High-strength prestressed steel strand wire rod and preparation method thereof

Abstract

The application discloses a high-strength prestressed steel strand wire rod and a preparation method thereof. The wire rod mainly comprises the following chemical components: C: 0.98-1.10%, Si: 0.85-1.20%, Mn: 0.30-0.60%, Cr: 0.15-0.35% and the like. The high-strength wire rod is prepared by designing the high-C and high-Si element components. The C element diffusion is promoted by using the high-temperature heating method before the continuous rolling and cogging. The hot-rolled wire rod adopts the online EDC water bath controlled cooling mode, the cooling speed is improved, and the sorbitizing rate of more than 90% can be obtained. The slow cooling mode is used after the wire rod is taken out of the water, the internal stress is released, and the wire rod drawing performance is improved. The wire rod prepared by the method has the following advantages: good uniformity, no low-temperature structure, reticular cementite ≤ 1 level, tensile strength of 1420-1460 MPa, and the area reduction of ≥ 25%. The wire rod can be used for preparing 2230 MPa grade prestressed steel strand products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a high-strength pre-stressed steel strand wire rod and a preparation method thereof. BACKGROUND

[0002] As one of the main products of high-carbon steel wire rods, pre-stressed steel strands are widely used in the construction of large-span structural components, such as bridge engineering, high-rise buildings, water conservancy construction, and highways and railways. With the continuous progress of industrial technology, large-span structural components have higher requirements for the strength and plasticity of steel strands. The domestic mainstream 1860 MPa grade pre-stressed steel strand has already failed to meet the development needs of lightweight, high quality, and low energy consumption, and therefore it is necessary to develop pre-stressed steel strands with higher strength and higher performance. High-quality pre-stressed steel strands have higher requirements for the organization and performance of wire rods, and it is of great significance to develop hot-rolled wire rods for pre-stressed steel strands with high strength, high toughness, and excellent deep processing performance.

[0003] At present, wire rod manufacturers for pre-stressed steel strands improve the comprehensive performance of wire rods by increasing the content of alloy elements such as Cr and V through micro-alloying, and by improving the microstructure to improve the strength and plasticity of wire rods. However, the increase of Cr and V alloy element content not only increases the production cost, but also is likely to cause composition segregation and produce low-temperature organization, reducing the drawing performance of the wire rod. At present, the main controlled cooling method for pre-stressed steel strand wire rods is Stelmor controlled cooling, which has a limited range and is extremely difficult to produce wire rods for ultra-high solvus transformation rate steel strands, resulting in the strength and plasticity of pre-stressed steel strands not being able to reach the best. For example, the patent with publication number CN 113981312 A provides a high-strength low-relaxation pre-stressed steel strand hot-rolled wire rod and a preparation method thereof. The wire rod adopts the traditional Stelmor air cooling process, and the controlled cooling effect is poor, and the strength of the wire rod is low. For example, the patent with publication number CN 113897544 B provides a rare earth high-strength high-toughness pre-stressed steel strand wire rod and a smelting and rolling method thereof. The smelting process is complex, and the rare earth resources are scarce. The raw material of rare earth elements is expensive, and the production cost is high. For example, the patent with publication number CN 115261735 B provides a pre-stressed steel strand wire rod and a production process thereof. The main problems are that there are many types of alloy elements, the smelting process is complex, the production cost is high, it is not conducive to resource saving, and the controlled cooling method of the wire rod adopts the conventional Stelmor air cooling, which has a slow air cooling speed and uneven cooling. SUMMARY

[0004] In order to overcome the defects of the prior art, the present application fully considers the influence of alloying elements such as C, Si, Mn and Cr on the structure and performance of the wire rod for prestressed steel strand, adjusts and optimizes the content of alloying elements, realizes the non-addition of expensive alloying elements such as V, achieves low-cost control, and produces Φ13 mm-15 mm specification high-strength wire rod. And by optimizing the wire rod rolling and EDC controlled cooling process, the hot-rolled wire rod has high sorbite rate, uniform microstructure, good drawing performance and excellent mechanical properties, which can meet the requirements of 2230 MPa or above grade prestressed steel strand products.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides a wire rod for high-strength prestressed steel strand, the chemical composition of the wire rod is C: 0.98%-1.10%, Si: 0.85%-1.20%, Mn: 0.30%-0.60%, P≤0.02%, S≤0.02%, Cr: 0.15%-0.35%, and the rest is Fe and inevitable impurities.

[0006] Further, the tensile strength of the wire rod is 1420-1460 MPa, the reduction of area is ≥25%, and the elongation after fracture is ≥10%. The sorbite rate of the microstructure of the wire rod is more than 90%, the net carbon is ≤1 level, and there is no low-temperature structure such as martensite.

[0007] The selection of the adding amount (wt%) of each element in the above-mentioned steel and its role are as follows:

[0008] C: C is the most basic strengthening element in steel, the increase of C content in the wire rod can obviously improve the strength of the wire rod, but too high C content can easily lead to center segregation of the wire rod, and the formation of net-shaped carbide at the grain boundary of the wire rod during the cooling process, which affects the uniformity of the structure and reduces the deep processing performance and plasticity and toughness of the steel, the C content range of the present application is determined to be 0.98%-1.10%.

[0009] Si: Si has a large solubility in steel, mainly exists in solid solution form, can strengthen ferrite, and can also inhibit the formation of cementite, prevent the formation of net-shaped cementite in the wire rod during the cooling process, and improve the uniformity of the structure of the wire rod, but too high Si content can reduce the plasticity and toughness of the steel, and also increase the decarburization sensitivity of the wire rod; the Si content range of the present application is determined to be 0.85%-1.20%.

[0010] Mn: Mn dissolved in steel can play a solid solution strengthening role, its dissolution into ferrite can improve the strength of the steel, and can make the wire rod after rolling obtain finer pearlite interlamellar spacing, but too high Mn content can easily combine with S to form MnS inclusions, which affects the deep processing performance of the wire rod, therefore, the Mn content range of the present application is determined to be 0.30%-0.60%.

[0011] Cr: Cr is a carbide forming element, which can increase the austenite stability, refine the austenite grain, and improve the strength and plasticity of the steel. However, if the content of Cr is too high, it will not only form large carbides with C, but also cause composition segregation, which makes the wire rod prone to low-temperature structure and reduces the drawing performance of the wire rod. Therefore, the content of Cr in the wire rod is determined to be 0.15% to 0.35%.

[0012] P and S: P and S in the steel are harmful elements. P element is easy to cause solidification segregation and increase cold brittleness. Therefore, the content of P is controlled to be ≤0.02%. S element can cause hot brittleness of the steel and reduce the plasticity and toughness of the wire rod. Therefore, the content of S is controlled to be ≤0.02%.

[0013] A preparation method of the above-mentioned high-strength prestressed steel strand wire rod, the method comprises the following steps: smelting, bloom continuous casting, continuous rolling, wire rod rolling, controlled cooling and the like.

[0014] ①Smelting: the steel for the wire rod is mainly obtained through pre-desulfurization of molten iron, converter smelting and LF furnace refining. The contents of P and S elements are strictly controlled during the steelmaking process. The content of P element is controlled to be ≤0.02% and the content of S element is controlled to be ≤0.02% at the end of the converter.

[0015] ②Bloom continuous casting: the bloom continuous casting process adopts measures such as crystallizer electromagnetic stirring and end electromagnetic stirring to reduce the composition segregation phenomenon of the casting blank. The overheat degree of the molten steel continuous casting tundish is 20℃ to 25℃, the continuous casting speed is controlled to be 0.4 to 0.6 m / min, the crystallizer electromagnetic stirring current is 300 to 500 A, and the frequency is 3.0 to 5.0 Hz.

[0016] ③Continuous rolling: the steel blank in the technical solution has high contents of C and Si elements. Increasing the heating temperature of the steel blank can promote the diffusion of C element and reduce the composition segregation phenomenon. The heating section temperature is 950℃ to 1150℃, the soaking section temperature is 1100℃ to 1250℃, and the total heating time before the continuous rolling is controlled to be not less than 4 h to ensure that the steel blank is uniformly heated.

[0017] ④Wire rod rolling: the wire rod is rolled into a high-strength wire rod with a diameter of Φ13 mm to Φ15 mm after the wire rod is broken down, and the rolling speed is strictly controlled to ensure the surface quality of the wire rod. The rolling temperature is 1050℃±15℃, the wire rod entering temperature and the double module temperature are controlled to be 930℃±30℃, the rolling speed is 23 to 28 m / s, and the wire laying temperature is 920℃±20℃.

[0018] ⑤Controlled cooling: the wire rod is cooled by adopting the online EDC water bath cooling and water-out slow cooling mode, the EDC water tank temperature is 85-95 DEG C, the temperature of the wire rod entering the water tank is controlled to be 880 DEG C ± 30 DEG C, and the wire rod water-out temperature is controlled to be 580 DEG C ± 30 DEG C. The EDC water bath cooling speed is greater than 15 DEG C / s, so that the wire rod can be quickly cooled to the pearlite phase transition zone, the interlamellar spacing is reduced, and the wire rod sorbite rate is improved. After the wire rod is out of the EDC water tank, the online heat preservation cover is closed, and the average cooling speed of the hot-rolled wire rod is controlled to be less than 0.8 DEG C / s, so that the low-temperature structure is avoided due to the too fast cooling speed of the wire rod, and the drawing performance of the wire rod is affected.

[0019] Compared with the prior art, the beneficial effects of the present application are:

[0020] ①The wire rod of the present application increases the content of C and Si elements, improves the tensile strength of the steel strand, reduces the composition segregation by reducing the content of Cr alloy elements and not adding V alloy elements, avoids the generation of low-temperature structure, and ensures the plasticity and toughness of the wire rod. By optimizing the chemical composition, the main mechanical property indexes of the wire rod such as tensile strength, reduction of area and elongation after fracture are improved, the production cost of the wire rod is reduced, and the resources of Cr and V alloy elements are saved.

[0021] ②The wire rod after hot rolling is cooled by adopting the online EDC water bath cooling mode, so that the hot-rolled wire rod can be quickly cooled to the pearlite transition temperature, the size of the pearlite group and the interlamellar spacing of the pearlite are reduced, and the sorbite rate of more than 90% can be obtained. After the wire rod is out of the water, the slow cooling mode is adopted, so that the generation of low-temperature structure is greatly reduced, and the drawing performance of the wire rod is improved. The hot-rolled wire rod produced by the method of the present application has good uniformity of microstructure, high sorbite rate, less low-temperature structure, good strength and plasticity, meets the requirements of various indexes of the wire rod for high-strength prestressed steel strand, and reduces the production cost of the high-strength prestressed steel strand. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The microstructure picture of the wire rod prepared in Example 1. DETAILED DESCRIPTION

[0023] The present application is further described below in combination with specific embodiments, but does not limit the present application in any way. In order to avoid redundancy, the raw materials in the following examples are all commercially available products if not specifically stated, and the methods used are all conventional methods if not specifically stated.

[0024] A wire rod for high-strength prestressed steel strand, the chemical composition of the wire rod is C: 0.98%-1.10%, Si: 0.85%-1.20%, Mn: 0.30%-0.60%, P≤0.02%, S≤0.02%, Cr: 0.15%-0.35%, and the rest is Fe and inevitable impurities.

[0025] A preparation method of the high-strength prestressed steel wire rod, the method comprising the following steps: smelting, bloom continuous casting, continuous rolling breakdown, wire rod rolling, controlled cooling;

[0026] The heating section temperature of the continuous rolling breakdown step is 950-1150℃, the soaking section temperature is 1100-1250℃, and the total heating time before the continuous rolling breakdown is controlled to be not less than 4h;

[0027] The open rolling temperature of the wire rod rolling step is 1050℃±15℃, the wire rod is controlled to enter the finishing rolling temperature and the double module temperature to be 930℃±30℃, and the wire rod is controlled to be discharged at a temperature of 920℃±20℃;

[0028] The controlled cooling step adopts the online EDC water bath cooling and water outlet slow cooling mode, the EDC water tank temperature is 85-95℃, the wire rod is controlled to enter the water tank at a temperature of 880℃±30℃, the wire rod outlet temperature is controlled to be 580℃±30℃, and the EDC water bath cooling speed is greater than 15℃ / s.

[0029] In the following examples, the unexplained contents are the same as the contents described in the above specific embodiment.

[0030] Embodiment

[0031] A high-strength prestressed steel wire rod and a preparation method thereof, and the specific production process is as follows:

[0032] The chemical composition of the prestressed steel wire rod in examples 1-3 is shown in table 1, by increasing the content of C and Si elements, the tensile strength of the steel wire is improved, by reducing the content of Cr alloy element and not adding V alloy element, the composition segregation is reduced, and the plasticity and toughness of the wire rod are ensured.

[0033] Table 1 Chemical composition of the prestressed steel wire rod in examples 1-3

[0034] Chemical composition C Si Mn Cr P S Standard 0.98-1.10 0.85-1.20 0.3-0.6 0.15-0.35 ≤0.02 ≤0.02 Example 1 0.99 0.95 0.45 0.25 0.012 0.003 Example 2 1.00 0.92 0.47 0.24 0.013 0.002 Example 3 1.02 0.97 0.42 0.21 0.015 0.005

[0035] The controlled cooling process parameters of the wire rod for prestressed steel strand in Examples 1-3 are shown in Table 2. In the smelting step, the molten iron is pre-desulfurized, the converter is smelted, and the LF furnace is refined. The terminal point of the converter is controlled to have P content ≤0.02% and S content ≤0.02%. The bloom is continuously cast, the superheat of the liquid steel in the tundish is controlled to be 20-25°C, the casting speed is controlled to be 0.4-0.6 m / min, the electromagnetic stirring current of the crystallizer is 300-500 A, and the frequency is 3.0-5.0 Hz. In the rolling process, the wire rod is rolled after being roughed, medium-rolled, pre-rolled, and fine-rolled by a double-module unit, and the rolling speed is 23-28 m / s. In the controlled cooling step, after the wire rod is discharged from the EDC water tank, the online heat preservation cover is closed, and the average cooling speed of the hot-rolled wire rod is controlled to be less than 0.8°C / s. By adjusting the controlled cooling process, the microstructure and mechanical properties of the wire rod are improved.

[0036] Table 2: Controlled cooling process parameters of the wire rod for prestressed steel strand in Examples 1-3

[0037]

[0038] The microstructure and mechanical property test results of the wire rod for prestressed steel strand in Examples 1-3 are shown in Table 3. The tensile strength of the wire rod is 1420-1460 MPa, the reduction of area (area reduction) is ≥25%, and the elongation after fracture is ≥10%. The sorbitizing rate of the microstructure of the wire rod is more than 90%, the net carbon is ≤1 level, and no low-temperature structure is generated. The microstructure picture of the wire rod prepared in Example 1 is shown in Figure 1 , and the sorbitizing rate thereof is 92%, and the grain size is ≥8 levels.

[0039] Table 3: Microstructure and mechanical property test results of the wire rod for prestressed steel strand in Examples 1-3

[0040]

[0041] The above examples show that by optimizing the alloy composition and the EDC controlled cooling technology of the wire rod, increasing the contents of C and Si elements, reducing the content of Cr element, not adding V and other alloy elements, reducing the composition segregation and low-temperature structure, the sorbitizing rate and strength-plasticity of the wire rod are improved, and the production cost is reduced.

[0042] For any person skilled in the art, many possible changes and modifications, or equivalent embodiments with equivalent changes, can be made to the technical solutions of the present application by using the technical content disclosed above without departing from the scope of the technical solutions of the present application. Therefore, any simple modification, equivalent change, and modification made to the above examples according to the technical essence of the present application should still be within the scope of protection of the technical solutions of the present application.

Claims

1. A method of manufacturing a high strength pre-stressed steel strand wire rod, characterized by, The chemical composition of the wire rod for the prestressed steel strand is C: 0.98% to 1.10%, Si: 0.85% to 1.20%, Mn: 0.30% to 0.60%, P≤0.02%, S≤0.02%, Cr: 0.15% to 0.35%, and the rest is Fe and inevitable impurities; The preparation method of the wire rod for the high-strength prestressed steel strand comprises the following steps: smelting, bloom continuous casting, continuous rolling breakdown, wire rod rolling, and controlled cooling. The heating section temperature of the continuous rolling breakdown step is 950°C to 1150°C, the soaking section temperature is 1100°C to 1250°C, and the total heating time before the continuous rolling breakdown is controlled to be not less than 4 hours; The wire rod rolling step has a bloom opening rolling temperature of 1050°C±15°C, a wire rod entering the finishing rolling temperature and a double module entering temperature of 930°C±30°C, and a wire rod laying temperature of 920°C±20°C; The controlled cooling step adopts an online EDC water bath cooling and water outlet slow cooling mode, the EDC water tank temperature is 85°C to 95°C, the wire rod entering the water tank temperature is controlled to be 880°C±30°C, and the wire rod water outlet temperature is controlled to be 580°C±30°C; the EDC water bath cooling speed is greater than 15°C / s; In the controlled cooling step, after the wire rod exits the EDC water tank, the online heat preservation cover is closed, and the average cooling speed of the hot rolling wire rod is controlled to be less than 0.8°C / s.

2. The production method according to claim 1, characterized by, The wire rod for the prestressed steel strand has a tensile strength of 1420 to 1460 MPa, a reduction of area of ≥25%, and an elongation after fracture of ≥10%.

3. The preparation method according to claim 1, characterized in that, The wire rod for the prestressed steel strand has a sorbite ratio of microstructure of more than 90%, a network cementite of ≤1 level, and no martensite low-temperature structure.

4. The method of claim 1, wherein, In the smelting step, the molten iron is pre-desulfurized, the converter is smelted, and the LF furnace is refined, the converter controls the terminal P element content to be ≤0.02%, and the S element content to be ≤0.02%.

5. The production method according to claim 1, characterized by, In the bloom continuous casting, the steel liquid continuous casting tundish superheat is 20°C to 25°C, the continuous casting speed is controlled to be 0.4 to 0.6 m / min, the crystallizer electromagnetic stirring current is 300 to 500 A, and the frequency is 3.0 to 5.0 Hz.

6. The production method according to claim 1, characterized by, In the wire rod rolling process, the wire rod is rolled after breakdown, intermediate rolling, pre-finishing rolling, finishing rolling, and double module unit rolling, and the rolling speed is 23 to 28 m / s.

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