A method of producing a steel sheet

Abstract

The application discloses a steel plate production method, and belongs to the technical field of steelmaking. The steel plate production method comprises the following steps: carrying out deoxidization and alloying treatment on molten iron to obtain first molten steel; the iron-steel ratio of the molten iron is 880 kg / t-920 kg / t; carrying out refining treatment on the first molten steel to obtain second molten steel and refining slag; sequentially carrying out vacuum treatment, calcium wire feeding and argon blowing treatment on the second molten steel to obtain third molten steel; transferring the third molten steel into a tundish, adding a covering agent and carrying out static treatment to obtain fourth molten steel; distributing the fourth molten steel to a crystallizer for casting, adding continuous casting protective slag into the crystallizer after casting, and then carrying out strand drawing to obtain a casting strand; and carrying out head cutting treatment and rolling treatment on the casting strand to obtain a steel plate. The production method can significantly reduce the cleanliness risk of the molten steel, stabilize the quality of the casting head strand, and greatly improve the flaw detection qualified rate of the casting head strand steel plate.

Description

Technical Field

[0001] This application belongs to the field of steelmaking technology, and in particular relates to a method for producing steel plates. Background Technology

[0002] The initial casting stage of continuous casting is an unsteady-state casting process. During this stage, molten steel is highly susceptible to contact with air, resulting in air absorption, increased nitrogen and hydrogen content, and a greater number of inclusions. This directly leads to a low pass rate for steel plate flaw detection. The pass rate for flaw detection is a crucial indicator of the quality of heavy plate products and directly affects their competitiveness in the market.

[0003] Currently, to ensure contract fulfillment, most steel mills typically add one heat of non-flaw-inspected steel as the first casting heat when scheduling production. While this reduces the production of billets without owner contracts, it increases losses from mixed casting and re-judgment, raising production costs. More importantly, when the first casting steel cannot be continuously cast with the non-flaw-inspected steel, the only way to guarantee the quality of subsequent products is to increase the scrap rate of the first billet. Typically, the scrap rate of the first billet per heat can reach 15-30 tons, resulting in serious steel waste and economic losses.

[0004] It should be noted that the above content is not necessarily prior art, nor is it intended to limit the scope of protection of this application. Summary of the Invention

[0005] This application discloses a method for producing steel plates, which aims to solve the technical problems of large scrap rate of first blanks and high non-destructive testing pass rate in the existing steel plate preparation process.

[0006] To achieve the above objectives, the technical solution of this application is: A first aspect of this application provides a method for producing a steel plate, the method comprising: The molten iron is deoxidized and alloyed to obtain the first molten steel; the iron-to-steel ratio of the molten iron is 880 kg / t-920 kg / t. The first molten steel is refined to obtain a second molten steel and refining slag; the basicity of the refining slag is 6.3-8.0, and the residence time of the refining slag in the second molten steel is at least 10 min; The second molten steel is subjected to vacuum treatment, calcium wire feeding, and argon blowing in sequence to obtain a third molten steel, wherein the total oxygen content of the third molten steel is ≤0.001%; The third molten steel is transferred to an intermediate ladle, a covering agent is added, and the steel is killed to obtain a fourth molten steel, wherein the hydrogen content of the fourth molten steel is ≤0.9 ppm and the nitrogen content is ≤35 ppm. The fourth molten steel is distributed to the crystallizer for initial casting. After initial casting, continuous casting protective slag is added to the crystallizer and then the billet is pulled to obtain a billet. The pulling includes at least one alternating process of increasing speed pulling and constant speed pulling. The cast billet is then subjected to head-cutting and rolling processes to obtain a steel plate.

[0007] In conjunction with the first aspect, preferably, the accelerated drawing and the uniform drawing are based on a speed control curve; The speed control curve includes: First gradient segment: Accelerate the first initial velocity to the first final velocity with the first acceleration and maintain the first uniform velocity for the first duration; Second gradient segment: Accelerate the first endpoint velocity to the second endpoint velocity with the second acceleration, and maintain the second constant velocity for the second duration; The third gradient segment: the third acceleration is used to accelerate the second terminal velocity to the third terminal velocity, and the third uniform velocity is maintained for the third duration; Fourth gradient segment: The third endpoint velocity is accelerated to the preset endpoint velocity with the fourth acceleration, and the fourth constant velocity is maintained for the fourth duration.

[0008] Preferably, in conjunction with the first aspect, the first acceleration is 2.5 m / min. 2 The first initial velocity is 0 m / min, the first final velocity is 0.4 m / min, and the first uniform velocity duration is 0.5 min; The second acceleration is 0.2 m / min 2 The second endpoint velocity is 0.8 m / min, and the first uniform velocity duration is 1.5 min; The third acceleration is 0.1 m / min 2 The third endpoint velocity is 1 m / min, and the third uniform velocity duration is 2 min; The fourth acceleration is 0.1 m / min 2 The preset endpoint speed is 1-1.5 m / min, and the fourth uniform speed duration is 2 min.

[0009] Preferably, in conjunction with the first aspect, prior to the billet pulling process, the superheat of the continuously cast molten steel is controlled to be 15-25 °C; and / or The vacuum treatment includes: ultimate vacuum degree ≤ 67 Pa, holding time ≥ 15 min.

[0010] Preferably, in conjunction with the first aspect, the step of transferring the second molten steel into the tundish further includes: The intermediate batch uses dry material and is baked at a temperature ≥1100℃, and then purged with argon gas to remove residual oxygen in the intermediate batch. Furthermore, during the step of adding the covering agent and quenching, argon gas is continuously injected into the intermediate ladle until the added covering agent completely covers the molten steel.

[0011] Preferably, in conjunction with the first aspect, the covering agent includes one or more of wollastonite and vermiculite; The amount of the covering agent added is 1.0 kg / ton of steel to 1.3 kg / ton of steel; The process also includes drying the covering agent before it is added; The drying process includes baking at 100 ℃-150 ℃ for 6 min-15 min in the 0.5 h-2 h before adding the covering agent.

[0012] Preferably, in conjunction with the first aspect, the calcium treatment includes: a wire feeding rate of 0.8 kg / t-1.2 kg / t, and the calcium content of the molten steel controlled at 0.0006%-0.002%.

[0013] Preferably, in conjunction with the first aspect, the continuous casting protective slag has a viscosity of 0.11 Pa·s-0.12 Pa·s, a melting point of 1200 ℃-1210 ℃, a dissolution rate of 45 g / s-50 g / s, and a bulk density of 0.60 g / cm³. 3 -0.62 g / cm 3 ; The continuous casting protective slag comprises, by mass percentage: SiO2: 26-27%, Al2O3: 3.8-4.2%, CaO: 38.5-39.5%, F: 10.5-11.5%, C: 5.1-6.1%, K2O+Na2O: 5.5-6.5%, with the balance being volatile matter and unavoidable impurities; The amount of continuous casting protective slag added is 0.4 kg / ton of steel to 0.5 kg / ton of steel.

[0014] Preferably, in conjunction with the first aspect, the head-cutting process includes: removing a length of 1 m to 1.5 m from the front of the cast billet; and / or The rolling process includes at least two rolling passes; The casting thickness of the billet is 200 mm-360 mm, and the rolling compression ratio is ≥4.0.

[0015] The second aspect of this application provides a steel plate manufactured by the production method described in the first aspect, wherein the steel plate has a flaw detection pass rate of ≥95%.

[0016] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following: The production method provided in this application, by controlling the iron-to-steel ratio of molten iron and sequentially optimizing the refining, vacuuming, calcium feeding line, argon blowing, killing, casting, billet pulling, head cutting, and rolling processes, can significantly reduce the risk of molten steel cleanliness, control the content of inclusions and gases, and stabilize the quality of the first-cast billet. This greatly improves the flaw detection pass rate of the first-cast billet steel plate, while enhancing production stability and economy, demonstrating significant technical effects and broad industrial application value. Detailed Implementation

[0017] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0018] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0019] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0020] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0021] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0022] It should be noted that all raw materials and / or reagents in the embodiments of this application were purchased on the market or prepared according to conventional methods known to those skilled in the art.

[0023] In a first aspect, this application provides a method for producing a steel plate, the method comprising: The molten iron is deoxidized and alloyed to obtain the first molten steel; the iron-to-steel ratio of the molten iron is 880 kg / t-920 kg / t. The first molten steel is refined to obtain a second molten steel and refining slag; the basicity of the refining slag is 6.3-8.0, and the residence time of the refining slag in the second molten steel is at least 10 min; The second molten steel is subjected to vacuum treatment, calcium wire feeding, and argon blowing in sequence to obtain a third molten steel, wherein the total oxygen content of the third molten steel is ≤0.001%; The third molten steel is transferred to an intermediate ladle, a covering agent is added, and the steel is killed to obtain a fourth molten steel, wherein the hydrogen content of the fourth molten steel is ≤0.9 ppm and the nitrogen content is ≤35 ppm. The fourth molten steel is distributed to the crystallizer for initial casting. After initial casting, continuous casting protective slag is added to the crystallizer and then the billet is pulled to obtain a billet. The pulling includes at least one alternating process of increasing speed pulling and constant speed pulling. The cast billet is then subjected to head-cutting and rolling processes to obtain a steel plate.

[0024] It should be noted that the silicon-manganese weak deoxidizer used in this application is preferably a silicon-manganese alloy with the following composition: Mn: 0.65%-0.72%, Si: 0.17%-0.50%, C: ≤1.8%. The preferred amount of silicon-manganese alloy added is 16-21 kg / t. The silicon-manganese weak deoxidizer used in steelmaking controls oxygen, stabilizes oxygen potential, suppresses nitrogen absorption, and creates liquid inclusions that are easy to float, all with a low-cost alloy. Al is added later to avoid high oxygen burn-off and severe nitrogen absorption. This process improves aluminum yield, reduces alloy costs, reduces nitrogen addition, purifies molten steel, and improves billet quality. It is a classic process route for low-cost clean steel smelting.

[0025] It should be noted that during the reduction stage of the LF furnace or electric arc furnace, the black oxide slag with high FeO and strong oxidizing properties is first removed. Then, deoxidizers such as carbon powder are added to the slag surface for diffusion deoxidation. Under the action of high temperature and argon gas stirring, the content of FeO and other oxidizing oxides in the slag is continuously reduced, while the slag's reducing capacity and desulfurization and inclusion removal effects are improved. As the FeO in the slag continues to decrease, the slag color gradually changes from black and yellow to grayish-white and then to pure white, eventually forming white slag. The white slag should be kept for at least 10 minutes.

[0026] It should be noted that, firstly, by controlling the iron-to-steel ratio at 880 kg / t-920 kg / t, heat balance can be ensured, and nitrogen and hydrogen increases can be avoided due to insufficient heat causing later melting of scrap steel. At the same time, a stable refining slag system is formed by high basicity refining slag of 6.3-8.0 and long residence time, which can efficiently remove oxide and sulfide inclusions. Secondly, this application also employs multiple measures to strictly control the sources of hydrogen and nitrogen, such as baking the silicon-manganese alloy at a temperature ≥400 ℃ to reduce hydrogen increase caused by moisture, reducing nitrogen increase during steel tapping due to weak deoxidation of the silicon-manganese system, and achieving deep removal of hydrogen and nitrogen through deep vacuum and sufficient holding time, thereby reducing defects such as porosity, pinholes, and white spots. Thirdly, by adding a covering agent to the tundish and covering it with multiple layers of wollastonite and vermiculite, air can be isolated. By controlling the tundish temperature, molten steel volume, and liquid level rise rate, the ladle drop height is 100-200 mm, and the slide plate is opened in stages to avoid secondary oxidation and slag entrapment. When the liquid level in the crystallizer submerges the side hole of the nozzle, protective slag is added to ensure slag film stability and reduce fatal defects such as slag entrapment and oxide inclusions in the billet.

[0027] Furthermore, this application employs a segmented acceleration curve, allowing the billet to gradually transition from initial to stable casting speed, avoiding sudden cooling / heating and stress abrupt changes: an initial velocity of 0 m / min, followed by a short period of high acceleration, then gradually increasing to 0.8 m / min, 1.0 m / min, and finally reaching the preset endpoint casting speed. This acceleration method reduces fluctuations in the crystallizer liquid level, resulting in uniform billet shell growth, reducing the risk of internal cracks and surface scratches, and significantly improving the uniformity of the first billet and subsequent billets. Finally, this application uses a 1-2 m head-cutting length for the billet, fully removing the head region most prone to defects during initial casting, with a scrap volume of only 3.3-6.6 t; simultaneously, the rolling thickness is ≤ slab thickness / 4, ensuring a compression ratio ≥ 4:1, which allows for sufficient compaction of central segregation and porosity in the billet, resulting in a more uniform microstructure distribution and further improving internal density; it also reduces the scrap volume of the billet, thereby significantly improving the flaw detection pass rate of the first billet steel plate.

[0028] Specifically, the production method adopted in this application achieves a 10%-25% increase in the flaw detection pass rate, a significant decrease in the blank scrap rate, a more stable production rhythm, and obvious economic benefits without increasing equipment investment, through optimization of existing processes.

[0029] In this embodiment, the accelerated drawing and constant-speed drawing are based on a speed control curve; the speed control curve includes: a first gradient segment: accelerating from a first initial speed to a first final speed with a first acceleration, and maintaining a first constant speed for a first duration; the first acceleration is 2.5 m / min. 2The first initial velocity is 0 m / min, the first final velocity is 0.4 m / min, and the first uniform velocity duration is 0.5 min; the second gradient segment: the first final velocity is increased to the second final velocity by a second acceleration, and the second uniform velocity duration is maintained; the second acceleration is 0.2 m / min. 2 The second endpoint velocity is 0.8 m / min, and the first uniform velocity duration is 1.5 min; the third gradient segment: the second endpoint velocity is increased to the third endpoint velocity with a third acceleration, and the third uniform velocity duration is maintained; the third acceleration is 0.1 m / min. 2 The third endpoint velocity is 1 m / min, and the third uniform velocity duration is 2 min; the fourth gradient segment: the third endpoint velocity is increased to the preset endpoint velocity with a fourth acceleration, and the fourth uniform velocity duration is maintained; the fourth acceleration is 0.1 m / min. 2 The preset endpoint speed is 1-1.5 m / min, and the fourth uniform speed duration is 2 min. By setting a multi-gradient acceleration and uniform speed alternation mode, the billet speed is gradually and smoothly increased from the initial state to the target speed, avoiding problems such as uneven billet shell growth and excessive fluctuations in the liquid level in the crystallizer caused by single acceleration or uniform speed billet drawing. The orderly transition of each gradient segment can effectively control the cooling rate and growth rate of the billet shell, reduce stress concentration inside the billet shell, and reduce the probability of defects such as internal cracks and surface scratches in the billet. At the same time, the setting of the uniform speed dwell time can allow the molten steel in the crystallizer to fully solidify, ensuring uniform billet shell thickness, further improving the billet quality, providing a guarantee for improving the subsequent steel plate flaw detection pass rate, and making the billet drawing process more controllable and stable.

[0030] Specifically, the first gradient stage uses high acceleration to rapidly increase the speed to 0.4 m / min, which quickly establishes a stable billet shell and avoids the risk of steel leakage caused by an excessively thin shell in the early stages of casting. Subsequent gradient stages use lower acceleration to gradually increase the speed, combined with a reasonable constant speed dwell time, which effectively alleviates stress accumulation during the billet shell growth process and avoids crack formation. This ensures the consistency of billet quality across different batches, further improves the stability of the steel plate flaw detection pass rate, and also takes production efficiency into account.

[0031] In this embodiment, before the billet pulling process, the superheat of the continuously cast molten steel is controlled at 15-25 ℃; the vacuum treatment includes: ultimate vacuum degree ≤ 67 Pa, holding time ≥ 15 min. By controlling the superheat of the cast molten steel, it is possible to ensure that the molten steel has good fluidity and avoid defects such as excessively rapid solidification, blockage of the nozzle, or cold shuts and porosity in the billet caused by excessively low superheat; and to avoid problems such as accelerated secondary oxidation of the molten steel, developed columnar crystals in the billet, and severe internal segregation caused by excessively high superheat, thus ensuring uniform solidification of the billet and improving the internal quality of the billet.

[0032] Specifically, by limiting the ultimate vacuum level and holding time of vacuum treatment, deep degassing and inclusion removal of molten steel can be achieved, which can more effectively reduce the hydrogen and nitrogen content in molten steel, and stably control the total oxygen content of molten steel at ≤0.001%, reducing gas defects and inclusion defects, and providing a more reliable guarantee for improving the pass rate of steel plate flaw detection; at the same time, sufficient vacuum holding time ensures that degassing and inclusion flotation reactions are sufficient, avoiding quality fluctuations caused by incomplete treatment.

[0033] In this embodiment, before transferring the second molten steel into the tundish, the method further includes: using a dry material in the tundish, baking the tundish at a temperature ≥1100℃, and then purging it with argon gas to remove residual oxygen; and in the step of adding a covering agent and quenching, argon gas is continuously injected into the tundish until the added covering agent completely covers the molten steel. This effectively removes moisture and residual impurities from the tundish, preventing moisture from introducing into the molten steel and increasing the hydrogen content, while also improving the temperature stability of the tundish and preventing a sudden drop in temperature after the molten steel enters the tundish, which could lead to decreased fluidity and inclusion precipitation; argon purging can thoroughly remove residual oxygen from the tundish, preventing secondary oxidation of the molten steel after it enters the tundish, and reducing the generation of oxidized inclusions from the source.

[0034] In this embodiment, the covering agent includes one or more of wollastonite and vermiculite; the amount of the covering agent added is 1.0 kg / ton of steel to 1.3 kg / ton of steel; before adding the covering agent, the covering agent is further subjected to a drying treatment; the drying treatment includes baking at a temperature of 100 ℃ to 150 ℃ for 6 min to 15 min in the first 0.5 h to 2 h before adding the covering agent.

[0035] Specifically, this type of covering agent possesses excellent heat insulation, oxygen barrier, and inclusion adsorption properties. It can effectively isolate air, reduce secondary oxidation of molten steel, and simultaneously adsorb residual inclusions in the molten steel, further improving the cleanliness of the steel. Controlling the dosage ensures that the covering agent completely covers the surface of the molten steel, achieving good oxygen barrier and heat insulation effects. It also avoids excessive dosage leading to the covering agent being drawn into the molten steel and forming inclusions, or insufficient dosage resulting in inadequate coverage and secondary oxidation of the molten steel. Drying the covering agent before addition effectively removes moisture, preventing water from entering the molten steel and increasing hydrogen content. It also improves the fluidity and spreadability of the covering agent, ensuring stable covering effects, further reducing the gas content of the molten steel, and minimizing defects such as porosity and white spots.

[0036] It should be noted that when the ladle capacity is 15 tons, ≥50 kg of wollastonite should be added to the stopper rod area; when the ladle capacity is 30 tons, ≥75 kg of wollastonite should be added to the impact area; and when the ladle is full, ≥25 kg of wollastonite should be added to both the stopper rod area and the impact area. Vermiculite should be added during the casting process, ensuring complete coverage of the molten steel surface. Wollastonite has the following composition: SiO2: 45%, CaO: 48%, fixed C: 0.5%, melting point 1355 ℃; vermiculite has the following composition: SiO2: 54%, CaO: 19%, Al2O3: 19%, fixed C: 0.5%, melting point 1325 ℃.

[0037] In this embodiment of the application, the calcium treatment includes: a wire feeding rate of 0.8 kg / t-1.0 kg / t, and calcium content in the molten steel controlled at 0.0006%-0.002%. By controlling the calcium content in the molten steel, it is possible to ensure that inclusions are fully modified, while avoiding secondary defects caused by excessive calcium, significantly improving the cleanliness of the molten steel and the internal quality of the steel plate, and further improving the pass rate of flaw detection.

[0038] In this embodiment, the viscosity of the continuous casting protective slag is preferably 0.11 Pa·s-0.12 Pa·s, the melting point is preferably 1200 ℃-1210 ℃, the dissolution rate is preferably 45 g / s-50 g / s, and the bulk density is preferably 0.60 g / cm³. 3 -0.62 g / cm 3 The continuous casting protective slag comprises, by mass percentage: SiO2: 26-27%, Al2O3: 3.8-4.2%, CaO: 38.5-39.5%, F: 10.5-11.5%, C: 5.1-6.1%, K2O+Na2O: 5.5-6.5%, with the balance being volatile matter and unavoidable impurities. The amount of protective slag added is 0.4 kg / ton to 0.5 kg / ton of steel. This ensures rapid melting of the protective slag to form a uniform slag film, providing excellent lubrication, heat preservation, oxygen isolation, and inclusion adsorption. It avoids the billet shell sticking to the crystallizer and causing scratches due to excessively high viscosity, or the slag film being too thin and resulting in poor protective effect due to excessively low viscosity.

[0039] In this embodiment of the application, the head-cutting process includes: cutting off the length of the billet before casting, which is 1-2 m; removing the defective area caused by unstable molten steel flow, concentrated inclusions, and poor billet quality in the early stage of casting, so as to prevent the defective part from entering the subsequent rolling process, improve the quality of steel plate from the source, and reduce the number of non-conforming points in the flaw detection.

[0040] In this embodiment, the rolling process includes at least two rolling passes; the casting thickness of the billet is 200 mm-360 mm, the rolling compression ratio is preferably ≥4.0, the thickness of the resulting steel plate is ≤ billet thickness / 4 mm, and the thickness of the resulting steel plate is preferably 50-90 mm. Multi-pass rolling gradually compacts the internal porosity of the billet, eliminates central segregation, and improves the internal density of the steel plate; a rolling compression ratio of ≥4.0 ensures that internal defects in the billet are fully compacted, significantly improving the mechanical properties and internal quality of the steel plate; by limiting the thickness of the billet and the steel plate, the rolling process is ensured to be stable, the steel plate thickness is uniform, further improving the flaw detection pass rate, and simultaneously meeting the quality requirements of thick plate production.

[0041] It should be noted that, in order to reduce secondary oxidation of molten steel, this application requires that before each heat is poured, the ladle operator and the tap operator confirm that the ladle level is 100-200 mm above the slag surface before pouring. When pouring from the ladle, the slide gate should be opened to about 1 / 2, and then slowly opened until the molten steel flows out; it is strictly forbidden to open it fully at once. After pouring from the ladle, to prevent slag entrapment in the tundish, the molten steel level should rise slowly and evenly, controlled at a rising rate of 0.03 t / s. The time from the lowest molten steel level in the tundish to the automatic opening of the ladle should be controlled within (300±30) s.

[0042] The technical solution of this application will be further described below with reference to specific embodiments, but the scope of protection of this application is not limited to the following embodiments.

[0043] Example This embodiment uses Q370R steel and a slab cross-section of 250 mm. Taking 2000 mm as an example, the production method of the provided steel plate specifically includes: S101: Smelted in a 150-ton converter, with a total charge of 165 tons of molten iron and scrap steel, and an iron-to-steel ratio of 880 kg / t, including 145.2 tons of molten iron and 19.8 tons of scrap steel. Silicon-manganese deoxidation and alloying treatment is employed. The alloy is baked at 450℃ before use to reduce hydrogen accumulation due to moisture. After tapping, the [H] content of the molten steel is 2.4 ppm. Silicon-manganese alloy deoxidation is used during tapping at a rate of 21.7 kg / t to reduce nitrogen accumulation. After tapping, the [N] content of the molten steel is 0.003% (30 ppm).

[0044] S102: Refining process, submerged arc control, to avoid nitrogen increase during electrode heating, control the formation of white slag in refining slag, and control the white slag, the white slag holding time is 12 min. The refining slag adopts high alkalinity control, the slag alkalinity is 6.5, and the output composition [S] is 0.002% (20 ppm).

[0045] S103: Perform RH vacuum treatment again, with a vacuum degree ≤67 Pa, vacuum holding time 16 min, soft argon blowing time 8-10 min, and control [H] <0.8×10 -4 %, [N] < 32 × 10 -4 %, [O] < 10 × 10 -4 %; calcium treatment was adopted, the wire feed rate was 0.9 kg / t, and the Ca content of the molten steel was 0.00012%.

[0046] S104: The tundish material uses a dry-material tundish, baked at 1130 ℃. Tundish superheat is controlled at 20 ℃. Argon is purged into the tundish for 3.5 minutes using an argon blowing tube; the tundish height is 820 mm. When the tundish tonnage is 15 tons, add 50 kg of wollastonite to the stopper rod area. The composition is: SiO2: 45%, CaO: 48%, fixed C 0.5%, melting point 1355 ℃. When the tundish tonnage is 30 tons, add 75 kg of wollastonite to the impact zone. When the tundish is full, add 15 kg of wollastonite to both the stopper rod area and the impact zone. During casting, vermiculite is added, with a composition of: SiO2: 54%, CaO: 19%, Al2O3: 19%, fixed C 0.5%, melting point 1325 ℃. The amount added should completely cover the molten steel surface. When the tundish steel volume reaches 30 tons, casting begins.

[0047] S105: When the liquid level in the crystallizer submerges the side hole of the nozzle, 0.45 kg / ton of continuous casting protective slag is introduced. The viscosity of the protective slag is 0.115 Pa·s, the melting point is 1206 ℃, the dissolution rate is 48 g / s, and the bulk density is 0.61 g / cm³. 3 The continuous casting protective slag comprises, by mass percentage: SiO2: 26-27%, Al2O3: 3.8-4.2%, CaO: 38.5-39.5%, F: 10.5-11.5%, C: 5.1-6.1%, K2O+Na2O: 5.5-6.5%, with the balance being volatile matter and unavoidable impurities. The protective slag should be added slowly and evenly. Pay attention to the melting of the protective slag around the crystallizer and the sprue, and use a bamboo stick to gently agitate the liquid surface to melt away any cold steel. Upon start-up, the casting machine will automatically increase its pulling speed, set at 1.2 m / min. The speed-up curve is shown in Table 1. Table 1 Acceleration Curve

[0048] To reduce secondary oxidation of molten steel, before each heat is poured, the ladle operator and the nozzle installer must confirm that the ladle level is 150 mm above the slag surface before pouring. When pouring from the ladle, the slide gate should be opened to about half its original position, and then slowly opened until the molten steel flows out; it is strictly forbidden to open it fully at once. After pouring from the ladle, to prevent slag entrapment in the tundish, the molten steel level must rise slowly and evenly, controlled at a rate of 0.03 tons per second. The time from the lowest molten steel level in the tundish to the full ladle before automatic pouring should be controlled within 5 minutes to obtain the cast billet. The cross-section of the continuously cast billet can be 250 mm. 2000 mm.

[0049] S106: The cut length shall be 1.5 m. Rolling requirements: the billet shall be in the heating furnace for ≥270 min, the furnace exit temperature shall be 1160 ℃-1200 ℃, the soaking time shall be ≥45 min, the rough rolling shall be carried out with low speed bite (bite speed ≤1.0 m / s) and large reduction mode (single pass reduction ≥30 mm), the final rolling temperature shall be 790 ℃-830 ℃, the final cooling temperature shall be 580 ℃-630 ℃, and the steel plate shall be obtained after slow cooling treatment after final rolling.

[0050] Following the steps described above, the process parameters in the production method are controlled as shown in Table 2, resulting in embodiments and comparative examples.

[0051] Table 2. Main production process parameters of each embodiment and comparative example of this application.

[0052] Meanwhile, to verify the overall performance of the steel plate generation method provided in the above embodiments, this application provides the following comparative examples for detailed explanation.

[0053] Comparative Example 1 This comparative example provides a method for preparing B1-steel plates with the same component ratio, preparation operation, and process parameters as Example 1. The difference is that in step S101 of this comparative example, the iron-to-steel ratio is 850 kg / t, with 140.2 t of molten iron and 24.8 t of scrap steel, to prepare B1-steel plates.

[0054] Comparative Example 2 This comparative example provides a method for preparing B2-steel plates with the same component ratio, preparation operation, and process parameters as Example 1. The difference is that in step S101 of this comparative example, the iron-to-steel ratio is 950 kg / t, with 156.7 t of molten iron and 8.3 t of scrap steel, to prepare B2-steel plates.

[0055] Comparative Example 3 This comparative example provides a method for preparing B3-steel plates with the same component ratios, preparation operations, and process parameters as Example 1. The difference is that in step S102 of this comparative example, the basicity of the refining slag is 6.0, and B3-steel plates are prepared.

[0056] Comparative Example 4 This comparative example provides a method for preparing B4-steel plates with the same component ratios, preparation operations, and process parameters as Example 1. The difference is that in step S102 of this comparative example, the basicity of the refining slag is 8.3, and B4-steel plates are prepared.

[0057] Comparative Example 5 This comparative example provides a method for preparing B5 steel plates with the same component ratio, preparation operation, and process parameters as Example 1. The difference is that in step S105 of this comparative example, the casting speed of the billet is directly set to a fixed value of 1.2 m / min, that is, the casting is carried out at the directly set speed, without using a gradient speed-up mode, and B5 steel plates are prepared.

[0058] Comparative Example 6 This comparative example provides a method for preparing B6 steel plates with the same component ratios, preparation operations, and process parameters as Example 1. The difference is that in step S106 of this comparative example, during the rolling process, the final rolling thickness is controlled to be 70 mm, that is, a 70 mm B6 steel plate is prepared.

[0059] In addition, the amount of scrap cut from the steel plates of each embodiment of this application was statistically analyzed. At the same time, other parts of the steel plates were flame-purified to observe cracks, and their flaw detection pass rate was measured. The results are listed in Table 3.

[0060] Table 3. Performance statistics of steel plates from the embodiments and comparative examples of this application.

[0061] Table 3 shows that all comparative sample groups exhibited problems such as cracks, a significant decrease in the flaw detection pass rate, an increase in the level of Class A inclusions, and a significant increase in the amount of scrap cut. Comparative Sample 1 used an iron-to-steel ratio of 850 kg / t. A low iron-to-steel ratio means that too much scrap steel was added, which easily introduces inclusions into the scrap steel, and the molten pool heats up slowly, resulting in an unstable smelting process and a decrease in the purity of the molten steel. At the same time, the oxides on the surface of the scrap steel increase the oxidizability of the molten steel, causing cracks and excessive inclusions.

[0062] Comparative Example 2 uses an iron-to-steel ratio of 950 kg / t, indicating that if the iron-to-steel ratio is too high, the proportion of molten iron will be too large, the content of harmful elements such as sulfur, phosphorus and hydrogen in the molten iron will increase, and it will be difficult to completely remove them in the refining process. At the same time, the molten pool is too oxidizing, which can easily form internal inclusions and intergranular cracks.

[0063] Comparative Example 3 used refining slag with a basicity of 6.0, which was too low. This resulted in a significant decrease in the refining slag's strong desulfurization and inclusion adsorption capabilities, making it impossible to effectively remove sulfide inclusions in the molten steel. This became a core cause of crack formation. Furthermore, the low basicity made it difficult to form stable reducing white slag, leading to insufficient deoxidation and high oxidizing properties in the molten steel. Comparative Example 4 used refining slag with a basicity of 8.3. Excessively high basicity in the refining slag caused an increase in the slag's melting point and decreased fluidity, preventing sufficient contact with the molten steel. This drastically reduced the efficiency of desulfurization, deoxidation, and inclusion adsorption. Moreover, the viscous slag easily became entangled in the molten steel, forming large inclusions, ultimately leading to a significant decrease in the flaw detection pass rate.

[0064] Comparative Example 5 directly adopted a fixed casting speed without gradient speed increase, which resulted in uneven cooling of molten steel in the crystallizer and inconsistent thickness of the billet shell growth. This easily led to internal cracks and surface cracks. At the same time, the molten steel flow was turbulent, which easily caused the inclusion of protective slag, resulting in the highest proportion of cracks and a significant increase in the amount of scrap.

[0065] In Comparative Example 6, directly increasing the rolling thickness to 70 mm without adjusting the rolling process leads to insufficient deformation of the billet, coarse grains, concentrated rolling stress, easy generation of rolling cracks, and thick plates have higher requirements for the purity of molten steel, and inclusions are more likely to accumulate inside the thick plates, resulting in a decrease in the pass rate of flaw detection.

[0066] In addition, this application compares the costs before and after the improvement: Before the improvement: From August 2024 to January 2025, the pass rate for flaw detection of steel plates was only 70%; After adopting the improvement of Example 1 of this application: from February to October 2025, a total of 3,200 tons of steel plates were inspected after the process improvement, averaging 400 tons per month, with an inspection pass rate of 95.5%; If the downgrade and reassessment loss due to non-compliance in flaw detection is calculated at a cost of 600 yuan / ton, then the expected benefit in 2026 is 400 × 12 × (95.5% - 70%) × 600 yuan / ton = 734,400 yuan.

[0067] Therefore, the steel plate production process adopted in this application can significantly improve the steel plate flaw detection pass rate, reduce the occurrence rate of surface cracks and inclusions, reduce the amount of scrap and downgrade losses, and has significant industrial application value and economic benefits.

[0068] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0069] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for producing steel plates, characterized in that, The production method includes: The molten iron is deoxidized and alloyed to obtain the first molten steel; the iron-to-steel ratio of the molten iron is 880 kg / t-920 kg / t. The first molten steel is refined to obtain a second molten steel and refining slag; the basicity of the refining slag is 6.3-8.0, and the residence time of the refining slag in the second molten steel is at least 10 min; The second molten steel is subjected to vacuum treatment, calcium wire feeding, and argon blowing in sequence to obtain a third molten steel, wherein the total oxygen content of the third molten steel is ≤0.001%; The third molten steel is transferred to an intermediate ladle, a covering agent is added, and the steel is killed to obtain a fourth molten steel, wherein the hydrogen content of the fourth molten steel is ≤0.9 ppm and the nitrogen content is ≤35 ppm. The fourth molten steel is distributed to the crystallizer for initial casting. After initial casting, continuous casting protective slag is added to the crystallizer and then the billet is pulled to obtain a billet. The pulling includes at least one alternating process of increasing speed pulling and constant speed pulling. The cast billet is then subjected to head-cutting and rolling processes to obtain a steel plate.

2. The production method according to claim 1, characterized in that, The accelerated and constant speed drawing processes are based on a speed control curve. The speed control curve includes: First gradient segment: Accelerate the first initial velocity to the first final velocity with the first acceleration and maintain the first uniform velocity for the first duration; Second gradient segment: Accelerate the first endpoint velocity to the second endpoint velocity with the second acceleration, and maintain the second constant velocity for the second duration; The third gradient segment: the third acceleration is used to accelerate the second terminal velocity to the third terminal velocity, and the third uniform velocity is maintained for the third duration; Fourth gradient segment: The third endpoint velocity is accelerated to the preset endpoint velocity with the fourth acceleration, and the fourth constant velocity is maintained for the fourth duration.

3. The production method according to claim 2, characterized in that, The first acceleration is 2.5 m / min 2 The first initial velocity is 0 m / min, the first final velocity is 0.4 m / min, and the first uniform velocity duration is 0.5 min; The second acceleration is 0.2 m / min 2 The second endpoint velocity is 0.8 m / min, and the first uniform velocity duration is 1.5 min; The third acceleration is 0.1 m / min 2 The third endpoint velocity is 1 m / min, and the third uniform velocity duration is 2 min; The fourth acceleration is 0.1 m / min. 2 The preset endpoint speed is 1 m / min-1.5 m / min, and the fourth uniform speed duration is 2 min.

4. The production method according to claim 1, characterized in that, Before the billet pulling process, the superheat of the continuously cast molten steel is controlled to be 15 ℃-25 ℃; and / or The vacuum treatment includes: ultimate vacuum degree ≤ 67 Pa, holding time ≥ 15 min.

5. The production method according to claim 1, characterized in that, The process includes the following steps before the second molten steel is transferred to the tundish: The intermediate batch uses dry material and is baked at a temperature ≥1100℃, and then purged with argon gas to remove residual oxygen in the intermediate batch. Furthermore, during the step of adding the covering agent and quenching, argon gas is continuously injected into the intermediate ladle until the added covering agent completely covers the molten steel.

6. The production method according to claim 5, characterized in that, The covering agent includes one or more of wollastonite and vermiculite; and / or The amount of the covering agent added is 1.0 kg / ton of steel to 1.3 kg / ton of steel; and / or The process also includes drying the covering agent before it is added; The drying process includes baking at 100 ℃-150 ℃ for 6 min-15 min in the 0.5 h-2 h before adding the covering agent.

7. The production method according to claim 1, characterized in that, The calcium treatment includes: feeding wire at a rate of 0.8 kg / t to 1.2 kg / t, and controlling the calcium content of the molten steel at 0.0006% to 0.002%.

8. The production method according to claim 1, characterized in that, The continuous casting protective slag has a viscosity of 0.11 Pa·s-0.12 Pa·s, a melting point of 1200 ℃-1210 ℃, a dissolution rate of 45 g / s-50 g / s, and a bulk density of 0.60 g / cm³. 3 -0.62 g / cm 3 ; The continuous casting protective slag comprises, by mass percentage: SiO2: 26-27%, Al2O3: 3.8-4.2%, CaO: 38.5-39.5%, F: 10.5-11.5%, C: 5.1-6.1%, K2O+Na2O: 5.5-6.5%, with the balance being volatile matter and unavoidable impurities; The amount of continuous casting protective slag added is 0.4 kg / ton of steel to 0.5 kg / ton of steel.

9. The production method according to claim 1, characterized in that, The head-cutting process includes: cutting off a length of 1 m-2 m from the front of the cast billet; and / or The rolling process includes at least two rolling passes; The casting thickness of the billet is 200 mm-360 mm, and the rolling compression ratio is ≥4.

0.

10. A steel plate manufactured by the production method according to any one of claims 1-9, characterized in that, The flaw detection pass rate of the steel plate is ≥95%.

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