Method for controlling nitrogen increase of molten steel of continuous casting tundish, preparation method of continuous casting billet and steel product

Abstract

The invention discloses a method for controlling nitrogen increase of continuous casting tundish molten steel, a preparation method of a continuous casting billet and a steel product. The method comprises the steps that molten steel in multiple batches of large ladles is introduced into a tundish through a long nozzle, and the depth of the long nozzle inserted into the tundish is 250-350 mm; molten steel in multiple batches of tundishes is introduced into a crystallizer and subjected to continuous casting and cooling, continuous casting billets are manufactured, in the process of changing different batches of tundishes, the lifting speed of the molten steel in the tundishes is 4-6 t / min, and t represents per ton of molten steel. By means of the method, it can be guaranteed that the mass fraction of nitrogen in the continuous casting billet meets the product design and quality requirements, and waste judgment losses caused by unqualified molten steel components are reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel plate smelting, and particularly relates to a method for controlling nitrogen increase of molten steel in a continuous casting tundish, a preparation method of a continuous casting billet and a steel product. BACKGROUND

[0002] In the process of steel smelting and continuous casting production, if the content of nitrogen in steel exceeds the standard, problems such as aging brittleness, cold brittleness, pitting and uneven structure of the steel will occur, thereby adversely affecting the mechanical properties, welding performance and service reliability of the steel. Therefore, the control of nitrogen increase of molten steel is a crucial process target in the whole process of steelmaking.

[0003] As an important link of the final shaping of molten steel, the continuous casting process is directly related to the cleanliness and product performance of the steel. However, in the process of continuous casting, the molten steel is prone to secondary oxidation and nitrogen increase. Therefore, it is urgent to propose a new method to effectively reduce the risk of nitrogen increase of the molten steel in the process of continuous casting and ensure the cleanliness of the molten steel and the quality of the product. SUMMARY

[0004] In view of this, the application provides a method for controlling nitrogen increase of molten steel in a continuous casting tundish, a preparation method of a continuous casting billet and a steel product, which can control the content of N in the continuous casting billet and ensure that the mass fraction of nitrogen in the continuous casting billet meets the requirements of product design and quality, thereby reducing the loss caused by unqualified molten steel composition.

[0005] In a first aspect, the embodiments of the application provide a method for controlling nitrogen increase of molten steel in a continuous casting tundish, comprising:

[0006] passing the molten steel in multiple batches of ladles into the tundish through a long nozzle, wherein the depth of the long nozzle inserted into the tundish is 250-350 mm;

[0007] passing the molten steel in multiple batches of tundishes into a crystallizer and performing continuous casting and cooling to obtain a continuous casting billet, wherein during the tundish replacement of different batches, the lifting speed of the molten steel in the tundish is 4-6 t / min, and t represents per ton of molten steel.

[0008] In some embodiments, during the tundish replacement of different batches, the time for replacing the tundish each time is 1-2 min.

[0009] In some embodiments, before passing the molten steel in multiple batches of ladles into the tundish through the long nozzle, the method comprises:

[0010] blowing argon to the long nozzle before the ladle is opened for pouring, the blowing time is ≥5 min, and the sealing flow rate of the blowing is 120-150 NL / min.

[0011] In some embodiments, the included angle of the long nozzle along the vertical direction is ≤3°.

[0012] In some embodiments, in the step of passing the molten steel in the multiple batches of tundish into the crystallizer and continuously casting and cooling to obtain the continuously cast slab, the casting speed is 1.1 m / min-1.2 m / min.

[0013] In some embodiments, the molten steel includes, in mass percentage: C: 0.0025%-0.0050%; Si: 0.15%-0.25%; Mn: 0.40%-0.50%; S≤0.015%; P≤0.020%; Als: 0.015%-0.04%; N≤0.0040%, and the balance of Fe and unavoidable impurities.

[0014] In some embodiments, the continuously cast slab includes, in mass percentage: C: 0.0025%-0.0050%; Si: 0.15%-0.25%; Mn: 0.40%-0.50%; S≤0.015%; P≤0.020%; Als: 0.015%-0.04%; N≤0.0040%, O≤0.003%; and the balance of Fe and unavoidable impurities.

[0015] In some embodiments, the molten steel in the multiple batches of tundish is passed into the crystallizer through the down nozzle, the opening of the down nozzle and the long nozzle is controlled, and the cross-sectional area of the continuously cast slab prepared by the crystallizer, the casting speed of the continuously cast slab, the density of the molten steel, and the flow rate of the molten steel are controlled, so that the lifting speed of the molten steel in the tundish is 4-6 t / min, and t represents per ton of molten steel.

[0016] In the second aspect, the embodiments of the present application provide a preparation method of a continuously cast slab.

[0017] In the third aspect, the embodiments of the present application provide a steel product, which is prepared from the continuously cast slab prepared by the method of the first aspect or the preparation method of the second aspect.

[0018] The present application has at least the following beneficial effects:

[0019] The method provided in the application is characterized in that, in the process of replacing the tundish in different batches, the molten steel in the tundish is first lowered, and then raised after the tundish of the next furnace is opened, and the rising and falling speeds are stably controlled at 4-6 t / min to maintain the stability of the molten steel liquid level in the tundish, so as to reduce the air suction caused by the too fast rising and falling speed and reduce the nitrogen increase caused by the air suction of the molten steel; the insertion depth of the long nozzle of the ladle is controlled at 250-350 mm, and the insertion depth of the long nozzle of the ladle is too deep, which affects the safe operation of the tundish, and the insertion depth of the long nozzle of the ladle is too shallow, which easily causes the liquid level in the impact zone of the tundish to be stirred, and also increases the contact between the molten steel and the air, thereby causing the molten steel to increase in nitrogen, and thus the method can guarantee that the nitrogen content of the continuous casting billet meets the product design and quality requirements, and reduces the loss caused by the unqualified molten steel composition. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings required to be used in the embodiments of the application will be briefly introduced as follows, and other drawings can also be obtained by those of ordinary skill in the art without creative labor on the basis of these drawings.

[0021] Figure 1 The structural schematic diagram of part of the structure in the molten steel continuous casting process of the embodiments of the application is shown.

[0022] Explanation of reference numerals: 10, ladle; 20, long nozzle; 30, tundish; 40, crystallizer; 50, continuous casting billet. DETAILED DESCRIPTION

[0023] In order to make the application purposes, technical solutions and beneficial technical effects of the application clearer, the application will be further described in detail in combination with the embodiments. It should be understood that the embodiments described in the specification are only for the purpose of explaining the application, and are not intended to limit the application.

[0024] For the sake of simplicity, only some numerical ranges are explicitly disclosed in the application. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, every point or single numerical value between the range endpoints is included in the range. Thus, every point or single numerical value can be combined as a lower limit or an upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0025] In the description of the application, it should be noted that, unless otherwise specified, "above", "below" include the number, and the meaning of "multiple" in "one or more" is two and more than two.

[0026] The foregoing summary of the application is not intended to describe every disclosed embodiment or implementation of the application. The following description more particularly exemplifies the illustrative embodiments. In various places throughout the application, guidance is provided through a series of examples, which can be used in various combinations. In each of the various examples, the representative groupings are exemplified, but should not be construed as exhaustive.

[0027] As the background, in the continuous casting process, the molten steel is prone to secondary oxidation and nitrogen increase. Through research, it is found that the molten steel can be as much as possible to avoid contact with air in the tundish and intermediate ladle transfer, long nozzle insertion, argon sealing and molten steel liquid level fluctuation, so as to avoid the rapid dissolution of nitrogen element into the molten steel. Especially during the tundish transfer, reduce the phenomenon of intermediate ladle liquid level fluctuation and molten steel boiling, reduce the absorption of nitrogen, so as to improve the quality of continuous casting billet.

[0028] However, these measures still have limitations in actual production. For example, the argon blowing time and argon flow rate control is unreasonable, it is often difficult to ensure the stability of molten steel flow while realizing effective nitrogen content control; when the angle matching of long nozzle and intermediate ladle is not good and the insertion depth control is not accurate, it will still cause the increase of molten steel and air contact area; when the molten steel liquid level changes too fast during the tundish transfer, it is also easy to cause the secondary nitrogen increase of molten steel. As a result, the nitrogen content of molten steel in the tundish is often difficult to be stably controlled in a reasonable range, which affects the quality and yield of the product.

[0029] Therefore, by optimizing the liquid level control of the tundish and the insertion depth of the long nozzle, the risk of nitrogen increase of the molten steel in the continuous casting process is effectively reduced, and the cleanliness of the molten steel and the product quality are ensured.

[0030] Figure 1 The structure diagram of part of the structure in the molten steel continuous casting process of the embodiment of the application is shown.

[0031] Please refer to Figure 1 , Figure 1 The molten steel in the tundish 10 passes through the long nozzle 20, the long nozzle 20 is inserted into the tundish 30, the transfer of the molten steel is realized, the molten steel in the tundish 30 passes through the downcomer, enters the crystallizer 40, and after the subsequent process, the continuous casting billet 50 is prepared.

[0032] The embodiment of the application provides a method for controlling the nitrogen increase of the molten steel in the continuous casting tundish, which comprises steps 100 and 200.

[0033] In step 100, the molten steel in the multiple batches of ladles is passed into the tundish through a long nozzle, wherein the long nozzle is inserted into the tundish at a depth of 250-350 mm; optionally, the long nozzle is inserted into the tundish at a depth of any value or a range composed of values selected from 250 mm, 280 mm, 300 mm, 320 mm and 350 mm. In this way, the depth of the steel flow impact and the temperature field distribution can be precisely controlled, and the cleanliness and homogenization production of high-speed continuous casting can be realized.

[0034] If the long nozzle of the ladle is inserted too deeply, the safe operation of the tundish is affected, and if the insertion depth is too shallow, the liquid level in the tundish impact area is easily stirred, which also increases the contact between the molten steel and air, resulting in serious nitrogen increase in the molten steel.

[0035] In step 200, the molten steel in the multiple batches of tundishes is passed into the mold and subjected to continuous casting and cooling to obtain a continuous casting billet, wherein during the tundish replacement process of different batches, the lifting and lowering speed of the molten steel in the tundish is 4-6 t / min, and t represents per ton of molten steel. Optionally, the lifting and lowering speed of the molten steel in the tundish can be any value or a range composed of values selected from 4.0 t / min, 4.5 t / min, 5.0 t / min, 5.5 t / min and 6.0 t / min.

[0036] According to the embodiments of the present application, in order to maintain the stability of the molten steel liquid level in the tundish, during the replacement of the tundish, in order to reduce the air suction during the rapid lifting and lowering process of the mold, the lifting and lowering speed is required to reduce the nitrogen increase caused by the air suction of the molten steel.

[0037] The process of lowering and then raising the tundish molten steel is a normal tundish replacement operation, but if the lifting and lowering speed is too slow, the continuous casting tundish tonnage will be too low, and there is a risk of slag rolling. If the lifting and lowering speed is too fast, there is also a certain risk of slag rolling, which must be controlled within a certain range.

[0038] In some embodiments, during the tundish replacement process of different batches, the time for replacing the tundish each time is 1-2 min; the time for replacing the tundish each time can be any value or a range composed of values selected from 1.0 min, 1.2 min, 1.5 min, 1.8 min and 2.0 min. In this way, the production continuity and operation safety can be balanced, and the operation rate and billet quality of efficient continuous casting can be improved.

[0039] In some embodiments, before the molten steel in the multiple batches of ladles is passed into the tundish through the long nozzle, the method comprises:

[0040] The long nozzle is subjected to argon blowing before ladle casting, the blowing time is ≥5 min, and the sealing flow rate of the blowing is 120-150 NL / min. Alternatively, the blowing time can be any value or range composed of 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min; and the sealing flow rate of the blowing can be any value or range composed of 120 NL / min, 130 NL / min, 140 NL / min, or 150 NL / min.

[0041] According to the embodiments of the present application, the argon blowing operation of the ladle adopts the above operation, the sealing measures of the ladle and the tundish are optimized, the nitrogen increase of the molten steel during the casting and continuous casting is reduced, the secondary oxidation of the molten steel is reduced, the nitrogen increase is controlled, and the purity of the molten steel and the energy consumption efficiency are cooperatively optimized.

[0042] For example, the air invasion can be reduced by long nozzle argon protection; and the argon blowing operation can be adjusted accordingly, for example, the bottom argon blowing stirring is used to improve the uniformity of the molten steel composition.

[0043] Compared with the prior art, the long nozzle is subjected to argon blowing before ladle casting, the blowing time is 3-4 min, and the argon sealing flow rate of the long nozzle of the ladle is 30-50 NL / min; the blowing time and the sealing flow rate of the blowing of the present application further ensure that the molten steel is in an argon environment during the ladle casting and casting of the continuous casting, and the nitrogen content in the casting blank is reduced.

[0044] If the continuous casting protection casting is not in place, the secondary oxidation of the molten steel in the tundish is serious, which not only causes serious N increase of the molten steel and further causes the whole-steel molten steel to be judged as waste or rejudged, affects the realization of product orders, but also affects the cleanliness of the continuous casting molten steel and has a negative impact on the castability of the continuous casting molten steel. Therefore, the N increase of the continuous casting tundish is controlled, the product loss due to judgment as waste is reduced, and the quality of the product is improved.

[0045] In addition, the oxygen content is further controlled, the cleanliness of the molten steel is improved, and the product quality is improved.

[0046] In some embodiments, the included angle of the long nozzle along the vertical direction is ≤3°; the included angle of the long nozzle along the vertical direction can be any value or range composed of 0.5°, 1.0°, 1.5°, 2.0°, 2.5°, or 3.0°.

[0047] According to the embodiments of the present application, the relative angle between the long nozzle and the tundish is accurately controlled during the whole argon blowing process and the tundish changing process, the sealing is not strict due to the inclination of the long nozzle, the long nozzle is in a negative pressure state and is easy to suck in air, the nitrogen content of the molten steel is increased, and the quality of the continuous casting blank is further ensured.

[0048] In some embodiments, the nitrogen increase in the continuous casting billet compared to the tundish is ≤5 ppm, optionally ≤3 ppm; optionally, the nitrogen increase can be any value or range composed of 0.0 ppm, 0.5 ppm, 1.0 ppm, 1.5 ppm, 2.0 ppm, 2.5 ppm, 3.0 ppm, 3.5 ppm, 4.0 ppm, 4.5 ppm, 5.0 ppm.

[0049] Thus, the ductility of the steel material can be strictly guaranteed, and the high toughness is maintained when the nitrogen increase is ≤2.0 ppm. For example, the impact energy is >100 J, and the denitrogenation process, for example, RH vacuum treatment, needs to be started when the nitrogen increase is ≥3.5 ppm. Thus, the formability and fatigue life of the continuous casting billet can be synergistically optimized, and the quality of the continuous casting billet is further ensured.

[0050] According to the embodiments of the present application, the method meets the requirements of product design and quality, the proportion of continuous casting with nitrogen increase ≤3 ppm, i.e., the compliance proportion is improved; and the proportion of waste caused by unqualified molten steel composition is reduced.

[0051] In some embodiments, in the step of passing the molten steel in the multiple batches of tundishes into the crystallizer and continuously casting and cooling to obtain the continuous casting billet, the casting speed is 1.1 m / min-1.2 m / min; optionally, the casting speed can be any value or range composed of 1.10 m / min, 1.11 m / min, 1.12 m / min, 1.13 m / min, 1.14 m / min, 1.15 m / min, 1.16 m / min, 1.17 m / min, 1.18 m / min, 1.19 m / min, 1.20 m / min. Thus, the solidification quality and production efficiency can be accurately balanced, and the efficient continuous production of high-purity steel billets is realized.

[0052] In some embodiments, the molten steel includes, in mass percentage: C: 0.0025%-0.0050%; Si: 0.15%-0.25%; Mn: 0.40%-0.50%; S≤0.015%; P≤0.020%; Als: 0.015%-0.04%; N≤0.0040%, and the balance is Fe and unavoidable impurities.

[0053] The molten steel in the ladle can be prepared by LF refining, optional RH smelting, etc. through molten iron, and the composition is relatively stable, for example, Si is 0.30-0.60%, P≤0.15%, and S≤0.045%. The molten iron can be pretreated, such as desulfurization and dephosphorization, which can reduce the burden of the converter, improve the efficiency and quality stability.

[0054] In some embodiments, the continuously cast slab comprises, in mass percent: C: 0.0025% to 0.0050%; Si: 0.15% to 0.25%; Mn: 0.40% to 0.50%; S≤0.015%; P≤0.020%; Als: 0.015% to 0.04%; N≤0.0040%, O≤0.003%; balance Fe and unavoidable impurities.

[0055] The continuously cast slab can be a continuously cast SPHC-B slab.

[0056] The continuously cast slab can be subsequently rolled, and the finish rolling temperature is generally in the range of 880 to 920°C. Subsequently, coiling can be performed, and the coiling temperature is controlled to be in the range of 580 to 620°C.

[0057] In some embodiments, the molten steel in the tundish of the multiple batches is passed into the crystallizer through the downspout, the opening of the downspout and the shroud is controlled, and the cross-sectional area of the continuously cast slab prepared by the crystallizer, the casting speed of the continuously cast slab, the density of the molten steel, and the flow rate of the molten steel are controlled, so that the lifting speed of the molten steel in the tundish is 4 to 6 t / min, and t represents per ton of molten steel.

[0058] For example, in order to make the lifting speed of the molten steel in the tundish 4 to 6 t / min, the casting speed can be first reduced slightly, and then the small slide valve of the downspout or the tundish is closed to an opening that can meet the above formula; the liquid level is stably lowered to the tundish changing window without being lower than the minimum safe liquid level of the tundish (with the steel ladle cover slag / wall exposed margin).

[0059] In addition, when the new ladle is started, the slide valve is given a suitable opening, such as an S-shaped curve opening, and at the same time the casting speed is maintained slightly lower than the steady state value, if the liquid level rises too fast, the casting speed is increased first, this operation responds quickly and is more friendly to nitrogen; secondly, the slide valve is slightly closed; if the rise is insufficient, first open the valve, and then reduce the casting speed to compensate for the insufficient.

[0060] When the tundish liquid level reaches the target working band median, it is smoothly converged to, and enters the liquid level constant control. Control the liquid level slope and powder feeding; prohibit drastic operation when changing the ladle; keep the shroud insertion depth and vertical angle within the process window. If the initial temperature of the new ladle is too low or the flow is insufficient, the casting speed is reduced first to maintain the liquid level; if the slide valve is stuck, the fixed emergency opening table and bypass scheme are enabled.

[0061] The embodiments of the present application can set a hard interlock in the ladle or tundish, realize low liquid level reducing casting speed / opening valve, high liquid level increasing casting speed / closing valve, and have a limit position emergency stop strategy, to control the upper and lower limits of the liquid level, that is, the lifting speed of the molten steel in the tundish is 4 to 6 t / min.

[0062] In a second aspect, the embodiments of the present application provide a method for preparing a continuously cast slab, comprising the method of the first aspect.

[0063] In a third aspect, the embodiments of the present application provide a steel product, which is made of the continuous casting billet prepared by the method of the first aspect or the continuous casting billet prepared by the preparation method of the second aspect.

[0064] Examples

[0065] The present application is described in more detail by the following examples, which are merely illustrative and not limiting. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used without further purification, and the instruments used in the examples are commercially available.

[0066] Example 1

[0067] The method for preparing a continuous casting billet of the present embodiment includes a method for controlling N increase of molten steel in a tundish during continuous casting, which includes the following operation steps:

[0068] The argon blowing time before starting casting in the tundish is 5.5 min, and the argon sealing flow rate of the long nozzle of the tundish is 130 NL / min.

[0069] The vertical angle between the long nozzle of the tundish and the tundish is 89°, wherein the molten steel in the tundish includes, in mass percentage, C: 0.0040%; Si: 0.20%; Mn: 0.45%; S: 0.012%; P: 0.012%; Als: 0.028%; N: 0.0032%, and the balance of Fe and unavoidable impurities.

[0070] The molten steel in the tundish is introduced into the tundish through the long nozzle, wherein the depth of the long nozzle inserted into the tundish is 300 mm.

[0071] The molten steel in the tundish is introduced into the mold and continuously cast and cooled to obtain a continuous casting billet, wherein the casting speed is 1.18 m / min; the time for replacing the tundish is 1.5 min; the ascending and descending speed of the molten steel in the tundish during the replacement of the tundish is 4.5 t / min, t representing per ton of molten steel; and the continuous casting billet includes, in mass percentage, C: 0.0040%; Si: 0.20%; Mn: 0.45%; S: 0.012%; P: 0.012%; Als: 0.028%; N: 0.0032%; O≤0.003%; and the balance of Fe and unavoidable impurities.

[0072] Examples 2-3

[0073] The difference between this example and Example 1 is that the depth of the shroud in the tundish is different, and is 250 mm and 350 mm in turn.

[0074] Examples 4-5

[0075] The difference between this example and Example 1 is that the ascending and descending speed of the molten steel in the tundish is different. The ascending and descending speed of the molten steel in the tundish is 4 t / min and 6 t / min in turn.

[0076] Examples 6-7

[0077] The difference between this example and Example 1 is that the angle of the shroud in the vertical direction is different, and the angle is 92° and 100°.

[0078] Comparative Examples 1-2

[0079] The difference between this comparative example and Example 1 is that the ascending and descending speed of the molten steel in the tundish is different during the tundish changing process of different batches. The ascending and descending speed of the molten steel in the tundish is 3.5 t / min and 6.8 t / min in turn.

[0080] Comparative Example 3

[0081] The difference between this comparative example and Example 1 is that the time for changing the tundish is 5 min.

[0082] Comparative Examples 4-5

[0083] The difference between this comparative example and Example 1 is that the depth of the shroud in the tundish is different, and is 240 mm and 400 mm in turn.

[0084] Test section

[0085] The target continuous casting billets prepared by the method of the examples and comparative examples are SPHC-B continuous casting billets. The chemical components in the continuous casting billets prepared by the examples and comparative examples are detected according to the method of GB / T 20066-2006.

[0086] The proportion of the continuous casting billets with nitrogen content ≤3 ppm = the quality of the continuous casting billets with nitrogen content ≤3 ppm in the quality of the total preparation of the continuous casting billets per batch.

[0087] The proportion of the continuous casting billets with unqualified components leading to rejection = (the quality of the continuous casting billets with nitrogen content in the continuous casting billets of SPHC-B per batch) / the quality of the total preparation of the continuous casting billets per batch.

[0088] Table 1: Test results of the continuous casting billets of the examples and comparative examples.

[0089]

[0090] The measured performance parameters above are averaged.

[0091] The proportion of rejection caused by unqualified composition of continuous casting billets, i.e. the proportion of nitrogen content > 40 ppm.

[0092] The method of the embodiment of the application effectively controls the N increase of the molten steel in the continuous casting tundish, reduces the quality loss, improves the qualified composition of the molten steel in the tundish, and reduces the proportion of rejection caused by unqualified composition of the molten steel.

[0093] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art or substitution should be covered within the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for controlling nitrogen addition in molten steel in a continuous casting tundish, characterized in that, include: Molten steel from multiple batches of ladles is introduced into the tundish through a long nozzle, wherein the long nozzle is inserted into the tundish to a depth of 250-350 mm. Molten steel from multiple batches of tundishes is fed into a crystallizer for continuous casting and cooling to produce continuously cast billets. During the process of changing tundishes between different batches, the molten steel rises and falls at a rate of 4 to 6 t / min, where t represents the volume of molten steel per ton.

2. The method according to claim 1, characterized in that, During the intermediate package replacement process between different batches, the time for each intermediate package replacement is 1 to 2 minutes.

3. The method according to claim 1, characterized in that, Before introducing molten steel from multiple batches of ladles into the tundish through a long nozzle, the method includes: Before pouring the large package, the long nozzle is purged with argon for ≥5 minutes, and the sealing flow rate of the argon purging is 120-150 NL / min.

4. The method according to claim 1, characterized in that, The included angle of the long water inlet along the vertical direction is ≤3°.

5. The method according to claim 1, characterized in that, In the step of passing molten steel from multiple batches of tundishes into a crystallizer for continuous casting and cooling to obtain a continuously cast billet, the casting speed is 1.1 m / min to 1.2 m / min.

6. The method according to claim 1, characterized in that, The molten steel comprises, by mass percentage: C: 0.0025%–0.0050%; Si: 0.15%–0.25%; Mn: 0.40%–0.50%; S≤0.015%; P≤0.020%; Als: 0.015%–0.04%; N≤0.0040%, with the balance being Fe and unavoidable impurities.

7. The method according to claim 1, characterized in that, The continuously cast billet comprises, by mass percentage: C: 0.0025%–0.0050%; Si: 0.15%–0.25%; Mn: 0.40%–0.50%; S≤0.015%; P≤0.020%; Als: 0.015%–0.04%; N≤0.0040%; O≤0.003%; with the balance being Fe and unavoidable impurities.

8. The method according to claim 1, characterized in that, Molten steel from multiple batches of tundishes is fed into the crystallizer through the drain outlet. The opening of the drain outlet and the long outlet is controlled, as are the cross-sectional area of ​​the continuously cast billet prepared in the crystallizer, the casting speed of the continuously cast billet, the density of the molten steel, and the flow rate of the molten steel, so that the lifting speed of the molten steel in the tundish is 4 to 6 t / min, where t represents the ton of molten steel.

9. A method for preparing a continuously cast billet, characterized in that, The method comprising any one of claims 1 to 8.

10. A steel product, characterized in that, The continuously cast billet obtained by the preparation method according to any one of claims 1 to 8 or the continuously cast billet obtained by the preparation method according to claim 9 is used to make steel products.

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