustment is performed on the first batch of low-phosphorus steel produced in the converter; 2) After the last furnace is tapped, the slag is left, splashed and solidified, and then scrap steel and molten iron are added to smelt the low-phosphorus steel furnace; 3) Oxygen supply and slagging in the main blowing stage; 4) Auxiliary blowing; 5) Draining slag; 6) After the slag is poured, stir it; 7) Steel tapping and slag blocking; 8) Alloy is added during the converter tapping process, and tapping is completed; In step 1), the adjustment method is specifically: using lime and magnesium-containing materials to make slag, and controlling the slag basicity and MgO content in the slag under different molten iron silicon content conditions; specifically: For hot metal with silicon content of 0.1%<Si≤0.2%, the slag basicity should be controlled at 5.0-7.1, and the MgO content in the slag should be 0-5%; For hot metal with silicon content of 0.2%<Si≤0.3%, the slag basicity should be controlled at 3.8-5.4, and the MgO content in the slag should be 3-6%; For hot metal with silicon content of 0.3%<Si≤0.4%, the slag basicity should be controlled at 3.2-4.4, and the MgO content in the slag should be 4-8%; For hot metal with silicon content of 0.4%<Si≤0.5%, the slag basicity should be controlled at 2.8-3.8, and the MgO content in the slag should be 4-8%; For hot metal with silicon content of 0.5%<Si≤0.7%, the slag basicity should be controlled at 2.5-3.4, and the MgO content in the slag should be 4-8%; The adjustment method also includes: the top blowing strength of the first batch of low-phosphorus steel is 2.8-5.0Nm 3 / (t.min); lance position in the early stage of smelting is 1.15×(32~45)×Dthroat, 1.15×(35~50)×Dthroat in the middle stage, and 1.15×(30~38)×Dthroat in the final stage. The Dthroat is the diameter of the oxygen lance nozzle throat, in mm; bottom blowing intensity is 0.02~0.40 Nm 3 / (t.min); converter endpoint temperature>1580℃, endpoint phosphorus mass percentage ≤0.020%; In step 3), the slag basicity and MgO content are controlled according to the silicon content of the molten iron, as follows: For hot metal with silicon content of 0.1%≤Si≤0.2%, the slag basicity should be controlled at 6.8±0.3 and the MgO content in the slag should be 0-5%; For hot metal with silicon content of 0.2%<Si≤0.3%, the slag basicity should be controlled at 5.1±0.3, and the MgO content in the slag should be 2-5%; For hot metal with silicon content of 0.3%<Si≤0.4%, the slag basicity should be controlled at 4.2±0.2, and the MgO content in the slag should be 4-7%; For hot metal with silicon content of 0.4%<Si≤0.5%, the slag basicity should be controlled at 3.7±0.2, and the MgO content in the slag should be 4-7%; For molten iron with silicon content of 0.5%<Si≤0.7%, the slag basicity is controlled at 3.2±0.2, and the MgO content in the slag is 4-7%.

2. The method according to claim 1, characterized in that In step 2), the slag is retained, and the amount of slag retained is 30-80 kg / t steel.

3. The method according to claim 1 or 2, characterized in that In step 2), the molten iron has the following composition and temperature: Si 0.10% wt% to 0.70% wt%, P≤0.13 wt%, [C]>4.0 wt%, and the temperature of the molten iron entering the furnace is 1200-1450°C.

4. The method according to claim 1, wherein Step 3) specifically includes the following controls: 3-1) Oxygen lance position and flow rate: The converter oxygen supply adopts a staged constant flow and variable lance position operation mode, with an oxygen supply intensity of 2.8 to 4.5 m 3 / (min.t); the lance position in the early stage of smelting is 1.15×(32-45)×Dthroat, the lance position in the middle stage is 1.15×(35-50)×Dthroat, and the lance position in the final stage is 1.15×(30-38)×Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, mm; 3-2) Bottom blowing intensity: Bottom blowing intensity in the main blowing stage is 0.03~0.15 m 3 / (min.t); 3-3) Quantity and timing of converter slag material addition: Lime and magnesium-containing materials are used to make slag. The first batch of slag is added within 1.5 minutes of the start of blowing. The amount of lime added is not less than 50% of the total amount, and the amount of magnesium-containing materials is not less than 70% of the total amount. The second batch of slag is added between the addition of the first batch of slag and the start of blowing for 3.5 minutes. The cumulative amount of lime added is not less than 70% of the total amount, and all magnesium-containing materials are added. The remaining amount of lime is added between the addition of the second batch of slag and 7 minutes before oxygen blowing. The magnesium-containing materials include light-burned dolomite, dolomite, and magnesium balls. The amount and timing of coolant addition: 0-50% of the required coolant is added within 1-3 minutes of blowing. After 6 minutes, the remaining coolant is added in batches.

5. The method according to claim 1, wherein In step 4), after carbon and temperature are measured, if T+[C]%×10000>1610, add ore to the auxiliary blowing gun to adjust the ore addition amount W O =(T+[C]% ×10000-1610)×β×BV÷10, where: [C] is the [C] content, unit is wt%; T is the molten steel temperature, unit is ℃; W O is the amount of ore added, kg; β is the coefficient, ranging from 1.2 to 3.0; BV is the nominal capacity of the converter, t.

6. The method according to claim 1 or 5, characterized in that In step 4), the auxiliary blowing is specifically: bottom blowing intensity is 0.05~0.30 m 3 / (min.t), lance position 1.15× (30~38) × Dthroat, where Dthroat is the diameter of the oxygen lance nozzle throat, mm; converter end temperature 1580~1630℃, active oxygen content of molten steel 0.015%~0.080%.

7. The method according to claim 1, characterized in that Step 5) The slag is poured after the auxiliary blowing is completed, and the converter is tilted 85-88 degrees toward the slag surface, so that no slag falls from the furnace mouth and the remaining slag amount is not less than 30kg / t steel.

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