Semi-deoxidation refining-free straight continuous casting process

Abstract

The invention belongs to the technical field of molten steel direct-feeding continuous casting, and particularly discloses a semi-deoxidation refining-free direct-feeding continuous casting process which comprises the following steps: before entering a furnace, desulfurizing molten iron, controlling the adding amount of a stirring paddle, desulfurized powder and the ratio of molten iron, controlling the content of carbon and phosphorus and the tapping temperature during entering the furnace for smelting, entering a steel ladle after smelting, and carrying out continuous casting on the molten iron, so as to obtain the semi-deoxidation refining-free direct-feeding continuous casting. When the tapping amount of the molten steel reaches 30% of the total amount, lime is added, when the tapping amount of the molten steel reaches 50% of the total amount, alloy is added, adding is completed when the tapping amount of the molten steel reaches 80% of the total amount, a top slag modifier is added into the molten steel after entering a steel ladle, then the steel ladle is fed into an argon blowing station, strong stirring is conducted firstly, when top slag becomes brown, aluminum wires are fed, and soft blowing is conducted at the same time; performing continuous casting after soft blowing, and performing argon sealing in the whole process; refining is not needed after argon blowing is finished, and the calcium element adding amount during refining is reduced, so that inclusions in molten steel are reduced, the molten steel flowability is improved, and the problem that the molten steel flowability is poor due to excessive calcium element during refining in the straight continuous casting process is solved.

Description

Technical Field

[0001] The invention relates to the technical field of molten steel straight-up continuous casting, in particular to a semi-deoxidation and non-refining straight-up continuous casting process. Background Art

[0002] The steel production process primarily consists of three core steps: ironmaking, steelmaking, and steel rolling. Steelmaking begins by heating raw materials in equipment such as converters or electric arc furnaces. Impurities such as carbon, sulfur, and phosphorus are removed from the molten iron through oxygen blowing and slag formation. Furthermore, alloying elements such as manganese, silicon, and chromium are precisely added to adjust the chemical composition based on the desired steel grade. Refining further purifies the molten steel and achieves uniform composition. Finally, the molten steel is cast into various shapes, such as slabs and billets, to prepare for subsequent rolling operations. Direct continuous steel casting is an advanced process that directly casts high-temperature molten steel into billets. Molten steel of acceptable composition, temperature, deoxidation level, and purity is first loaded into a ladle. This is then transported to the pouring position via a ladle turret and poured into a tundish. When the molten steel level reaches a certain level, the sprue at the bottom of the tundish is opened, allowing the molten steel to flow into a forced-water-cooled crystallizer, where it gradually solidifies along its perimeter to form a billet shell. In the traditional production process, after full deoxidation, the steel is subjected to LF refining treatment before continuous casting, or calcium treatment is used before direct continuous casting. However, excessive calcium may cause new inclusion problems in the steel, such as an increase in calcium aluminate inclusions, which in turn affects the quality of the steel. Summary of the Invention

[0003] The object of the present invention is to provide a semi-deoxidation and non-refining straight-up continuous casting process to solve the problem of poor fluidity of molten steel caused by excessive calcium during refining in the straight-up continuous casting process.

[0004] To achieve the above object, the present invention provides a basic solution: a semi-deoxidation and non-refining straight-up continuous casting process, comprising the following steps:

[0005] S1. The molten iron is pretreated for desulfurization, and the stirring paddle parameters and the amount of desulfurization powder added are controlled so that the sulfur content of the molten iron entering the furnace is ≤0.005%;

[0006] S2 strictly controls the total charge amount of molten iron ratio, and the treated molten iron is fed into the converter for smelting, controlling the carbon and phosphorus content and the furnace temperature during smelting;

[0007] S3. The molten steel is fed into the ladle for tapping. When the tapping volume reaches 30% of the total amount of molten steel, lime is added. When the tapping volume reaches 50% of the total amount of molten steel, alloys are added. When the tapping volume reaches 80% of the total amount of molten steel, the addition is complete.

[0008] S4. Add top slag modifier to the molten steel in the ladle to control Fe2O3 + MnO ≤ 3%, and send the ladle to the argon blowing station;

[0009] S5. In the argon blowing station, strong stirring is performed for 2 minutes. When the top slag turns brown, the aluminum wire is fed according to the oxygen content in the ladle and soft blowing is performed at the same time. The soft blowing time is ≥8 minutes. After the soft blowing, the molten steel is sampled. The argon blowing station treatment time is controlled within 15 minutes, and the carbon-oxygen product is controlled at 0.0021-0.0032%;

[0010] S6. After the soft blowing is completed, continuous casting is carried out directly. The entire casting process is sealed with argon gas. Low-silicon carbon-free and ordinary covering agents are added to the impact area and stopper area of ​​the start-up furnace in sequence.

[0011] The principle and beneficial effect of the present invention are as follows: since the converter adopts the "semi-deoxidation" process, the control ability of sulfur element after entering the furnace is zero, so the molten iron entering the furnace needs to be treated, first the molten iron is pretreated to control the sulfur content in the molten iron, then the molten iron ratio of the molten iron entering the furnace is controlled, and then it enters the converter for smelting, and the carbon and phosphorus content and the furnace temperature are controlled during smelting. When the smelted molten steel enters the ladle, the order and timing of adding lime and alloy are strictly controlled, so as to control the composition and purity of the molten steel. After all the molten steel enters the molten steel, the top slag modifier is added, and then the ladle is sent to the ladle. Enter the argon blowing station, and after 2 minutes of strong stirring at the argon blowing station until the top slag turns brown, aluminum wire is fed according to the oxygen content in the ladle to reduce the oxygen content in the molten steel. No refining is required after the argon blowing is completed, and the amount of calcium added during refining is reduced, thereby reducing inclusions in the molten steel and increasing the fluidity of the molten steel. Straight-up continuous casting is carried out directly, and argon is sealed throughout the casting process. Low-silicon carbon-free and ordinary covering agents are added to the impact zone and stopper rod zone of the startup furnace in turn. The original deoxidation and alloying process is changed to semi-deoxidation combined with aluminum wire feeding process, which reduces inclusions in the molten steel and improves the fluidity and purity of the molten steel.

[0012] Option 2 is the preferred option of the basic option. In step S1, the stirring paddle in the 120t molten iron ladle is inserted to a depth of 800-1200mm below the liquid surface, the stirring paddle speed is 400-800r, and the amount of desulfurization powder added is 6.1-10.7kg / t; the parameters of the stirring paddle are controlled, the stirring intensity and range are balanced, and efficient mixing of the molten iron, maximum utilization of the desulfurizer and reaction uniformity are achieved with minimum energy consumption and material loss. The molten steel is pretreated before entering the furnace to reduce the sulfur element in the molten steel.

[0013] Option 3 is the preferred basic option. In step S2, the iron-to-metal ratio is strictly controlled to be ≥80% before smelting, the converter slag basicity is ≥3.2 during smelting, the magnesium oxide content is ≥8%, the molten iron temperature is ≥1320°C, the final carbon content after smelting is 0.04-0.09%, and the phosphorus content is <0.025%. Precise control of parameters can achieve efficient dephosphorization and desulfurization, improve the final hit rate, extend the life of the furnace lining, reduce alloy consumption and stabilize the molten steel quality, creating conditions for subsequent continuous casting processes.

[0014] Option 4 is the preferred option of the basic option. In step S3, the steel is tapped using a slide plate to block the slag, the amount of lime added is 0.8-1.5 kg / t, the alloy is low-carbon ferromanganese and ferroaluminum, low-carbon ferromanganese is added first, and then ferroaluminum is added, and the total amount of alloy added is 3 kg / t; by strictly controlling the order and timing of adding lime and alloy, the inclusions in the molten steel are reduced, thereby controlling the composition and purity of the molten steel.

[0015] Option 5 is the preferred option of the basic option. In step S4, the main components of the top slag modifier are 42% Al2O3, 15%-20% lime, 20% aluminum alloy, and 10% SiO2. The total amount of the top slag modifier added is 1.4-1.7 kg / t.

[0016] Solution 6: This is the preferred solution for the basic solution. In step S5, the flow rate of strong stirring argon blowing is 20 Nm 3 / h, the aluminum wire diameter is 12.5mm, the wire feeding speed is controlled at 4-6m / s, the aluminum wire deoxidation rate is 10ppm / m, and the soft blowing flow rate is 1-4Nm 3 / h; through multi-parameter linkage regulation, a dynamic balance of deoxidation-inclusion removal-precise composition control is achieved, and high-cleanliness molten steel is obtained at the lowest cost.

[0017] Option 7, which is the preferred basic option, in step S6, when starting to bake the tundish, the argon flow rate of the upper water inlet is 3-5L / min, the argon flow rate of the E-type tube is 200L / min, during casting, the argon flow rate of the long water inlet of the large ladle is 100-120L / min, and the argon flow rate between the plates is 8-10L / min. When starting the furnace, 60-80kg of low-silicon and carbon-free covering agent is first added to the impact zone, and then 30-40kg of ordinary covering agent is added; 250kg of low-silicon and carbon-free covering agent is first added to the stopper rod zone. Then add 120kg of ordinary covering agent, add 40kg / furnace of low-silicon and carbon-free covering agent to the impact zone of the continuous casting furnace, and add 20kg / furnace of ordinary covering agent. If there is brightness in the later stage of casting, add low-silicon and carbon-free and ordinary covering agents in a ratio of 2:1; brightness in the later stage of casting refers to an abnormally bright area on the surface of the tail or the finishing stage of the ingot. This phenomenon is mainly related to the enrichment of solute elements and the behavior of protective slag at the end of solidification. Commonly used ordinary covering agents include: carbon black + expanded graphite; perlite + broken glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a graph showing the detection results of non-metallic inclusions in a steel billet produced by a semi-deoxidation and non-refining straight-up continuous casting process of the present invention before improvement;

[0019] Figure 2 This is a graph showing the detection results of non-metallic inclusions in steel billets produced after an improved semi-deoxidation and non-refining straight-up continuous casting process according to the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below through specific embodiments:

[0021] Example

[0022] A semi-deoxidation and non-refining straight-up continuous casting process comprises the following steps:

[0023] S1. The molten iron is pretreated for desulfurization. The stirring paddle in the 120t ladle is inserted to a depth of 800-1200mm below the liquid level. The stirring paddle speed is 400-800r. The amount of desulfurization powder added is 6.1-10.7kg / t, so that the sulfur content of the molten iron is ≤0.005%;

[0024] S2. Strictly control the total charge ratio of molten iron, and send the treated molten iron into the converter for smelting. Strictly control the molten iron ratio ≥80% before smelting, the converter slag basicity ≥3.2, the magnesium oxide content ≥8%, the furnace molten iron temperature ≥1320 ° C, the end point carbon content after smelting is 0.04-0.09%, and the phosphorus content is <0.025%;

[0025] S3. The molten steel is fed into the ladle for tapping, and the slag is removed by a slide block. When the tapping volume reaches 30% of the total amount of molten steel, the amount of lime added is 0.8-1.5kg / t. When the tapping volume reaches 50% of the total amount of molten steel, the alloy is added. The alloy is low-carbon ferromanganese and aluminum-iron. Low-carbon ferromanganese is added first, and then aluminum-iron is added. The total amount of alloy added is 3kg / t. When the tapping volume reaches 80% of the total amount of molten steel, the addition is complete.

[0026] S4. Add top slag modifier to the molten steel in the ladle. The main components of the top slag modifier are AL2O342%, lime 15-20%, aluminum alloy 20%, SiO210%, and the total amount of top slag modifier added is 1.4-1.7kg / t. Control Fe2O3+MnO≤3%, and send the ladle to the argon blowing station.

[0027] S5. Perform strong stirring for 2 minutes at the argon blowing station. The flow rate of strong stirring argon blowing is 20Nm 3 / h. When the top slag turns brown, aluminum wire is fed according to the oxygen content in the ladle. The diameter of the aluminum wire is 12.5mm, the wire feeding speed is controlled at 4-6m / s, the aluminum wire deoxidation rate is 10ppm / m, and soft blowing is carried out at the same time. The flow rate of soft blowing is 1-4Nm 3 / h, soft blowing time ≥ 8 minutes, molten steel sampling is carried out after soft blowing, the treatment time of argon blowing station is controlled within 15 minutes, and the carbon and oxygen content is controlled at 0.0021-0.0032%;

[0028] S6. After the soft blowing is completed, continuous casting is carried out directly. Argon is sealed throughout the casting process. When the baking of the tundish begins, the argon flow rate of the upper water inlet is 3-5L / min, and the argon flow rate of the E-type tube is 200L / min. During casting, the argon flow rate of the long water inlet of the large ladle is 100-120L / min, and the argon flow rate between the plates is 8-10L / min. First, add 60-80kg of low-silicon and carbon-free covering agent to the impact zone of the startup furnace, and then add 30-40kg of ordinary covering agent; first add 250kg of low-silicon and carbon-free covering agent to the stopper rod area, and then add 120kg of ordinary covering agent; add 40kg / furnace of low-silicon and carbon-free covering agent to the impact zone of the continuous casting furnace, and add 20kg / furnace of ordinary covering agent. If there is any shine in the later stage of casting, add low-silicon and carbon-free and ordinary covering agents in a ratio of 2:1.

[0029] The implementation method of this embodiment is as follows: before smelting, 113 tons of molten iron and 23 tons of pure scrap steel are mixed, the mixed molten iron is first pretreated, the stirring paddle in the molten iron ladle is controlled to be inserted to a depth of 800 mm below the liquid surface, the stirring paddle speed is 400 r, the amount of desulfurization powder added is 6.1 kg / t, the sulfur content of the molten iron before entering the furnace is controlled to be ≤0.005%, the converter molten iron ratio is controlled to be above 80%, and then the molten iron is sent to the converter to start smelting. During the smelting process, the converter slag basicity ≥3.2 and the magnesium oxide content ≥8% are strictly observed to make the molten steel composition uniform and stable.

[0030] The smelted molten steel is sent to the ladle, and the slide plate is used to block the slag when tapping. When the molten steel tapping volume reaches 30% of the total molten steel volume, the amount of lime added is 0.8kg / t. When the molten steel tapping volume reaches 50% of the total molten steel volume, alloy is added. The alloy is low-carbon ferromanganese and ferroaluminum. Low-carbon ferromanganese is added first, and then ferroaluminum. The total amount of alloy added is 3kg / t. When the molten steel tapping volume reaches 80% of the total molten steel volume, the addition is completed. After tapping, top slag modifier is added to the molten steel in the ladle. The main components of the top slag modifier are AL2O342%, lime 15%, aluminum series alloy 20%, SiO210%, and the total amount of top slag modifier added is 1.4kg / t. Fe2O3+MnO≤3% is controlled. The ladle is sent to the argon blowing station, and strong stirring is carried out for 2 minutes at the argon blowing station. The flow rate of strong stirring argon blowing is 20Nm 3 / h. When the top slag turns brown, aluminum wire is fed according to the oxygen content in the ladle. The diameter of the aluminum wire is 12.5mm, the wire feeding speed is controlled at 5m / s, the aluminum wire deoxidation rate is 10ppm / m, and soft blowing is carried out at the same time. The flow rate of soft blowing is 2Nm 3 / h, soft blowing time ≥ 8 minutes, molten steel sampling after soft blowing, argon blowing station treatment time is controlled within 15 minutes, carbon and oxygen content is controlled at 0.0021%, oxygen content in the ladle and the amount of aluminum wire added are shown in Table 1 below, and the corresponding amount of aluminum and iron added after the end of smelting is shown in Table 2 below:

[0031] Table 1 Oxygen content in ladle and amount of aluminum wire added

[0032] Serial number Oxygen in the bag / ppm Thin aluminum wire (12.5mm) In the package

Al

[0033] Table 2 End point carbon and oxygen content corresponding to aluminum and iron addition amount

[0034] End point [C]% End point [O] ppm Amount of aluminum and iron added kg End point temperature ℃ 0.04-0.05 530-620 130-180 1640-1650 0.05-0.06 500-580 100-130 1640-1650 0.04-0.05 600-650 130-180 1650-1660 0.05-0.06 550-600 100-130 1650-1660 0.04-0.05 700-750 150-180 ＞1660 0.05-0.06 650-700 120-150 ＞1660

[0035] After the soft blowing is completed, continuous casting is carried out directly. Argon is sealed throughout the casting process. When the baking of the tundish begins, the argon flow rate of the upper water inlet is 3L / min, and the argon flow rate of the E-type tube is 200L / min. During casting, the argon flow rate of the long water inlet of the large ladle is 100L / min, and the argon flow rate between the plates is 8L / min. 60kg of low-silicon and carbon-free covering agent is first added to the impact zone of the startup furnace, and then 30kg of ordinary covering agent is added; 250kg of low-silicon and carbon-free covering agent is first added to the stopper rod area, and then 120kg of ordinary covering agent is added. 40kg / furnace of low-silicon and carbon-free covering agent is added to the impact zone of the continuous casting furnace, and 20kg / furnace of ordinary covering agent is added. If there is any shiny situation in the later stage of casting, low-silicon and carbon-free and ordinary covering agents are added in a ratio of 2:1. The rolled steel billet is tested for non-metallic inclusions. The test results are shown in Table 3 below:

[0036] Table 3 Non-metallic inclusions in improved billets

[0037]

[0038] The same type of steel billets were produced using the production process before the improvement, and the non-metallic inclusions of the rolled steel billets were tested. The test results are shown in Table 4 below:

[0039] Table 4 Non-metallic inclusions in steel billets before improvement

[0040]

[0041] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A semi-deoxidation and non-refining straight-up continuous casting process, characterized in that: The following steps are involved: S1. The molten iron is pretreated for desulfurization, and the stirring parameters and the amount of desulfurization powder added are controlled so that the sulfur content of the molten iron entering the furnace is ≤0.005%; S2 strictly controls the total charge amount of molten iron ratio, and sends the treated molten iron into the converter for smelting, controlling the carbon and phosphorus content and the furnace temperature during smelting; S3. The molten steel is fed into the ladle for tapping. When the tapping volume reaches 30% of the total amount of molten steel, lime is added. When the tapping volume reaches 50% of the total amount of molten steel, alloys are added. When the tapping volume reaches 80% of the total amount of molten steel, the addition is complete. S4. Add top slag modifier to the molten steel in the ladle to control Fe2O3+MnO≤3%, and send the ladle to the argon blowing station; S5. In the argon blowing station, strong stirring is performed for 2 minutes. When the top slag turns brown, the aluminum wire is fed according to the oxygen content in the ladle and soft blowing is performed at the same time. The soft blowing time is ≥8 minutes. After the soft blowing, the molten steel is sampled. The argon blowing station treatment time is controlled within 15 minutes, and the carbon-oxygen product is controlled at 0.0021-0.0032%; S6. After the soft blowing is completed, continuous casting is carried out directly. The entire casting process is sealed with argon gas. Low-silicon and carbon-free and ordinary covering agents are added to the impact area and stopper area of ​​the start-up furnace in sequence.

2. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S1, a stirring paddle in a 120t molten iron ladle is inserted to a depth of 800-1200mm below the liquid surface, the stirring paddle speed is 400-800r, and the amount of desulfurization powder added is 6.1-10.7kg / t.

3. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S2, the molten iron ratio is strictly controlled to be ≥80% before smelting, the converter slag basicity is ≥3.2 during smelting, the magnesium oxide content is ≥8%, the molten iron temperature is ≥1320°C, the final carbon content after smelting is 0.04-0.09%, and the phosphorus content is <0.025%.

4. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S3, the steel is tapped using a slide plate to block slag, the amount of lime added is 0.8-1.5 kg / t, the alloy is low-carbon ferromanganese and ferroaluminum, low-carbon ferromanganese is added first, and then ferroaluminum is added, and the total amount of alloy added is 3 kg / t.

5. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S4, the main components of the top slag modifier are Al2O3 42%, lime 15%-20%, aluminum series alloy 20%, and SiO2 10%, and the total addition amount of the top slag modifier is 1.4-1.7 kg / t.

6. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S5, the flow rate of strong stirring argon blowing is 20Nm 3 / h, the aluminum wire diameter is 12.5mm, the wire feeding speed is controlled at 4-6m / s, the aluminum wire deoxidation rate is 10ppm / m, and the soft blowing flow rate is 1-4Nm 3 / h.

7. A semi-deoxidation and non-refining straight-up continuous casting process according to claim 1, characterized in that: In step S6, when the baking of the middle ladle begins, the argon flow rate of the upper water inlet is 3-5L / min, and the argon flow rate of the E-type tube is 200L / min. During casting, the argon flow rate of the long water inlet of the large ladle is 100-120L / min, and the argon flow rate between the plates is 8-10L / min. First, add 60-80kg of low-silicon carbon-free covering agent to the impact zone of the startup furnace, and then add 30-40kg of ordinary covering agent; first add 250kg of low-silicon carbon-free covering agent to the stopper rod area, and then add 120kg of ordinary covering agent. Add 40kg / furnace of low-silicon carbon-free covering agent to the impact zone of the continuous casting furnace, and add 20kg / furnace of ordinary covering agent. If there is any shine in the later stage of casting, add low-silicon carbon-free and ordinary covering agents in a ratio of 2:1.

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