Production method of wire rod for ultrahigh-strength bridge cable steel wire

Abstract

The invention relates to a production method of a wire rod for an ultrahigh-strength bridge cable steel wire, and belongs to the technical field of iron-based alloys. The method comprises the steps that blank heating, controlled rolling and controlled cooling are conducted, the heated blank is rolled with the large area reduction rate, the spinning temperature is 800-960 DEG C, a composite cooling mode composed of online spraying, online water bath and stelmor air cooling is sequentially adopted for a wire rod coil obtained after spinning, spraying is conducted on the lap joint point position of the wire rod coil, and spraying is conducted on the lap joint point position of the wire rod coil; the temperature of the whole circle of the wire rod after spraying is reduced to 750-900 DEG C, the water bath temperature is 100 + / -(0-5) DEG C, the water outlet temperature is 550-680 DEG C, and the temperature of the wire rod after air cooling through Stelmor is 450-580 DEG C. The temperature in the cooling process of the wire rod is accurately controlled, a product with more uniform structure performance and higher strength is obtained, the sorbite content of the produced wire rod is larger than or equal to 95%, the tensile strength is larger than or equal to 1500 MPa, the fluctuation of the tensile strength of the same circle of the wire rod is smaller than or equal to 40 MPa, and the tensile strength of a machined steel wire is larger than or equal to 2200 MPa.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron-based alloys, and specifically provides a production method for wire rods used for bridge cable wires. Background Art

[0002] In recent years, the bridge cable industry has developed rapidly. With the continuous progress of technologies in steel enterprises and downstream metal products processing industries, wire rods for 1960 MPa-class bridge cable wires have been mass-produced stably, and the toughening treatment generally adopts the Stelmor air-cooling process. In terms of ultra-high-strength bridge cables, wire rods for 2060 MPa - 2200 MPa and above-class bridge cable wires have been partially applied, and the toughening treatment is produced by water bath technology or salt bath technology. Research data shows that for every 100 MPa increase in the strength level of bridge cables, the self-weight can be reduced by 10%, the total construction cost can be reduced by 2% - 3%, and at the same time, the bridge type design is more beautiful and the bridge safety performance is more reliable.

[0003] For wire rod products used for bridge cable wires, the key lies in the control of the microstructure. The wire rods produced by the Stelmor air-cooling process are limited by insufficient cooling capacity, the content of sorbite in the structure is less than 90%. At the same time, there are temperature differences between the lapping points and non-lapping points of the wire rods, and their through-bar uniformity is poor. The tensile strength fluctuation of the wire rods in the same coil is about 100 MPa. Although the salt bath process can improve the strength of the wire rods, this process has high energy consumption, great environmental impact, and low production efficiency, and does not conform to the advocated low-energy consumption and green environmental protection production process. Summary of the Invention

[0004] The purpose of the present invention is to provide a production method for wire rods used for bridge cable wires. The wire rods produced by using this method have a high rate of sorbitization and good uniformity in the same coil. The technical route for the production of the wire rods of the present invention is: billet → heating → controlled rolling → controlled cooling. During the rolling process, the methods of controlled rolling and controlled cooling are adopted to produce wire rods with specifications of Φ11.0 mm - Φ16.0 mm, the sorbite content is not less than 95%, and the tensile strength fluctuation of the wire rods in the same coil does not exceed 40 MPa. The tensile strength of the bridge cable wires produced by using this wire rod can reach 2200 MPa.

[0005] The technical solution adopted by the present invention is as follows: The blank is the blank after blooming of continuous casting bloom or continuous casting round billet, and the uniformity of the cross-sectional composition of the blank after blooming is better. The blank is heated in a heating furnace and then subjected to controlled rolling and controlled cooling. In terms of controlled rolling, the temperature at different stages of rolling deformation is strictly controlled to ensure precise control of austenite grain size and precipitates. In terms of controlled cooling, a composite controlled cooling method consisting of online spraying + online water bath + Stelmor air cooling is adopted. After the wire rod is spun, it is first spray-cooled before entering the water bath, with key spraying on the lapping points to reduce the temperature of the lapping points; then the wire rod enters the online water bath, and the water bath cooling can achieve strong cooling capacity and uniform cooling; finally, after the wire rod exits the water bath, it is continuously cooled by Stelmor air cooling. Using the composite controlled cooling system to cool the wire rod for bridge cable steel wire can ensure the uniformity of the structure and mechanical properties of the lapping points and non-lapping points of the wire rod, thereby further reducing the strength fluctuation of the wire rod in the same coil. The specific process and specific operations are as follows:

[0006] 1. Blank preparation

[0007] The blank after blooming of continuous casting bloom or continuous casting round billet is adopted, and the blooming reduction ratio ≥ 4. The surface of the blank is finished to ensure that the surface quality of the blank meets the control requirements. The chemical element composition of the blank in weight percentage is: C: 0.90 - 1.00%, Si: 0.60 - 1.30%, Mn: 0.50 - 0.80%, Cr: 0.20 - 0.50%, Al: 0.010 - 0.050%, V: 0.02 - 0.20%, Nb: 0.005 - 0.035%, Ti: 0.005 - 0.035%, P ≤ 0.015%, S ≤ 0.015%, Cu: ≤ 0.05%, and the others are Fe and inevitable residual elements.

[0008] 2. Blank heating

[0009] The heating temperature of the blank is strictly controlled to reduce the generation of precipitates. The temperature of the first stage of the heating furnace is 880 - 980 °C, the temperature of the second stage of heating is 980 - 1080 °C, the soaking temperature is 1080 - 1250 °C, and the soaking time in the soaking section ≥ 2 hours. After the blank is taken out of the furnace, controlled rolling + controlled cooling is used to produce wire rods.

[0010] 3. Controlled rolling

[0011] The starting rolling temperature of the blank is in the range of 1000 °C - 1150 °C. The blank is rolled with a large reduction ratio during the rolling stage, and the total rolling ratio ≥ 12. The temperature at each node during the whole rolling process is controlled within the designed temperature range. The number of open nozzles and the cooling water pressure in the cooling water tank before each node are precisely controlled to ensure that the temperature of the rolled material meets the temperature requirements of the current rolling stage. The temperature entering the finishing mill is controlled at 880 - 980 °C, the finishing rolling temperature is controlled at 800 °C - 960 °C, and the spinning temperature is controlled at 800 °C - 960 °C.

[0012] 4. Controlled Cooling

[0013] The wire rod adopts an online spray + online water bath + Stelmor air cooling combined composite controlled cooling system for cooling control. After the wire rod is spun, it undergoes online spraying. The spraying focuses on the lap position of the wire rod coil. After spraying, the temperature of the entire coil of the wire rod is reduced to 750 - 900 °C. The wire rod passes through the water bath for cooling after online spraying. The water bath temperature is 100 °C, and the water outlet temperature after passing through the water bath is 550 °C - 680 °C. The wire rod passes through the Stelmor air cooling after the online water bath. More than 4 fans are turned on, the air volume of the fans is set to 100%, the heat preservation cover is opened, and the temperature after passing through the Stelmor air cooling is 450 °C - 580 °C. By adopting the above process, the uniformity of the cooling temperature of the wire rod in the same coil can be ensured, and the temperature difference in the same coil is controlled within the range of ≤25 °C.

[0014] Compared with the prior art, the advantages of the present invention are as follows: The production of wire rods combines controlled rolling and controlled cooling, adopts a composite controlled cooling method consisting of online spraying + online water bath + Stelmor air cooling, precisely controls the temperature during the cooling process of the wire rod, solves the problem that the wire rod returns to temperature due to the heat released during the phase change after leaving the water bath, which affects the strength and plasticity, and obtains a product with more uniform tissue properties and higher strength. The wire rods produced by the present invention have excellent comprehensive properties, the sorbite content is ≥95%, the tensile strength of the wire rod is ≥1500 MPa, the tensile strength fluctuation of the same coil of the wire rod is ≤40 MPa, and the tensile strength of the processed steel wire is ≥2200 MPa. Description of the Drawings

[0015] Figure 1 Metallographic diagram of the microstructure of the wire rod in Example 1 of the present invention

[0016] Figure 2 Metallographic diagram of the microstructure of the wire rod in Comparative Example 1 of the present invention;

[0017] Figure 3 SEM diagram of the microstructure of the wire rod in Example 2 of the present invention. Detailed Embodiments

[0018] The following describes in more detail the method for controlling the microstructure of controlled rolling and controlled cooling in the present invention in combination with the preferred embodiments of the present invention. However, this embodiment is only a description of the preferred implementation mode of the present invention and cannot impose any limitation on the scope of the present invention.

[0019] Example 1

[0020] The following component billets are used: C: 0.90 - 1.00%, Si: 0.80 - 1.30%, Mn: 0.50 - 0.80%, Cr: 0.20 - 0.50%, Al: 0.010 - 0.050%, V: 0.02 - 0.20%, Nb: 0.005 - 0.025%, Ti: 0.005 - 0.025%, P ≤ 0.010%, S ≤ 0.010%, Cu: ≤ 0.05%, and the rest is Fe and inevitable residual elements.

[0021] The billet uses a continuous casting bloom with a specification of 390 * 510 mm, and is rolled into an intermediate billet with a specification of 200 * 200 mm. After the surface of the billet is finish-treated, it enters the heating furnace for heating. The heating temperature is 1200 °C and the holding time is 2 hours. After the billet is taken out of the furnace, controlled rolling production is carried out. The temperatures at each rolling node are as follows: the starting rolling temperature of the billet is in the range of 1050 °C - 1150 °C, the temperature entering the finishing mill is controlled at 900 - 970 °C, the finishing rolling temperature is controlled in the range of 830 °C - 930 °C, the coiling temperature is controlled in the range of 830 °C - 930 °C, and the wire rod rolling specification is Φ15.0 mm.

[0022] After the wire rod is rolled into the specified specification by high-speed wire rod rolling, coiling is carried out, and the cooling is controlled according to the following process parameters: the coiling temperature of the wire rod is 830 °C - 930 °C; after the wire rod is coiled, it passes through online spraying, and the temperature is 750 - 900 °C. After the wire rod passes through online spraying, it is cooled by water bath. The water bath temperature is 100 °C, and the outlet water temperature is 550 °C - 680 °C; after the wire rod passes through the online water bath, it is air-cooled by Stelmor, and the temperature after air-cooling is 450 °C - 580 °C.

[0023] The wire rod produced by the present invention has a structure of sorbite + pearlite, the sorbite content is ≥ 95%, the tensile strength of the wire rod is ≥ 1500 MPa, the tensile strength fluctuation of the same coil is ≤ 40 MPa, the wire diameter after drawing is Φ7.0 mm, and the tensile strength of the wire is ≥ 2100 MPa. The specific test results are shown in Table 1.

[0024] Table 1

[0025] Test Items Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8 Sorbite Content % 95 97 98 95 96 97 97 97 Wire Rod Tensile Strength MPa 1507 1532 1536 1524 1516 1509 1517 1530 Steel Wire Tensile Strength MPa 2135 2156 2145 2132 2152 2147 2139 2151

[0026] Comparative Example 1

[0027] The following component billets are used: C: 0.90 - 1.00%, Si: 0.80 - 1.30%, Mn: 0.50 - 0.80%, Cr: 0.20 - 0.50%, Al: 0.010 - 0.050%, V: 0.02 - 0.20%, Nb: 0.005 - 0.025%, Ti: 0.005 - 0.025%, P ≤ 0.010%, S ≤ 0.010%, Cu: ≤ 0.05%, and the rest is Fe and inevitable residual elements. The component system is the same as that in Example 1.

[0028] The blank is a continuously cast bloom with a specification of 390*510 mm, which is rolled into an intermediate billet with a specification of 200*200 mm. After the surface of the blank is finish-treated, it enters the heating furnace for heating. The heating temperature is 1200 °C and the holding time is 2 hours. After the blank is taken out of the furnace, controlled rolling production is carried out. The temperatures at each rolling node are as follows: the starting rolling temperature of the blank is in the range of 1050 °C - 1150 °C, the temperature entering the finishing mill is controlled at 900 - 970 °C, the finishing rolling temperature is controlled in the range of 830 °C - 930 °C, the laying head temperature is controlled in the range of 830 °C - 930 °C, and the wire rod rolling specification is Φ15.0 mm.

[0029] After the wire rod is rolled into the specified specification by high-speed wire rod rolling, it lays its head, and the cooling is controlled according to the following process parameters: the laying head temperature of the wire rod is 830 °C - 930 °C; after the wire rod lays its head, it is cooled by water bath, the water bath temperature is 100 °C, and the water outlet temperature is 550 °C - 700 °C; after the wire rod passes through the on-line water bath, it is air-cooled by Stelmor, and the temperature after air-cooling is 450 °C - 600 °C.

[0030] The wire rod produced by the present invention has a structure of sorbite + pearlite, the sorbite content is ≥90%, the tensile strength of the wire rod is ≥1470 MPa, the tensile strength fluctuation of the same coil is ≤70 MPa, the wire diameter after drawing is Φ7.0 mm, and the tensile strength of the wire is ≥2100 MPa. The specific test results are shown in Table 2.

[0031] Table 2

[0032] Test Items Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8 Sorbite Content % 90 95 93 95 92 97 92 95 Wire Rod Tensile Strength MPa 1472 1503 1538 1517 1528 1510 1527 1486 Steel Wire Tensile Strength MPa 2109 2130 2149 2132 2129 2119 2108 2136

[0033] Example 2

[0034] The following composition blank is used: C: 0.92 - 0.98%, Si: 0.90 - 1.30%, Mn: 0.50 - 0.80%, Cr: 0.30 - 0.50%, Al: 0.010 - 0.050%, V: 0.02 - 0.10%, Nb: 0.005 - 0.025%, Ti: 0.005 - 0.025%, P≤0.010%, S≤0.010%, Cu: ≤0.05%, and the others are Fe and inevitable residual elements.

[0035] The blank is a continuously cast large round billet with a specification of 600 mm, and is rolled into an intermediate billet with a specification of 200*200 mm. After the surface of the blank is finish-treated, it enters the heating furnace for heating. The heating temperature is 1150°C and the holding time is 3 hours. After the blank is taken out of the furnace, controlled rolling production is carried out. The temperatures at each rolling node are as follows: the starting rolling temperature of the blank is in the range of 1000°C - 1100°C, the temperature entering the finishing mill is controlled at 900 - 980°C, the finishing rolling temperature is controlled in the range of 860°C - 960°C, the coiling temperature is controlled in the range of 860°C - 960°C, and the wire rod rolling specification is Φ14.0 mm.

[0036] After the wire rod is rolled into the specified specification by high-speed wire rod rolling, coiling is carried out, and the cooling is controlled according to the following process parameters: the coiling temperature of the wire rod is 860°C - 960°C; after the wire rod is coiled, it passes through online spraying, and the temperature is 750 - 900°C. After the wire rod passes through online spraying, it is cooled by water bath, and the water outlet temperature is 550°C - 680°C; after the wire rod passes through the online water bath, it is air-cooled by Stelmor, and the temperature after air-cooling is 450°C - 580°C.

[0037] The wire rod produced by the present invention has a structure of sorbite + pearlite, the sorbite content is ≥95%, the tensile strength of the wire rod is ≥1500 MPa, the fluctuation of the tensile strength in the same coil is ≤40 MPa, the wire diameter after drawing is Φ5.6 mm, and the tensile strength of the wire is ≥2200 MPa. The specific test results are shown in Table 3.

[0038] Table 3

[0039] Test Items Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8 Sorbite Content % 96 95 97 98 95 97 97 97 Wire Rod Tensile Strength MPa 1550 1537 1552 1540 1529 1559 1547 1542 Steel Wire Tensile Strength MPa 2278 2266 2254 2248 2259 2272 2257 2258

Claims

1. A method for producing a wire rod for ultra-high strength bridge cable steel wire, characterized in that: It includes billet heating, controlled rolling and controlled cooling. The heated billet is rolled with a large surface reduction rate. The wire drawing temperature is 800℃-960℃. The wire rod coil after wire drawing adopts a composite cooling method consisting of online spraying, online water bath and Stelmor air cooling. The spray is aimed at the overlap point of the wire rod coil. After spraying, the temperature of the entire wire rod circle is reduced to 750-900℃, the water bath temperature is 100±(0-5)℃, the water outlet temperature is 550℃-680℃, and the wire rod temperature after Stelmor air cooling is 450℃-580℃.

2. The method according to claim 1, characterized in that: The billet is obtained by slab rolling of continuous casting billet, and the slab rolling compression ratio is ≥4.

3. The method according to claim 1, characterized in that: The billet heating adopts a segmented heating process, the first stage temperature: 880-980℃, the second stage temperature: 980-1080℃, the soaking section temperature: 1080-1250℃, and the soaking section insulation time ≥2 hours.

4. The method according to claim 1, characterized in that: The starting rolling temperature is controlled to be 1000℃-1150℃, the total rolling ratio is ≥12, rough rolling is performed first and then finishing rolling, the finishing rolling control temperature is 880℃-980℃, and the final rolling temperature is controlled to be 800℃-960℃. The temperature of the billet is controlled by a cooling water tank before each node in the rolling process.

5. The method according to claim 1, characterized in that: During the Stelmore air cooling stage, more than 4 fans are turned on, the fan air volume is set to 100%, and the insulation cover is opened.

6. The method according to claim 1, characterized in that: The chemical element composition of the wire rod produced by the method is C: 0.90-1.00%, Si: 0.60-1.30%, Mn: 0.50-0.80%, Cr: 0.20-0.50%, Al: 0.010-0.050%, V: 0.02-0.20%, Nb: 0.005-0.035%, Ti: 0.005-0.035%, P≤0.015%, S≤0.015%, Cu: ≤0.05%, and the others are Fe and inevitable residual elements.

7. The method according to claim 6, characterized in that: The wire rod obtained by the method has a troostite content of ≥95%, a tensile strength of ≥1500MPa, a tensile strength fluctuation of the same coil of the wire rod of ≤40MPa, and a tensile strength of the steel wire after the wire rod is processed of ≥2200MPa.

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