Wire rod for tire bead wire and inclusion control method of wire rod

Abstract

The invention provides a wire rod for a tire bead steel wire and an inclusion control method of the wire rod. The wire rod comprises the following components in percentage by weight: 0.08%-0.13% of [C], 0.15%-0.30% of [Si], 0.40%-0.60% of [Mn], less than or equal to 0.013% of [P], 0.0030%-0.015% of [S], 0.0020%-0.0040% of [O], 0.01%-0.05% of [Cr], 0.01%-0.06% of [Cu] and the balance of Fe and inevitable impurities. The control method comprises the steps of smelting, continuous casting, heating, rolling, wire rod rolling and wire rod cooling. The size of the inclusions of the wire rod produced by the method is not larger than 20 microns, the inclusions are spherical, the tensile strength of the wire rod is 400-450 MPa, the area reduction rate is 60%-75%, the ductility is 30%-38%, and the quality requirement of a user for the wire rod for the low-carbon-content tire bead steel wire is met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a wire rod for bead wire and a method for controlling inclusions of the wire rod. BACKGROUND

[0002] High-strength bead wire needs to have good service performance, so low-strength bead wire is applied to the production process of high-strength bead wire to prevent the phenomenon of fracture of the bead wire from occurring in the service process. The raw material wire rod for producing such a steel wire needs to have the characteristic of small inclusions.

[0003] The patent document "Manufacturing method of wire rod for high-strength bead wire" (publication number: CN112342452B) discloses a wire rod, the composition of which is as follows: C: 0.83-0.86%, Si: 0.18-0.22%, Mn: 0.52-0.58%, P≤0.015%, S≤0.010%, Al≤0.005%, and the rest is Fe and inevitable impurities. The preparation method comprises a molten iron pretreatment process, a converter smelting process, an LF refining process, a CCM continuous casting process, a controlled rolling process, and a controlled cooling process. The wire rod is scattered on a Stelmor roller after passing through a wire feeding machine for air cooling. The specification of the wire rod is that the finished wire specification after drawing and copper plating is a middle wire that does not need to be spheroidized, the reduction rate can reach 93.2%, and at the same time, the wire has good strength and toughness combination, the strength of the steel wire is ≥2005 MPa, the torsion frequency is ≥16 times, and can be used for producing high-strength bead wire.

[0004] The above-mentioned wire rod mainly reduces the size and quantity of inclusions in the steel through refining slag in the refining process and covering agent in the continuous casting process to improve the drawing performance of the wire rod. Although the refining slag in the refining process and the covering agent in the continuous casting process can adsorb inclusions, they are also easy to cause the refining slag or the covering agent to be wrapped into the steel to form inclusions. With the increasingly strict requirements of the automobile industry on the quality of bead wire, it is urgent to develop a new way of wire rod for bead wire and control of inclusions to avoid removing inclusions by using refining slag and covering agent, improve the service performance of bead wire, and meet the quality requirements of users on the wire rod. SUMMARY

[0005] The purpose of the present application is to provide a wire rod for bead wire with inclusion size not greater than 20um and a method for controlling inclusions of the wire rod to overcome the above-mentioned problems and deficiencies.

[0006] The purpose of the present application is achieved as follows:

[0007] A wire rod for bead wire, the composition of the wire rod is as follows in percentage by weight: [C] 0.08%~0.13% [Si] 0.15%~0.30% [Mn] 0.40%~0.60% [P] ≤0.013% [S] 0.0030%~0.015% [O] 0.0020%~0.0040% [Cr] 0.01%~0.05% [Cu] 0.01%~0.06%, the rest is Fe and inevitable impurities.

[0008] The inclusion size in the wire rod is not more than 20um.

[0009] The tensile strength of the wire rod is 400~450MPa, the area reduction is 60%~75%, and the elongation is 30%~38%.

[0010] The component design reason of the wire rod is as follows:

[0011] C: carbon element is used for controlling the strength of the wire rod and the wire. Too low carbon content of the wire rod is not conducive to meet the strength requirement of the wire for the user. Too high carbon content of the wire rod, the wire rod has high wire breakage rate in the drawing and cabling process during the preparation of the wire. The present application uses low carbon content wire rod to prepare the bead wire, which improves the overall service performance of the bead wire as the tire reinforcing material together with the high carbon content bead wire. Therefore, the carbon content of the present application is controlled at 0.08%~0.13%.

[0012] Si: silicon element is mainly used for controlling the deoxidization degree of the steel. Too low silicon content in the steel, the oxygen content of the wire rod is high, and the drawing and cabling performance of the wire rod is reduced. Too high silicon content in the steel, the deoxidization product in the wire rod is increased, and the temperature of austenite to pearlite transformation of the wire rod is increased, which are not conducive to the mechanical processing performance of the wire rod. Therefore, the silicon content of the present application is controlled at 0.15%~0.30%.

[0013] Mn: manganese is an element for controlling the strength of the steel, so that the strength of the wire rod meets the requirement of the user. Therefore, the manganese content of the wire rod of the present application is controlled at 0.40%~0.60%.

[0014] P: the phosphorus element in the wire rod reduces the drawing performance of the wire rod in the preparation process of the bead wire, so its content is controlled at ≤0.013%.

[0015] S: the sulfur in the wire rod is a surface active element, which can promote the oxidation inclusion in the steel to be discharged from the molten steel, and reduce the size of the oxide inclusion in the steel. However, too high sulfur content in the wire rod will reduce the drawing performance of the wire rod. Therefore, the sulfur content of the wire rod of the present application is controlled at 0.0030%~0.015%.

[0016] O: Oxygen in steel is a surface active element, which can reduce the surface tension of molten steel in the smelting process, promote the absorption of oxidized inclusions by the top slag, thereby reducing the size of inclusions in molten steel. At the same time, the oxygen in the wire rod can control the deformation of inclusions in steel, reduce the harm of oxide inclusions to low-carbon steel wire during the deformation process of tire cord steel wire drawing. However, the oxygen content in steel should not be too high, otherwise it will reduce the drawing performance of the wire rod. Therefore, the oxygen content in the wire rod of the present application is controlled at 0.0020% to 0.0040%.

[0017] Cr, Cu: The chromium and copper content in the wire rod should not be too high, otherwise it will cause the strength fluctuation of the steel wire after heat treatment, increase the wire breaking rate during the steel wire drawing process. However, a certain amount of chromium and copper elements can improve the stability of the wire rod structure, refine the wire rod structure and improve the drawing performance of the wire rod. Therefore, the chromium and copper in the wire rod of the present application are controlled at 0.01% to 0.05% and 0.01% to 0.06% respectively.

[0018] The second technical scheme of the present application is to provide a wire rod for tire cord steel wire and a method for controlling inclusions, which comprises smelting, continuous casting, heating, rolling, wire rod rolling and wire rod cooling.

[0019] (1) Smelting and continuous casting:

[0020] The molten steel is smelted by molten iron + scrap steel, and the scrap steel ratio is 5% to 15%;

[0021] The molten iron carbon content used in the converter smelting is 4.1% to 4.5%, the silicon content is 0.20% to 0.25%, the manganese content is 0.50% to 0.55%, the phosphorus content is 0.045% to 0.07%, and the molten iron sulfur content is 0.03% to 0.045%. The temperature of the molten iron is 1280℃ to 1350℃. The alloy drying time before converter smelting should not be less than 4 hours, the manganese content in the manganese iron is 60% to 70%, and the sulfur content is not more than 0.03%, so as to prevent the sulfur content in the steel from being too high, which will cause the wire rod drawing process to break; the oxygen activity of the molten steel after converter smelting is controlled at 100 to 260ppm, which lays the foundation for the total oxygen content of the wire rod;

[0022] The molten steel is refined by LF refining, and the molten steel LF furnace refining time is controlled at 35 to 50min, and the refining temperature is controlled at 1490℃ to 1550℃; the Al2O3 of the refining molten steel tank is not more than 10%, which prevents large size inclusions from appearing in the steel, causing the wire rod drawing process to break.

[0023] The molten steel is continuously cast after refining, and the continuous casting billet section size is (300 to 340)mm*(400 to 440)mm, the continuous casting speed is 0.45m / min to 0.60m / min, and the intermediate package molten steel superheat is ≤30℃ during the continuous casting process.

[0024] (2) Heating:

[0025] Continuous casting billet heating and rolling: the continuous casting billet is hot charged, and the total furnace time is 3.2-4.0 hours; the preheating section temperature is not higher than 500 DEG C, the soaking section temperature is controlled at 1120-1140 DEG C, the holding time is 30-50 min, the continuous casting billet is heated at high temperature, the segregation of the billet is reduced, and the drawing performance of the wire rod is improved;

[0026] (3) Rolling:

[0027] The continuous casting billet is treated by high-pressure water descaling after heating, the descaling pressure is not lower than 18 MPa; the continuous casting billet is continuously rolled after high-pressure water descaling treatment; the final rolling temperature of continuous rolling is controlled at 920 DEG C-990 DEG C; the section size of the continuous rolling billet is (140-180) mm*(140-180) mm;

[0028] (4) Wire rod rolling:

[0029] The wire rod is produced by square billet, the total furnace time of the billet is 145 min-180 min, the soaking section temperature is at 1050 DEG C-1100 DEG C, and the soaking section holding time of the billet is 35-60 min; the high-temperature diffusion of the billet is carried out, the inclusions in the steel are uniformly deformed, and the basis for reducing the size of the inclusions is laid.

[0030] After the billet is heated, the wire rod is drawn after rough rolling, intermediate rolling, pre-precision rolling and precision rolling; the wire rod temperature out of the pre-precision rolling is 980 DEG C-1030 DEG C; the wire rod temperature into the precision rolling is 900 DEG C-960 DEG C; the wire rod temperature into the double module is 900 DEG C-920 DEG C; the wire rod rolling speed into the double module is 90-100 m / s; the wire rod drawing temperature is controlled at 870 DEG C-910 DEG C; through the implementation of the above process, the drawing performance of the wire rod is ensured to meet the user's requirements. The wire rod rolling specification is 5.0-8 mm;

[0031] (5) Wire rod cooling:

[0032] After drawing, the wire rod is cooled on the air-cooling roller way, the phase change temperature of the wire rod is controlled at 620 DEG C-670 DEG C, the phase change time of the wire rod on the air-cooling line is 10-25 s, the austenite of the wire rod is fully transformed into ferrite+pearlite structure, the appearance of martensite in the wire rod is prevented, the thickness of the iron oxide skin of the wire rod is controlled at 10 um-25 um. The wire rod coiling temperature is 250 DEG C-450 DEG C, the wire rod is packed after cooling, the packing pressure is 28 tons-33 tons. After the wire rod is packed, a packaging bag is added, so that the surface of the wire rod is prevented from being scratched during storage and transportation.

[0033] The beneficial effects of the present application are that:

[0034] The wire rod produced by the present application has an inclusion size of not more than 20 um, the inclusion type is spherical, the tensile strength of the wire rod is at 400-450 MPa, the area reduction is 60%-75%, and the elongation is 30%-38%, which meets the quality requirements of the user for the wire rod for low-carbon content bead wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The morphology and size of wire rod inclusions.

[0036] Figure 2 The morphology and thickness of the iron oxide scale on the wire rod surface. DETAILED DESCRIPTION

[0037] The present invention will be further described below by way of examples.

[0038] The embodiment of the present invention performs smelting, continuous casting, heating, rolling, wire rod rolling, and wire rod cooling according to the component ratio of the technical solution.

[0039] heating:

[0040] Heating and rolling of continuous casting slabs: The continuous casting slabs are hot charged, with a total furnace time of 3.2 to 4.0 hours; the preheating section temperature is not higher than 500°C, the soaking section temperature is controlled at 1120 to 1140°C, and the holding time is 30 to 50 minutes;

[0041] Rolling:

[0042] After heating, the continuous casting billet is subjected to high-pressure water descaling treatment, with the descaling pressure being not less than 18 MPa; the continuous casting billet is subjected to continuous rolling after the high-pressure water descaling treatment; the final rolling temperature is controlled at 920°C to 990°C; the cross-sectional size of the continuous rolling billet is (140-180) mm*(140-180) mm;

[0043] Wire rod rolling:

[0044] The wire rod is produced from billets. The total billet time in the furnace is 145 to 180 minutes. The soaking section temperature is 1050 to 1100 degrees Celsius. The billet soaking section holding time is 35 to 60 minutes.

[0045] After the billet is heated, it undergoes rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling before the wire rod extrusion operation. The wire rod exiting the pre-finishing rolling process is 980°C to 1030°C; the wire rod entering the finishing rolling process is 900°C to 960°C; the wire rod entering the dual module is 900°C to 920°C; the wire rod entering the dual module has a rolling speed of 90 to 100 m / s; the wire rod extrusion temperature is controlled at 870°C to 910°C; the wire rod rolling specification is 5 to 8 mm.

[0046] Wire rod cooling:

[0047] After spinning, the wire rod is cooled on an air-cooled roller, and the phase change temperature of the wire rod is controlled at 620°C to 670°C. The phase change time of the wire rod on the air-cooled line is 10 to 25 seconds.

[0048] Further, the molten steel is smelted by using molten iron and scrap steel; the oxygen activity of the molten steel after converter smelting is controlled to be 100-260ppm; the molten steel is refined by using LF refining, the LF refining time of the molten steel is controlled to be 35-50min, and the refining temperature is controlled to be 1490-1560℃; after the molten steel is refined, the continuous casting is carried out, the cross-sectional size of the continuous casting blank is (300-340)mm*(400-440)mm, the continuous casting speed is 0.45-0.60m / min, and the overheat degree of the molten steel in the tundish during the continuous casting process is less than or equal to 30℃.

[0049] Further, the proportion of the scrap steel is 5-15%.

[0050] Further, the carbon content of the molten iron used in the converter smelting is 4.1-4.5%, the silicon content is 0.20-0.25%, the manganese content is 0.50-0.55%, the phosphorus content is 0.045-0.07%, and the sulfur content of the molten iron is 0.03-0.045%; the temperature of the molten iron is 1280-1350℃.

[0051] Further, the drying time of the alloy before the converter smelting is not less than 4 hours, the manganese content in the ferromanganese is 60-70%, and the sulfur content is not more than 0.03%.

[0052] Further, the Al2O3 content of the magnesium-carbon brick of the refined molten steel tank is not more than 10%.

[0053] Further, during the cooling process of the wire rod, the thickness of the iron oxide skin of the wire rod is controlled to be 10-25um, the wire rod collecting temperature is 250-450℃, and the wire rod is packed after being cooled, and the packing pressure is 28-33 tons.

[0054] The composition of the wire rod in the embodiment of the application is shown in Table 1. The performance and inclusion size of the wire rod in the embodiment of the application are shown in Table 2. The main process parameters of the wire rod smelting in the embodiment of the application are shown in Table 3. The main process parameters of the wire rod smelting in the embodiment of the application are shown in Table 4. The main process parameters of the wire rod continuous casting in the embodiment of the application are shown in Table 5. The main process parameters of the wire rod rolling in the embodiment of the application are shown in Table 6.

[0055] Table 1 Composition of the wire rod in the embodiment of the application (wt%)

[0056] Examples C Si Mn P S Total oxygen Cr Cu 1 0.12 0.15 0.50 0.012 0.0092 0.0026 0.021 0.025 2 0.05 0.24 0.52 0.011 0.0078 0.0024 0.032 0.032 3 0.09 0.22 0.51 0.007 0.0082 0.0025 0.025 0.043 4 0.08 0.16 0.52 0.008 0.0047 0.0022 0.033 0.030 5 0.11 0.21 0.53 0.011 0.0032 0.0026 0.024 0.026 6 0.09 0.17 0.55 0.012 0.0085 0.0024 0.036 0.033

[0057] Table 2 Performance and inclusion size of the wire rod in the embodiment of the application

[0058] Examples Tensile strength, MPa Surface reduction, % Elongation, % Inclusion size, um 1 437 70 32 16 2 425 72 35 18 3 418 68 34 17 4 431 67 33 16 5 422 68 34 17 6 417 65 35 19

[0059] Table 3 Main process parameters of the wire rod smelting in the embodiment of the application

[0060]

[0061] Table 4 Main process parameters of the wire rod smelting in the embodiment of the present application

[0062]

[0063] Table 5 Main process parameters of the wire rod continuous casting in the embodiment of the present application

[0064]

[0065] Table 6 Main process parameters of the wire rod rolling in the embodiment of the present application

[0066]

[0067] As can be seen from the above, the wire rod produced by using the present application has the inclusion size of not more than 20um, the inclusion type is spherical, the tensile strength of the wire rod is 400-450MPa, the area reduction is 60%-75%, and the elongation is 30%-38%, which meet the quality requirements of the user for the wire rod for low-carbon content bead wire.

[0068] In order to describe the present application, the above embodiment has been properly and sufficiently described in the above. The above embodiment is only used for describing the present application, but not for limiting the present application. Any modification, equivalent replacement, improvement, etc. made by the ordinary skilled in the art without departing from the spirit and scope of the present application should be included in the protection scope of the present application. The patent protection scope of the present application should be defined by the claims.

Claims

1. A wire rod for bead wire, characterized in that: The components of the wire rod are as follows by weight percentage: [C] 0.08% to 0.13%, [Si] 0.15% to 0.30%, [Mn] 0.40% to 0.60%, [P] ≤ 0.013%, [S] 0.0030% to 0.015%, [O] 0.0020% to 0.0040%, [Cr] 0.01% to 0.05%, [Cu] 0.01% to 0.06%, and the rest is Fe and unavoidable impurities.

2. The wire rod for bead wire according to claim 1, characterized in that: The size of inclusions in the wire rod is no greater than 20 μm.

3. The wire rod for bead wire according to claim 1, characterized in that: The wire rod has a tensile strength of 400-450 MPa, an area shrinkage of 60%-75%, and an elongation of 30%-38%.

4. A method for controlling inclusions in a wire rod for bead 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: heating: Heating and rolling of continuous casting slabs: The continuous casting slabs are hot charged, with a total furnace time of 3.2 to 4.0 hours; the preheating section temperature is not higher than 500°C, the soaking section temperature is controlled at 1120 to 1140°C, and the holding time is 30 to 50 minutes; Rolling: After heating, the continuous casting billet is subjected to high-pressure water descaling treatment, with the descaling pressure being not less than 18 MPa; the continuous casting billet is subjected to continuous rolling after the high-pressure water descaling treatment; the final rolling temperature is controlled at 920°C to 990°C; the cross-sectional size of the continuous rolling billet is (140-180) mm*(140-180) mm; Wire rod rolling: The wire rod is produced from billets. The total billet time in the furnace is 145 to 180 minutes. The soaking section temperature is 1050 to 1100 degrees Celsius. The billet soaking section holding time is 35 to 60 minutes. After the billet is heated, it undergoes rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling before the wire rod extrusion operation. The wire rod exiting the pre-finishing rolling process is 980°C to 1030°C; the wire rod entering the finishing rolling process is 900°C to 960°C; the wire rod entering the dual module is 900°C to 920°C; the wire rod entering the dual module has a rolling speed of 90 to 100 m / s; the wire rod extrusion temperature is controlled at 870°C to 910°C; the wire rod rolling specification is 5 to 8 mm. Wire rod cooling: After spinning, the wire rod is cooled on an air-cooled roller, and the phase change temperature of the wire rod is controlled at 620°C to 670°C. The phase change time of the wire rod on the air-cooled line is 10 to 25 seconds.

5. The method for controlling inclusions in bead wire according to claim 4, wherein: Smelting and continuous casting: Molten steel is smelted with molten iron + scrap steel; The oxygen activity of molten steel after converter smelting is controlled at 100-260ppm; The molten steel is refined by LF, the LF furnace refining time of the molten steel is controlled at 35 to 50 minutes, and the refining temperature is controlled at 1490℃ to 1560℃; 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 in the intermediate ladle during the continuous casting process is ≤30°C.

6. The method for controlling inclusions in bead wire according to claim 5, wherein: The proportion of scrap steel is 5% to 15%.

7. The method for controlling inclusions in bead wire according to claim 5, wherein: The molten iron used in converter smelting has a carbon content of 4.1% to 4.5%, a silicon content of 0.20% to 0.25%, a manganese content of 0.50% to 0.55%, a phosphorus content of 0.045% to 0.07%, and a sulfur content of 0.03% to 0.045%; the molten iron temperature is 1280°C to 1350°C.

8. The method for controlling inclusions in bead wire according to claim 5, wherein: The alloy drying time before converter smelting shall not be less than 4 hours, the manganese content in ferromanganese shall be 60% to 70%, and the sulfur content shall not exceed 0.03%.

9. The method for controlling inclusions in bead wire according to claim 5, wherein: The Al2O3 content of magnesia carbon bricks in refined steel tanks shall not exceed 10%.

10. The method for controlling inclusions in bead wire according to claim 4, wherein: During the wire rod cooling process, the thickness of the wire rod iron oxide scale is controlled at 10-25um, the wire rod coiling temperature is 250℃-450℃, and the wire rod is packaged after cooling with a packaging pressure of 28-33 tons.

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