Efficient utilization method of low carbon steel smelting endpoint slag

Abstract

The present application relates to a kind of low carbon steel smelting endpoint slag high-efficiency utilization method, comprising the following steps: (1) low carbon steel smelting endpoint is made high FeO furnace slag, and the FeO of final slag reaches 35-40%, R is 2.8-4.0;(2) remain slag and do not splash slag operation, and the amount of remaining slag is 50-58Kg / t iron, and smelting endpoint stops top blowing oxygen, and weak argon gas is blown at the bottom of converter;(3) extend iron mixing time, and no scrap steel is added before iron mixing;(4) efficient dephosphorization during iron mixing, after iron mixing starts, gas flow is adjusted to 400-500L / min, bottom blowing gas is switched to CO, and CO is continuously bottom blown during the whole iron mixing process;(5) after iron mixing, bottom blowing gas is switched to argon, and argon flow is increased to 850-950L / min, and the total dephosphorization rate can reach 35-45% by continuously stirring for 2-3min to complete continuous dephosphorization;The method of the present application deliberately increases the FeO content in the slag at the end of low carbon steel smelting to 35-40%, utilizes the characteristics of smelting process, and realizes effective dephosphorization before the start of blowing in converter by reasonable slag remaining operation and adjusting iron mixing mode, reduces the dephosphorization pressure in the smelting process, and saves the dephosphorization cost.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, in particular to a method for efficiently utilizing low-carbon steel smelting end slag. Background Art

[0002] For low-carbon steel with a melting carbon content of ≤0.05%, efficient low-carbon smelting is generally required in converter smelting to achieve a final carbon content of ≤0.03%, considering that smelting, refining, and continuous casting all involve carbonization steps, such as alloying during alloying and electrode carbonization during refining. Once the final carbon content reaches <0.03%, the carbon-oxygen reaction is extremely weak. The oxidation reaction during the continuous oxygen supply in the converter is primarily [O] + Fe = (FeO). During the continuous top-blowing oxygen lance low-carbon drawing process, the FeO content in the slag increases dramatically, typically reaching over 30%. When the final carbon content is below 0.03%, the longer the carbon drawing time, the higher the final slag FeO content, reaching a maximum of over 40%. Considering that the FeO content in conventional steel smelting is generally below 20%, the thermodynamic principle that high FeO is beneficial for dephosphorization can be utilized to improve and enhance converter dephosphorization efficiency. The present invention is based on the technical feature that the FeO content in the final slag of low-carbon steel is much higher than that in conventional steel grades. It focuses on how to make the most efficient use of this feature of high FeO content in low-carbon steel and applies and develops new technologies. Summary of the Invention

[0003] The purpose of the present invention is to utilize the characteristic of high FeO content in the low-carbon steel smelting end slag and provide a method for efficiently utilizing the low-carbon steel smelting end slag. By adopting the method of the present invention, efficient dephosphorization can be achieved in the converter iron adding process.

[0004] A method for efficiently utilizing low-carbon steel smelting end slag of the present invention comprises the following steps:

[0005] (1) Making high FeO slag at the end of low carbon steel smelting: After the auxiliary lance predicts that the carbon content is lower than 0.03% at the end of smelting, continue to blow oxygen from the oxygen lance to pull carbon for 60-90s until the final slag FeO reaches 35-40% and the slag basicity R is 2.8-4.0; the oxygen flow rate of the oxygen lance is 36000-38000m 3 / h, oxygen lance position 700-800mm;

[0006] (2) Slag retention and non-slag splashing operation: The slag retention is required at the end point without slag splashing. The slag retention amount is 50-58 kg / t iron. At the end of smelting, the top oxygen blowing is stopped until the next furnace is added with iron. The argon flow rate of the converter bottom is adjusted to weak blowing, and the argon flow rate is 50 L / min. The purpose of adjusting the bottom blowing argon flow rate to weak blowing is to avoid a large temperature drop of the final slag (if the slag temperature is low, the slag will solidify and the fluidity will deteriorate);

[0007] (3) Extend the iron adding time and adjust the feeding sequence: by slowly adding iron, the iron adding operation is controlled within 5-6 minutes, and the loading sequence is to add iron first, without adding scrap steel before adding iron;

[0008] (4) Efficient dephosphorization during the iron addition process: After the iron addition process begins, the gas flow rate is adjusted to 400-500 L / min, and the bottom blowing gas is switched from argon to carbon monoxide gas. Carbon monoxide is continuously blown from the bottom during the entire iron addition process. This step mainly utilizes CO gas to undergo an oxidation-reduction reaction with high (FeO) in the slag under high temperature conditions to produce CO2 gas, which can increase the dephosphorization reaction interface. The specific reaction formula is CO+FeO=Fe+CO2. During the iron addition process, the iron-slag reaction interface is large, and the bottom blowing CO gas, the CO2 produced by secondary oxidation, the C in the iron and the high-temperature slag (FeO) produce endogenous CO gas. The strong mechanical impact stirring generated during the iron addition operation and the good temperature conditions of the iron addition process all intensify the dephosphorization reaction in the molten pool.

[0009] (5) Strong bottom stirring dephosphorization after iron addition: After the iron addition is completed, the bottom blowing gas is switched to argon, and the argon flow rate is increased to 850-950L / min. The continuous stirring is continued for 2-3 minutes to complete the continuous dephosphorization, and the total dephosphorization rate can reach 35-45%.

[0010] After completing the above-mentioned iron addition and dephosphorization operations, scrap steel is added to the converter and blown normally. The converter can then complete subsequent smelting operations according to normal procedures.

[0011] The process principle of the method of the present invention is: taking advantage of the relatively high FeO content of the low-carbon steel converter final slag, and further raising the FeO content to 35-40%. When the FeO content is high, the corresponding slag has good fluidity and also has the characteristics of high basicity. By tracking the entire smelting process, the following design is carried out: at the end of the smelting of the first furnace of low-carbon steel, the FeO content is increased to more than 35% by extending the end carbon pulling time, and the final slag composition is maintained unchanged, retaining the technical characteristics of high FeO, high basicity and fluidity. The final slag is reserved for the second furnace as pre-melted slag, so that the thermodynamic conditions for dephosphorization are already met at the initial stage of the second furnace. By utilizing the good stirring conditions of the iron addition process and the carbon-oxygen reaction between high FeO and iron, and by utilizing the bottom stirring of the converter and the selection of the bottom stirring gas, dephosphorization can be achieved during the iron addition stage and before the start of blowing.

[0012] The principle of dephosphorization reaction in steelmaking is: 2[P]+5(FeO)+4(CaO)=(Ca4P2O9)+5[Fe]+heat.

[0013] In conventional smelting methods, the final slag FeO content is generally less than 20%. Using conventional slag tackification methods, the final slag FeO content can even be less than 15%. The present method, leveraging the technical characteristic of requiring low carbon steel at the end point, intentionally increases the slag FeO content compared to conventional final slag (compared to conventional final slag, the slag FeO content in this method is 35-40%, an increase of at least 15%). This method achieves a significantly higher FeO content than conventional methods, and through rational design and utilization, taking advantage of the smelting process, dephosphorization can be rapidly completed during the next iron addition process.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The present invention utilizes the technical feature that low-carbon steel needs to be pulled to a low carbon finish, deliberately increases the slag (FeO) content by 35-40%, and utilizes the characteristics of the smelting process to greatly improve the converter operation efficiency;

[0016] (2) Through reasonable slag retention operation, the secondary utilization of waste slag is achieved, which has good social and economic benefits;

[0017] (3) The present invention achieves effective dephosphorization before the converter starts blowing, reduces the dephosphorization pressure during the smelting process, and saves dephosphorization costs;

[0018] (4) The process flow of the present invention is simple and clear, highly operable and easy to control. DETAILED DESCRIPTION

[0019] To better explain the technical solution of the present invention, the technical solution of the present invention is further described below with reference to specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any form. Any changes or equivalent substitutions that do not deviate from the concept of the present invention are included in the scope of protection of the present invention.

[0020] Example 1

[0021] Heat No. 1, molten iron composition: w(P)%: 0.110%.

[0022] A method for efficiently utilizing low-carbon steel smelting end slag in this embodiment includes the following steps:

[0023] (1) Create high FeO% slag at the end of low carbon steel smelting: After the auxiliary lance predicts the carbon content to be 0.03% at the end of smelting, continue to blow oxygen from the top of the oxygen lance for 1 minute, and the oxygen flow rate is 36000m 3 / h, oxygen lance position 700mm, the final slag FeO is required to reach 35%, R is 2.8;

[0024] (2) Slag retention and no slag splashing operation: The slag retention and no slag splashing are required at the end point, and the slag retention amount is 50 kg / t iron. At the end of smelting, the top oxygen blowing is stopped until the next furnace is added with iron. The argon flow rate of the converter bottom is adjusted to weak blowing, and the argon flow rate is 50 L / min;

[0025] (3) Extend the iron adding time and adjust the feeding sequence: by slowly adding iron, the iron adding operation is controlled within 5 minutes, and the loading sequence is to add iron first, without adding scrap steel before adding iron;

[0026] (4) Efficient dephosphorization during iron addition: After iron addition begins, the bottom blowing gas is switched from argon to CO gas, and the flow rate is adjusted to 400L / min. After the gas flow rate is adjusted, the bottom blowing gas of the converter is switched to CO;

[0027] (5) Strong bottom stirring dephosphorization after iron addition: After the iron addition is completed, the bottom blowing gas is switched to argon, the argon flow rate is increased to 850L / min, and continuous stirring is continued for 2 minutes to complete continuous dephosphorization, and the total dephosphorization rate can reach 35%;

[0028] (6) After the iron addition and dephosphorization operations are completed, scrap steel is added and normal blowing is performed, and the converter completes subsequent smelting operations according to normal procedures.

[0029] After the converter was charged with iron, samples were taken for analysis, and w[P] was 0.0715%. In this embodiment, the comprehensive dephosphorization efficiency of the converter charged with iron reached 35%.

[0030] Example 2

[0031] Heat No. 2, molten iron composition: w(P)%: 0.120%.

[0032] A method for efficiently utilizing low-carbon steel smelting end slag comprises the following steps:

[0033] (1) Create high FeO% slag at the end of smelting: After the auxiliary lance predicts the carbon content to be 0.03% at the end of smelting, continue to blow oxygen from the top of the oxygen lance to pull carbon for 80 seconds, with an oxygen flow rate of 37000m 3 / h, oxygen lance position 750mm, the final slag FeO is required to reach 38%, R is 3.5;

[0034] (2) Slag retention and no slag splashing operation: The slag retention and no slag splashing are required at the end point, and the slag retention amount is 55 kg / t iron. At the end of smelting, the top oxygen blowing is stopped until the next furnace is added with iron. The argon flow rate of the converter bottom is adjusted to weak blowing, and the argon flow rate is 50 L / min;

[0035] (3) Extend the iron adding time and adjust the order of adding materials: By slowly adding iron, the iron adding operation is controlled within 5 minutes and 30 seconds. The loading order is to add iron first, and do not add scrap steel before adding iron;

[0036] (4) Efficient dephosphorization during iron addition: After iron addition begins, the bottom blowing gas is switched from argon to CO gas, and the flow rate is adjusted to 450L / min. After the gas flow rate is adjusted, the bottom blowing gas of the converter is switched to CO;

[0037] (5) Strong bottom stirring dephosphorization after iron addition: After the iron addition is completed, the bottom blowing gas is switched to argon, the argon flow rate is increased to 900L / min, and continuous stirring is continued for 2.5min to complete continuous dephosphorization, and the total dephosphorization rate can reach 40%;

[0038] (6) After the iron addition and dephosphorization operations are completed, scrap steel is added and normal blowing is performed, and the converter completes subsequent smelting operations according to normal procedures.

[0039] After the converter was charged with iron, samples were taken for analysis, and w[P] was 0.072%. In this embodiment, the comprehensive dephosphorization efficiency of the converter charged with iron reached 40%.

[0040] Example 3

[0041] Heat No. 3, molten iron composition: w(P)%: 0.130%.

[0042] A method for efficiently utilizing low-carbon steel smelting end slag, comprising the following steps:

[0043] (1) Create high FeO% slag at the end of smelting. After the auxiliary lance predicts the carbon content to be 0.03% at the end of smelting, continue to blow oxygen from the top of the oxygen lance to pull carbon for 90s, with an oxygen flow rate of 38000m 3 / h, oxygen lance position 800mm, the final slag FeO is required to reach 40%, R is 4.0;

[0044] (2) Slag retention and no slag splashing operation: The slag retention and no slag splashing are required at the end point, and the slag retention amount is 58 kg / t iron. At the end of smelting, the top oxygen blowing is stopped until the next furnace is added with iron. The argon flow rate of the converter bottom is adjusted to weak blowing, and the argon flow rate is 50 L / min;

[0045] (3) Extend the iron adding time and adjust the charging sequence: by slowly adding iron, the iron adding operation is controlled within 6 minutes, and the loading sequence is to add iron first, without adding scrap steel before adding iron;

[0046] (4) Efficient dephosphorization during iron addition: After iron addition begins, the bottom blowing gas is switched from argon to CO gas, and the flow rate is adjusted to 500 l / min. After the gas flow rate is adjusted, the bottom blowing gas of the converter is switched to CO;

[0047] (5) Strong bottom stirring dephosphorization after iron addition: After the iron addition is completed, the bottom blowing gas is switched to argon, and the argon flow rate is increased to 950L / min. The continuous stirring is continued for 2-3 minutes to complete the continuous dephosphorization, and the total dephosphorization rate can reach 45%;

[0048] (6) After the iron addition and dephosphorization operations are completed, scrap steel is added and normal blowing is performed, and the converter completes subsequent smelting operations according to normal procedures.

[0049] After the converter was charged with iron, samples were taken for analysis, and w[P] was 0.0715%. In this embodiment, the comprehensive dephosphorization efficiency of the converter charged with iron reached 45%.

[0050] The method of the present invention was compared with the conventional converter iron charging mode, and the results are shown in Table 1 below.

[0051] Table 1 Comparison of the converter iron charging method according to the embodiment of the present invention and the conventional converter iron charging mode

[0052]

[0053] The comprehensive dephosphorization rate before the converter blowing is started by adopting the present invention can reach 35-45%, while the conventional mode has basically no dephosphorization ability during iron addition and the dephosphorization rate is only 1%.

Claims

1. A method for efficiently utilizing slag at the end of low-carbon steel smelting, characterized in that The steps include: (1) Making high FeO slag at the end of low carbon steel smelting: After the auxiliary lance predicts that the carbon content is lower than 0.03% at the end of smelting, continue to blow oxygen from the oxygen lance to pull carbon for 60-90s until the final slag FeO is 35-40% and the slag basicity R is 2.8-4.0; the oxygen flow rate of the oxygen lance is 36000-38000m 3 / h, oxygen lance position 700-800mm; (2) Slag retention and non-slag splashing operation: The slag retention at the end point is required to be non-slag splashing, and the slag retention amount is 50-58kg / t iron. At the end of smelting, the top oxygen blowing is stopped until the next furnace is added with iron. The argon flow rate of the converter bottom blowing is adjusted to weak blowing, and the argon flow rate is 50L / min; (3) Extend the iron adding time and adjust the feeding sequence: by slowly adding iron, the iron adding operation is controlled within 5-6 minutes, and the loading sequence is to add iron first, without adding scrap steel before adding iron; (4) Efficient dephosphorization during the iron addition process: After the iron addition begins, the gas flow rate is adjusted to 400-500 L / min, and the bottom blowing gas is switched from argon to carbon monoxide gas. Carbon monoxide is continuously blown at the bottom during the entire iron addition process. (5) Strong bottom stirring dephosphorization after iron addition: After the iron addition is completed, the bottom blowing gas is switched to argon, and the argon flow rate is increased to 850-950L / min. Stirring is continued for 2-3 minutes to complete continuous dephosphorization, and the total dephosphorization rate is 35-45%.

2. The method for efficiently utilizing low-carbon steel smelting end slag according to claim 1, characterized in that: After completing the iron addition and dephosphorization operations, scrap steel is added to the converter and blown normally. The converter then completes subsequent smelting operations according to normal procedures.

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