High-carbon steel wire rod for steel wire with grade of 3600MPa and above and production method of high-carbon steel wire rod

Abstract

The invention relates to a high-carbon steel wire rod for a steel wire with the grade of 3600 MPa and above and a production method of the high-carbon steel wire rod. The high-carbon steel wire rod comprises the following chemical components in percentage by mass: 0.79%-0.85% of C, 0.15%-0.25% of Si, 0.40%-0.55% of Mn, 0.0040%-0.014% of P, 0.0040%-0.015% of S, 0.0020%-0.0050% of N, 0.0010%-0.0030% of total oxygen, 0.0005%-0.0020% of Als, 0.01%-0.04% of Cr, 0.0003%-0.0010% of V, 0.0015%-0.0030% of Als + V, 3%-10% of N / V and the balance of Fe and inevitable impurities. The production method comprises the steps of molten steel smelting and continuous casting, continuous casting billet heating and rolling, wire rod rolling, wire rod cooling and the like. According to the invention, systematic design is carried out from the aspects of chemical components, a smelting process and a rolling process, so that the manufactured wire rod meets the production requirements of steel wires at the grade of 3600MPa and above, the strength of tire cord steel wires can be effectively improved, the weight of tires is reduced, and the safety performance of the tires is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wire rod production, and in particular to a high carbon steel wire rod for 3600MPa and above grade steel wire and a production method thereof. Background Art

[0002] In order to reduce the manufacturing cost of automobile tires, it is necessary to increase the single-filament strength of tire cords, thereby reducing the amount of steel wire used and reducing tire manufacturing costs. On the other hand, the safety performance of tires can also be improved by increasing the single-filament strength of tire cords.

[0003] The Chinese invention patent with patent number CN202110817518.4 discloses a 70-grade high-performance cord steel and its rolling process. The chemical composition of the cord steel includes, by mass fraction: C: 0.70-0.75%, Si: 0.15-0.25%, Mn: 0.15-0.25%, P≤0.01%, S≤0.01%, Cr: 0.31-0.38%, B: 0.0005-0 .0009%, Nb: 0.006-0.012%, V: 0.006-0.012%, Als≤0.0008%, Ti≤0.0005%, and the rest are Fe and inevitable impurities; the metallographic structure of the cord steel includes lamellar pearlite, and the spacing of the lamellar pearlite is 160-180nm; in terms of volume fraction, the lamellar pearlite includes 85-90% troostite, and the remainder is pearlite ; The preparation process of the cord steel includes obtaining a cast billet; heating the cast billet in multiple stages to obtain a heated cast billet; rolling and air cooling the heated cast billet in sequence to obtain the cord steel; the steel movement rate in the air cooling is 40-45m / min, and the cooling rate of the air cooling is 16-20℃ / s; in the rolling, the entering finishing rolling temperature is 950-990℃, the entering sizing temperature is 940-980℃, and the spinning temperature is 925-955℃; the multi-stage heating includes preheating, heating stage one, heating stage two and soaking stage, the preheating includes heating at a temperature of ≤400℃ for ≥5min; the heating stage one includes heating at 400℃-800℃ for ≥10min, the heating stage two includes heating at 800℃-1000℃ for 60min-100min, and the soaking stage includes heating at 1000℃-1040℃ for 20min-60min.

[0004] The above-mentioned prior art focuses on the chemical composition of grade 70 high-performance cord steel and its rolling process, but does not disclose a technical solution for preparing wire rods for steel wires of 3600 MPa and above. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a high carbon steel wire rod for 3600MPa and above grade steel wire and a production method thereof, and to carry out a systematic design from the aspects of chemical composition, smelting process and rolling process, so that the manufactured wire rod can meet the production requirements of 3600MPa steel wire, thereby effectively improving the strength of tire cord steel wire, reducing tire weight, and improving tire safety performance.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The high carbon steel wire rod for steel wire of level 3600MPa and above proposed by the present invention comprises the following chemical components in mass percentage: C: 0.79%-0.85%, Si: 0.15%-0.25%, Mn: 0.40%-0.55%, P: 0.0040%-0.014%, S: 0.0040%-0.015%, N: 0.0020%-0.0050%, total oxygen: 0.0010%-0.0030%, Als: 0.0005%-0.0020%, Cr: 0.01%-0.04%, V: 0.0003%-0.0010%, Als+V: 0.0015%-0.0030%, N / V: 3-10, and the balance is Fe and unavoidable impurities.

[0008] A method for producing a high carbon steel wire rod for steel wire of 3600 MPa or above, the method comprising the following steps:

[0009] S1. Molten steel smelting and continuous casting: Molten steel is smelted by molten iron + scrap steel, and then continuously cast to obtain continuous casting billets;

[0010] S2. Heating and rolling of continuous casting billets: hot charging of continuous casting billets, continuous rolling of continuous casting billets after heating, and final rolling temperature of continuous rolling is controlled at 840℃-940℃;

[0011] S3. Wire rod rolling: Wire rod is produced by billet, the total furnace time of billet is 150min-170min, the temperature of soaking section is 1100℃-1150℃, and the insulation time of billet soaking section is 30-50min; after billet is heated, it goes through rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling, and then wire rod spinning operation is carried out;

[0012] S4, wire rod cooling.

[0013] Furthermore, in step S1, the oxygen activity of the molten steel after converter smelting is controlled at 60-120 ppm.

[0014] Furthermore, in step S1, the molten steel is refined by LF, the LF refining time of the molten steel is controlled at 30-50min, and the refining temperature is controlled at 1470°C-1540°C; the cross-sectional size of the continuous casting billet is (300mm-340mm)*(400mm-430mm), the starting straightening temperature of the continuous casting billet is ≥920°C, and the ingot segregation of the continuous casting billet is ≤level 1.

[0015] Furthermore, in step S2, the total furnace time for heating the continuous casting billet is controlled at 3.6-4.7 hours; the temperature of the soaking section is controlled at 1200-1220° C., and the holding time is 30-50 minutes.

[0016] Furthermore, in step S2, the cross-sectional size of the continuous rolling billet is (140-180)*(140-180); the inclusion size in the core of the continuous rolling billet is ≤35μm, the inclusion size at a position 1 / 4 of the thickness from the surface of the continuous rolling billet is ≤30μm, and the inclusion size at the surface of the continuous rolling billet is ≤25μm; the ingot segregation of the continuous rolling billet is ≤level 1, the thickness of the pro-eutectoid cementite of the continuous rolling billet is ≤5μm, and the thickness of the decarburized layer on the surface of the continuous rolling billet is ≤500μm.

[0017] Furthermore, in step S3, during the heating process of the steel billet in the austenite high temperature zone, the carbon content at the interface between austenite and cementite is 1.35%-1.6%.

[0018] Furthermore, in step S3, the pre-finishing rolling temperature of the wire rod is 980°C-995°C, the finishing rolling temperature is 850°C-930°C, and the double module temperature is 910°C-940°C; the wire rod spinning temperature is controlled at 910°C-940°C.

[0019] Furthermore, the rolling specification of the wire rod is 5.0-6.5 mm.

[0020] Furthermore, the step S4 specifically includes: placing the wire rod after spinning on an air-cooled roller for cooling; before cooling to 700°C, the wire rod cooling rate is 5-8°C / s, the wire rod phase change temperature is controlled at 620°C-670°C, the wire rod phase change time on the air-cooled line is 10-20s, the temperature difference of the wire rod in the same circle during the wire rod cooling process is ≤35°C, and the FeO thickness in the wire rod iron oxide scale is 8μm-12μm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention adopts a unique design of trace element content in high carbon steel and quality design of the entire smelting process. The produced wire rod has a tensile strength of 1100MPa-1200MPa, network cementite ≤level 1, ingot segregation ≤level 1, inclusion size ≤20mm, high drawing and stranding performance, and can stably manufacture steel wire for cords of 3600MPa and above, with a wire breakage rate ≤1 time / ton. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic flow chart of a method for producing a high carbon steel wire rod for steel wires of 3600 MPa or above proposed by the present invention; DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] The high carbon steel wire rod for steel wire of 3600MPa and above proposed by the present invention comprises the following chemical components in mass percentage: C: 0.79%-0.85%, Si: 0.15%-0.25%, Mn: 0.40%-0.55%, P: 0.0040%-0.014%, S: 0.0040%-0.015%, N: 0.0020%-0.0050%, total oxygen: 0.0010%-0.0030%, Als: 0.0005%-0.0020%, Cr: 0.01%-0.04%, V: 0.0003%-0.0010%, and the balance is Fe and unavoidable impurities, wherein Als+V: 0.0015%-0.0030%, N / V: 3-10.

[0026] The reasons for setting the range of the above ingredients are as follows:

[0027] Too high a carbon content in the wire rod will cause the strength of the steel wire processed from the wire rod to exceed the user's required range; too low a carbon content in the wire rod cannot meet the user's strength requirements for the steel wire. Therefore, in the present invention, the carbon content is controlled within a range of 0.79% to 0.85%.

[0028] Silicon element will increase the eutectoid transformation temperature of steel, make the pearlite structure of wire rod coarse, which is not conducive to the complex deformation of cord wire processing. Silicon is the main deoxidizing element in high carbon steel. If the silicon content in steel is too high, coarse silicates and impurities will appear after the steel liquid is deoxidized. If the silicon content is low, the steel liquid will be insufficiently deoxidized, thereby reducing the deformation ability of the wire rod during the steel wire processing process. Therefore, in the present invention, the silicon content is controlled at 0.15% to 0.25%.

[0029] Manganese is an element that improves the strength of wire rods, which helps to ensure that the steel wire processed from wire rods meets the tensile strength requirements of users; manganese has the effect of reducing the eutectoid transformation temperature of steel, refining the pearlite structure of wire rods, and improving the deformation ability of wire rods in the process of processing cord steel wires. Therefore, in the present invention, the manganese content is controlled at 0.40% to 0.55%.

[0030] Phosphorus can reduce the Fe between the wire rod matrix and the iron oxide scale. 2 SiO 4 The melting point of the FeO eutectic product improves the removal performance of the iron oxide scale on the surface of the steel wire in the high-pressure water descaling process, thereby improving the removal performance of the iron oxide scale on the surface of the wire rod in the user's mechanical dephosphorization process. Therefore, in the present invention, the phosphorus content is controlled at 0.0040% to 0.014%.

[0031] A higher sulfur content in steel will reduce the cold working performance of the wire rod. Since MnS inclusions have good deformation ability, an appropriate amount of sulfur in the steel can reduce the harm of crystal inclusions. At the same time, the S element can also reduce the Fe between the wire rod matrix and the iron oxide scale. 2 SiO 4 The melting point of the FeO eutectic product is increased, and the removal performance of the iron oxide scale on the surface of the steel wire in the high-pressure water descaling process is improved. Therefore, in the present invention, the sulfur content is controlled to be 0.0040% to 0.015%.

[0032] The nitrogen content needs to be controlled within an appropriate range so that the nitrogen element and the V element in the steel form fine precipitation phases to improve the fracture resistance of the steel wire. Therefore, in the present invention, the nitrogen content is controlled within a range of 0.0020% to 0.0050%.

[0033] 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 steel wire; when the oxygen content in the wire rod is high, the inclusions in the steel are large in size and large in number, which easily leads to cracking and breaking of the bead wire during processing. Therefore, in the present invention, the total oxygen content in the wire rod is controlled to be 0.0010% to 0.0030%.

[0034] When the acid-soluble aluminum content is high, larger Al particles will appear in the steel. 2 O 3 Inclusions: 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 cracks are likely to occur between the inclusions and the matrix during processing, resulting in cracking and breaking of the cord steel wire during processing. Therefore, in the present invention, the acid-soluble aluminum content is controlled to be 0.0005% to 0.0020%.

[0035] Chromium can improve the strength of wire rods and steel wires, improve the stability of austenite, and promote the decrease of the transformation temperature from austenite to pearlite. During the heat treatment process of low-carbon steel wire, the fluctuation of the chromium content in the steel wire leads to the difference in the phase transition point of the steel wire, thereby causing the strength fluctuation of the steel wire. In order to improve the stability of the strength of the steel wire, the chromium content is controlled within 0.01% to 0.04% in the present invention.

[0036] The vanadium element is dissolved in the steel to improve the strength of the steel. However, the vanadium content in the steel should not be too high to prevent the higher wire rod strength from reducing the drawing performance of the wire rod. The vanadium element can inhibit the growth of the grains of the steel billet when the billet is heated, thereby refining the pearlite structure of the wire rod, which is beneficial to improving the uniform deformation ability of the wire rod during the cord wire processing process. Therefore, in the present invention, the vanadium content is controlled at 0.0003% to 0.0010%.

[0037] High nitrogen content in steel will cause strain aging and reduce the drawing performance of steel wire. Therefore, the present invention controls the N / V ratio in steel to 3-10, on the one hand, to exert the microstructure refinement effect of V, and on the other hand, to reduce the strain aging effect of nitrogen in steel.

[0038] In order to give full play to the effects of aluminum and vanadium elements, in the present invention, Als+V is controlled to 0.0015%-0.0030%.

[0039] A method for producing a high carbon steel wire rod for steel wire of 3600MPa or above, the production method specifically comprising the following steps:

[0040] S1. Molten steel smelting and continuous casting: Molten steel is smelted in a converter using molten iron + scrap steel, and then continuously cast to obtain a continuous casting billet; wherein, the oxygen activity of the molten steel after converter smelting is controlled at 60-120ppm; the molten steel is refined by LF, the LF refining time of the molten steel is controlled at 30-50min, and the refining temperature is controlled at 1470℃-1540℃.

[0041] The cross-sectional dimensions of the continuous casting billet are (300mm-340mm)*(400mm-430mm), the starting straightening temperature of the continuous casting billet is ≥920℃, and the ingot segregation of the continuous casting billet is ≤level 1.

[0042] S2. Heating and rolling of continuous casting slabs: hot charging of continuous casting slabs, continuous rolling of continuous casting slabs after heating, and final rolling temperature of continuous rolling is controlled at 840℃-940℃; wherein, the total furnace time of continuous casting slab heating is controlled at 3.6-4.7 hours, the temperature of soaking section is controlled at 1200-1220℃, and the holding time is 30-50min;

[0043] The cross-sectional size of the continuous rolling billet is (140-180)*(140-180); the size of inclusions in the core of the continuous rolling billet is ≤35mm, the size of inclusions at a distance of 1 / 4 of the thickness from the surface of the continuous rolling billet is ≤30μm, and the size of inclusions at the surface of the continuous rolling billet is ≤25μm. The ingot segregation of the continuous rolling billet is ≤1 level, the thickness of the pro-eutectoid cementite of the continuous rolling billet is ≤5μm, and the thickness of the decarburized layer on the surface of the continuous rolling billet is ≤500μm.

[0044] S3. Wire rod rolling: Wire rod is produced from square billet, the total furnace time of billet is 150min-170min, the temperature of soaking section is 1100℃-1150℃, the soaking section holding time of billet is 30-50min; the billet heating process is in the austenite high temperature zone, the carbon content at the interface of austenite and cementite is 1.35%-1.6%. Through the high temperature diffusion of the billet, the segregation of carbon, manganese and other elements is reduced.

[0045] After the billet is heated, it goes through rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling before the wire rod spouting operation is carried out; the pre-finishing rolling temperature of the wire rod is 980℃-995℃, the finishing rolling temperature is 850℃-930℃, and the double module temperature is 910℃-940℃; the wire rod spouting temperature is controlled at 910℃-940℃. The higher spouting temperature of the wire rod increases the cooling speed of the wire rod on the air-cooled roller, laying the foundation for controlling the final structure of the wire rod.

[0046] The rolling specification of the wire rod is 5.0-6.5 mm.

[0047] S4, wire rod cooling: Place the wire rod after spinning on the air cooling roller for cooling. Before cooling to 700℃, the wire rod cooling speed is 5-8℃ / s, the wire rod phase change temperature is controlled at 620℃-670℃, the wire rod phase change time on the air cooling line is 10-20s, the wire rod cooling process temperature difference in the same circle is ≤35℃, and the FeO thickness in the wire rod oxide scale is 8μm-12μm.

[0048] The technical solution of the present invention is further described below by means of specific embodiments:

[0049]

[0050]

[0051]

[0052] The present invention adopts a unique design of trace element content of high carbon steel and quality design of the whole smelting process, and the tensile strength of the produced wire rod can reach 1100MPa-1200MPa. Taking the wire rod with a diameter of 5.5mm as an example, it is initially drawn to 1.4mm, and then further drawn to 0.20mm after sorbitization treatment. The final steel wire strength can reach 3610MPa-3670MPa, network cementite ≤1 level, ingot segregation ≤1 level, inclusion size ≤20mm, and high drawing and plying performance. Therefore, it can stably manufacture steel wire for cords of 3600MPa and above, and the wire breakage rate is ≤1 time / ton, which fully meets the production needs of users for ultra-high strength steel cords.

[0053] Matters not described in detail in the present invention are all known technologies.

[0054] The embodiments described above are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A high carbon steel wire rod for steel wire of 3600MPa and above, characterized in that: The high carbon steel wire rod includes the following chemical components in mass percentage: C: 0.79%-0.85%, Si: 0.15%-0.25%, Mn: 0.40%-0.55%, P: 0.0040%-0.014%, S: 0.0040%-0.015%, N: 0.0020%-0.0050%, total oxygen: 0.0010%-0.0030%, Als: 0.0005%-0.0020%, Cr: 0.01%-0.04%, V: 0.0003%-0.0010%, Als+V: 0.0015%-0.0030%, N / V: 3-10, and the balance is Fe and unavoidable impurities.

2. The method for producing a high carbon steel wire rod for steel wire of 3600MPa and above according to claim 1, characterized in that: The method comprises the following steps: S1. Molten steel smelting and continuous casting: Molten steel is smelted by molten iron + scrap steel, and then continuously cast to obtain continuous casting billets; S2. Heating and rolling of continuous casting billets: hot charging of continuous casting billets, continuous rolling of continuous casting billets after heating, and final rolling temperature of continuous rolling is controlled at 840℃-940℃; S3. Wire rod rolling: Wire rod is produced by billet, the total furnace time of billet is 150min-170min, the temperature of soaking section is 1100℃-1150℃, and the insulation time of billet soaking section is 30-50min; after billet is heated, it goes through rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling, and then wire rod spinning operation is carried out; S4, wire rod cooling.

3. The method for producing a high carbon steel wire rod for steel wire of 3600 MPa and above according to claim 2, characterized in that: In the step S1, the oxygen activity of the molten steel after converter smelting is controlled at 60-120 ppm.

4. The method for producing a high carbon steel wire rod for steel wire of 3600MPa and above according to claim 2, characterized in that: In the step S1, the molten steel is refined by LF, the LF refining time of the molten steel is controlled at 30-50min, and the refining temperature is controlled at 1470°C-1540°C; the cross-sectional size of the continuous casting billet is (300mm-340mm)*(400mm-430mm), the starting straightening temperature of the continuous casting billet is ≥920°C, and the ingot segregation of the continuous casting billet is ≤1 level.

5. The method for producing a high carbon steel wire rod for steel wire of 3600MPa and above according to claim 1, characterized in that: In the step S2, the total furnace time of the continuous casting billet is controlled at 3.6-4.7 hours; the temperature of the soaking section is controlled at 1200-1220°C, and the holding time is 30-50 minutes.

6. The method for producing a high carbon steel wire rod for steel wire of 3600 MPa and above according to claim 5, characterized in that: In the step S2, the cross-sectional size of the continuous rolling billet is (140-180)*(140-180); the inclusion size in the core of the continuous rolling billet is ≤35μm, the inclusion size at a position 1 / 4 of the thickness of the continuous rolling billet from the surface is ≤30μm, and the inclusion size at the surface of the continuous rolling billet is ≤25μm; the ingot segregation of the continuous rolling billet is ≤1 level, the thickness of the pro-eutectoid cementite of the continuous rolling billet is ≤5μm, and the thickness of the decarburized layer on the surface of the continuous rolling billet is ≤500μm.

7. The method for producing a high carbon steel wire rod for steel wire of 3600MPa and above according to claim 1, characterized in that: In step S3, during the heating process of the steel billet, the carbon content at the interface between austenite and cementite is 1.35%-1.6% in the austenite high temperature zone.

8. The method for producing a high carbon steel wire rod for steel wire of 3600 MPa and above according to claim 7, characterized in that: In step S3, the pre-finishing rolling temperature of the wire rod is 980°C-995°C, the finishing rolling temperature is 850°C-930°C, and the double module temperature is 910°C-940°C; the wire rod spinning temperature is controlled at 910°C-940°C.

9. The method for producing a high carbon steel wire rod for steel wire of 3600 MPa and above according to claim 8, characterized in that: The rolling specification of the wire rod is 5.0-6.5 mm.

10. The method for producing a high carbon steel wire rod for steel wire of 3600MPa and above according to claim 1, characterized in that: The step S4 specifically includes: placing the wire rod after spinning on an air-cooled roller for cooling; before cooling to 700°C, the wire rod cooling rate is 5-8°C / s, the wire rod phase change temperature is controlled to be 620°C-670°C, the wire rod phase change time on the air-cooled line is 10-20s, the temperature difference of the wire rod in the same circle during the wire rod cooling process is ≤35°C, and the FeO thickness in the wire rod iron oxide scale is 8μm-12μm.

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