Deformed steel bar and preparation method thereof

Abstract

The invention provides a deformed steel bar and a preparation method thereof, and the preparation method comprises the following steps: carrying out refining treatment on waste steel and molten iron smelted by a converter to prepare refined molten steel; the refined molten steel is subjected to continuous casting treatment, and a casting blank is prepared; the casting blank is rolled, and the deformed steel bar is prepared; wherein in the continuous casting treatment process, when the continuous casting pulling speed is changed, the absolute value of the change difference of the pulling speed before and after any pulling speed change is smaller than or equal to 0.3 m / min, and the difference value of the maximum pulling speed and the minimum pulling speed is smaller than or equal to 0.4 m / min within any 3 min. The preparation method can reduce the probability of longitudinal cracks on the transverse ribs of the deformed steel bar and improve the quality of the deformed steel bar.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and particularly to a ribbed steel bar and a preparation method thereof. Background Art

[0002] Ribbed steel bars are a common type of construction steel. Their main characteristics are high strength, good durability, and convenient construction. Therefore, they are widely used in construction fields such as bridges, roads, and buildings. In the construction field, due to their high strength, ribbed steel bars can effectively improve the load-bearing capacity of buildings. At the same time, the good durability of ribbed steel bars can effectively ensure the long-term use of buildings. Moreover, ribbed steel bars have good processing performance and welding performance, which can facilitate processing and installation during construction. In addition, ribbed steel bars can also adopt the prestressed tensioning process, which can improve the crack resistance and load-bearing capacity of components, thereby further shortening the construction period.

[0003] In traditional technology, the production process of ribbed steel bars mainly includes refining, continuous casting process, and rolling process. In the continuous casting process, molten steel is poured into a mold through a tundish, and a slab is formed through cooling and solidification. Then, after cutting, cleaning, straightening, rolling, and cooling, ribbed steel bars of different specifications are finally formed. However, in the preparation of ribbed steel bars by traditional technology, especially in the preparation of larger-sized ribbed steel bars, longitudinal cracks often appear on the transverse ribs of the ribbed steel bars, seriously affecting the quality of the ribbed steel bars. In severe cases, they cannot meet the standards for use, increasing the production cost.

[0004] Therefore, traditional technology still needs to be improved. Summary of the Invention

[0005] Based on this, the present application provides a ribbed steel bar and a preparation method thereof. This preparation method can reduce the probability of longitudinal cracks appearing on the transverse ribs of the ribbed steel bar, thereby improving the quality of the ribbed steel bar.

[0006] The technical solution of the present application is as follows.

[0007] In the first aspect of the present application, a preparation method of a ribbed steel bar is provided, including the following steps:

[0008] Refine the scrap steel and the molten iron after converter smelting to make refined molten steel;

[0009] Perform continuous casting on the refined molten steel to prepare a slab;

[0010] Perform rolling on the slab to prepare a ribbed steel bar;

[0011] Wherein, during the continuous casting process, when changing the continuous casting drawing speed, in any one drawing speed change, the absolute value of the change difference between the drawing speeds before and after the change ≤ 0.3 m / min, and within any 3 minutes, the difference between the maximum drawing speed and the minimum drawing speed ≤ 0.4 m / min.

[0012] In the above preparation method, during the continuous casting process, by controlling the casting speed when changing the continuous casting speed, reducing the amplitude of the continuously changing casting speed, the purpose of keeping the casting speed as stable as possible is achieved, which can reduce the probability of longitudinal cracks appearing on the transverse ribs of the deformed steel bar and improve the quality of the deformed steel bar.

[0013] In some of the embodiments, before the step of refining treatment, the following steps are included:

[0014] The scrap steel is subjected to high-fire baking treatment for 8 min to 15 min.

[0015] In some of the embodiments, the continuous casting treatment is carried out under the action of a tundish, and the preparation of the tundish includes the following steps:

[0016] The newly built tundish is successively placed for natural environment drying, low-fire baking treatment and high-fire baking treatment.

[0017] In some of the embodiments, the time for natural environment drying is ≥ 36 h, the time for low-fire baking treatment is ≥ 2 h, and the time for high-fire baking treatment is ≥ 1 h.

[0018] In some of the embodiments, in the high-fire baking treatment, the volume content of gas is 20% - 30%, and the volume content of air is 70% - 80%; and / or

[0019] In the low-fire baking treatment, the volume content of gas is 0.1% - 10%, and the volume content of oxygen-containing gas is 90% - 99.9%.

[0020] In some of the embodiments, the process of refining the scrap steel and the molten iron after converter smelting includes the following steps:

[0021] The molten iron after converter smelting is placed in a refining furnace, then temperature-raising treatment is carried out, and during the temperature-raising treatment, refining lime is added, and then the scrap steel is added for the refining treatment.

[0022] In some of the embodiments, the target temperature of the temperature-raising treatment is 1600 °C - 1610 °C.

[0023] In some of the embodiments, based on the total mass of the scrap steel and the molten iron, the addition amount of the refining lime is 2 kg / t - 6 kg / t.

[0024] In some of the embodiments, the specification of the deformed steel bar is φ > 25 mm.

[0025] In the second aspect of the present application, a deformed steel bar is provided, which is obtained by using the preparation method of the deformed steel bar in the first aspect.

[0026] The longitudinal ribs of this deformed steel bar have few longitudinal cracks and excellent and stable quality. Description of the Drawings

[0027] Figure 1 It is a physical diagram of the deformed steel bar obtained in Example 1;

[0028] Figure 2 It is a physical diagram of the deformed steel bar obtained in Comparative Example 1. Detailed Implementation Modes

[0029] To facilitate the understanding of this application, the following will give a more comprehensive description of this application and provide preferred embodiments of this application. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of this application more thorough and comprehensive.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application in this specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0031] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means two or more unless otherwise specifically defined.

[0032] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values. Any end value can be independently included or excluded, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are understood to be contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are also listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to listing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when stating that a certain parameter is an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0033] In this application, "optionally", "optional", "option" mean that it can be either present or absent, that is, it refers to any one of the two alternative options of "present" or "absent". If "optional" appears multiple times in a technical solution, unless otherwise specified and there are no contradictions or mutual restrictions, each "optional" is independent.

[0034] Referring to "embodiment" in this context means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment of this application. The occurrence of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0035] Research findings show that in the production process of ribbed steel bars, the casting speed in continuous casting has an obvious impact on longitudinal cracks. In the traditional technology, the casting speed is continuously adjusted within 1 minute, and the change amplitude reaches 0.7 m / min. There are obvious surface cracks in the transverse ribs of the ribbed steel bars after rolling because the continuous adjustment of the casting speed results in uneven thickness when the billet shell is formed, which is prone to generating thermal stress and causing cracks in the billet. After a large number of tests and verifications, the method of this application for reducing surface transverse rib cracks in large-sized ribbed steel bars is obtained.

[0036] An embodiment of the present application provides a method for preparing ribbed steel, including the following steps S10 to S30.

[0037] S10: Refine scrap steel and molten iron after converter smelting to make refined molten steel.

[0038] S20: Carry out continuous casting on the refined molten steel to prepare a continuous casting billet; wherein, during the continuous casting process, when changing the continuous casting drawing speed, make the absolute value of the change difference between the drawing speeds before and after any change in the drawing speed ≤ 0.3 m / min, and within any 3 minutes, the difference between the maximum drawing speed and the minimum drawing speed ≤ 0.4 m / min.

[0039] S30: Roll the continuous casting billet to prepare ribbed steel.

[0040] In the above preparation method, during the continuous casting process, by controlling the drawing speed when changing the continuous casting drawing speed, reducing the amplitude of the continuously changing drawing speed, achieving the purpose of keeping the drawing speed as stable as possible, it can reduce the probability of longitudinal cracks appearing on the transverse ribs of the ribbed steel and improve the quality of the ribbed steel.

[0041] It can be understood that the "absolute value of the change difference between the drawing speeds before and after any change in the drawing speed" refers to the absolute value of the difference between the drawing speed before the change and the drawing speed after the change in the dimension of time progression when changing the drawing speed. In the dimension of time, among the two drawing speeds that change before and after, the drawing speed that occurs first can be greater than or less than the drawing speed that occurs later, and there is no special requirement; further, there is no special requirement for the frequency of changing the drawing speed, as long as it can adapt to the rhythm of continuous production and ensure the smooth progress of continuous casting; the method for controlling the change of the drawing speed can adopt various known methods in the art that can affect the drawing speed. For example, continuous casting machines all have devices for automatically controlling the height of the molten steel surface in the tundish, which can automatically control the opening degree of the sliding nozzle of the ladle and control the drawing speed by controlling the amount of molten steel in the tundish.

[0042] It can be understood that "within any 3 minutes" refers to within any continuously proceeding 3 minutes.

[0043] In some embodiments, 0 ≤ the absolute value of the change difference between the drawing speeds before and after ≤ 0.3 m / min; optionally, 0 < the absolute value of the change difference between the drawing speeds before and after ≤ 0.3 m / min; specifically, it can be 0.3 m / min, 0.2 m / min, 0.1 m / min, 0.05 m / min.

[0044] In some embodiments, 0 ≤ the difference between the maximum drawing speed and the minimum drawing speed ≤ 0.4 m / min; optionally, 0 < the difference between the maximum drawing speed and the minimum drawing speed ≤ 0.4 m / min; specifically, it can be 0.4 m / min, 0.3 m / min, 0.2 m / min, 0.1 m / min, 0.05 m / min.

[0045] In some of these embodiments, during the continuous casting process, the drawing speed is 2.5 m / min to 3.2 m / min; optionally 2.8 m / min to 3 m / min.

[0046] In some of these embodiments, before the refining treatment step, the following steps are included:

[0047] The scrap steel is subjected to a high-fire baking treatment for 8 min to 15 min.

[0048] In some of these embodiments, the continuous casting treatment is carried out under the action of a tundish. The preparation of the tundish includes the following steps:

[0049] The newly lined tundish is successively placed for natural environment drying, low-fire baking treatment, and high-fire baking treatment.

[0050] It can be understood that in order to transport the refined molten steel from the ladle to the mold of the continuous caster, an intermediate container called a tundish is used between the ladle and the mold. There is one or several nozzles at the bottom of the tundish, and a slide plate or a stopper rod for controlling the steel flow rate is installed. The tundish is a rectangular container with a large top and a small bottom, lined with refractory materials. There is also a cover lined with refractory materials at its top. The common tundish materials in the art can be used, and there are no specific requirements for the materials.

[0051] In actual production research, it is found that: since ribbed steel generally contains nitrogen (nitrogen is contained in hot metal or scrap steel), if the scrap steel or the tundish is not baked well, the water in the scrap steel and the tundish will split into hydrogen and enter the molten steel. H in the molten steel is easy to gather in nitrogen bubbles, generating huge stress. During the rolling process, the rolling force and the bubble stress interact with each other, and finally the transverse ribs crack. Therefore, the high-fire baking treatment makes the surface of the scrap steel reach a red-hot state to remove impurities such as moisture and oil stains on the surface of the scrap steel, avoid adverse effects such as gas generation during the smelting process, and further reduce longitudinal cracks; and / or perform specific drying treatment on the tundish to reduce stress and reduce longitudinal cracks.

[0052] In some of these embodiments, the refined molten steel contains nitrogen element.

[0053] In some of these embodiments, during the high-fire baking treatment, the volume content of gas is 20% - 30%, and the volume content of air is 70% - 80%.

[0054] In some of these embodiments, during the low-fire baking treatment, the volume content of gas is 0.1% - 10%, and the volume content of oxygen-containing gas is 90% - 99.9%.

[0055] Further, the oxygen-containing gas is a mixture of air and oxygen, and the volume content ratio of oxygen to air is (10 - 30):(60 - 80).

[0056] In some of these embodiments, the drying time in the natural environment is ≥ 36 h, the time for baking with a small fire is ≥ 2 h, and the time for baking with a large fire is ≥ 1 h.

[0057] It should be noted that the natural environment refers to an environment without deliberately heating with external technology, with a temperature of 10°C to 35°C and a humidity of 20% to 60%.

[0058] Optionally, the drying time in the natural environment is 36 h to 48 h, the time for baking with a small fire is 2 h to 5 h, and the time for baking with a large fire is 1 h to 3 h.

[0059] In some of these embodiments, the process of refining the scrap steel and the molten iron after converter smelting includes the following steps:

[0060] Place the molten iron after converter smelting in a refining furnace, then perform a temperature-raising treatment, and add refining lime during the temperature-raising treatment, and then add scrap steel for refining treatment.

[0061] In some of these embodiments, the target temperature for the temperature-raising treatment is 1600°C to 1610°C.

[0062] In some of these embodiments, during the process of adding scrap steel, argon is blown from the bottom of the refining furnace, with a flow rate of 1500 L / min to 2500 L / min.

[0063] In some of these embodiments, based on the total mass of the scrap steel and the molten iron, the addition amount of refining lime is 2 kg / t - 6 kg / t.

[0064] In some of these embodiments, the temperature for the refining treatment is 1550°C to 1600°C.

[0065] In some of these embodiments, the rolling process includes: placing the continuous casting billet in a heating furnace, heating for 100 min, with the tapping temperature being 1020°C - 1060°C, and then sending it to a cooling bed for rolling, with the temperature being 900°C - 940°C.

[0066] In some of these embodiments, the rolling process includes multiple passes until the target model is obtained, which can be 15 to 20 passes.

[0067] In some of these embodiments, before the rolling process, it may also include processes such as cutting or grinding the continuous casting billet.

[0068] The processes of cutting or grinding can adopt the commonly used processes in the art and are not particularly limited.

[0069] In some of these embodiments, the scrap steel can be selected from at least one of briquetted scrap steel, loose scrap steel, and rebar pellets.

[0070] Another embodiment of the present application provides a deformed steel bar, which is prepared by the preparation method of the deformed steel bar described above.

[0071] The longitudinal cracks of the deformed steel bar prepared by the above method are few, and the quality is excellent and stable.

[0072] The present application will be described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. It should be understood that the appended claims define the scope of the present application. Under the guidance of the concept of the present application, those skilled in the art should realize that certain changes made to the embodiments of the present application will be covered by the spirit and scope of the claims of the present application.

[0073] The following are specific embodiments.

[0074] Example 1

[0075] (1) Put the selected scrap steel into the scrap steel tank, bake it with a large fire (the volume content of gas is 30%, and the volume content of air is 70%) for 10 minutes until the surface of the scrap steel reaches a red-hot state, and set it aside; prepare 85t of molten steel from the converter for use.

[0076] (2) Check the operating status of the refining furnace equipment to ensure that components such as electrodes and furnace linings are normal and have good electrical conductivity and high-temperature resistance. Then, use a crane to lift 85t of molten steel from the converter into the refining furnace for heating treatment. Based on the total mass of the molten steel, 4.6 kg / t of refining lime is added during the heating process until it reaches 1601°C. Move the ladle car under the scrap steel preheating tank and add 15t of red-hot scrap steel. During the addition process, the bottom blowing argon flow rate is 2000 L / min. After the scrap steel is added, move the ladle car to the steel water treatment position and send electricity to heat up to melt the scrap steel. After the temperature reaches 1540°C, take a sample and adjust the composition according to the decomposition result of the sample. After the molten steel composition is qualified, it leaves the station.

[0077] (3) The qualified molten steel after refining enters the tundish. The preparation of the tundish includes the following operations:

[0078] Naturally dry the newly built tundish for 36h, bake it with a small fire (the volume content of gas is 70%, and the volume content of air is 30%) for 2h, and bake it with a large fire (the volume content of gas is 30%, and the volume content of air is 70%) for 1.2h.

[0079] The molten steel temperature in the tundish is maintained at 1535 °C. A long nozzle is used for sealed protection from the ladle to the tundish, and an immersion nozzle is used for sealed protection from the tundish to the mold to ensure good sealing and prevent secondary oxidation of the molten steel. The tundish is lifted to the casting position to prepare for pouring. The sliding nozzle at the bottom of the ladle is opened. During normal steel drawing, the tundish liquid level is controlled above 600 mm. The initial drawing speed is controlled at 2.8 m / min and then remains stable. During continuous casting, the absolute value of the difference in drawing speed before and after a single adjustment is 0.1 m / min, and within 3 minutes, the difference between the maximum and minimum drawing speeds is 0.2 m / min. The final drawing speed is 3.0 m / min. After continuous casting is completed, a billet of 165 mm × 165 mm × 12000 mm is obtained through cutting equipment.

[0080] (3) Feed the casting rod into the heating furnace and heat it for 100 min. The furnace outlet temperature is 1020 °C - 1060 °C. Then transfer it to the cooling bed for rolling at a temperature of 900 °C - 940 °C. After 17 rolling passes, it becomes deformed steel bars of φ32.

[0081] (4) Inspect the surfaces of the deformed steel bars produced in the same batch. The results show that there are no transverse rib crack defects on the surfaces of the produced deformed steel bars of φ32 specification. The physical diagram is as Figure 1 shown.

[0082] Example 2

[0083] Example 2 is basically the same as Example 1, except that: during the continuous casting process in step (2), the initial drawing speed is controlled at 3.0 m / min and then remains stable. The drawing speed is adjusted twice during the continuous casting process. The absolute values of the differences in drawing speed before and after a single adjustment are 0.1 m / min and 0.3 m / min respectively, and within any 3 minutes, the difference between the maximum and minimum drawing speeds is 0.4 m / min. The final drawing speed is 3.4 m / min.

[0084] Other steps and conditions are the same as those in Example 1.

[0085] The test results show that there are no transverse rib crack defects on the surfaces of the produced deformed steel bars of φ32 specification.

[0086] Comparative Example 1

[0087] Comparative Example 1 is basically the same as Example 1, except that: during the continuous casting process in step (2), within 3 minutes, the difference between the maximum and minimum drawing speeds is 0.7 m / min, and the final drawing speed is 3.4 m / min.

[0088] Other steps and conditions are the same as those in Example 1.

[0089] The test results show that among the produced deformed steel bars of φ32 specification, most of the products have obvious transverse rib crack defects. The physical diagram is asFigure 2 as shown

[0090] The test results of the above examples and comparative examples show that the preparation method of the present application can reduce the probability of longitudinal cracks appearing on the transverse ribs of ribbed steel, thereby improving the quality of ribbed steel.

[0091] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0092] The above embodiments only represent several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of this patent shall be subject to the appended claims.

Claims

1. A method for preparing threaded steel, characterized in that: The steps include: Refining scrap steel and molten iron from converter smelting to produce refined molten steel; The refined molten steel is continuously cast to prepare a casting billet; The ingot is rolled to prepare threaded steel; Wherein, during the continuous casting process, when the continuous casting pulling speed is changed, the absolute value of the difference in pulling speed before and after any pulling speed change is ≤0.3m / min, and the difference between the maximum pulling speed and the minimum pulling speed within any 3 minutes is ≤0.4m / min.

2. The method for preparing threaded steel according to claim 1, characterized in that: Before the refining step, the following steps are included: The scrap steel is subjected to high-fire baking treatment for 8 minutes to 15 minutes.

3. The method for preparing threaded steel according to claim 1, characterized in that: The continuous casting process is carried out under the action of a tundish, and the preparation of the tundish includes the following steps: The newly built tundish is placed in natural environment drying, low-fire baking and high-fire baking in sequence.

4. The method for preparing threaded steel according to claim 3, characterized in that: The natural environment drying time is ≥36 hours, the low-fire baking time is ≥2 hours, and the high-fire baking time is ≥1 hour.

5. The method for preparing threaded steel according to any one of claims 3 to 4, characterized in that: In the high-fire baking process, the volume content of coal gas is 20%-30%, and the volume content of air is 70%-80%; and / or In the low-fire baking process, the volume content of the coal gas is 0.1%-10%, and the volume content of the oxygen-containing gas is 90%-99.9%.

6. The method for preparing threaded steel according to any one of claims 1 to 2, characterized in that: The process of refining the scrap steel and the molten iron after converter smelting comprises the following steps: The molten iron after the converter smelting is placed in a refining furnace, and then subjected to a temperature increase treatment. During the temperature increase treatment, refining lime is added, and then the scrap steel is added for the refining treatment.

7. The method for preparing threaded steel according to claim 6, characterized in that: The target temperature of the temperature increase treatment is 1600°C to 1610°C.

8. The method for preparing threaded steel according to claim 6, characterized in that: Based on the total mass of the scrap steel and the molten iron, the addition amount of the refined lime is 2kg / t to 6kg / t.

9. The method for preparing threaded steel according to any one of claims 1 to 2, characterized in that: The specification of the threaded steel is φ>25mm.

10. A threaded steel bar, characterized in that: The threaded steel is prepared by the method for preparing threaded steel as described in any one of claims 1 to 9.

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