Method for controlling forms of non-metallic inclusions in tire cord steel

Abstract

The invention relates to a method for controlling the form of non-metallic inclusions in tire cord steel, which comprises the following steps: 1) controlling the components of molten steel: preparing a Fe-Si-Mg-Al quaternary alloy and adding the Fe-Si-Mg-Al quaternary alloy in the form of a cored wire; (2) controlling a refining slag system; and the refining slag system comprises the following components: w (CaO) / w (SiO2) = 0.8-1.2, w (MgO) = 6-9%, and w (Al2O3) is less than 10.0%. According to the tire cord steel quality control requirement, the powerful non-metallic inclusion control function of magnesium metal and the converter-refining-continuous casting production technology are combined, the tire cord steel non-metallic inclusions are controlled from the two aspects of tire cord steel molten steel component control and refining slag component control, and the tire cord steel quality is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of cord steel production technology, and in particular to a method for controlling the morphology of non-metallic inclusions in cord steel. Background Technology

[0002] Cord steel is a key material in the production of radial tire carcasses for automobiles, effectively improving tire load-bearing capacity, safety, and wear resistance. The quality of cord steel is primarily affected by its chemical composition and non-metallic inclusions. Chemical composition mainly influences the microstructure and mechanical properties of cord steel. With the development and application of modern hot metal pretreatment and ladle refining technologies, the chemical composition of cord steel, such as carbon, sulfur, and phosphorus, has been precisely controlled. Therefore, the key to improving the quality of cord steel currently lies in controlling non-metallic inclusions.

[0003] Non-metallic inclusions mainly affect the yield. In the production of steel cord, it is usually required that the wires do not break when drawn 200m or that the number of wire breaks does not exceed 4 when drawn 1 ton of wire. This requires strict control of non-metallic inclusions in the steel. First, the type of inclusions must be controlled. Hard non-metallic inclusions such as Al2O3, TiN, and Ti(CN) do not deform with the steel matrix during rolling, drawing, and twisting, which can easily lead to wire breakage during wire drawing and stranding. Therefore, it is necessary to control the plasticity of inclusions. Second, the particle size of inclusions must be controlled. The diameter of a single wire in steel cord can be as small as 0.15mm or even smaller. It is generally believed that an inclusion particle size exceeding 2% of the single wire diameter can lead to wire breakage. Therefore, it is necessary to control the fineness and dispersion of inclusions.

[0004] To control the properties of non-metallic inclusions in tire cord steel, various methods have been tried, including chemical composition control, slag formation process optimization, and rare earth treatment. These methods have achieved certain beneficial results and effectively improved the quality control level of tire cord steel. However, in industrial production, tire cord steel quality problems caused by non-metallic inclusions still exist to varying degrees.

[0005] Magnesium metal possesses strong inclusion modification capabilities due to its high reactivity. More importantly, the magnesium-based non-metallic inclusions it forms exhibit significant dispersion characteristics, making them less prone to agglomeration into large particles within steel. This, in turn, benefits the mechanical and processing properties of steel. Currently, the application of magnesium metal in steel is receiving increasing attention and is gradually being promoted, but its application in tire cord steel has not yet been reported. Summary of the Invention

[0006] This invention provides a method for controlling the morphology of non-metallic inclusions in cord steel. Based on the quality control requirements of cord steel, and combining the powerful non-metallic inclusion control function of magnesium metal and the converter-refining-continuous casting production process, the non-metallic inclusions in cord steel are controlled from two aspects: the control of molten steel composition and the control of refining slag composition, which effectively improves the quality of cord steel.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for controlling the morphology of non-metallic inclusions in steel cord includes the following steps: 1) Steel composition control; (1) Preparation of Fe-Si-Mg-Al quaternary alloy: Fe-Si-Mg-Al quaternary alloys were prepared using an intermediate alloy smelting process. The Fe-Si-Mg-Al quaternary alloys contained 30%–40% Si, 8.5%–10% Mg, and 1.0%–3.0% Al by mass percentage, with the remainder being Fe and unavoidable impurities. The total content of Ca, S, and P among the impurities was less than 1.0%. (2) Add Fe-Si-Mg-Al quaternary alloy: The Fe-Si-Mg-Al alloy is added to the molten steel using a cored wire method. After LF refining and alloying adjustments, the cored wire is fed into the molten steel at a temperature controlled between 1580 and 1620°C. The feeding rate is 1.8–4.0 m / t of steel, fed in batches at a feeding speed of 2.5–3.0 m / s. The feeding position is opposite the bottom permeable brick of the ladle. The soft blowing time of argon gas after feeding is ≥18 min. 2) Refining slag system control; In the early stage of LF furnace smelting, slag-forming materials are added in batches to form foamy reducing slag and maintain it for more than 20 minutes. The composition of the refining slag system is: w(CaO) / w(SiO2)=0.8~1.2, w(MgO)=6%~9%, w(Al2O3)<10.0%; the melting temperature of the refining slag is ≤1350℃, the viscosity is 0.5~1.0Pa·s, and the surface tension is 0.3~0.5N / m.

[0008] The parameters of the cored wire are: wire diameter ø9mm~ø11mm, sheet thickness 0.40~0.50mm, wire weight 470~490g / m, and core weight 215~240g / m.

[0009] The cored wires are fed in batches with an interval of more than 1 minute.

[0010] The slag-forming materials include lime and aluminum ash balls.

[0011] Compared with the prior art, the beneficial effects of the present invention are: (1) Fe-Si-Mg-Al quaternary alloy is used and fed into the molten steel in the form of cored wire. No obvious splashing is generated, which is environmentally friendly and can ensure that the alloy composition of the cord steel meets the control range requirements. Moreover, the magnesium recovery rate is between 25% and 35%, and the non-metallic inclusion control effect is significant.

[0012] (2) After magnesium treatment, most of the Si-Mn-O plastic inclusions in the steel are transformed into fine-sized Mg-Si-O inclusions; the maximum particle size of brittle inclusions on the longitudinal section of the wire rod is 5.06 μm, and the average particle size is 1.48 μm; the maximum particle size of plastic inclusions is 3.82 μm, and the average particle size is 1.23 μm; compared with the non-magnesium treatment process, the control effect of plastic inclusions and brittle inclusions is improved by more than 30%, especially the sulfides are significantly improved, not only in size but also in distribution, such as Figure 1 , Figure 2 As shown.

[0013] (3) The cord steel produced by this invention has a grade of 0 for both A and C inclusions, and a maximum grade of 0.5 for B, D and Ds inclusions, with a pass rate of 100%. Compared with the non-magnesium-treated furnace, the control effect of B, D and Ds inclusions after magnesium treatment is improved by 50%, 25% and 25% respectively.

[0014] (4) The drawing performance of cord steel is improved; the wire breakage rate of cord steel is reduced by more than 75%, and the yield rate is increased from more than 90% to more than 95%, meeting the requirement of no wire breakage when drawing 200m. Attached Figure Description

[0015] Figure 1 This is a diagram showing the size and distribution of sulfides in cord steel after conventional non-magnesium treatment.

[0016] Figure 2 This is a diagram showing the size and distribution of sulfides in cord steel after magnesium treatment according to the present invention. Detailed Implementation

[0017] The present invention discloses a method for controlling the morphology of non-metallic inclusions in tire cord steel. The tire cord steel production adopts a converter-refining-continuous casting process, and improvements are made in two aspects: control of molten steel composition and control of refining slag composition, as detailed below: 1. Steel composition control; Non-metallic inclusions are formed in molten steel. The premise of controlling the morphology of non-metallic inclusions is to control their composition. Since non-metallic inclusions coexist in equilibrium with molten steel, the essence of controlling non-metallic inclusions is to control the composition of molten steel.

[0018] This invention controls non-metallic inclusions in tire cord steel in two ways: firstly, by reducing particle size to weaken the overall harmfulness of non-metallic inclusions; and secondly, by leveraging the metallurgical function of magnesium-based non-metallic inclusions, which act as precipitation nuclei for MnS inclusions, thereby promoting the precipitation and dispersion of MnS inclusions. This is particularly important for tire cord steel, which is typically refined using low-basicity refining slag. The refining slag has weak desulfurization capabilities, making it prone to forming large-sized MnS inclusions in the steel and deteriorating its drawing performance. Therefore, this invention designs and develops a dedicated multi-element alloy and its addition process specifically for tire cord steel to control the steel composition.

[0019] (1) Preparation of multi-component alloys for controlling the composition of cord steel; The Fe-Si-Mg-Al quaternary alloy is prepared by intermediate alloy smelting process. The Fe-Si-Mg-Al quaternary alloy has a mass content of 30% to 40% Si, 8.5% to 10% Mg, and 1.0% to 3.0% Al. The remainder is Fe and unavoidable impurities. The total mass content of Ca, S and P among the impurities is less than 1.0%.

[0020] In the Fe-Si-Mg-Al quaternary alloy, the main functions of Fe and Si are to form an alloy with Mg to control the release rate of Mg in molten steel, thereby improving the Mg yield and the effect of inclusion modification; the main function of Al is to form finely dispersed Mg-Al-O with Mg, which then becomes precipitation sites for MnS.

[0021] (2) Alloy addition process; Addition method: In order to improve the alloy yield and inclusion control, the Fe-Si-Mg-Al quaternary alloy is added to the molten steel using a cored wire method.

[0022] Cored wire parameters: wire diameter ø9~ø11mm, sheet metal thickness 0.40~0.50mm, weight per meter of wire 470~490g, core weight per meter 215~240g.

[0023] Timing of wire feeding: After the LF refining and alloying adjustment, the cored wire is fed in when the temperature of the molten steel is controlled at 1580~1620℃.

[0024] Wire feeding rate: 1.8-4.0m per ton of steel, fed in batches (with intervals of more than 1 minute), wire feeding speed 2.5-3.0m / s, wire feeding position is opposite the bottom permeable brick of the ladle.

[0025] Post-feeding operation: After feeding the wire, the soft blowing time of argon gas should be ≥18min to control the uniformity of the composition and temperature of the molten steel.

[0026] 2. Control of refining slag composition; In the early stage of LF furnace smelting, slag-forming materials (preferably lime and aluminum ash balls) are added in batches to form a foamy reducing slag (white slag) and maintain it for more than 20 minutes. Magnesium is a highly reactive metallic element that easily reacts with the refining slag, weakening its control effect on non-metallic inclusions in the steel. This invention comprehensively considers the physical properties of the refining slag, such as melting temperature, viscosity, and surface tension, and optimizes the design of a refining slag system suitable for magnesium-containing cord steel with the goal of suppressing slag-metal reaction. The composition control targets are as follows: w(CaO) / w(SiO2) = 0.8~1.2, w(MgO) = 6%~9%, w(Al2O3) < 10.0%. The refining slag melting temperature is ≤1350℃, viscosity is 0.5~1.0 Pa·s, and surface tension is 0.3~0.5 N / m.

[0027] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0028]

Example 1

[0029] In the early stage of LF smelting, slag-forming materials (lime and aluminum ash balls) are added in batches to form a foamy reducing slag (white slag) and maintain it for 20 minutes. The final slag composition of the refining slag, by mass percentage, includes CaO: 45.2%, SiO2: 41.15%, MgO: 7.1%, Al2O3: 6.2%, TFe: 0.35%; basicity 1.1, refining slag melting temperature 1270℃, viscosity 0.83 Pa·s, and surface tension 0.42 N / m.

[0030] The test results of the finished cord steel products are as follows: Inclusion particle size: brittle inclusions have an average particle size of 1.32 μm, and ductile inclusions have an average particle size of 1.28 μm.

[0031] Inclusion rating: Class A and Class C inclusions are both grade 0, while Class B and Class D inclusions are grade 0.5 at most. The pass rate is 100%, and the wire breakage rate has been reduced from about 4 times / ton to less than 1 time / ton.

[0032]

Example 2

[0033] In the early stage of LF smelting, slag-forming materials (lime and aluminum ash balls) are added in batches to form a foamy reducing slag (white slag) and maintain it for 20 minutes. The final slag composition, by mass percentage, includes CaO: 42.5%, SiO2: 43.7%, MgO: 8.2%, Al2O3: 5.2%, TFe: 0.4%, and basicity: 0.97. The refining slag has a melting temperature of 1310℃, a viscosity of 0.65 Pa·s, and a surface tension of 0.34 N / m.

[0034] The test results of the finished cord steel products are as follows: Inclusion particle size: brittle inclusions have an average particle size of 1.35 μm, and ductile inclusions have an average particle size of 1.21 μm.

[0035] Inclusion rating: Class A and Class C inclusions are both grade 0, while Class B and Class D inclusions are grade 0.5 at most. The pass rate is 100%, and the wire breakage rate has been reduced from about 4 times / ton to less than 1 time / ton.

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the morphology of non-metallic inclusions in steel cord, characterized in that, The process includes the following: 1) Steel composition control; (1) Preparation of Fe-Si-Mg-Al quaternary alloy: Fe-Si-Mg-Al quaternary alloys were prepared using an intermediate alloy smelting process. The Fe-Si-Mg-Al quaternary alloys contained 30%–40% Si, 8.5%–10% Mg, and 1.0%–3.0% Al by mass percentage, with the remainder being Fe and unavoidable impurities. The total content of Ca, S, and P among the impurities was less than 1.0%. (2) Add Fe-Si-Mg-Al quaternary alloy: The Fe-Si-Mg-Al alloy is added to the molten steel using a cored wire method. After LF refining and alloying adjustments, the cored wire is fed into the molten steel at a temperature controlled between 1580 and 1620°C. The feeding rate is 1.8–4.0 m / t of steel, fed in batches at a feeding speed of 2.5–3.0 m / s. The feeding position is opposite the bottom permeable brick of the ladle. The soft blowing time of argon gas after feeding is ≥18 min. 2) Refining slag system control; In the early stage of LF furnace smelting, slag-forming materials are added in batches to form foamy reducing slag and maintain it for more than 20 minutes. The composition of the refining slag system is: w(CaO) / w(SiO2)=0.8~1.2, w(MgO)=6%~9%, w(Al2O3)<10.0%; the melting temperature of the refining slag is ≤1350℃, the viscosity is 0.5~1.0Pa·s, and the surface tension is 0.3~0.5N / m.

2. The method for controlling the morphology of non-metallic inclusions in cord steel according to claim 1, characterized in that, The parameters of the cored wire are: wire diameter ø9~ø11mm, sheet thickness 0.40~0.50mm, wire weight 470~490g / m, and core weight 215~240g / m.

3. The method for controlling the morphology of non-metallic inclusions in cord steel according to claim 1, characterized in that, The cored wires are fed in batches with an interval of more than 1 minute.

4. The method for controlling the morphology of non-metallic inclusions in cord steel according to claim 1, characterized in that, The slag-forming materials include lime and aluminum ash balls.

Images