Wire rod for high-strength tire bead wire and manufacturing process of wire rod

Abstract

The invention provides a wire rod for a high-strength tire bead steel wire. The wire rod comprises the following components in percentage by weight: 0.05%-0.12% of [C], 0.12%-0.24% of [Si], 0.40%-0.53% of [Mn], less than or equal to 0.010% of [P], 0.0060%-0.015% of [S], 0.0020%-0.0050% of [N], 0.0010%-0.0030% of total oxygen, 0.0007%-0.0020% of [Als], 0.0003%-0.0010% of [Nb], 0.0005%-0.0012% of [Mg] and 0.00005%-0.0004% of [Se]. And the balance of Fe and inevitable impurities. The manufacturing process comprises the steps of smelting, continuous casting, heating, rolling, wire rod rolling and wire rod cooling. The tensile strength of the wire rod produced through the method ranges from 410 MPa to 450 MPa, the area reduction rate ranges from 65% to 70%, the surface crack depth is not larger than 0.1 mm, and the inclusions are not larger than 20 micrometers. The wire rod structure is composed of ferrite and pearlite, the ferrite content is larger than 90%, and the grain size is not larger than 25 micrometers. The tire bead steel wire made of the wire rod has good service performance, the phenomenon that the low-carbon-content steel wire is broken in the machining process of the high-strength tire bead steel wire is avoided, and wire breakage is not larger than 2 times per ton.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a manufacturing process of a high-strength bead wire rod. BACKGROUND

[0002] The high-strength bead wire is a main component for ensuring the safety performance of a tire and plays a key role in the safe operation of an automobile. By using a steel wire with a low carbon content in the manufacturing process of the bead wire, the toughness of the bead wire during use can be improved, and the service life of the bead wire can be improved. In the actual manufacturing process, process measures are also taken to prevent the low-carbon-content steel wire from breaking prematurely during the service of the bead wire.

[0003] The patent document "High-carbon steel rod with tensile strength above 1200 MPa and surface shrinkage rate above 35% and preparation process thereof" (Patent No. CN101649416A) discloses a rod whose composition contains basic components such as C, Si, Mn, Cr and V, and optional components such as Ni, Cu, Al, B, Ti, Nb and Mo, and also contains the balance of Fe and impurities. The preparation process includes smelting, casting, rolling and controlled cooling processes in sequence. The rolling process is controlled at a rolling temperature of 1000-1100℃, and the wire drawing temperature is 870-930℃. The controlled cooling process adopts Stelmor controlled cooling, and fast cooling is adopted before and during the phase change, and slow cooling is adopted during the late phase change. The high-carbon steel rod has excellent mechanical properties, fewer alloying elements, low cost, and the preparation process is only a small adjustment to the existing high-carbon steel rod production process, and almost does not increase any production cost. The disadvantage is that it does not provide a technical solution to the problem of preventing the low-carbon-content steel wire in the high-strength bead wire from breaking. SUMMARY

[0004] The purpose of the present application is to overcome the above problems and deficiencies and provide a high-strength bead wire rod and a manufacturing process thereof, which prevents the low-carbon-content steel wire from breaking during service and improves the overall service life of the high-strength bead wire.

[0005] The purpose of the present application is achieved as follows:

[0006] A wire rod for bead wire, the composition of the wire rod is as follows in percentage by weight: [C] 0.05%~0.12%, [Si] 0.12%~0.24%, [Mn] 0.40%~0.53%, [P] ≤0.010%, [S] 0.0060%~0.015%, [N] 0.0020%~0.0050%, total oxygen 0.0010%~0.0030%, [Als] 0.0007%~0.0020%, [Nb] 0.0003%~0.0010%, [Mg] 0.0005%~0.0012%, [Se] 0.00005%~0.0004%; the rest is Fe and inevitable impurities.

[0007] The tensile strength of the wire rod is 410~450MPa MPa, the area reduction is 65%~70%, the wire rod scale thickness is 10um~20um, and the wire breaking is not more than 2 times per ton.

[0008] The microstructure of the wire rod is composed of ferrite and pearlite, and the ferrite content is greater than 90% in volume percentage; the inclusion is not more than 20um, and the grain size is not more than 25um.

[0009] The component design reasons of the wire rod are as follows:

[0010] [C]: the excessive carbon content in the wire rod will lead to the decrease of the service performance of the bead wire processed from the wire rod; the low carbon content of the wire rod cannot meet the strength requirement of the bead wire for the user; therefore, the carbon content is controlled to be 0.05%~0.12% in the application.

[0011] [Si]: the silicon element increases the eutectoid transformation temperature of the steel, makes the ferrite+pearlite structure of the wire rod coarse, and is not conducive to the complex deformation in the processing of the low-carbon bead wire; the silicon is the main deoxidizing element in the high-carbon steel; the excessive silicon content in the steel will cause the coarse silicate and inclusions after the deoxidization of the steel liquid; the low silicon content will cause the insufficient deoxidization of the steel liquid, thereby reducing the deformation capacity of the wire rod in the processing of the low-carbon steel wire; therefore, the silicon content is controlled to be 0.12%~0.24% in the application.

[0012] [Mn]: manganese is an element for improving the strength of the wire rod, which is conducive to ensuring that the bead wire processed from the wire rod meets the tensile strength requirement of the user; the manganese element has the effect of reducing the eutectoid transformation temperature of the steel, refining the ferrite+pearlite structure of the wire rod, improving the deformation capacity in the processing of the bead wire, and is conducive to the improvement of the fatigue life of the bead wire made of the wire rod; therefore, the manganese content is controlled to be 0.40%~0.53% in the application.

[0013] [P]: phosphorus reduces the deformation capacity of the wire rod in the processing of the bead wire, causes the cracking and breaking of the steel wire, and therefore, the phosphorus content is controlled to be ≤0.010% in the application.

[0014] [S]: Higher sulfur content in steel reduces the cold workability of the wire rod. Since MnS inclusions have good deformation ability, an appropriate amount of sulfur in the steel can reduce the harm of crystalline inclusions and improve the service performance of the wire rod made into rubber hose steel wire. Therefore, the sulfur content in the present application is controlled at 0.0060% to 0.015%.

[0015] [N]: The nitrogen content needs to be controlled within an appropriate range, so that the nitrogen element forms fine precipitates with Nb and V elements in the steel, improving the fracture resistance of the steel wire and improving the service performance of the steel wire. Therefore, the nitrogen content in the present application is controlled at 0.0020% to 0.0050%.

[0016] Total oxygen: When the oxygen content is low, the inclusions in the wire rod have poor deformation ability, which is not conducive to the processing of the bead steel wire. When the oxygen content in the wire rod is high, the inclusions in the steel are large in size and numerous, which can easily lead to cracking and breaking of the bead steel wire during processing. Therefore, the total oxygen content in the wire rod in the present application is controlled at 0.0010% to 0.0030%.

[0017] [Als]: When the acid-soluble aluminum content is high, large-sized Al2O3 inclusions will appear in the steel. When the acid-soluble aluminum content in the wire rod is too low, the melting point of the inclusions in the steel is high, and cracking can easily occur between the inclusions and the matrix during processing, leading to cracking and breaking of the bead steel wire during processing. Therefore, the acid-soluble aluminum content in the present application is controlled at 0.0007% to 0.0020%.

[0018] [Nb]: The niobium element can inhibit the grain growth of the billet during heating, thereby refining the ferrite and pearlite structure of the wire rod, improving the deformation ability of the wire rod during the processing of the bead steel wire, and improving the fatigue life of the wire rod made into the bead steel wire. However, a higher niobium content leads to a higher content of niobium carbonitride in the steel, and the wire rod is severely work-hardened during wire processing, which can easily lead to cracking and breaking of the steel wire. Therefore, the niobium content in the present application is controlled at 0.0003% to 0.0010%.

[0019] [Mg]: Magnesium element expands the low-melting-point region of oxidation, improves the deformation ability of the oxide, improves the drawing performance of the wire rod, improves the deformation performance of the high-strength bead steel wire, and also improves the deformation ability of the wire rod surface scale, making the wire rod surface scale easy to remove, improving the surface quality of the wire rod and the steel wire during processing, and improving the fatigue life of the wire rod made into the bead steel wire. However, too high magnesium content leads to the presence of magnesium aluminum spinel inclusions in the steel, which reduces the drawing performance of the wire rod. Therefore, the magnesium content in the present application is in the range of 0.0005% to 0.0012%.

[0020] [Se]: Selenium in steel with manganese, niobium and other elements form selenide, selenide than sulfide more fine, help to reduce the crack sensitivity of wire rod and steel wire in the process of processing, help to improve the wire rod processability, also help to improve the fatigue life of the tire bead wire made of wire rod in service process. But the high selenium content of steel reduces the drawing performance of wire rod. Therefore, the selenium content of the present application is controlled at 0.00005% to 0.0004%.

[0021] The second technical scheme of the present application is to provide a manufacturing process of a wire rod for tire bead wire, including smelting, continuous casting, heating, rolling, wire rod rolling, and wire rod cooling.

[0022] Smelting and continuous casting:

[0023] The molten steel is smelted by using molten iron + scrap steel; the molten iron has a carbon content of 4.0% to 4.7%, a phosphorus content of 0.03% to 0.07%, and a sulfur content of 0.030% to 0.047%. The temperature of the molten iron is 1250°C to 1350°C. High-quality molten iron is used to lay a foundation for improving the cleanliness of the steel.

[0024] The dolomite has a phosphorus content of not more than 0.05% and a sulfur content of not more than 0.04%, and a particle size of 10 to 50 mm; the small-particle lime has a phosphorus content of not more than 0.03% and a sulfur content of not more than 0.03%. By controlling the residual components of the steelmaking raw materials, a foundation is laid for controlling the sulfur content of the wire rod and improving the service performance of the tire bead wire made of the wire rod.

[0025] After the molten steel is smelted by the converter, the oxygen activity is controlled at 60 to 120 ppm, which promotes the transformation of inclusions in the steel into low-melting-point inclusions, and is beneficial to improving the fatigue life of the tire bead wire made of the rubber tube wire;

[0026] The molten steel is refined by LF, the refining time of the molten steel in the LF furnace is controlled at 30 to 45 min, and the refining temperature is controlled at 1470°C to 1540°C; the argon blowing flow rate of the molten steel during the refining process is 100-400 NL / min;

[0027] After the molten steel is refined, it is continuously cast, the cross-sectional size of the continuously cast billet is (300-340) mm * (400-440) mm, the continuous casting speed is 0.45 m / min to 0.60 m / min, and the superheat degree of the molten steel during the continuous casting process is not more than 28°C;

[0028] Heating: The continuously cast billet is hot-charged, the total time in the furnace is 3.6 to 4.7 hours, the temperature in the soaking section is controlled at 1120 to 1160°C, and the holding time is 30 to 50 min; through high-temperature diffusion of the continuously cast billet, the composition uniformity of the continuously cast billet is improved, laying a foundation for improving the service performance of the tire bead wire made of the wire rod.

[0029] Rolling: after the continuous casting billet is heated, continuous rolling is carried out, and the final rolling temperature of the continuous rolling is controlled at 880-980 DEG C; the section size of the continuous rolling billet is (140-180) mm * (140-180) mm; the above process makes the billet fully deform and improves the uniformity of the wire rod structure.

[0030] Wire rod rolling: the wire rod is produced by using the square billet, the total billet time in the furnace is 150-170 min, the soaking temperature is 1100-1150 DEG C, and the soaking time of the billet is 35-50 min. During the heating process of the billet, the residual oxygen content in the heating furnace is not more than 7%. After the billet is heated, the wire rod is drawn after the rough rolling, the intermediate rolling, the pre-precision rolling and the precision rolling. The wire rod temperature after the pre-precision rolling is 980-995 DEG C; the wire rod temperature after the precision rolling is 850-930 DEG C; the wire rod temperature after entering the double module is 910-940 DEG C; and the wire rod drawing temperature is controlled at 890-910 DEG C. Through the high wire rod drawing temperature, the cooling speed of the wire rod on the air cooling roller is improved, which lays a foundation for controlling the final structure of the wire rod. The wire rod rolling specification is 5.0-8 mm.

[0031] Wire rod cooling: after the wire rod is drawn, the wire rod is cooled on the air cooling roller, the phase change temperature of the wire rod is controlled at 570-590 DEG C, the phase change time of the wire rod on the air cooling line is 15-30 s, and the wire rod oxide scale thickness is 10-20 um. Through the implementation of the wire rod cooling process, a foundation is laid for improving the service performance of the wire rod for making the rubber tube steel wire; the wire rod oxide scale thickness is 10-20 um, which plays a role in protecting the surface structure of the wire rod from being corroded during storage and transportation. After the wire rod is collected and baled, the baling pressure is 28-32 tons, and the wire rod is packaged after baling to prevent the wire rod from being scratched during storage and transportation.

[0032] The wire rod has the beneficial effects that the tensile strength of the wire rod is 410-450 MPa, the surface reduction rate is 65-70%, the surface crack depth is not more than 0.1 mm, and the inclusion is not more than 20 um. The wire rod structure is composed of ferrite and pearlite, the ferrite content is greater than 90%, and the grain size is not more than 25 um. The wire rod for making the bead steel wire has good service performance, and the phenomenon of broken wire of the low-carbon content steel wire during the processing of the high-strength bead steel wire is avoided, and the broken wire is not more than 2 times per ton. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The figure is the inclusion size of the wire rod.

[0034] Figure 2 The figure is the microstructure metallographic diagram of the wire rod. DETAILED DESCRIPTION

[0035] The application is further described below through examples.

[0036] The embodiment of the present application smelts, continuously casts, heats, rolls, and cools the wire rod according to the component proportioning ratio of the technical scheme.

[0037] Wire rod rolling: the wire rod is produced by square billet, the total billet time in the furnace is 150 min to 170 min, the soaking section temperature is 1100 DEG C to 1150 DEG C, the billet soaking section holding time is 35 min to 50 min; the residual oxygen content in the heating furnace during the billet heating process is not more than 7%; after the billet is heated, the wire rod is operated after rough rolling, intermediate rolling, pre-precision rolling and precision rolling; the wire rod temperature after pre-precision rolling is 980 DEG C to 995 DEG C; the wire rod temperature before precision rolling is 850 DEG C to 930 DEG C; the wire rod temperature before entering the double module is 910 DEG C to 940 DEG C; the wire rod temperature after wire drawing is controlled at 890 DEG C to 910 DEG C; the wire rod rolling specification is 5 to 8 mm;

[0038] Wire rod cooling: the wire rod is cooled on the air cooling roller way after wire drawing, the wire rod phase change temperature is controlled at 570 DEG C to 590 DEG C, and the wire rod phase change time on the air cooling line is 5 to 15 s.

[0039] Further, smelting: the molten steel is smelted by molten iron + scrap steel; the molten iron carbon content used in the converter smelting is 4.0% to 4.7%, the phosphorus content is 0.03% to 0.07%, and the molten iron sulfur content is 0.030% to 0.047%; the molten iron temperature is 1250 DEG C to 1350 DEG C;

[0040] The dolomite phosphorus content is not more than 0.05%, the sulfur content is not more than 0.04%, and the particle size is 10 to 50 mm; the small particle white ash phosphorus content is not more than 0.03%, and the sulfur content is not more than 0.03%;

[0041] The molten steel oxygen activity is controlled at 60 to 120 ppm after the converter smelting.

[0042] The molten steel is refined by LF, the molten steel LF furnace refining time is controlled at 30 to 45 min, the refining temperature is controlled at 1470 DEG C to 1540 DEG C, and the molten steel argon blowing flow rate is 100 to 400 NL / min during the refining process.

[0043] Further, the molten steel is continuously cast after refining, the continuous casting billet section size is (300 to 340) mm * (400 to 440) mm, the continuous casting speed is 0.45 m / min to 0.60 m / min, and the molten steel superheat is not more than 28 DEG C during the continuous casting process.

[0044] Further, heating: the continuous casting billet is hot charged, the total time in the furnace is 3.6 to 4.7 hours; the soaking section temperature is controlled at 1120 DEG C to 1160 DEG C, and the holding time is 30 to 50 min;

[0045] Rolling: the continuous casting billet is heated and then continuously rolled, and the final rolling temperature is controlled at 880-980 DEG C; the cross-sectional size of the continuously rolled billet is (140-180) mm*(140-180) mm.

[0046] The component of the steel of the embodiment of the present application is shown in Table 1. The performance and structure of the wire rod of the embodiment of the present application are shown in Table 2. The main process parameters of the converter smelting of the wire rod of the embodiment of the present application are shown in Table 3. The main process parameters of the LF refining and continuous casting of the wire rod of the embodiment of the present application are shown in Table 4. The main process parameters of the heating and rolling of the wire rod of the embodiment of the present application are shown in Table 5. The main process parameters of the rolling of the wire rod of the embodiment of the present application are shown in Table 6. The wire rod scale thickness and wire breaking rate of the wire rod of the embodiment of the present application are shown in Table 7.

[0047] Table 1 Component of the steel of the embodiment of the present application (wt%)

[0048]

[0049] Table 2 Performance and structure of the wire rod of the embodiment of the present application

[0050]

[0051] Table 3 Main process parameters of the converter smelting of the wire rod of the embodiment of the present application

[0052]

[0053] Table 4 Main process parameters of the LF refining and continuous casting of the wire rod of the embodiment of the present application

[0054]

[0055] Table 5 Main process parameters of the heating and rolling of the wire rod of the embodiment of the present application

[0056]

[0057] Table 6 Main process parameters of the rolling of the wire rod of the embodiment of the present application

[0058]

[0059] Table 7 Wire rod scale thickness and wire breaking rate of the wire rod of the embodiment of the present application

[0060]

[0061] The tensile strength of the wire rod produced by the application is 410-450 MPa, the area reduction is 65%-70%, the surface crack depth is not more than 0.1 mm, and the inclusion is not more than 20 um. The wire rod is composed of ferrite and pearlite, the ferrite content is greater than 90%, and the grain size is not more than 25 um. The tire bead wire made of the wire rod has good service performance, and the phenomenon of broken wire of low-carbon content wire in the processing of high-strength tire bead wire is avoided, and the broken wire is not more than 2 times per ton.

[0062] In order to describe the application, the application is appropriately and sufficiently described by the above examples, the above embodiments are only used to illustrate the application, and are not limited to the application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the spirit and scope of the application should be included in the protection scope of the application, and the patent protection scope of the application should be limited by the claims.

Claims

1. A high-strength bead wire wire rod, characterized in that: The components of the wire rod are as follows by weight percentage: [C] 0.05% to 0.12%, [Si] 0.12% to 0.24%, [Mn] 0.40% to 0.53%, [P] ≤ 0.010%, [S] 0.0060% to 0.015%, [N] 0.0020% to 0.0050%, total oxygen 0.0010% to 0.0030%, [Als] 0.0007% to 0.0020%, [Nb] 0.0003% to 0.0010%, [Mg] 0.0005% to 0.0012%, [Se] 0.00005% to 0.0004%; the rest is Fe and unavoidable impurities.

2. The high-strength bead wire wire according to claim 1, characterized in that: The wire rod has a tensile strength of 410-450 MPaMPa, an area shrinkage of 65%-70%, a thickness of oxidized iron scale of 10um-20um, and wire breakage of no more than 2 times per ton.

3. The high-strength bead wire wire according to claim 1, characterized in that: The wire rod microstructure consists of ferrite and pearlite, and in terms of volume percentage, the ferrite content is greater than 90%, the inclusions are no greater than 20 μm, and the grain size is no greater than 25 μm.

4. A process for manufacturing a high-strength bead wire wire according to any one of claims 1 to 3, comprising smelting, continuous casting, heating, rolling, wire rod rolling, and wire rod cooling; characterized in that: Wire rod rolling: Wire rod is produced from square billets. The total billet in-furnace time is 150-170 minutes, the soaking section temperature is 1100-1150°C, and the soaking section holding time is 35-50 minutes. During the billet heating process, the residual oxygen content in the heating furnace is not more than 7%. After heating, the billet undergoes rough rolling, intermediate rolling, pre-finishing rolling, and finishing rolling before the wire rod is laid. The wire rod exiting pre-finishing rolling is 980-995°C; the wire rod entering finishing rolling is 850-930°C; the wire rod entering the double die is 910-940°C; the wire rod laying temperature is controlled at 890-910°C; the wire rod rolling specification is 5-8mm. Wire rod cooling: After spinning, the wire rod is cooled on an air-cooled roller. The phase change temperature of the wire rod is controlled at 570℃~590℃. The phase change time of the wire rod on the air-cooled line is 5~30s. The packaging pressure of the wire rod after coiling is 28 tons~32 tons.

5. The process for manufacturing a high-strength bead wire according to claim 4, characterized in that: Smelting: The molten steel is smelted with molten iron and scrap steel; the carbon content of the molten iron used in converter smelting is 4.0% to 4.7%, the phosphorus content is 0.03% to 0.07%, and the sulfur content is 0.030% to 0.047%; the molten iron temperature is 1250℃ to 1350℃; Dolomite has a phosphorus content of no more than 0.05%, a sulfur content of no more than 0.04%, and a particle size of 10 to 50 mm; small-grain white ash has a phosphorus content of no more than 0.03%, and a sulfur content of no more than 0.03%; The oxygen activity of molten steel after converter smelting is controlled at 60-120ppm; The molten steel is refined by LF, the LF furnace refining time of the molten steel is controlled at 30 to 45 minutes, and the refining temperature is controlled at 1470°C to 1540°C; the argon blowing flow rate of the molten steel during the refining process is 100 to 400NL / min.

6. The process for manufacturing a high-strength bead wire according to claim 4, characterized in that: After the molten steel is refined, it is continuously cast. The cross-sectional size of the continuous casting billet is (300-340) mm*(400-440) mm. The continuous casting speed is 0.45 m / min-0.60 m / min. The superheat of the molten steel during the continuous casting process is not greater than 28°C.

7. The process for manufacturing a high-strength bead wire according to claim 4, characterized in that: Heating: The continuous casting billet is hot charged, with a total furnace time of 3.6 to 4.7 hours; the soaking section temperature is controlled at 1120 to 1160°C, with a holding time of 30 to 50 minutes; Rolling: The continuous casting billet is heated and then continuously rolled, and the final rolling temperature is controlled at 880℃~980℃; the cross-sectional size of the continuous rolling billet is (140~180)mm*(140~180)mm.

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