Application of microalloyed 72C wire rod in intensive steel cord

Abstract

The invention discloses an application of a microalloyed 72C wire rod in an intensive steel cord. The application comprises the following steps: (1) drawing a microalloyed 72DACr wire rod with the diameter of 5.5 mm to obtain a heavy drawn steel wire; (2) drawing the heavy drawn steel wire by using a servo direct-driven wire drawing machine to obtain a medium drawn steel wire; (3) treating the medium-drawn steel wire to obtain a brass-plated steel wire; (4) the brass-plated steel wire is drawn into a wet-drawn steel wire with the diameter of 0.18-0.35 mm through wet-drawing equipment, the wet-drawing equipment comprises single dies of the first to twenty-first passes and double dies of the second to twenty-third passes, during double-die drawing, one drawing pass adopts two dies for drawing, the compression ratio of the double wire-drawing dies adopts an average distribution principle, the number of winding coils of the first-pass die is 1.0, the number of winding coils of the second-pass die is 1.0, the number of winding coils of the third-pass die is 1.0, and the number of winding coils of the fourth-pass die is 1.0; the winding number of turns of the second to tenth pass molds is 3.5, the winding number of turns of the eleventh pass mold is 3.0, the winding number of turns of the twelfth to fifteenth pass molds is 3.5, the winding number of turns of the sixteenth to seventeenth pass molds is 2.5, and the winding number of turns of the eighteenth to twenty-third pass molds is 1.5. The steel cord is used as a raw material for replacing 82C to produce the intensive steel cord for the TBR tire.

Description

Technical Field

[0001] The invention relates to the application of 72DACr wire rod, and in particular to the application of micro-alloyed 72C wire rod in dense steel cord. Background Art

[0002] With the establishment and implementation of my country's "green and low-carbon" environmental protection strategy, the production of steel cords in the future will adopt new technologies, new processes and new materials to create a market, so as to adapt to the development of green tire manufacturing and reduce carbon dioxide emissions. As a high-value-added product, higher-strength steel cords can reduce the use of steel cords and rubber in tires, reduce tire rolling resistance and fuel consumption, and achieve tire lightweighting while ensuring tire safety, thus contributing to the development of "green and low-carbon" environmental protection.

[0003] The diameter of the single wire of the TBR carcass steel cord is very thin, and the structure is mainly intensive. For the development of steel cord for TBR tires, the single wire diameter is generally controlled at 0.20~0.35mm. With the continuous optimization of tire design technology, some tire structure designs require the single wire diameter of the steel cord to be around 0.18mm. In order to meet customer requirements, the strength and performance of the steel cord are usually improved by increasing the carbon content of the wire rod, but high-carbon wire rods often have problems such as center segregation, grain boundary cementite and uneven organization, and are prone to hypereutectoid cementite and uneven organization, which reduces the plasticity of the wire rod and is not conducive to drawing performance. After the high-carbon wire rod is processed into brass-plated steel wire in the semi-finished process, the wire breakage rate is high during the wet drawing process to draw into single wire and the cord process to twist; and the curling degree of the wet-drawn single wire is not easy to control, resulting in poor bulging of the finished cord, thereby affecting production efficiency and yield rate.

[0004] In order to solve the above problems, the present invention proposes an application of microalloyed 72C wire rod in dense steel cord. Microalloyed wire rod actually reduces the carbon and manganese content in the wire rod and increases the chromium content. By reasonably improving the chromium and manganese content, the pearlite lamellae can be effectively refined and the formation of grain boundary network cementite can be inhibited, thereby improving the troostite conversion rate and drawing performance, and achieving high plasticity and high strength of the material. Under the premise of ensuring product performance and quality, the wire breakage rate of the steel cord in the entire production process is reduced, and the production efficiency and yield rate are improved. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention proposes an application of a micro-alloyed 72C wire rod in a dense steel cord, and uses the micro-alloyed 72DACr wire rod as a raw material to replace 82C to produce a dense steel cord for TBR tires.

[0006] The technical solution adopted by the present invention is: application of a micro-alloyed 72C wire rod in a dense steel cord. (1) Drawing a microalloyed 72DACr wire rod with a diameter of 5.5 mm to obtain a large drawn steel wire; (2) using a servo direct-drive wire drawing machine to draw the large-drawn steel wire to obtain a medium-drawn steel wire; (3) Processing the middle drawn steel wire to obtain brass plated steel wire; (4) The brass-plated steel wire is drawn into a wet-drawn steel wire with a diameter of 0.18-0.35 mm by a wet-drawing device. The wet-drawing device includes a single die for the 1st to 21st passes and a double die for the 22nd to 23rd passes. During double-die drawing, two dies are used for drawing in one drawing pass. The compression rate of the double drawing die adopts the principle of average distribution. The number of winding coils of the first die is 1.0, the number of winding coils of the 2nd to 10th die is 3.5, the number of winding coils of the 11th die is 3.0, the number of winding coils of the 12th to 15th die is 3.5, the number of winding coils of the 16th to 17th die is 2.5, and the number of winding coils of the 18th to 23rd die is 1.5.

[0007] On the basis of the above scheme, as a preference, the carbon equivalent CEQ of the microalloyed 72DACr wire rod as raw material is controlled at 0.900%~1.000%, and the components, by mass percentage, include: C: 0.700%~0.750%, Si: 0.150%~0.300%, Mn: 0.100%~0.300%, P: ≤0.020%, S: ≤0.020%, Cr: 0.300%~0.360%, Ni: ≤0.08%, Cu: ≤0.08%, Al: ≤0.008%, and the balance is Fe and unavoidable impurities.

[0008] On the basis of the above scheme, as a preferred embodiment, the medium-drawn steel wire is heated to make it austenitized, and then quenched in AQ liquid to form a microstructure of troostite and a small amount of coarse lamellar pearlite, and then pickled and alloyed in sequence, and then passed through a medium-frequency diffusion furnace to make copper and zinc atoms diffuse with each other to form a brass-plated alloy layer, and the copper content in the coating is 63.5±2.5%.

[0009] On the basis of the above scheme, as a preferred embodiment, in the AQ slot process, after the steel wire passes through the WT1 water bath zone, the temperature is cooled to 600°C, and the transformation process from austenite to pearlite is carried out in the air cooling zone. As the transformation heats up, a heating zone will appear in the second half of the air cooling zone, so that the temperature of the steel wire rises to 630°C, and at the same time, the pearlite transformation rate is above 60% in the air cooling zone; then after passing through the WT2 water bath zone, the pearlite transformation rate is above 80%, and finally in the WT2 air cooling zone, the pearlite transformation rate is 100% completed.

[0010] Based on the above scheme, preferably, the diameter of the large drawn steel wire is 2.90~3.25 mm.

[0011] Based on the above solution, preferably, the diameter of the middle drawn steel wire is 1.15 mm to 2.10 mm.

[0012] Compared with the prior art, the present invention has the following beneficial effects: using micro-alloyed 72DACr wire rod as raw material to replace 82C to produce dense steel cord for TBR tires, micro-alloyed wire rod actually reduces the carbon and manganese contents in the wire rod and increases the chromium content, and through reasonable improvement of the chromium and manganese contents, the pearlite lamellae can be effectively refined, and the formation of grain boundary network cementite can be inhibited, thereby improving the troostite conversion rate and drawing performance, and due to the reduction in carbon content, during the drawing process, the friction between the steel wire and the die chain can be effectively improved, the surface quality of the steel wire can be improved, and the die loss can be reduced; under the premise of ensuring that the performance meets customer requirements, by using micro-alloyed 72DACr wire rod as raw material to produce dense steel cord for TBR tires, the wire breakage rate in the entire production process is reduced and the yield rate is improved, and an important contribution is made to the development of low-carbon and environmentally friendly tires.

[0013] The strength of 82C wire rod meets the application of dense steel cord for TBR tires, but the carbon content of 0.82% is too high, which is prone to problems such as eutectoid network cementite and center segregation, which deteriorates the plasticity of the wire rod and increases the risk of wire breakage during drawing, affecting the yield rate. By replacing 82C with 72DACr wire rod, the carbon content of the wire rod is reduced to 0.72%, which can produce a large amount of ferrite structure, improve the plasticity of the wire rod, and add chromium elements (content 0.300% ~ 0.360%) to improve the strength of the wire rod and improve the performance of the wire rod. Under the premise of ensuring that the breaking tensile force of the finished product meets customer requirements, it reduces the risk of work hardening and improves the drawing effect; reducing the carbon content of the wire rod from 0.82% to 0.72% not only meets the development of lightweight tires, but also meets the direction of green and low-carbon development. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the microstructure diagram of alloy steel wire Φ1.25mm.

[0015] Figure 2 This is the fracture morphology of a wet-drawn single-filament Φ0.18mm.

[0016] Figure 3 This is a comparison chart of the wire breakage rate of steel cord in the wet drawing process and the original process, 1-original process; 2-this invention.

[0017] Figure 4 This is a comparison chart of the broken wire rate of steel cord in the cord process and the original process, 1-original process; 2-the present invention; Figure 5 It is a schematic diagram of the tower wheel; Figure 6It is a schematic diagram of the counter-tension force of each pass. DETAILED DESCRIPTION

[0018] The present invention will be further described below by way of examples, but the scope of the present invention is not limited thereto.

[0019] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] like Figure 1-6 As shown, taking the production of 0.20+6+11x0.18HT dense steel cord as an example, the specific steps include: (1) Φ5.5 mm microalloyed 72DACr wire rod is used as raw material, with a carbon equivalent CEQ of 0.937%. The composition of the wire rod is calculated by mass percentage, including: C: 0.725%, Si: 0.202%, Mn: 0.230%, P: 0.009%, S: 0.012%, Cr: 0.335%, Ni: 0.010%, Cu: 0.012%, Al: 0.001%, and the balance is Fe and unavoidable impurities; (2) The above-mentioned Φ5.5 mm microalloyed 72DACr wire rod is paid out by a C-type hook, and the wire rod is passed through a descaling box to remove the surface oxide scale, and then pickled, rinsed with water, coated with boron, and drawn by a servo direct-drive wire drawing machine through 6 passes of a die to obtain a Φ2.90 mm large drawn steel wire with a stable surface residual coating, and then the wire is taken up on a take-up rack; (3) The above-mentioned Φ2.90 mm large drawn steel wire is pulled onto a servo direct-drive wire drawing machine by a wire take-up frame, and after 9 passes of die drawing, a Φ1.25 mm medium drawn steel wire with stable roughness and good surface quality is obtained, and then the wire is taken up onto an I-shaped wheel; (4) The Φ1.25 mm medium-drawn steel wire is subjected to degreasing, heating in a heating furnace, AQ quenching, water cooling, pickling, water rinsing, copper plating, water rinsing, galvanizing, water rinsing, hot water washing, medium frequency diffusion, water cooling, phosphoric acid washing, water rinsing, soap dipping in the alloy process, and finally wound onto an I-shaped wheel. By selecting the diameter of the medium-drawn steel wire and the line speed of the alloy process, a Φ1.25 mm brass-plated steel wire can be obtained, the copper content in the coating is about 63.5%, and the tensile strength is 1220 N / mm 2 about;

[0021] Table 1: Alloy steel wire Φ1.25mm test performance table During the production of Φ1.15 mm brass-plated steel wire, due to the high carbon content of 82C wire rod and the thin diameter of the steel wire, overheating and decarburization of the steel wire surface are prone to occur during the heating process of the heating furnace, resulting in poor ductility of the steel wire; and the brass coating is prone to fall off during the wet drawing process, resulting in black lines and poor elongation during the wet drawing process. Although the overheating and decarburization problems of brass-plated steel wire can be significantly improved by increasing the line speed, the pearlite transformation rate of the steel wire in the AQ quenching tank will be affected after the line speed is increased, and the ratio of undeveloped pearlite will increase, affecting the tensile strength and plasticity of the steel wire. At present, the cooling speed of the steel wire can be reduced by adding insulation blankets and covers to the AQ quenching tank to ensure that the transformation point of the steel wire is within a reasonable range, which can significantly improve the quality of the steel wire. However, when the production line switches specifications and changes hands, the insulation blankets and insulation covers in the AQ quenching tank need to be frequently removed, which affects production capacity and increases production costs. By using microalloyed 72DACr wire rod, optimizing the wire speed and increasing the wire diameter, the temperature of the steel wire can be cooled to about 600℃ after passing through the WT1 water bath section of the AQ slot; the transformation process from austenite to pearlite occurs in the air cooling section. As the transformation heats up, a heating section will appear in the second half of the air cooling section, which raises the temperature of the steel wire to about 630℃. At the same time, the pearlite transformation rate is above 60% in the air cooling section; after passing through the WT2 water bath section, the pearlite transformation rate is above 80%, and finally in the WT2 air cooling section, the pearlite transformation rate is 100%. Through the above process optimization, the Φ1.25 mm brass-plated steel wire obtained has stable performance and good microstructure, providing high-quality raw materials for the wet drawing process.

[0022] (5) The wet-drawing equipment draws the Φ1.25 mm brass-plated steel wire into a Φ0.18 mm wet-drawn steel wire through 23 die chain drawing passes.

[0023] The tensile force F on the wire is equal to the sum of the friction force W acting on the wire drawing die and the counter-tensile force f acting on the tower wheel. The tensile force F is fixed by the drawing machine design. Changing the number of wire windings on the tower wheel can change the counter-tensile force f on the tower wheel in this pass, thereby affecting the force W on the wire drawing die. The change of winding combinations in different passes will affect the final steel wire performance and wire breakage rate.

[0024] Counter-tension f: The force acting in the opposite direction of the pulling direction during the drawing process. In the wet pulling equipment, the slip tension generated by the slip of the steel wire on the tower pulley is called counter-tension.

[0025] In the wet drawing equipment, since the drawing die elongation coefficient is greater than the mechanical elongation coefficient, if the drawing die elongation is less than or equal to the mechanical elongation, the steel wire cannot be drawn by the drawing die. If the steel wire is drawn according to the mechanical elongation, it is equivalent to the dry drawing principle and the wire will break.

[0026] Explanation: The counter-pulling force of dry pulling is almost 0 because when the tower wheel is curled enough, the slippage is almost 0.

[0027] On the surface of the tower wheel, the slippage comes from the linear speed of the tower wheel > the linear speed of the wire. If the tower wheel is curled less, the slippage will be greater and the counter-tension will increase.

[0028] F (pulling force) = f (counter-pulling force) + W (friction force of wire drawing die). Because the pulling force is a fixed value, when the counter-pulling force increases, the friction force W of the wire drawing die will decrease, the linear speed of the steel wire passing through the wire drawing die will decrease, and the die loss will decrease.

[0029] Passes 1-17: lower part of finished mold; Passes 18-22, 23: upper part of finished product mold and exit mold.

[0030] The test shows that: the pulling force F is a constant, the counter-pulling force f of each pass shows a downward trend, and the friction force of the wire drawing die shows an increasing trend.

[0031] The first pass: Since the first pass is the wire feeding pass, the elongation of the wire drawing die is ≤ the mechanical elongation. To avoid the wire being dry-drawn and causing wire breakage, the number of winding coils of the first pass die is set to 1.0 turns to increase slippage, thereby increasing the counter-pulling force.

[0032] Passes 2-10: The elongation of the wire drawing die is greater than the mechanical elongation, and the elongation of the wire drawing die shows a gradually increasing trend. The wire drawing deformation is the maximum. By increasing the number of winding coils to 3.5 turns, the counter-pulling force can be effectively reduced and the friction of the wire drawing die can be increased, thereby increasing the deformation of the steel wire in the wire drawing die and ensuring that the steel wire is fully drawn.

[0033] The 11th pass: the elongation of the wire drawing die is greater than the mechanical elongation. It is the intermediate transition pass between the 2nd to 10th passes and the 12th to 15th passes. The number of winding coils is set to 3.0 turns. Due to the elongation, it first increases and then decreases. By optimizing the number of winding coils for the 11th pass, it is ensured that the steel wire is evenly stressed during the drawing process to avoid the coating falling off due to the hardening of the coating.

[0034] Passes 12-15: The elongation of the wire drawing die is greater than the mechanical elongation, and the elongation of the wire drawing die shows a gradually decreasing trend. The wire drawing deformation decreases gradually. By increasing the number of winding coils to 3.5 turns, the slippage is gradually reduced, thereby preventing wire scratches caused by adhesion slippage.

[0035] Pass 16-17: The elongation of the wire drawing die is greater than the mechanical elongation. Because the finished cord has a problem of stranding, the cord bulging problem is significantly improved by optimizing Pass 16-17 and reducing it from 3.5 turns to 2.5 turns.

[0036] Passes 18-23: Elongation of wire drawing die > mechanical elongation, upper part of finished die, and exit die: have a great influence on the performance of steel wire. Reducing the number of winding coils to 1.5 turns can effectively increase the counter-pulling force, reduce the friction of wire drawing die, and reduce die consumption, thereby ensuring that the final wire diameter of the steel wire is within the qualified range and avoiding excessive diameter of wet-drawn steel wire and defective products due to large wear of wire drawing die.

[0037] The 22nd and 23rd double-die process: The double-die process can share wear and stress, reduce the temperature of the steel wire, and reduce cuppy wire breakage. However, too many double-dies will cause scratches on the steel wire, resulting in delamination wire breakage; in the 22nd and 23rd double-die process, the compression ratio of each die is half of that of the single-die drawing, which reduces the wire temperature and wire breakage rate at the exit die position, and improves the torsional performance of the steel wire. For example, at a compression rate of 15%, the first and second dies bear a compression rate of about 7.5% respectively. When the steel wire passes through the two dies, there is plastic deformation during drawing, less heat is generated during drawing, and the cooling effect is better, which prevents the steel wire from overheating, ensures uniform drawing, avoids the loss of the steel wire surface coating, and better controls the steel wire diameter.

[0038]

[0039] By optimizing the above-mentioned wet-drawing process, wet-drawn monofilaments with good loop diameter and low warping can be obtained, thereby reducing the risk of warping in the finished product and providing high-quality raw materials for the cord process. The wire breakage rate in the wet-drawing process is reduced from 0.5 times / ton to 0.2 times / ton, a 60% decrease compared to the original process.

[0040] (6) Combined with the above process optimization, the Φ1.25mm brass-plated steel wire is drawn into a wet-drawn steel wire with a diameter of Φ0.18mm. It is also used to produce 0.20+6+11x0.18HT intensive steel cord. One Φ0.20mm monofilament is used as the core wire and six Φ0.18mm monofilaments are used as the outer wires. The 0.20+6x0.18HT core strands are obtained through a double-twisting and plying process. Eleven Φ0.18mm monofilaments are used as outer wires and double-twisted and plyed twice with the 0.20+6x0.18HT core strands to obtain the required finished product 0.20+6+11x0.18HT intensive steel cord. Micro-alloyed 72DACr wire rod replaces 82C and is used to produce 0.20+6+11x0.18HT intensive steel cord, which significantly improves the cord bulging problem and wire breakage rate. The wire breakage rate is reduced from 1.5 times / ton to 0.8 times / ton, a 47% decrease compared with the original process. The average breaking force of its finished cord products is 1530N (standard>1450N), and other performances meet customer requirements.

[0041] (7) Steel cords that have passed the inspection must be packaged and stored according to different types and specifications.

[0042] In combination with the above 0.20+6+11x0.18HT embodiment, it can be known that the dense steel cord for TBR tires obtained by the method of the present invention ensures that the performance of the finished product meets customer requirements, reduces the wire breakage rate of the entire production process, and improves the yield rate and reduces the production cost by optimizing the process of the semi-finished product process, while reducing the carbon and manganese contents in the wire rod and effectively increasing the chromium content.

[0043] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. Application of microalloyed 72C wire rod in dense steel cord, characterized in that: (1) Drawing a microalloyed 72DACr wire rod with a diameter of 5.5 mm to obtain a large drawn steel wire; (2) using a servo direct-drive wire drawing machine to draw the large-drawn steel wire to obtain a medium-drawn steel wire; (3) Processing the middle drawn steel wire to obtain brass plated steel wire; (4) The brass-plated steel wire is drawn into a wet-drawn steel wire with a diameter of 0.18-0.35 mm by a wet-drawing device. The wet-drawing device includes a single die for the 1st to 21st passes and a double die for the 22nd to 23rd passes. During double-die drawing, two dies are used for drawing in one drawing pass. The compression rate of the double drawing die adopts the principle of average distribution. The number of winding coils of the first die is 1.0, the number of winding coils of the 2nd to 10th die is 3.5, the number of winding coils of the 11th die is 3.0, the number of winding coils of the 12th to 15th die is 3.5, the number of winding coils of the 16th to 17th die is 2.5, and the number of winding coils of the 18th to 23rd die is 1.

5.

2. The application of a microalloyed 72C wire rod in a dense steel cord as claimed in claim 1, characterized in that: The carbon equivalent CEQ of the microalloyed 72DACr wire rod as raw material is controlled at 0.900%~1.000%, and the components, by mass percentage, include: C: 0.700%~0.750%, Si: 0.150%~0.300%, Mn: 0.100%~0.300%, P: ≤0.020%, S: ≤0.020%, Cr: 0.300%~0.360%, Ni: ≤0.08%, Cu: ≤0.08%, Al: ≤0.008%, and the balance is Fe and unavoidable impurities.

3. The application of a microalloyed 72C wire rod in a dense steel cord as claimed in claim 2, characterized in that: The drawn steel wire is heated to austenitize, and then quenched in AQ liquid to form the microstructure of troostite and a small amount of coarse lamellar pearlite, then pickled and alloy plated in sequence, and then passed through a medium frequency diffusion furnace to make copper and zinc atoms diffuse with each other to form a brass alloy layer. The copper content in the coating is 63.5±2.5%.

4. The application of a microalloyed 72C wire rod in a dense steel cord as claimed in claim 1, characterized in that: In the AQ slot process, after the steel wire passes through the WT1 water bath section, the temperature is cooled to 600℃, and then passes through the air cooling section for the transformation process from austenite to pearlite. As the transformation heats up, a heating section will appear in the second half of the air cooling section, causing the temperature of the steel wire to rise to 630℃. At the same time, the pearlite transformation rate is above 60% in the air cooling section. After passing through the WT2 water bath section, the pearlite transformation rate is above 80%, and finally in the WT2 air cooling section, the pearlite transformation rate is 100% completed.

5. The application of a microalloyed 72C wire rod in a dense steel cord as claimed in claim 1, characterized in that: The diameter of the large drawn steel wire is 2.90~3.25 mm.

6. The use of a microalloyed 72C wire rod in a dense steel cord as claimed in claim 1, characterized in that: The diameter of the medium drawn steel wire is 1.15mm~2.10 mm.

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