Production process of 200mm*200mm section continuous casting billet of high-strength hard wire steel

Abstract

The invention provides a production process of a high-strength hard wire steel continuous casting billet, which comprises the following steps of: pouring refined molten steel in a steel ladle into a tundish for replacing the tundish, pouring the molten steel into a crystallizer of a continuous casting machine from the tundish, and cooling the molten steel through a secondary cooling area and an air cooling area under the pulling speed of the continuous casting machine to obtain a continuous casting square billet with the section size of 200mm * 200mm; the pulling speed of the continuous casting machine ranges from 1.37 m / min to 1.43 m / min; the secondary cooling area is cooled in a weak cooling mode. Continuous production of the 200 mm * 200 mm continuous casting billet of the high-strength hard wire steel is achieved, the high-quality continuous casting billet is formed through innovative and scientific regulation and control of the continuous casting equipment technology, the casting billet is low in power and free of obvious defects, the center segregation ratio is lower than 1.10, the proportion of the center grain boundary cementite grade smaller than or equal to 2.0 is larger than or equal to 93%, and the wire rod drawing and breaking frequency is controlled to be 1.2 times per hundred tons or below.

Description

Technical Field

[0001] The invention belongs to the technical field of high-carbon hard wire steel continuous casting billets, and relates to a production process and application of high-strength hard wire steel continuous casting billets, and in particular to a production process of high-strength hard wire steel 200mm×200mm cross-section continuous casting billets. Background Art

[0002] High carbon hard wire steel is the main variety used to prepare high-strength cold-drawn steel wire. It is widely used in infrastructure construction and has important value for social development. For example, SWRH82B high carbon wire rod steel is the main raw material for the production of metal products such as prestressed steel wire, prestressed steel strand, high-strength steel wire and steel rope. Among them, the prestressed steel strand prepared with SWRH82B wire rod as raw material has been promoted and applied in my country's construction industry, and its development trend has continued to expand in recent years. In addition, the product is also widely used in marine engineering, energy engineering and water conservancy engineering. The product exhibits the characteristics of high strength, corrosion resistance, low relaxation and high toughness. Because its added value is greater than that of similar wire products, it is welcomed by the market industry.

[0003] With the rapid development of the economy and society, the requirements for the mechanical properties of high-carbon hard wire products are constantly increasing. For example, the tensile strength of ordinary high-carbon hard wire SWRH82B is generally 1150-1180MPa, while the tensile strength of high-strength hard wire reaches 1300MPa. At present, increasing the alloy content in steel is still one of the important technical means to improve the mechanical properties of steel. In high-strength hard wire steel, the carbon content is 0.06%-0.07% higher than that of ordinary hard wire SWRH82B, that is, from 0.78%-0.82% to 0.85%-0.88%. However, when the carbon content in the molten steel increases, the physical and chemical properties of the steel change, so the solid-liquid phase temperature range increases, and the tendency of central segregation is aggravated, which is a key. This change brings huge process challenges to the high-quality production of high-strength hard wire. Although some scholars have also carried out a series of studies on SWRH82B steel, they are mainly focused on product quality defect analysis and related control process technology research. For example, a high carbon wire rod steel production process disclosed in patent CN201710914175, a method for producing SWRH82B wire rod disclosed in CN109207837, a low nitrogen SWRH82B steel smelting method disclosed in CN103667581, an inclusion control method for producing SWRH82B steel using a carbon-free ladle disclosed in CN108998626, and a dynamic soft reduction process for continuous casting of prestressed steel SWRH82B large square billets disclosed in CN10164821. However, the above-mentioned processes for the preparation of SWRH82B do not involve the improvement of the production process of continuous casting billets.

[0004] Therefore, how to find a more suitable way to solve the above-mentioned technical problems existing in the existing process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a production process and application of high-strength hard wire steel continuous casting billets, in particular, a production process of high-strength hard wire steel 200mm×200mm cross-section continuous casting billets. The production process provided by the present invention can achieve low-multiple high-strength hard wire steel casting billets with a cross-section of 200mm×200mm without obvious defects, a central segregation ratio of less than 1.10, a ratio of cementite rating ≤2.0 at the center grain boundary of the wire rod ≥93%, and the number of wire rod breakages during drawing is controlled below 1.2 times / hundred tons; and the process flow is simple, controllable, and stable, which is more suitable for industrial promotion and application.

[0006] The present invention provides a production process of high-strength hard wire steel continuous casting billet, comprising the following steps:

[0007] The molten steel in the ladle is poured into the tundish for ladle replacement, and then poured from the tundish into the crystallizer of the continuous casting machine. Under the pulling speed of the continuous casting machine, after cooling in the secondary cooling zone and the air cooling zone, a continuous casting square billet with a cross-sectional size of 200mm×200mm is obtained;

[0008] The casting speed of the continuous casting machine is 1.37-1.43 m / min;

[0009] The secondary cooling zone is cooled by a weak cooling method.

[0010] Preferably, the molten steel is obtained by sequentially subjecting semi-steel to converter semi-steel smelting, LF refining and RH vacuum treatment.

[0011] Preferably, the high-strength hard wire steel comprises SWRH82B steel having a C mass content of 0.85% to 0.88%.

[0012] Preferably, the casting superheat degree of the molten steel in the tundish is 30-35°C.

[0013] Preferably, the crystallizer is an electromagnetically stirred crystallizer.

[0014] Preferably, the central magnetic field strength of the electromagnetic stirring is 475×10 -4 ~495×10 -4 T;

[0015] The stirring current frequency of the electromagnetic stirring is 2-3 Hz.

[0016] Preferably, the secondary cooling water volume of the secondary cooling zone is 0.51 to 0.55 L / kg 钢 .

[0017] Preferably, the final stirring in the air cooling zone is arranged at 20% to 30% of the length of the liquid core of the casting.

[0018] Preferably, the central magnetic field strength of the unstirred magnetic field is 245×10 -4 ~275×10 -4 T;

[0019] The stirring current frequency of the final stirring is 7 to 8 Hz.

[0020] The present invention provides the use of a high-strength hard wire steel continuous casting billet produced by the production process described in any one of the above technical solutions in the preparation of wire rod steel.

[0021] The present invention provides a production process for high-strength hard wire steel continuous casting billet, comprising the following steps: pouring the molten steel in the ladle into the tundish for ladle replacement, and then pouring the molten steel from the tundish into the crystallizer of the continuous casting machine, and obtaining a continuous casting square billet with a cross-sectional size of 200mm×200mm after cooling in the secondary cooling zone and the air cooling zone under the pulling speed of the continuous casting machine; the pulling speed of the continuous casting machine is 1.37-1.43m / min; and the secondary cooling zone is cooled by weak cooling. Compared with the prior art, the present invention believes that for high-strength hard wire steel, in order to achieve the control of the wire rod structure of high-strength hard wire steel and the ordinary wire rod structure (central grain boundary cementite) at the same level, the C segregation degree of the center of the casting billet should be reduced by more than 50%, that is, from 1.20 of ordinary hard wire to less than 1.10.

[0022] Based on this, the present invention specially designs a production process of 200mm×200mm continuous casting billet of high-strength hard wire steel with specific control parameters. By controlling the parameters of molten steel discharged from the converter, LF refining and RH vacuum treatment parameters, combined with specific casting control, especially the control process and parameters of the crystallizer and cooling, high-quality 200mm×200mm continuous casting billet is prepared, which further reflects the high efficiency of continuous casting and the advantages of regulating organizational properties.

[0023] The present invention realizes the continuous production of 200mm×200mm continuous casting billets of high-strength hard wire steel, and forms high-quality continuous casting billets through innovative and scientific regulation of continuous casting equipment and process, laying an important billet quality foundation for the drawing production of wire rod rolling and steel strands and other products. At the same time, the process flow is simple, controllable, and stable, which is more suitable for industrial promotion and application.

[0024] Experimental results show that the preparation method provided by the present invention can successfully achieve continuous production of 200mm×200mm continuous casting billets of high-strength hard wire steel, the high-strength hard wire steel billets have no obvious defects at low magnification, the central segregation ratio is lower than 1.10, the proportion of cementite rating ≤2.0 at the central grain boundary of the wire rod is ≥93%, and the number of wire breakages during wire rod drawing is controlled below 1.2 times / 100 tons. DETAILED DESCRIPTION

[0025] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the patent claims of the present invention.

[0026] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0027] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial purity or conventional purity in the field of low-phosphorus steel smelting.

[0028] The brands and abbreviations of all raw materials of the present invention are conventional brands and abbreviations in the art. Each brand and abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the brands, abbreviations and corresponding uses.

[0029] The present invention provides a production process of high-strength hard wire steel continuous casting billet, comprising the following steps:

[0030] The molten steel in the ladle is poured into the tundish for ladle replacement, and then poured from the tundish into the crystallizer of the continuous casting machine. Under the pulling speed of the continuous casting machine, after cooling in the secondary cooling zone and the air cooling zone, a continuous casting square billet with a cross-sectional size of 200mm×200mm is obtained;

[0031] The casting speed of the continuous casting machine is 1.37-1.43 m / min;

[0032] The secondary cooling zone is cooled by a weak cooling method.

[0033] In the present invention, the casting speed of the continuous casting machine is 1.37-1.43 m / min, can be 1.38-1.42 m / min, can be 1.39-1.41 m / min.

[0034] In the present invention, the secondary cooling zone is cooled by a weak cooling method.

[0035] In the present invention, the molten steel is preferably obtained by sequentially subjecting semi-steel to converter semi-steel smelting, LF refining and RH vacuum treatment.

[0036] In the present invention, the high-strength hard wire steel preferably comprises SWRH82B steel having a C mass content of 0.85% to 0.88%, more preferably 0.855% to 0.875%, and more preferably 0.86% to 0.87%.

[0037] In the present invention, the molten steel casting superheat of the smelting molten steel is preferably 30-35°C, more preferably 31-34°C, and more preferably 32-33°C.

[0038] In the present invention, the crystallizer is preferably an electromagnetically stirred crystallizer.

[0039] In the present invention, the central magnetic field strength of the electromagnetic stirring is preferably 475×10 -4 ~495×10 -4 T, preferably 479×10 -4 ~491×10 -4 T, more preferably 483×10 -4 ~487×10 -4 T.

[0040] In the present invention, the stirring current frequency of the electromagnetic stirring is preferably 2 to 3 Hz, more preferably 2.2 to 2.8 Hz, and more preferably 2.4 to 2.6 Hz.

[0041] In the present invention, the secondary cooling zone preferably includes secondary cooling zone 1, secondary cooling zone 2, secondary cooling zone 3 and secondary cooling zone 4.

[0042] In the present invention, the total water volume in the secondary cooling zone is preferably 0.51 to 0.55 L / kg, more preferably 0.515 to 0.545 L / kg, more preferably 0.52 to 0.54 L / kg, and more preferably 0.525 to 0.535 L / kg.

[0043] In the present invention, the final stirring is preferably set at 20% to 30% of the length of the liquid core of the casting billet, more preferably 22% to 28%, more preferably 24% to 26%. Specifically, 20% to 30% refers to 20% to 30% of the liquid core of the casting billet near the end of the casting billet.

[0044] In the present invention, the central magnetic field strength of the unstirred magnetic field is preferably 245×10 -4 ~275×10 -4 T, more preferably 250×10 -4 ~270×10 -4 T, preferably 255×10 -4 ~265×10 -4 T.

[0045] In the present invention, the stirring current frequency of the strong final stirring is preferably 7 to 8 Hz, more preferably 7.2 to 7.8 Hz, and more preferably 7.4 to 7.6 Hz.

[0046] The present invention provides the use of a high-strength hard wire steel continuous casting billet produced by the production process described in any one of the above technical solutions in the preparation of wire rod steel.

[0047] The present invention is to complete and refine the overall technical solution, better ensure the microstructure, composition and performance of the high carbon hard wire steel billet, and further improve the stability and efficiency of the preparation of the high strength hard wire steel 200mm×200mm continuous casting billet. The production process and application of the above-mentioned high strength hard wire steel 200mm×200mm continuous casting billet can specifically include the following contents:

[0048] The invention provides a production process for a 200mm×200mm continuous casting billet of high-strength hard wire steel, and the process technology flow is: converter semi-steel smelting--LF electric heating refining--RH vacuum treatment--200mm×200mm cross-section square billet continuous casting.

[0049] Specific key processes and parameters include: the superheat of molten steel casting is controlled at 25-35℃.

[0050] Specifically, the operating casting speed of the continuous casting machine is 1.40±0.03m / min.

[0051] Specifically, the crystallizer was stirred by electromagnetic stirring (the magnetic field strength at the center of the stirrer was controlled at (485±10)×10 -4 T, stirring current frequency: 2~3Hz).

[0052] Specifically, weak cooling is adopted, and the secondary cooling water volume is controlled at 0.51-0.55L / kg 钢 The final stirrer is installed at 20% to 30% of the liquid core ratio of the casting (the magnetic field strength of the stirrer center is controlled at (260±15)×10 -4 T, stirring current frequency: 7~8Hz).

[0053] In addition to the above key technical points that must be implemented as required, the present invention requires that other continuous casting system processes be implemented in a conventional manner.

[0054] The above content of the present invention provides a production process and application of a 200mm×200mm cross-section continuous casting billet of high-strength hard wire steel. The production process of a 200mm×200mm continuous casting billet of high-strength hard wire steel specially designed by the present invention with specific control parameters controls the parameters of the molten steel discharged from the converter smelting, the LF refining and the RH vacuum treatment parameters, and combines specific casting control, especially the control process and parameters of the crystallizer and cooling, so as to prepare a high-quality 200mm×200mm continuous casting billet, which further reflects the high efficiency of continuous casting and the advantages of regulating the organization and performance.

[0055] The present invention realizes the continuous production of 200mm×200mm continuous casting billets of high-strength hard wire steel, and forms high-quality continuous casting billets through innovative and scientific regulation of continuous casting equipment and process, laying an important billet quality foundation for the drawing production of wire rod rolling and steel strands and other products. At the same time, the process flow is simple, controllable, and stable, which is more suitable for industrial promotion and application.

[0056] Experimental results show that the preparation method provided by the present invention can successfully achieve continuous production of 200mm×200mm continuous casting billets of high-strength hard wire steel, the high-strength hard wire steel billets have no obvious defects at low magnification, the central segregation ratio is lower than 1.10, the proportion of cementite rating ≤2.0 at the central grain boundary of the wire rod is ≥93%, and the number of wire breakages during wire rod drawing is controlled below 1.2 times / 100 tons.

[0057] In order to further illustrate the present invention, the production process and application of a high-strength hard wire steel continuous casting billet provided by the present invention are described in detail below in combination with the embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention. The protection scope of the present invention is not limited to the following embodiments.

[0058] Example 1

[0059] The process of the present invention produces high-strength hardened wire steel, and its steel grade composition is shown in Table 1. Table 1 is the steel grade composition of the high-strength hardened wire steel in Example 1 of the present invention. The cross section of the ingot is 200 mm×200 mm, the working pulling speed is 1.37-1.41 m / min, the average superheat temperature of the molten steel in the tundish is 33-35°C, and the crystallizer is electromagnetically stirred (the magnetic field strength at the center of the stirrer is controlled at (485±5)×10 -4 T, stirring current frequency: 2~2.4Hz); adopt weak cooling method to cool, and the secondary cooling water volume is controlled at 0.51~0.53L / kg 钢 The final stirrer is installed at 25% to 30% of the liquid core ratio of the casting (the magnetic field strength at the center of the stirrer is controlled at (260±10)×10 -4T, stirring current frequency: 7~8Hz).

[0060] Table 1 Composition of high strength hard wire steel grades (mass percentage)

[0061] C Si Mn Cr P S Cu Fe other 0.86～0.87 0.55～0.60 0.6～0.8 0.25～0.30 ≤0.03 ≤0.03 ≤0.20 margin National Standard

[0062] The low-power quality of the ingot produced by this process is tested. There is no central looseness or shrinkage cavity, the CET is good in neutrality, and the C element segregation ratio at the center is 1.08-1.09. The proportion of cementite rating ≤2.0 at the center grain boundary of the wire rod is 94%, and the number of wire breakages during wire rod drawing is controlled at 1.2 times / 100 tons.

[0063] Example 2

[0064] The process of the present invention produces high-strength hardened wire steel, and its steel grade composition is shown in Table 2, which is the steel grade composition of the high-strength hardened wire steel in Example 2 of the present invention. The cross section of the ingot is 200 mm×200 mm, the working pulling speed is 1.39-1.43 m / min, the average superheat temperature of the molten steel in the tundish is 30-34°C, and the crystallizer is electromagnetically stirred (the magnetic field strength at the center of the stirrer is controlled at (485±7)×10 -4 T, stirring current frequency: 2.6~3Hz); adopt weak cooling method to cool, and the secondary cooling water volume is controlled at 0.52~0.54L / kg 钢 The final stirrer is installed at the position where the liquid core ratio of the casting is 26% to 30% (the magnetic field strength at the center of the stirrer is controlled at (260±6)×10 -4 T, stirring current frequency: 7.5~8Hz).

[0065] Table 2 Composition of high strength wire steel (mass percentage)

[0066] C Si Mn Cr P S Cu Fe other 0.85～0.86 0.55～0.60 0.6～0.8 0.25～0.30 ≤0.03 ≤0.03 ≤0.20 margin National Standard

[0067] The low-power quality of the ingot produced by this process is tested. There is no central looseness or shrinkage cavity, the CET is good in neutrality, and the C element segregation ratio at the center point is 1.07-1.09. The proportion of cementite rating ≤2.0 at the center grain boundary of the wire rod is 93%, and the number of wire breakages during wire rod drawing is controlled at 1.0 times / 100 tons.

[0068] Example 3

[0069] The process of the present invention produces high-strength hardened wire steel, and its steel grade composition is shown in Table 3, which is the steel grade composition of the high-strength hardened wire steel in Example 3 of the present invention. The cross section of the ingot is 200 mm×200 mm, the working pulling speed is 1.38-1.40 m / min, the average superheat temperature of the molten steel in the tundish is 32-34°C, and the crystallizer is electromagnetically stirred (the magnetic field strength at the center of the stirrer is controlled at (485±10)×10 -4T, stirring current frequency: 2.4~2.6Hz); adopt weak cooling method to cool, and the secondary cooling water volume is controlled at 0.54~0.55L / kg 钢 The final stirrer is installed at 20% to 24% of the liquid core ratio of the casting (the magnetic field strength at the center of the stirrer is controlled at (260 ± 15) × 10 -4 T, stirring current frequency: 7~7.4Hz).

[0070] Table 3 Composition of high strength wire steel (mass percentage)

[0071] C Si Mn Cr P S Cu Fe other 0.87～0.88 0.55～0.60 0.6～0.8 0.25～0.30 ≤0.03 ≤0.03 ≤0.20 margin National Standard

[0072] The low-power quality of the ingot produced by this process is tested. There is no central looseness or shrinkage cavity, the CET is good in neutrality, and the C element segregation ratio at the center is 1.07-1.08. The proportion of cementite rating ≤2.0 at the center grain boundary of the wire rod is 97%, and the number of wire breakages during wire rod drawing is controlled at 0.5 times / 100 tons.

[0073] The above implementation examples show that by adopting this technical invention, high-strength hard wire steel with low center segregation and high quality of 200mm×200mm section is successfully produced, the low-multiple quality of the ingot is good, the center segregation index of the ingot is low, and the center segregation ratio is lower than 1.10. It can better meet the microstructure control of wire rod rolling and the requirements of back-end drawing and stripping processing, the proportion of wire rod center grain boundary cementite rating ≤2.0 is ≥93%, and the number of wire rod drawing wire breakage is controlled below 1.2 times / 100 tons.

[0074] The above is a detailed introduction to the production process of a 200mm×200mm cross-section continuous casting billet of high-strength hard wire steel provided by the present invention. In this article, specific examples are used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and its core ideas of the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A production process for high-strength hard wire steel continuous casting billet, characterized in that: The following steps are involved: The molten steel in the ladle is poured into the tundish for ladle replacement, and then poured from the tundish into the crystallizer of the continuous casting machine. Under the pulling speed of the continuous casting machine, after cooling in the secondary cooling zone and the air cooling zone, a continuous casting square billet with a cross-sectional size of 200mm×200mm is obtained; The casting speed of the continuous casting machine is 1.37-1.43 m / min; The secondary cooling zone is cooled by a weak cooling method.

2. The production process according to claim 1, characterized in that: The molten steel is obtained by sequentially subjecting semi-steel to converter semi-steel smelting, LF refining and RH vacuum treatment.

3. The production process according to claim 1, characterized in that: The high-strength hard wire steel comprises SWRH82B steel with a C mass content of 0.85% to 0.88%.

4. The production process according to claim 1, characterized in that: The casting superheat degree of the molten steel in the tundish is 30-35°C.

5. The production process according to claim 1, characterized in that: The crystallizer is an electromagnetically stirred crystallizer.

6. The production process according to claim 5, characterized in that: The central magnetic field strength of the electromagnetic stirring is 475×10 -4 ~495×10 -4 T; The stirring current frequency of the electromagnetic stirring is 2-3 Hz.

7. The production process according to claim 1, characterized in that: The secondary cooling water volume of the secondary cooling zone is 0.51-0.55 L / kg 钢 .

8. The production process according to claim 1, characterized in that: The final stirring in the air cooling zone is arranged at 20% to 30% of the length of the liquid core of the casting.

9. The production process according to claim 8, characterized in that: The central magnetic field strength of the unstirred -4 ~275×10 -4 T; The stirring current frequency of the final stirring is 7 to 8 Hz.

10. Use of the high-strength hard wire steel continuous casting billet produced by the production process described in any one of claims 1 to 9 in the preparation of wire rod steel.