High strength high cycle ratio steel cord and green manufacturing process

Abstract

The application relates to the field of steel cord manufacturing, in particular to a high-strength high-cycle-ratio steel cord which comprises, in percentage by mass, C 0.7-0.96%, Si 0.2-0.35%, Mn 0.15-0.35%, Cr 0.03-0.1, V 0.01-0.02, Nb 0.01-0.02%, P<=0.01%, S<=0.08%, O<=0.0015%, N<=0.005%, Alt<=0.0008%, Ti<=0.0005%, Cu<=0.25%, Sn<=0.05%, the rest being Fe, and the molar ratio of Ca and O is defined as B, 0.9<=B<=1.5, the control of the parameter B is used to convert alumina and spinel inclusions into low-melting-point spherical calcium aluminate, so that the risk of thermal embrittlement in the drawing process is reduced, and the fatigue performance of the steel cord can also be improved.

Description

Technical Field

[0001] This application relates to the field of steel cord manufacturing, and in particular to a high-strength, high-cycle-ratio steel cord and a green manufacturing process. Background Technology

[0002] Currently, tire manufacturers not only require steel cords to have high strength and high fatigue performance, but also hope to reduce carbon emissions during the steel cord production process. In other words, they hope that the manufacturing process of steel cords will be low-carbon and environmentally friendly in order to meet relevant domestic and international policies.

[0003] In some steel cord manufacturing processes, electric furnace steel is used instead of traditional blast furnace steel or converter steel to reduce carbon emissions during wire rod manufacturing. At the same time, a certain proportion of scrap steel is also used in the steel smelting process. For example, CN120443061 A discloses an ultra-high strength steel cord with excellent fatigue properties and its production method.

[0004] When steel cord requires a high recycling ratio, that is, when a large proportion of scrap steel is used as raw material in the wire rod manufacturing process, such as 85% or more, a higher amount of titanium and aluminum will be introduced into the steel cord. This will increase the amount of non-deformable inclusions such as Al2O3 in the steel cord, that is, increase the amount of components that are difficult to undergo plastic deformation. The wire rod will have a higher risk of hot brittleness during the drawing process, which will make the fatigue life of the steel cord more likely to decrease. Summary of the Invention

[0005] In order to achieve both high cycle ratio and high fatigue performance in steel cord, this application provides a high-strength, high-cycle-ratio steel cord and a green manufacturing process.

[0006] Firstly, the high-strength, high-cycle-ratio steel cord provided in this application adopts the following technical solution.

[0007] A high-strength, high-recycling-ratio steel cord, by mass percentage, comprises: C 0.7-0.96%, Si 0.2-0.35%, Mn 0.15-0.35%, Cr 0.03-0.1%, V 0.01-0.02%, Nb 0.01-0.02%, P≤0.01%, S≤0.08%, O≤0.0015%, N≤0.005%, Alt≤0.0008%, Ti≤0.0005%, Cu≤0.25%, Sn≤0.05%, with the remainder being Fe, and the molar ratio of Ca to O is defined as B, where 0.9≤B≤1.5.

[0008] By adopting the above technical solution, parameter B is controlled to transform alumina and spinel impurities into low-melting-point spherical aluminates, thereby reducing the risk of hot brittleness caused by non-deformable impurities during the drawing process and improving the fatigue performance of steel cord.

[0009] Secondly, the green manufacturing process for high-strength, high-cycle-ratio steel cord provided in this application adopts the following technical solution.

[0010] A green manufacturing process for high-strength, high-cycle-ratio steel cord, specifically comprising the following steps, for manufacturing the aforementioned high-strength, high-cycle-ratio steel cord.

[0011] S1. Use a fluorine-free slag system and feed calcium-silicon wire during the wire rod manufacturing process to adjust B to the corresponding range;

[0012] S2. Surface treatment of wire rod to remove oxide scale;

[0013] S3, coarse drawing;

[0014] S4, heat treatment;

[0015] S5. Electrolytic cleaning and electroplating;

[0016] S6, wet stretching;

[0017] S7, twisting the strand.

[0018] By adopting the above technical solution, calcium-silicon wire is fed in, and silicon can deoxidize, thereby controlling the calcium and oxygen content in the steel cord. Fluorine-free slag system replaces fluorine-containing fluxes such as fluorite, reducing the generation of harmful gases and reducing the corrosion of the furnace lining by fluorine, so as to better meet the requirements of green environmental protection.

[0019] Optionally, in S5, acid-free and phosphorus-free neutral electrolytic cleaning and cyanide-free copper electroplating are performed.

[0020] By adopting the above technical solutions, the generation of strong acid, phosphorus ion and hydrogen ion waste liquid can be avoided, reducing the degree of harm to the environment and lowering the treatment cost.

[0021] Optionally, the neutral electrolytic cleaning uses a buffer system composed of borate and citrate.

[0022] By adopting the above technical solution, it is not easy to cause corrosion to the steel cord, and the citrate can complex a small amount of ferrous ions and copper ions, so that it is not easy to rust after cleaning. It can also provide a uniform nucleation surface for subsequent copper electroplating, and the electrolytic cleaning process is not easy to generate acidic waste liquid.

[0023] Optionally, the cyanide-free electroplated copper is formed into an inner and outer copper-zinc alloy, with the inner copper content being 68-72 wt% and the outer copper content being 62-68 wt%.

[0024] By adopting the above technical solution, the inner layer has a higher zinc content, which utilizes the ductility of high copper and low zinc to buffer the deformation of the monofilament and ensure that the inner layer and the monofilament are pulled synchronously without peeling; the outer layer has a higher copper content, which provides sufficient zinc to react with the rubber to form Cu-S-Zn bonds, taking into account both adhesion and fatigue resistance.

[0025] Optionally, the inner layer uses a complexing agent composed of citrate, ammonium salt, and amine salt phases.

[0026] By adopting the above technical solution, the inner layer is dense and has low porosity, so that the copper in the inner layer is not easily replaced during surface electroplating, thereby reducing the possibility of defects in the inner layer.

[0027] Optionally, the outer layer uses pyrophosphate as a complexing agent in an alkaline environment for copper-zinc electroplating.

[0028] By adopting the above technical solution, pyrophosphate can complex copper and zinc ions, making the potentials of copper and zinc ions close, thus achieving controllable co-deposition at low current density.

[0029] Optionally, the fluorine-free slag system in S1 is composed of calcium oxide, aluminum oxide and silicon dioxide, with a mass ratio of calcium oxide to silicon dioxide of 0.9-1.1.

[0030] By adopting the above technical solution, alumina is added to lower the melting point of the slag and improve its fluidity, thereby achieving a reaction balance between the slag and the steel. Furthermore, the added alumina reacts with calcium oxide and silicon dioxide to generate plastic inclusions, such as calcium feldspar or aluminum feldspar, which improves the fatigue performance of the steel cord.

[0031] In summary, this application includes at least the following beneficial effects:

[0032] 1. Control parameter B to transform alumina and spinel impurities into low-melting-point spherical aluminates, thereby reducing the risk of hot brittleness caused by non-deformable impurities during the drawing process and improving the fatigue performance of steel cord.

[0033] 2. Avoid the generation of strong acid, phosphorus ion and hydrogen ion waste liquid, reduce the degree of harm to the environment and reduce treatment costs. Attached Figure Description

[0034] Figure 1 This is a flowchart of the green manufacturing process for high-strength, high-cycle-ratio steel cords proposed in this application. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the accompanying drawings.

[0036] This application discloses a high-strength, high-cycle-ratio steel cord, comprising, by mass percentage: C 0.7-0.96%, Si 0.2-0.35%, Mn 0.15-0.35%, Cr 0.03-0.1%, V 0.01-0.02%, Nb 0.01-0.02%, P≤0.01%, S≤0.08%, O≤0.0015%, N≤0.005%, Alt≤0.0008%, Ti≤0.0005%, Cu≤0.25%, Sn≤0.05%, with the remainder being Fe. The molar ratio of Ca to O is defined as B, where 0.9≤B≤1.5. In this application, the C content can be further preferably 0.9-0.96% to meet the high-strength requirement.

[0037] This application also discloses a green manufacturing process for high-strength, high-cycle-ratio steel cord, referring to... Figure 1 Specifically, it includes the following steps.

[0038] S1. During the wire rod manufacturing process, a fluorine-free slag system is used and calcium-silicon wire is fed to adjust B to the corresponding range.

[0039] The raw steel used in the production process consists of 60-75% low-titanium and low-aluminum scrap, 10-25% direct reduced iron and hot-pressed iron blocks, and the remainder is controlled scrap. The manufacturing of wire rod involves several common steps: electric arc furnace smelting, refining, vacuum circulation degassing, continuous casting, diffusion annealing, and controlled rolling and cooling. During refining, a fluorine-free slag system composed of calcium oxide, alumina, and silica is used as top slag. The mass ratio of calcium oxide to silica is 0.9-1.1 to utilize sufficient alumina and low alkali to inhibit the reduction and transfer of aluminum between steel and slag, resulting in Al content in the wire rod below 5 ppm.

[0040] S2. Perform surface treatment on the wire rod, such as polishing, to remove the oxide scale.

[0041] S3, coarse drawing, to obtain monofilaments with a diameter range of 0.87-2.05mm.

[0042] S4. Heat treatment at 930-950℃ to austenitize the monofilament.

[0043] S5. Perform acid-free and phosphorus-free neutral electrolytic cleaning and cyanide-free copper electroplating.

[0044] Neutral electrolytic cleaning uses a buffer system composed of borate and citrate. The electrolyte solution is neutral, and the monofilament acts as the anode to dissolve and remove the oxide scale on the surface. Citrate can promptly complex the dissolved copper and ferrous ions. After closed-circuit membrane filtration, ion exchange, and electrochemical deposition, the metal ions can be used in the subsequent electroplating bath preparation, and the filtrate can be used for cleaning the monofilament after electroplating.

[0045] Copper electroplating involves forming two layers of copper-zinc alloy: an inner layer and a surface layer. The inner layer contains 68-72 wt% copper, with the remainder being zinc. The electroplating solution composition may include 25 g / L copper sulfate pentahydrate, 10 g / L zinc sulfate heptahydrate, 120 g / L trisodium citrate, 40 ml / L triethanolamine, and 20 g / L ammonium chloride. The pH of the electroplating solution is adjusted to 9.2-9.6 with potassium hydroxide solution. The inner layer thickness is 0.08-0.12 μm.

[0046] The surface layer contains 62-68 wt% copper, with the remainder being zinc. The electroplating solution composition can be 15 g / L copper sulfate pentahydrate, 15 g / L zinc sulfate heptahydrate, 200 g / L potassium pyrophosphate, and 30 g / L potassium sodium tartrate. The pH of the electroplating solution is adjusted to 10.3-10.5 with potassium hydroxide solution. The surface layer thickness is 0.15-0.25 μm.

[0047] After the surface electroplating is completed, the monofilament is subjected to high-frequency induction diffusion at 420–450 ℃ for 1.5–2 s, which enables the atoms of the two layers to interdiffused. This achieves the difference in copper content between the inner layer and the surface layer while ensuring the bonding force between the inner layer and the surface layer.

[0048] S6. Wet drawing to obtain monofilaments with a diameter of 0.2-0.6mm.

[0049] S7, twisting the strand.

[0050] The following provides a detailed description of each embodiment and comparative example.

[0051] Example 1:

[0052] A high-strength, high-cycle-ratio steel cord, by mass percentage, comprises: C 0.9%, Si 0.2%, Mn 0.15%, Cr 0.03%, V 0.01%, Nb 0.01%, P 0.01%, S 0.08%, O 0.0015%, N 0.005%, Alt 0.0008%, Ti 0.0005%, Cu 0.25%, Sn 0.05%, with the remainder being Fe, and B=0.9%.

[0053] This application also discloses a green manufacturing process for high-strength, high-cycle-ratio steel cord, referring to... Figure 1 Specifically, it includes the following steps.

[0054] S1. During the wire rod manufacturing process, a fluorine-free slag system is used and calcium-silicon wire is fed to adjust B to the corresponding range.

[0055] S2. Perform surface treatment on the wire rod, such as polishing, to remove the oxide scale.

[0056] S3. Coarse drawing to obtain monofilaments with a diameter range of 1 mm.

[0057] S4. Heat treatment at 950℃ to austenitize the monofilament.

[0058] S5. Perform acid-free and phosphorus-free neutral electrolytic cleaning and cyanide-free copper electroplating.

[0059] The inner layer contains 68 wt% copper and the remainder is zinc, while the outer layer contains 62 wt% copper and the remainder is zinc.

[0060] S6. Wet drawing to obtain a monofilament with a diameter of 0.3 mm.

[0061] S7, twisting the strand.

[0062] Example 2:

[0063] The difference from Example 1 is that:

[0064] A high-strength, high-cycle-ratio steel cord, by mass percentage, comprises: C 0.96%, Si 0.35%, Mn 0.35%, Cr 0.1%, V 0.02%, Nb 0.02%, P 0.01%, S 0.08%, O 0.0015%, N 0.005%, Alt 0.0008%, Ti 0.0005%, Cu 0.25%, Sn 0.05%, with the remainder being Fe, and B=1.5.

[0065] In S5, the inner layer contains 72 wt% copper and the remainder is zinc, while the outer layer contains 68 wt% copper and the remainder is zinc.

[0066] Example 3:

[0067] The difference from Example 1 is that B=1.2

[0068] Comparative Example 1:

[0069] The difference from Example 1 is that in S1, lime and wollastonite are used as slag in the refining process of the wire rod.

[0070] Comparative Example 2:

[0071] The difference from Example 1 is that B=0.5.

[0072] Comparative Example 3:

[0073] The difference from Example 1 is that B=2.

[0074] Comparative Example 4:

[0075] The difference from Example 1 is that S5 replaces neutral electrolytic cleaning with acid washing, using 15% hydrochloric acid.

[0076] Comparative Example 5:

[0077] The difference from Example 1 is that in S5, a single layer of copper-zinc alloy is electroplated, with copper accounting for 70 wt% and the remainder being zinc.

[0078] Comparative Example 6:

[0079] The difference from Example 1 is that the inner layer has a copper content of 62 wt% and the remainder is zinc, while the outer layer has a copper content of 68 wt% and the remainder is zinc.

[0080] Comparative Example 7:

[0081] The difference from Example 1 is that the inner layer has a copper content of 68 wt% and the remainder is zinc, while the outer layer has a copper content of 72 wt% and the remainder is zinc.

[0082] Ten steel cords from each embodiment and comparative example were randomly selected for testing.

[0083] Tensile testing was performed using a universal testing machine with a gauge length of 250 mm and a testing speed of 1 mm / min. Tensile strength and elongation at break were recorded.

[0084] Fatigue testing was conducted using an axial fatigue testing machine. The sample length was 300 mm, the clamping distance was 200 mm, and a sinusoidal cyclic load was applied at a frequency of 10 Hz. The stress ratio was 0.1, and the maximum stress was set to 50% of the tensile strength of each sample, until the steel cord broke or reached 2 × 10⁻⁶. 6 The cycle repeats, recording the final number of load cycles.

[0085] The specific results are shown in the table below.

[0086]

[0087] As can be seen from Examples 1 to 3 and Comparative Example 1, adding alumina during the wire rod refining process can lower the slag melting point, improve the slag fluidity, and achieve a reaction balance between the slag and the steel. Furthermore, the added alumina will react with calcium oxide and silicon dioxide to generate plastic inclusions, such as calcium feldspar or aluminum feldspar, thereby improving the fatigue performance of the steel cord.

[0088] As can be seen from Examples 1 to 3 and Comparative Examples 2 and 3, when B is low, the tensile strength decreases, but the fatigue life can be improved. Conversely, when B is high, the tensile strength increases, but the fatigue life is significantly reduced.

[0089] Based on Examples 1 to 3 and Comparative Example 4, it can be seen that the fatigue life of the pickled steel cord is poor, mainly due to hydrogen embrittlement.

[0090] As can be seen from Examples 1 to 3 and Comparative Examples 5 to 7, the setting of inner and outer layers with different copper contents can improve the fatigue life of steel cords, and if the copper content of the inner layer is lower than that of the outer layer, it will also affect the fatigue life of the steel cords.

[0091] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A green manufacturing process for high-strength, high-recyclability steel cord, characterized in that: A high-strength, high-recycling-ratio steel cord is manufactured, comprising, by mass percentage: C 0.7-0.96%, Si 0.2-0.35%, Mn 0.15-0.35%, Cr 0.03-0.1%, V 0.01-0.02%, Nb 0.01-0.02%, P≤0.01%, S≤0.08%, O≤0.0015%, N≤0.005%, Alt≤0.0008%, Ti≤0.0005%, Cu≤0.25%, Sn≤0.05%, with the remainder being Fe, and the molar ratio of Ca to O is defined as B, where 0.9≤B≤1.5; This green manufacturing process specifically includes the following steps: S1. Use a fluorine-free slag system and feed calcium-silicon wire during the wire rod manufacturing process to adjust B to the corresponding range; S2. Surface treatment of wire rod to remove oxide scale; S3, coarse drawing; S4, heat treatment; S5. Electrolytic cleaning and electroplating; S6, wet stretching; S7, twisting the strand; In S5, acid-free and phosphorus-free neutral electrolytic cleaning and cyanide-free copper electroplating are performed. The neutral electrolytic cleaning uses a buffer system composed of borate and citrate. The cyanide-free electroplated copper is formed into an inner and outer copper-zinc alloy, with the inner layer containing 68-72 wt% copper and the outer layer containing 62-68 wt% copper. The fluorine-free slag system in S1 is composed of calcium oxide, aluminum oxide and silicon dioxide, with a mass ratio of calcium oxide to silicon dioxide of 0.9-1.

1.

2. The green manufacturing process for high-strength, high-recycling-ratio steel cord according to claim 1, characterized in that: The inner layer uses a complexing agent composed of citrate, ammonium salt and amine salt phases for copper-zinc electroplating.

3. The green manufacturing process for high-strength, high-recycling-ratio steel cord according to claim 1, characterized in that: The surface layer is plated with copper-zinc using pyrophosphate as a complexing agent in an alkaline environment.

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