Controlled cooling method after rolling of high-strength bridge cable steel wire

Abstract

The invention relates to a controlled cooling method for a high-strength bridge cable steel wire after rolling, the wire is a high-carbon silicon wire, water bath cooling and air cooling modes are sequentially adopted after the wire is rolled, and the control parameters are as follows: the spinning temperature is 850-900 DEG C; cooling in a water bath: directly cooling in the water bath after spinning, controlling the temperature of the material discharged from the water bath to be 650-700 DEG C, and carrying out sorbite phase change; and fan cooling: performing air cooling on the wire rod after water bath to restrain temperature return. The wire comprises the following chemical components in percentage by mass: 0.85%-1.05% of C, 0.25%-0.90% of Mn, 0.20%-1.20% of Si, less than or equal to 0.024% of P, less than or equal to 0.011% of S, less than or equal to 0.50% of Cr, less than or equal to 0.06% of Cu and the balance of Fe and inevitable impurities. The tensile strength of the wire rod is 1300-1500 Mpa, the area shrinkage is 25-40%, the structure is sorbite, and no fully decarburized structure exists. According to the method, the tensile strength and area shrinkage of the bridge cable steel are improved, and meanwhile the structure of the hot-rolled wire rod is guaranteed.

Description

Technical Field

[0001] The present invention relates to a method for producing a wire rod, and in particular to a method for controlled cooling of a high-strength steel wire rod for bridge cables after rolling. Background Art

[0002] With the continuous advancement of technology in steel companies and downstream metal products processing industries, the market has increasingly higher requirements for the structure and performance of bridge cable products. However, if they are still implemented according to the relatively old and single controlled cooling process, there will always be various problems such as the wire rod structure or strength cannot meet the requirements. In order to match the continuous advancement of technology in the downstream metal products processing industry,

[0003] As for bridge cable steel wires, data shows that for every 100MPa increase in steel wire strength, its own weight can be reduced by 10%, the cable diameter will be reduced accordingly, and the wind resistance will be reduced accordingly, thereby reducing the impact of wind force and wind direction on the bridge, and also improving the safety of bridge operation.

[0004] At present, the domestic production of high carbon steel wire rods often uses a single cooling method, such as air cooling, water cooling or salt bath cooling. The wire rods produced cannot achieve the optimal balance of strength and metallographic structure at the same time. Summary of the Invention

[0005] The purpose of this application is to provide a production method for high-strength bridge cable steel wire, which improves the tensile strength and surface shrinkage of bridge cable steel through blanking rolling and controlled cooling, while ensuring the organization of hot-rolled wire rod.

[0006] The chemical composition mass percentage of the high-strength bridge cable steel wire of the present invention is: C: 0.85%-1.05%, Mn: 0.25%-0.90%, Si: 0.20%-1.20%, P≤0.024%, S≤0.011%, Cr≤0.50%, Cu≤0.06%, and the rest is Fe and unavoidable impurities.

[0007] The mechanism of action of C and Si elements in the high-strength bridge cable steel wire of the present invention is as follows: C is the main strengthening element in steel. It can significantly improve the strength of steel through solid solution strengthening and precipitation strengthening. With the increase of C content, the strength shows a clear upward trend. At the same time, the wire is significantly hardened after cold drawing, which helps to achieve the strength of the finished steel wire. Therefore, the C content is controlled at 0.85%~1.05%.

[0008] The Si element is a strong carbide-forming element and generally forms very stable special carbides in steel wires. These carbides have extremely high hardness and can effectively improve the wear resistance and tensile strength of bridge cable steel. They can also form silicon oxide with oxides to improve corrosion resistance. Therefore, the Si content is controlled at Si: 0.20%~1.20%.

[0009] The present invention adopts a composite cooling method of water bath cooling and air cooling after the wire is spun, and the material temperature after the water bath is controlled to be 650-700°C. The main reasons are as follows: By using water bath cooling, controlling the cooling rate, and rapidly cooling through the cementite precipitation zone, the sorbite structure is generated while avoiding the generation of network cementite, which leads to a decrease in the mechanical properties of the steel. The water outlet temperature is controlled at 650-700℃ to avoid the formation of martensite due to overcooling. Air cooling is used after the water bath to suppress the fragmentation of sorbite caused by the reheating after the phase transformation.

[0010] The production method of the high-strength bridge cable steel wire of the present invention is described as follows: The production process is KR (molten iron pretreatment) → BOF (converter) → LF (refining) → CCM (arc continuous casting 200mm*200mm) → billet finishing → heating → rolling → spinning → water bath cooling → air cooling → coiling → off-line → packaging.

[0011] After the production reaches the billet stage, the wire rod rolling production process is as follows: (1) Heating: The temperature of the high temperature section and the soaking section is 1100-1200℃, and the heating time is ≥45 minutes; after tapping, the steel is descaled by high-pressure water, and the rolling temperature is 1000-1100℃; (2) Rolling: After rough rolling, first intermediate rolling, second intermediate rolling and pre-finishing rolling, the billet is fed into the finishing mill at a controlled temperature of 870-960°C. After finishing rolling, it is cooled in two water tanks and fed into the sizing mill at a controlled temperature of 800-900°C. (3) Wire drawing: After the wire rod is finally rolled, it passes through a water tank for cooling, and the wire drawing temperature is controlled at 850-900℃; (4) Water bath cooling: After the wire rod is spun, it is directly cooled in a water bath, and the outlet water temperature is controlled at 650-700℃ to undergo the troostite phase transformation.

[0012] (5) Fan cooling: After water bath cooling, fan cooling is used to suppress phase change and temperature reversal.

[0013] Compared with the existing technology, this application adopts a high-carbon and high-silicon design, and adopts a composite cooling control method of water bath and air cooling after spinning, which achieves a balance between wire strength and structure, and meets the strength and structure requirements of downstream wire drawing. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The metallographic microstructure of the hot-rolled wire rod produced in Example 1 of the present invention; Figure 2 The metallographic microstructure of the hot-rolled wire rod produced in Example 1 of the present invention; Figure 3 The metallographic microstructure of the hot-rolled wire rod produced in Example 2 of the present invention; Figure 4 This is the metallographic microstructure of the hot-rolled wire rod produced in Example 2 of the present invention. DETAILED DESCRIPTION

[0015] The following describes in more detail the rolling process for the annealing-free, high-strength bridge cable steel hot-rolled wire rod according to the present invention, in conjunction with preferred embodiments of the present invention. However, this embodiment is merely a description of a preferred embodiment of the present invention and does not limit the scope of the present invention in any way. Example

[0016] The specification of the rolled wire rod is Φ13mm, and the chemical composition by mass percentage is C: 0.89%, Mn: 0.55%, Si: 1.10%, P≤0.012%, S≤0.005%, Cr: 0.30%, Al: 0.02%, and the rest is Fe and unavoidable impurities.

[0017] After continuous casting, the billet is rolled to a finishing temperature of 900°C, then to a sizing mill temperature of 870°C, and finally to a spinning temperature of 880°C. The wire rod is then cooled in a water bath and then air-cooled after exiting the water bath to prevent the wire rod from warming up and allowing the material temperature to continue to drop. The roller speed is controlled between 0.35 and 0.60 m / s. After the sorbite phase transformation, which is controlled by water bath cooling, air is blown to suppress sorbite fragmentation caused by the phase transformation and reheating. The wire rod properties are shown in Table 1. Example

[0018] The specification of the rolled wire rod is Φ14mm, and the chemical composition by mass percentage is C: 0.95%, Mn: 0.62%, Si: 0.95%, P≤0.012%, S≤0.005%, Cr: 0.25%, Al: 0.03%, and the rest is Fe and unavoidable impurities.

[0019] After continuous casting, the billet is rolled into a finishing mill at a controlled temperature of 900°C, then into a sizing mill at 870°C, and into a spinning mill at 880°C. The wire is then cooled in a water bath and then air-cooled. The air-cooling capacity must be sufficient to prevent the wire rod from warming up and continue to cool. The roller speed is controlled between 0.35 and 0.60 m / s. See Table 1 for wire rod properties.

[0020] Table 1

Claims

1. A method for controlled cooling of high-strength bridge cable steel wire after rolling, characterized in that: The wire is high carbon silicon wire. After rolling, the wire is cooled by water bath and air cooling. The control parameters are as follows: Spinning temperature: 850-900℃; Water bath cooling: After spinning, the silk goes directly into the water bath for cooling, and the material temperature out of the water bath is controlled at 650-700℃ to undergo the troostite phase transformation; Fan cooling: After exiting the water bath, the wire is cooled by air to prevent temperature from returning.

2. The method according to claim 1, characterized in that: The chemical composition of the wire material is as follows: C: 0.85%-1.05%, Mn: 0.25%-0.90%, Si: 0.20%-1.20%, P≤0.024%, S≤0.011%, Cr≤0.50%, Cu≤0.06%, and the rest is Fe and unavoidable impurities.

3. The method according to claim 2, characterized in that: The C content is 0.90-1.0%, and the Si content is 0.95-1.2%.

4. The method according to claim 1, characterized in that: The tensile strength of the wire is 1300-1500Mpa, and the surface shrinkage is 25-40%.

5. The method according to claim 1, characterized in that: The structure of the wire rod is troostite without complete decarburization structure.

6. The method according to claim 1, characterized in that: The wire rod is successively subjected to ingot heating and rolling before cooling, and the control parameters are as follows: Heating: The temperature of the high temperature section and the soaking section is 1100-1200℃, and the heating time is ≥45 minutes; after steel is tapped, it is descaled by high-pressure water, and the rolling temperature is 1000-1100℃; Rolling: After rough rolling, first intermediate rolling, second intermediate rolling and pre-finishing rolling, the billet temperature is controlled at 870-960℃ before entering the finishing mill. After finishing rolling, it is cooled by two-stage water tanks and the material temperature is controlled at 800-900℃ before entering the sizing mill. After the wire rod is finally rolled, it is cooled by a first-stage water tank to ensure that the wire is spun within the temperature range.

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