Efficient and high-purity SPHC smelting production method

Abstract

The invention belongs to the field of smelting, and relates to an efficient and high-purity SPHC smelting production method which is a high-cleanliness SPHC smelting process which is low in cost, high in operability, efficient and stable. According to the technical scheme, the method comprises the steps of molten iron optimization, converter primary smelting, steel tapping to oxygen-containing steel in an argon station steel ladle, argon blowing stirring rough refining, low-cost efficient stirring decarburization in the LF oxidation period, rapid desulfurization in the LF reduction period and inhibition of carbon return and nitrogen increase, and slab continuous casting.

Description

Technical Field

[0001] The present invention belongs to the smelting field and relates to a method for smelting and producing high-efficiency and high-purity SPHC. Background Art

[0002] For high-end SPHC (Steel Plate Hot Rolled Coil) used for cold rolling, the performance requirements are as follows: the cold rolling cracking rate after pickling and trimming is < 0.5%, the elongation rate in the cold-hardened state is ≥ 5% and it does not crack after being hammered or bent 180° by a cold bending machine, the elongation rate after annealing is ≥ 40% and the simulated deep drawing cracking rate is < 1%.

[0003] To meet the above requirements, higher cleanliness requirements are put forward for the molten steel in the SPHC smelting production method, that is, the mass percentages of some components in the molten steel are: [C] 0.020 - 0.040%, [Si] ≤ 0.03%, [Mn] 0.090 - 0.014%, [P] ≤ 0.012%, [S] ≤ 0.005%, [ALs] 0.020 - 0.045%, T[O] ≤ 0.0030%, [N] ≤ 0.0030%.

[0004] In the current technology, the general smelting process route for high-end SPHC used for cold rolling is: blast furnace hot metal → KR pre-desulfurization → converter decarburization and dephosphorization → tapping and deoxidation alloying in the argon station → LF refining desulfurization → slab continuous casting. Among them, the mass percentages of some components in the molten steel are: average [C] 4.50%, average [Si] 0.40%, [Mn] 0.35 - 0.45%, [P] ≤ 0.120%, [S] 0.010 - 0.070%.

[0005] During the tapping process of the converter, aluminum blocks and low-carbon ferromanganese are used for primary deep deoxidation and manganese alloying, lime and pre-melted slag are used to modify the top slag in advance, and direct power supply heating and reduction slag desulfurization operation are carried out in the LF furnace, which will cause various carbon-containing materials to enter the molten steel with a high probability during the LF furnace refining process, resulting in an increase in carbon in the molten steel by 0.01 - 0.03%. To make up for the influence of carbon increase during the LF furnace refining process, severe post-blowing and supplementary blowing operations must be carried out during the converter decarburization process to ensure that the carbon content at tapping is in the range of 0.020 - 0.030%.

[0006] Carrying out severe post-blowing and supplementary blowing operations during the converter decarburization process may cause the following problems:

[0007] 1. It is difficult to maintain the converter slag splashing and furnace condition;

[0008] 2. High consumption of iron and steel materials and aluminum for deoxidation;

[0009] 3. When the converter is overblown, the unbalanced oxygen in the steel and the fluctuation of the ferrous iron content in the final slag are large, resulting in the deoxidation product AL 2 O 3The generation amount is unstable. After the top slag is modified during the tapping process, the slag oxygen and the aluminum in the steel fluctuate greatly. It is forced to make aluminum-calcium slag with a relatively high melting point from the tapping stage, which in turn affects the stable control of the white slag composition, the speed of forming white slag, and the desulfurization effect and efficiency during the refining process of the LF furnace;

[0010] 4. Under the above conditions, there is a contradiction between preventing silicon and nitrogen increase during the refining desulfurization of the LF furnace and the large argon gas stirring in the ladle. The LF furnace can only control the argon blowing with a small amount of gas, and extending the white slag time can only achieve a desulfurization rate of 30% - 60%. Therefore, deep desulfurization must be carried out by KR for each furnace to ensure that the [S] in the hot metal entering the converter is ≤ 0.005%;

[0011] 5. To ensure the speed of forming white slag and reduce carbon increase in the LF furnace, a series of problems such as using high-performance electrofused aluminum-calcium pre-melted refining slag and fluorite for rapid slag melting, alloying with high-cost manganese alloys such as low-carbon ferromanganese, and fine-tuning manganese are required. Even so, situations where [C], [Si], [P], [S], [ALs], [N] exceed the standards and are rejudged often occur, and there are many problems such as high overall smelting costs, poor compositional stability, long LF furnace cycle, and high smelting production difficulty. Summary of the Invention

[0012] To overcome the defects in the above related technologies, the present invention proposes a high-efficiency and high-purity SPHC smelting production method, which has a high-cleanliness SPHC smelting process with low cost, strong operability, high efficiency and stability.

[0013] To achieve the above technical objectives, the present invention provides a high-efficiency and high-purity SPHC smelting production method. The high-efficiency and high-purity SPHC smelting production method includes: adding molten steel with a sulfur content not higher than 0.02% to a converter. Smelting the molten steel in the converter, and through end-point control, making the carbon content, phosphorus content and temperature of the molten steel meet the requirements when tapping. Using slag blocking to tap the molten steel into the ladle, and adding aluminum-calcium slag during the tapping process for slag-making operation. Transferring the ladle to the argon blowing station, blowing argon into the ladle, and strongly stirring the molten steel and the top slag for 3 - 5 minutes. Transferring the ladle into the refining furnace, blowing argon and adding a special decarburization composite slag-making agent, and strongly stirring for decarburization for 1 - 4 minutes. Blowing argon into the ladle again for 4 - 6 minutes, and adding aluminum and the first batch of slag-making materials into the ladle according to the oxygen content in the molten steel. Conducting the first power-on heating and slag melting operation on the refining furnace, and taking samples of the molten steel for temperature measurement. According to the test results of the molten steel samples, blowing argon into the molten steel in the ladle and supplementing aluminum. Conducting argon blowing stirring and desulfurization operations on the molten steel in the ladle. Fine-tuning the manganese content of the molten steel after the desulfurization operation and conducting calcium treatment. Adjusting the argon for soft blowing operation of the molten steel for 10 - 15 minutes. When the temperature and composition of the steel slag and the molten steel meet the requirements, transferring the molten steel to hot continuous rolling for the next operation.

[0014] Preferably, before performing argon blowing stirring and desulfurization operations on the molten steel in the ladle, the high-efficiency and high-purity SPHC smelting production method further includes: adding a pure aluminum-based diffusion deoxidizer and a second batch of slag-making materials to the molten steel in the ladle, and performing a second power-on heating operation on the refining furnace.

[0015] Preferably, the method of slag blocking and tapping steel into the ladle further includes: setting the tapping channel of the converter as a variable-diameter pipe, and the inner diameter of the tapping channel gradually decreases from the inside of the converter to the outside. The length of the tapping channel is 1100 - 1300 mm, the maximum inner diameter of the tapping channel is 170 - 180 mm, and the difference between the maximum inner diameter and the minimum inner diameter of the tapping channel is 10 mm.

[0016] Preferably, the aluminum-calcium slag includes the following components by mass percentage: calcium oxide is 50% - 55%, aluminum oxide is 45% - 50%, magnesium oxide is less than or equal to 1.0%, silicon dioxide is less than or equal to 1.0%, and the sum of iron oxide and manganese oxide is less than or equal to 1.5%. The content of particles with a particle size of 20 - 40 mm in the aluminum-calcium slag is not less than 90%.

[0017] Preferably, in the step of adding molten steel with a sulfur content not higher than 0.020% to the converter, the average [C] content of the molten steel with a sulfur content not higher than 0.020% is 4.50%, the average [Si] content is 0.40%, the [Mn] content is 0.35% - 0.45%, the [P] content ≤ 0.120%, and the [S] content is 0.010 - 0.020%. And the temperature when the molten steel with a sulfur content not higher than 0.020% is added to the converter is 1320 - 1370 °C.

[0018] Preferably, the special decarburization composite slag-making agent includes the following components by mass percentage: the content of calcium oxide is 30 - 40%, the content of aluminum oxide is 20 - 30%, the content of silicon dioxide is less than or equal to 5%, the content of magnesium oxide is 4 - 6%, the content of iron oxide is 10 - 15%, the content of manganese oxide is 8 - 15%, and the sulfur content is less than or equal to 0.20%. Transfer the ladle into the refining furnace, and perform argon blowing and add the special decarburization composite slag-making agent, and 3 - 6 kg of the special decarburization composite slag-making agent is added per ton of molten steel.

[0019] Preferably, when performing strong stirring decarburization for 1 - 4 min, the temperature of the molten steel is 1565 ± 10 °C.

[0020] Preferably, the first batch of slag-making materials includes: high-calcium active lime and aluminum-calcium slag; among them, the CaO of the high-calcium active lime 有效 ≥88%, and the activity ≥ 400 ml / g.

[0021] The beneficial effects of the present invention are as follows:

[0022] The applicant has found that there is the following relationship between the addition of a special decarburization compound slag former in molten steel and the decarburization amount by stirring. In the refining furnace, the optimal temperature range for decarburization by stirring after adding the special decarburization compound slag former in the ladle is 1565 ± 10 °C; the decarburization amount and decarburization rate are positively correlated with the carbon content of the molten steel in the ladle from tapping and the addition amount of the special decarburization compound slag former; when the carbon content in the molten steel is less than or equal to 0.02%, the decarburization amount has nothing to do with the addition amount of the special decarburization compound slag former.

[0023] In the present invention, first, the molten steel is deoxidized with an aluminum-calcium slag and the steel slag is formed, which can prevent carbon elements from entering the molten steel, reduce the decarburization treatment intensity of the molten steel in the subsequent process, reduce the difficulty of furnace condition maintenance, and reduce the aluminum used for deoxidation.

[0024] After that, the ladle is transferred to the refining furnace, which can ensure that the temperature of the molten steel is 1565 ± 10 °C. After adding the special decarburization compound slag former and strongly stirring for decarburization, it can ensure that the decarburization amount in the molten steel can reach 0.01% - 0.030%, and [O] in the molten steel can be reduced to 400 - 550 ppm. After that, when carrying out deoxidation alloying and desulfurization and then slab continuous casting operation, it can ensure that [C] is between 0.020% - 0.040%, realizing the smelting production of high-purity SPHC by using an LF furnace, with the advantages of high production efficiency and low cost.

[0025] In the present invention, the tapping channel of the converter is set as a variable-diameter pipe, which can reduce the probability of slag entrainment and scattering flow and increase the impact force of the molten steel fluid during tapping, promote the full mixing of the molten steel and the aluminum-calcium slag, and improve the quality of the molten steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is the flow chart of the present invention;

[0028] Figure 2 is the structural diagram of the tapping channel of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] To make the above objects, features, and advantages of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0030] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0031] The terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0032] As Figure 1 shown, some embodiments of the present invention are an efficient and high-purity SPHC smelting production method. The efficient and high-purity SPHC smelting production method is as follows:

[0033] S1. Add molten steel with a sulfur content not higher than 0.02% to the converter.

[0034] S2. Smelt the molten steel in the converter, and through end-point control, make the carbon content, phosphorus content, and temperature of the molten steel meet the requirements when tapping.

[0035] S3. Use slag-blocking tapping to the ladle, and add aluminum-calcium slag during the tapping process for slag-making operation.

[0036] S4. Transfer the ladle to the argon-blowing station, blow argon into the ladle, and strongly stir the molten steel and the top slag for 3 - 5 minutes.

[0037] S5. Transfer the ladle into the refining furnace, blow argon, and add a special decarburization compound slag-making agent for strong stirring decarburization for 1 - 4 minutes.

[0038] S6. Blow argon into the ladle again for 4 - 6 minutes, and add aluminum and the first batch of slag-making materials into the ladle according to the oxygen content in the molten steel.

[0039] S7. Conduct the first power-on operation to heat up the slag in the refining furnace, and take samples of the molten steel for temperature measurement. Argon is blown into the molten steel in the ladle and aluminum is supplemented according to the test results of the molten steel samples.

[0040] S9. Conduct argon blowing and stirring and desulfurization operations on the molten steel in the ladle.

[0041] S10. Fine-tune the manganese content of the molten steel after the desulfurization operation and conduct calcium treatment.

[0042] S11. Adjust the argon for soft blowing of the molten steel for 10 - 15 minutes. After the temperature and composition of the slag and the molten steel meet the requirements, transfer the molten steel to the hot strip mill for the next operation.

[0043] In some examples, the molten steel added to the converter can use blast furnace hot metal, and the conditions of the blast furnace hot metal are: average [C] 4.50%, average [Si] 0.40%, [Mn] 0.35 - 0.45%, [P] ≤ 0.120%, [S] 0.010 - 0.070%, and the temperature of the hot metal entering the furnace is 1320 - 1370 °C.

[0044] Table 1

[0045]

[0046] Among them, the blast furnace hot metal can be optimized according to the sulfur content grade: the blast furnace hot metal with [S] ≤ 0.020% can be directly poured into the converter. The blast furnace hot metal with [S] > 0.020% must be pretreated by KR for desulfurization until [S] ≤ 0.020% and then can be directly poured into the converter or be poured into the converter after being admixed with the straight-run iron with [S] ≤ 0.020%.

[0047] In step S2, the blast furnace hot metal and the self-produced high-quality scrap steel can be added to the converter according to the charging system. The self-produced high-quality scrap steel can be the head and tail billets, joint billets and the cut heads of the hot rolling line generated in the production process of ordinary SPHC. The length dimensions in all directions are ≤ 1.0 m, without impurities such as oil stains, and no other scrap steel is allowed to be used. The charging system is: the total charging amount is controlled at 127 ± 3 tons to ensure a net space of 400 - 600 mm in the ladle after tapping. And the hot metal ratio, the structure and the addition amount of the iron-containing materials and slag-making materials are adjusted timely according to the requirements of the production plan and the need of the heat balance temperature of the converter.

[0048] The methods to make the carbon content, phosphorus content and temperature of the molten steel meet the requirements when tapping the molten steel through end-point control include:

[0049] The automatic steelmaking model first conducts pre-simulation calculations before blowing, and gives the structures, total addition amounts of various iron-containing materials and slag materials, and the control curves of the feeding and lance position during the blowing process.

[0050] Flue gas detection and calculation are carried out 2 - 3 minutes after oxygen supply. The automatic steelmaking model dynamically adjusts according to the temperature conditions detected and calculated from the flue gas to ensure that during the decarburization period, it lasts for 2 - 3 minutes in the temperature range of 1380 - 1420 °C.

[0051] 2 minutes before the end of blowing, the sublance TSC bomb is launched for temperature measurement and carbon determination. The lance operator conducts dynamic interference on the automatic steelmaking model according to the temperature measurement and carbon determination results of the sublance TSC.

[0052] When lifting the oxygen lance at the end point, the sublance TSO bomb is launched for temperature measurement and sampling.

[0053] Control targets for the slag R (slag basicity): 1.5 - 2.0 during the decarburization period and 3.5 - 4.0 for the final slag.

[0054] Oxygen lance position: Adopt the mode curve of high → low → high → low → high → high → low. The lance is lowered to a high position of 1.5 m at the start of blowing. During the 2 - 6 minutes of oxygen supply after the first batch of materials is added, it is at a low position of 1.3 m to heat up the slag and initially dephosphorize. During the 6 - 9 minutes of oxygen supply, it is at a high position of 1.5 m to strengthen oxidation and dephosphorize. During the 9 - 11 minutes of oxygen supply, it is at a low position of 1.3 m for decarburization and temperature increase to prevent splashing. During the 11 - 12 minutes of oxygen supply, the lance is moved from 1.3 m to 1.6 m and during the 12 - 13 minutes of oxygen supply, it is moved from 1.6 m to 1.3 m for lance movement to evenly mix the molten bath. During the 13 - 13.5 minutes of oxygen supply, the lance is gradually lowered from 1.3 m to 1.1 m to eliminate the foamy slag. 40 - 60 seconds before the end point, the lance is lowered to 1.0 m for carbon tapping. To ensure that the one - time hit rate of the three indicators of end - point carbon, temperature, and phosphorus reaches over 92%. For the furnace heats with inappropriate sublance TSO temperature and composition, re - blowing operations are carried out. Finally, ensure that the molten steel for tapping: [C] ≤ 0.050%, [Si] trace, [Mn] 0.06 - 0.09%, [P] ≤ 0.008%, [S] ≤ 0.020%, [O] ≥ 600 PPm, and the temperature is 1620 ± 10 °C.

[0055] In this application, slag - stopping tapping is adopted into the ladle. The methods of slag - stopping tapping are: slag - stopping with a slag - stopping plug in the front and a slag - stopping cone in the back, and aluminum - calcium slag is added during the tapping process.

[0056] In the argon - blowing station, the molten steel in the ladle can be 115 tons and is produced with 2 bottom - blowing porous plugs.

[0057] In step S4, during the LF oxidation period, the oxygen-containing molten steel and slag are stirred, and the mechanism of decarburization of the molten steel occurs as follows: ① The [%C]·[%O] in the molten steel has a positive correlation with temperature. During the stirring process, the temperature of the molten steel drops by 15 - 30 °C, which promotes the escape of excess oxygen. ② From tapping to the LF stirring decarburization stage, it is almost entirely a strong argon-blowing stage. Argon bubbles have the effect of removing gases under rough vacuum. ③ The top slag contains a certain amount of oxides such as FeO and MnO. Under high-temperature and argon-blowing rough vacuum conditions, a carbon displacement reaction occurs, further promoting decarburization. ④ Oxygen and sulfur in the molten steel and top slag will inhibit nitrogen increase and phosphorus reversion during the stirring process. The applicant found that after the stirring decarburization operation: the decarburization amount can reach 0.01% - 0.030%, and the [O] in the molten steel can be reduced to 400 - 550 ppm, with the oxygen potential dropping by an average of 200 ppm compared to the tapping of the converter. This can reduce the comprehensive aluminum consumption and effectively alleviate the impact of carbon reversion during the LF reduction period.

[0058] In step S5, transferring the ladle to the refining furnace can ensure that the temperature of the molten steel is at 1565 ± 10 °C, which is convenient for decarburization and deoxidation, reduces the operation of severe post-blowing during tapping, and can lower the carbon content in the molten steel.

[0059] In step S6, after the stirring decarburization in the LF furnace oxidation period ends, the argon is adjusted to medium blowing. According to the oxygen determination of the molten steel and adding pure aluminum blocks into the ladle for deep deoxidation of the molten steel by precipitation, the first batch of slag-making materials is added synchronously, and then the first power-on heating and slag melting operation is carried out.

[0060] The first batch of slag-making materials includes: high-calcium active lime and aluminum-calcium slag; among them, the effective CaO of the high-calcium active lime is ≥88%, and the activity is ≥400 ml / g. The addition amount of high-calcium active lime is 8 - 10 Kg / t of molten steel, and the addition amount of aluminum-calcium slag is 3 - 5 Kg / t of molten steel.

[0061] The first batch of slag-making materials can quickly melt the slag and adjust the composition and fluidity of the top slag. The thickness of the top slag is controlled at 300 - 500 mm to ensure a good covering effect during the stirring desulfurization process, improve the desulfurization efficiency at the steel-slag interface, increase the sulfur capacity, and increase the desulfurization speed and desulfurization rate.

[0062] According to the detected oxygen content of the molten steel sample, pure aluminum is supplemented to ensure that [ALs] in the molten steel is 0.050 - 0.070% in the early stage of desulfurization in step S7, so as to improve the formation of white slag and desulfurization efficiency during the reduction period.

[0063] In this application, the pure aluminum block refers to that the aluminum element content is greater than or equal to 99%, added from a bulk high-position silo, and the particle size is 20 - 40 mm.

[0064] In step S9, the method for argon blowing and stirring and desulfurization operation of the molten steel in the ladle is as follows:

[0065] Take samples of the molten steel for temperature measurement, and perform slag dipping, slag adjustment, and desulfurization operation with a large amount of argon stirring during the period of steel sample test results.

[0066] According to the temperature measurement and the slag formation situation during slag dipping, perform power-on temperature rise compensation and selective addition of white slag again.

[0067] Take samples of the molten steel for temperature measurement again, and perform desulfurization operation with a large amount of argon stirring during the period of steel sample test results.

[0068] Desulfurization operation with a large amount of argon stirring: The argon blowing specification is strictly implemented according to requirements. It is required that the time from sampling to the test result is controlled within 2 - 4 minutes. For this reason, a fully equipped special spectral inspection room is set up near the LF furnace. The desulfurization rate of two stirrings can reach more than 80% or even 90%. Power-on temperature rise compensation and selective addition of white slag operation: According to the situation of primary desulfurization and slag dipping, add slag materials when necessary. According to production experience, consider the subsequent soft blowing and waiting time for samples, and the temperature drop during soft blowing and feeding calcium wire to perform the final temperature rise compensation for the molten steel. Ensure that the off-station temperature of the LF furnace meets the requirements for steel feeding in continuous casting. Before power-on temperature rise, the white slag must reach the target requirements, and the holding time of the white slag is ≥ 20 minutes until the LF furnace leaves the station.

[0069] After the first power-on temperature rise and slag melting of the LF furnace are completed, take the first sample of the molten steel for temperature measurement. During the period of waiting for the steel sample test results, perform slag dipping and medium blowing operations. Then, perform selective addition of pure aluminum according to the slag dipping situation or the results of the first steel sample test;

[0070] The argon blowing method is medium blowing. According to the oxygen content in the molten steel and put pure aluminum blocks into the ladle for deep deoxidation of the molten steel by precipitation, and synchronously add the first batch of slag-making materials, and then perform the first power-on temperature rise and slag melting operation. Among them, during the whole process from tapping to the argon station after the furnace, strong stirring operations must be carried out on the molten steel with oxygen content and top slag in the ladle: The argon blowing intensity of a single porous plug is 400 - 600 NL / min, and it is appropriate that the molten steel does not splash out of the ladle, and it lasts for 3 - 5 minutes.

[0071] According to the oxygen content determined after stirring decarburization, use pure aluminum blocks for precipitation deoxidation of the molten steel: The purpose is to ensure high-precision control of [ALs] at 0.050 - 0.070% to improve the formation of white slag and desulfurization efficiency during the reduction period.

[0072] In step S10, the method for fine-tuning the manganese content of the molten steel after desulfurization operation is: Before calcium treatment, according to the carbon content of the molten steel, metal manganese or low-carbon ferromanganese or silicomanganese is required for manganese supplementation, and it is required that the carbon return amount during the whole process after the reduction period and manganese supplementation is controlled within 80 PPm.

[0073] Calcium treatment operation: Select anti-splash pure calcium wire or high-calcium calcium-iron wire. The iron skin of the calcium wire is made of ultra-low carbon steel strip with a carbon content of 0.005% and is welded by a special process. This type of calcium wire can complete the wire feeding operation within 40S, with a temperature drop < 10°C, thereby improving the production efficiency of LF. The calcium recovery rate at the LF off-station reaches 35 - 40%, and the liquid state window range of [Ca] in the off-station molten steel is controlled at 0.0025 - 0.0035%.

[0074] In step S9, the soft blowing time ≥ 10 min. It is required that the liquid level shows a scaly micro-movement and the molten steel is not exposed during soft blowing. The final slag of the LF furnace: CaO / AL 2 O 3 is controlled to 1.7 - 1.8, and the color is white slag or white stripe color. After stable decarburization and oxygen control during the decarburization period, white slag is concentratedly formed. The stability of each component of the white slag is better.

[0075] In this application, the total refining cycle of the LF furnace is controlled within 40 - 50 min, and the argon blowing specifications in each step are strictly implemented in accordance with Table 2.

[0076] Table 2

[0077]

[0078] In some embodiments, before the argon blowing stirring and desulfurization operation on the molten steel in the ladle described in step S9, the high-efficiency and high-purity SPHC smelting production method further includes step S8.

[0079] Step S8: Add pure aluminum diffusion deoxidizer and the second batch of slag-making materials to the molten steel in the ladle, and perform the second power-on heating operation on the refining furnace.

[0080] In step S8, after the aluminum in the steel reaches the requirement, pure aluminum diffusion deoxidizer and the second batch of slag-making materials are added, and then the second power-on heating and white slag formation operations are carried out during the reduction period.

[0081] The pure aluminum diffusion deoxidizer is: aluminum grains and aluminum chips, with the addition amounts of 0.2 - 0.4 Kg / t steel and 0.4 - 0.7 Kg / t steel respectively, and the comprehensive consumption of aluminum blocks, grains and chips is 2.8 - 3.4 Kg / t steel. The second batch of slag-making materials: Appropriately supplement high-calcium ash or special aluminum-calcium slag according to the dipping slag color and texture, slag fluidity during argon blowing, and the sulfur content of the first sample, etc. The second power-on heating: According to the actual temperature measurement and production experience, the molten steel temperature is raised to 1600 - 1630°C at one time to ensure the subsequent stirring desulfurization and fine-tuning of slag addition and other temperature drop requirements.

[0082] The composition of the second slag-making material is the same as that of the first slag-making material. In step S61, slag-making and deoxidation can be carried out again according to the white slag condition in step S6 and the oxygen content in the molten steel. At the same time, the refining furnace performs the second power-on heating operation, which can raise the temperature of the molten steel to 1600-1630 °C to ensure the isothermal drop requirements for subsequent stirring desulfurization and fine-tuning slag feeding.

[0083] In some embodiments, the method of using slag blocking to tap the molten steel into the ladle further includes: setting the tapping channel of the converter as a variable-diameter pipe, and the inner diameter of the tapping channel gradually decreases from the inside of the converter to the outside. The length of the tapping channel is 1100-1300 mm, the maximum inner diameter of the tapping channel is 170-180 mm, and the difference between the maximum inner diameter and the minimum inner diameter of the tapping channel is 10 mm.

[0084] Exemplarily, as Figure 2 shown, the difference in the inner diameters at both ends of the tapping channel is 10 mm. The length of the tapping channel can be 1100 mm, 1200 mm or 1300 mm, and the maximum inner diameter of the tapping channel is 170 mm, 175 mm or 180 mm. In this example, the length of the tapping channel is 1248 mm, the maximum inner diameter is 180 mm, and the minimum inner diameter is 170 mm.

[0085] The tapping channel has a taper, which can reduce the probability of slag rolling and scattering and increase the impact force of the tapping steel flow. Before smelting high-end SPHC, the converter and the ladle must smelt 3 furnaces of ordinary SPHC for furnace flushing and ladle flushing. There should be no "beards" larger than 20 mm at the tapping hole to prevent the tapping from scattering. The slag accumulation at the furnace mouth and the furnace cap must be cleaned up for each furnace to ensure that no dry slag falls into the ladle. The number of times the tapping hole is used must ensure that the tapping time is ≥2.5 min to ensure sufficient time for the molten steel to impact and stir the special aluminum-calcium slag. The surface of the slag blocking cone frustum should be checked in advance, and cracks larger than 2 mm are not allowed. Requirements for the slag blocking success rate and the amount of slag rolling and falling: the slag blocking success rate of the slag blocking cone is ≥98%, and the amount of slag rolling and falling is ≤3.5 Kg / t of molten steel. When problems such as failure to block slag and the increase in the molten steel flow due to the enlargement of the cone during the late stage of slag blocking occur, the operation of lifting the furnace with remaining molten steel when seeing the slag should be taken.

[0086] In some embodiments, the aluminum-calcium slag includes the following components in mass percentages: calcium oxide is 50%-55%, aluminum oxide is 45%-50%, magnesium oxide is less than or equal to 1.0%, silicon dioxide is less than or equal to 1.0%, and the sum of iron oxide and manganese oxide is less than or equal to 1.5%; the content of particles with a particle size of 20-40 mm in the aluminum-calcium slag is not less than 90%.

[0087] In some examples, the aluminum-calcium slag may include the following components by mass percentage: calcium oxide is 50%, 53% or 55%, aluminum oxide is 45%, 47% or 50%, magnesium oxide is 1.0% or 0.5%, silicon dioxide is 1.0% or 0.5%, and the sum of iron oxide and manganese oxide is 1.5% or 1.0%.

[0088] The hemispherical melting point of the aluminum-calcium slag is 1400 - 1430°C, the particle size of 20 - 40 mm is ≥90%, and the compressive strength is ≥8 KN; specifically, it is the walnut-shaped, white original waste aluminum-calcium slag balls produced during the process of the calcium factory using aluminothermic reduction reaction to extract metallic calcium. The components of the aluminum-calcium slag are: one component, tricalcium aluminate (3C·A with a melting point of 1400°C), and four components, dodecacalcium heptaaluminate (12C·7A with a melting point of 1415°C). The price is half of the original high-performance electrofused aluminum-calcium pre-melted refining slag, and the contents of the main components, calcium oxide and aluminum oxide, are more stable, and the metallurgical effect is equivalent. Dosage and effect: 4 - 5 Kg / t of molten steel, added with the molten steel flow when pouring steel. It can be quickly and completely melted within 1 - 2 minutes, which can ensure that the molten steel in the ladle is completely covered under the soft blowing state of argon blowing and more than half of the molten steel is covered under the strong stirring condition, so as to reduce the temperature drop and oxidation loss of the molten steel during the oxidation stirring period. During the steel pouring process, except for the special aluminum-calcium slag, no other auxiliary slag materials and alloys are added.

[0089] The aluminum-calcium slag has a fast dissolution rate, does not increase the carbon content in the molten steel, and has a low price, and is suitable for the low-cost smelting of high-purity SPHC in this application.

[0090] In some embodiments, in the step of adding molten steel with a sulfur content not higher than 0.020% to the converter, the average [C] content of the molten steel with a sulfur content not higher than 0.020% is 4.50%, the average [Si] content is 0.40%, the [Mn] content is 0.35% - 0.45%, the [P] content ≤0.120%, and the [S] content is 0.010 - 0.020%; and the temperature of the molten steel with a sulfur content not higher than 0.020% when added to the converter is 1320 - 1370°C.

[0091] In some embodiments, the special decarburizing composite slag former includes the following components by mass percentage: the content of calcium oxide is 30 - 40%, the content of aluminum oxide is 20 - 30%, the content of silicon dioxide is less than or equal to 5%, the content of magnesium oxide is 4 - 6%, the content of iron oxide is 10 - 15%, the content of manganese oxide is 8 - 15%, and the sulfur content is less than or equal to 0.20%.

[0092] In some examples, the special decarburization compound slag former may include the following components by mass percentage: the content of calcium oxide is 30%, 35% or 40%, the content of aluminum oxide is 20%, 25% or 30%, the content of silicon dioxide is 5%, the content of magnesium oxide is 4%, 5% or 6%, the content of iron oxide is 10%, 13% or 15%, the content of manganese oxide is 8%, 10% or 15%, and the sulfur content is 0.20%.

[0093] Transfer the ladle into the refining furnace, blow argon, and add the special decarburization compound slag former, where 3 - 6 kg of the special decarburization compound slag former is added per ton of molten steel. The applicant also found that: the addition amount of the special decarburization compound slag former is positively correlated with the oxygen content in the steel after decarburization, and excessive addition will affect the comprehensive aluminum consumption and increase the difficulty of desulfurization. In this application, the optimal addition amount of the special decarburization compound slag former is 3 - 6 Kg / t of molten steel.

[0094] In some embodiments, when performing strong stirring decarburization for 1 - 4 min, the temperature of the molten steel is 1565 ± 10 °C.

[0095] In some comparative examples, the steel grade for smelting is also the high-end SPHC for four-bend, and the original smelting process is adopted: preferably blast furnace hot metal → KR deep desulfurization → converter decarburization and phosphorus removal → tapping and argon station deoxidation alloying → LF refining desulfurization → slab continuous casting. Adopt the preferred straight-line iron to pass through KR deep desulfurization to below 0.005%, the slag-making from tapping to LF is the same as high-calcium ash and the original fused electrofused aluminum-calcium refining slag, pure aluminum block is used for primary deoxidation during tapping and aluminum chips or aluminum grains are used for deoxidation to make white slag in LF, low-carbon ferromanganese is used for alloying during tapping, and the manganese content at the LF furnace off-station is also controlled according to the target of 0.12%. When necessary, metal manganese, low-carbon ferromanganese or silicomanganese alloy is used in LF to supplement and increase manganese.

[0096] The data such as the finished product composition control, LF carbon increase, and consumption of various related materials are shown in Tables 3 and 4.

[0097] Comparing the above examples with this comparative example, the process, finished product and composition are compared as shown in Table 3 below.

[0098] Table 3

[0099]

[0100]

[0101] Comparing the above examples with the comparative examples, the consumption of various materials and the LF cycle are compared as shown in Table 4 below.

[0102] Table 4

[0103]

[0104] Comparing the above embodiments with the comparative examples, the final compositions of the LF white slag are shown in Table 5 below.

[0105] Table 5

[0106]

[0107] Comparing the above embodiments with the comparative examples, the results of the cold hardness performance test and the cracking situation of the 90 / 180° bending test are shown in Table 6 below.

[0108] Table 6

[0109]

[0110] In Tables 3 to 6, Examples 1, 2, and 3 all adopt the technical solutions of this application for SPHC smelting production, and Comparative Examples 1, 2, and 3 adopt the original smelting process for production.

[0111] In Examples 1 to 3, the LF off-station compositions all meet the internal control target requirements of high-end SPHC. And the following effects are achieved: the average decarburization amount during the oxidation stirring period of the LF furnace is 0.021%, the comprehensive average decarburization amount from the converter tapping to the LF furnace off-station is 14PPm, and the average carbon reabsorption amount during the LF reduction period is 70PPm; the average silicon increase is 0.020% and the nitrogen increase is 14PPm from the converter tapping to the LF furnace off-station; the total desulfurization rate of the LF furnace reaches 87.79%; after adding a special decarburization compound slag-making agent to the LF furnace and reducing sulfur during the white slag reduction process, the manganese oxide is reduced and enters the molten steel, and the average addition of silicomanganese alloy is only 20 Kg / furnace, and other high-price ferromanganese is not used during the whole smelting process; high-quality [S]≤0.020% blast furnace hot metal is directly charged into the furnace, saving the KR desulfurization cost; the average LF refining cycle is shortened by 4 minutes to 47 minutes; the stability of the white slag components is significantly improved.

[0112] Since the cold-hardened material cannot be used to evaluate the forming performance in the thickness direction, the Z-direction performance improvement is evaluated based on the bending and rolling direction tensile tests and the user usage situation.

[0113] In Examples 1 to 3, for the cold-hardened four-bending test and the tensile test, there is no cracking in the 180° bending, and the average elongation rate reaches 5.3%, and the quality fully meets the user's usage requirements.

[0114] In Comparative Examples 1 to 3, the comprehensive aluminum consumption during the whole smelting process is 2.81 Kg / t steel. In Examples 1 to 3, the comprehensive aluminum consumption during the whole smelting process is 3.01 Kg / t steel, which is relatively high, mainly caused by iron oxide and manganese oxide in the special composite deoxidizing slag-making agent for reduction.

[0115] In Comparative Examples 1 to 3, the average carbon increase from the converter tapping to the LF furnace off-station is 0.023%, the average silicon increase is 0.040%, and the nitrogen increase is 43PPm; the total desulfurization rate of the LF furnace is only 56.84%; other high-price ferromanganese is used during the whole smelting process, with an average of 85 Kg / furnace.

[0116] For Comparative Examples 1 to 3, the average [C] of the LF off-station was 0.050%, which was all on the high side up to the release upper limit. Among them, the carbon content of Comparative Example 2 exceeded the standard and was rejudged; the average [N] reached 47 ppm and the average [O] reached 39 ppm, which were 26 ppm and 14 ppm higher than those of Examples 1 to 3 respectively; the average [Si] was 0.043% on the high side; the average [S] was 0.005% on the high side, and the LF refining process was significantly difficult. The above shows that the cleanliness of the original process is poor, which will affect the use of the material.

[0117] For Comparative Examples 1 to 3, in the cold-hard four-bending test and the tensile test, there were cracking problems in the 180° bending, and they could only be used for other purposes. The average elongation was 4.2%, which was slightly low. The quality could not meet the user's requirements.

[0118] Examples 1 to 3, cost comparison with Comparative Examples 1 to 3. The cost accounting was carried out according to the purchase reference price and the actual consumption when applying for this invention, as shown in Table 7. The comprehensive cost was reduced by 14.81 yuan / ton of steel, and the reduction rate was about 11% of the comprehensive cost of the original process refining and pretreatment.

[0119] Table 7

[0120]

[0121]

[0122] Thus, it can be seen that the high-end SPHC for cold-hard four-bending prepared in the examples of the present invention has significant advantages in many aspects such as smelting cost, cleanliness improvement, performance improvement, quality and operation stability, production efficiency, and rationality of process design. The product can fully meet the customer's use requirements.

[0123] In the description of this specification, specific features, structures, materials, or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0124] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A high-efficiency and high-purity SPHC smelting production method, characterized in that: include: Adding molten steel having a sulfur content not higher than 0.02% to the converter; The molten steel is smelted in the converter, and the carbon content, phosphorus content and temperature of the molten steel are controlled by endpoint so as to meet the requirements when the molten steel is tapped; The steel is tapped into the ladle by slag blocking, and aluminum-calcium slag is added during the tapping process to perform slag making operations; The ladle is transferred to an argon blowing station, argon is blown into the ladle, and the molten steel and top slag are strongly stirred for 3 to 5 minutes; The ladle is transferred to a refining furnace, and argon is blown and a special decarburizing composite slag-making agent is added, and strong stirring decarburization is performed for 1 to 4 minutes; The ladle is blown with argon again for 4 to 6 minutes, and aluminum and the first batch of slag-making materials are added into the ladle according to the oxygen content in the molten steel; The refining furnace is subjected to a first power transmission, temperature raising and slag melting operation, and molten steel is sampled and temperature measured, and argon is blown into the molten steel in the ladle and aluminum is supplemented according to the test results of the molten steel sample; Performing argon blowing, stirring and desulfurization operations on the molten steel in the ladle; Fine-tune the manganese content of the desulfurized steel and perform calcium treatment; The argon gas is adjusted to perform soft blowing of the molten steel for 10 to 15 minutes. When the temperature and composition of the slag and the molten steel meet the requirements, the molten steel is transferred to the hot rolling mill for the next step.

2. The high-efficiency and high-purity SPHC smelting production method according to claim 1 is characterized in that: Before the argon blowing, stirring and desulfurization operations are performed on the molten steel in the ladle, the high-efficiency and high-purity SPHC smelting production method further includes: A pure aluminum diffusion deoxidizer and a second batch of slag-making materials are added to the molten steel in the ladle, and a second power supply and temperature raising operation is performed on the refining furnace.

3. The high-efficiency and high-purity SPHC smelting production method according to claim 1 or 2, characterized in that: The method of tapping steel into a ladle using slag blocking also includes: The steel-outlet channel of the converter is set as a reducer, and the inner diameter of the steel-outlet channel gradually decreases from the inside of the converter to the outside. The length of the steel-outlet channel is 1100~1300mm, the maximum inner diameter of the steel-outlet channel is 170~180mm, and the difference between the maximum inner diameter and the minimum inner diameter of the steel-outlet channel is 10mm.

4. The high-efficiency and high-purity SPHC smelting production method according to claim 3 is characterized in that: The aluminum-calcium slag comprises the following components in percentage by mass: Calcium oxide is 50% to 55%, aluminum oxide is 45% to 50%, magnesium oxide is less than or equal to 1.0%, silicon dioxide is less than or equal to 1.0%, and the sum of iron oxide and manganese oxide is less than or equal to 1.5%; The content of particles with a particle size of 20-40 mm in the aluminum-calcium slag is not less than 90%.

5. The high-efficiency and high-purity SPHC smelting production method according to claim 3 is characterized in that: In the step of adding the molten steel having a sulfur content not higher than 0.020% to the converter, the molten steel having a sulfur content not higher than 0.020% has an average [C] content of 4.50%, an average [Si] content of 0.40%, a [Mn] content of 0.35% to 0.45%, a [P] content of ≤0.120%, and a [S] content of 0.010 to 0.020%; The temperature of the molten steel with a sulfur content not higher than 0.020% when added into the converter is 1320-1370°C.

6. The high-efficiency and high-purity SPHC smelting production method according to claim 3 is characterized in that: The special decarbonization composite slag-making agent comprises the following components in percentage by mass: calcium oxide content is 30-40%, aluminum oxide content is 20-30%, silicon dioxide content is less than or equal to 5%, magnesium oxide content is 4-6%, iron oxide content is 10-15%, manganese oxide content is 8-15%, and sulfur content is less than or equal to 0.20%; The ladle is transferred to a refining furnace, and argon is blown and a special decarburization composite slag-making agent is added, wherein 3-6 kg of the special decarburization composite slag-making agent is added to each ton of molten steel.

7. The high-efficiency and high-purity SPHC smelting production method according to claim 3 is characterized in that: When the strong stirring decarburization is performed for 1 to 4 minutes, the temperature of the molten steel is 1565±10°C.

8. The high-efficiency and high-purity SPHC smelting production method according to claim 3 is characterized in that: The first batch of slag making materials includes: high calcium active lime and calcium aluminum slag; wherein the CaO 有效 ≥88%, activity ≥400ml / g.

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