A hot-rolled wire rod for low-strain aging CP line and its production method and application

Abstract

The present invention belongs to the technical field of iron and steel metallurgy and discloses a hot-rolled wire rod for a low-strain aging CP line, a production method thereof, and an application thereof. The chemical composition and mass percentage content of the hot-rolled wire rod for a low-strain aging CP line of the present invention are as follows: C: 0.0010-0.0030%, Si: 0.005-0.010%, Mn: 0.025-0.070%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008-0.0030%, Cu+Cr≤0.030%, 5≤(Al+Ti+V+Nb) / N≤15, C+Si+Mn+P+S≤0.09%, and the remainder being Fe and unavoidable impurities. The hot-rolled wire rod of the present invention has a tensile strength of 280 to 310 MPa, an elongation of 45% or more, and a conductivity of 16.5% or more, taking into account both high conductivity and low strain aging requirements, ensuring that the elongation of the CP wire finished product is 18% or more, and there is no significant decrease in elongation after aging, meeting the latest needs of applications in industries such as electronic communications.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and in particular relates to a hot-rolled wire rod for a low-strain aging CP line, and a production method and application thereof. Background Art

[0002] CP wire, also known as tinned copper-clad steel wire, is a product made of low-carbon steel or ultra-low-carbon steel as the core wire, and its surface is sequentially plated with copper, tin or tin-based alloy layers. It is a new type of composite wire that combines the strength and toughness of steel with the conductivity and high-frequency properties of copper. It has the advantages of saving copper and reducing costs.

[0003] As the substrate for bimetallic composite wire, the deep processing of hot-rolled wire rod for CP wire requires a series of steps, including multiple drawing passes, heat treatment, and copper plating. The final finished wire diameter is typically very small, mainly ranging from 0.40 to 0.80 mm. However, the initial diameter of hot-rolled wire rod for CP wire is typically 6.5 mm or larger. Hot-rolled wire rod for CP wire must meet the required electrical conductivity while also exhibiting excellent processing properties, ensuring minimal or no breakage during the multiple drawing passes. It also must exhibit low strain aging properties to avoid breakage or elongation loss after aging, thus meeting the high-quality elongation requirement of CP wire of ≥18%. Therefore, hot-rolled wire rod for CP wire must exhibit low strength and high elongation, and the drawn wire must also exhibit low strain aging properties.

[0004] Chinese patent CN115491588A discloses a method for producing low-strain, high-speed wire for electronic leads. The method includes smelting, continuous casting, heating of ingots, wire rolling, spinning, and slow cooling of the wire, ultimately producing high-speed wire for electronic leads. This invention provides high levels of inclusion control, improving drawing performance, with a wire breakage rate of ≤0.3 times / ton during the drawing process, significantly improving processing efficiency and finished product quality. However, the wire rod used in this process exhibits low electrical conductivity, with tested examples showing electrical conductivity of only 14.3-14.7%. Therefore, achieving a balance between mechanical and electrical properties is a technical challenge in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies in the existing technology and provide a hot-rolled wire rod for a low-strain aging CP line, as well as a production method and application thereof. The hot-rolled wire rod has a tensile strength of 280 to 310 MPa, an elongation of ≥45%, and a conductivity of ≥16.5%. It takes into account both high conductivity and low strain aging requirements, ensuring that the elongation of the finished wire of the CP line is ≥18%, and there is no significant decrease in elongation after aging.

[0006] In order to solve the technical problem proposed by the present invention, the present invention provides a hot-rolled wire rod for a low-strain aging CP line, wherein the chemical composition and mass percentage content are as follows: C: 0.0010-0.0030%, Si: 0.005-0.010%, Mn: 0.025-0.070%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008-0.0030%, Cu+Cr≤0.030%, 5≤(Al+Ti+V+Nb) / N≤15, C+Si+Mn+P+S≤0.09%, and the rest are Fe and unavoidable impurities.

[0007] Preferably, the chemical composition and mass percentage content of the hot-rolled wire rod for the low strain aging CP line are: C: 0.0010-0.0020%, Si: 0.005-0.008%, Mn: 0.030-0.055%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008-0.0015%, Cu+Cr≤0.025%, 5≤(Al+Ti+V+Nb) / N≤10, C+Si+Mn+P+S≤0.08%, and the rest are Fe and unavoidable impurities.

[0008] In the above solution, the hot-rolled wire rod for the low-strain aging CP line has a diameter of 6.5 to 14.0 mm, a tensile strength of 280 to 310 MPa, an elongation of ≥45%, and a conductivity of ≥16.5%.

[0009] The present invention also provides a production method for hot-rolled wire rod for low-strain aging CP line, the process of which includes: smelting ingot → heating ingot → high-speed wire rolling → cooling → coiling.

[0010] In the above solution, the heating of the ingot includes a preheating section, a heating section, and a soaking section.

[0011] Furthermore, the casting temperature in the preheating section is 20-400°C and preheated to 600-800°C.

[0012] Furthermore, if the heating section is a one-stage heating, the heating temperature is 1150-1230° C., and the heating time is 80-100 minutes.

[0013] Furthermore, if the heating section is a two-stage heating section, the heating temperatures of the first section and the second section are 1100-1180° C. and 1150-1230° C., respectively, and the heating times are 40-50 min and 30-40 min, respectively.

[0014] Furthermore, the temperature of the soaking section is 1160-1200° C., and the soaking time is 20-30 minutes.

[0015] In the above scheme, the starting rolling temperature of the high-speed wire rolling is 1060-1100°C, and water cooling is used in the rolling mill during the entire rolling process to control the temperature entering the finishing rolling at 970-1000°C and the temperature entering the sizing and reducing unit at 960-990°C. Water tank cooling is used from the sizing and reducing unit to the spinning machine to control the spinning temperature at 930-950°C.

[0016] In the above solution, the cooling is carried out in a Stelmore air cooling line, using a delayed cooling mode, with the insulation cover fully covered and slowly cooled at a rate of 0.5 to 2.5°C / s.

[0017] Furthermore, the Stelmor air-cooling line has a total of 10 to 16 sections of air-cooled rollers, the speed of the first section of rollers is 0.12 to 0.20 m / s, and the speed of the latter section of rollers increases by a multiple of 1.04 to 1.09 based on the previous section of rollers. The overlap point of the wire rods is not fixed, which reduces the difference in the same circle of the wire rods.

[0018] In the above scheme, the Stelmor air cooling line only starts the last fan, which has a rated air volume of 100,000 to 120,000 m 3 / h, air volume is opened at 30-50%.

[0019] In the above solution, the coiling temperature is 630-670°C.

[0020] The present invention also provides an application of a hot-rolled wire rod for a low-strain aging CP line. The application method is as follows: the hot-rolled wire rod is drawn to 1.3 to 2.0 mm as a core wire, and a heat treatment is performed at an annealing temperature of 650 to 720°C to obtain an annealed wire with a tensile strength of 280 to 320 MPa. The surface of the annealed wire is copper-plated, and the wire is further drawn and tinned to finally obtain a low-strain aging CP wire finished product with a diameter of 0.2 to 0.8 mm.

[0021] In the above solution, the elongation of the low-strain aged CP wire is ≥18%, and the elongation reduction rate after 7 days of aging is ≤1%.

[0022] The chemical composition design of the hot-rolled wire rod for the low strain aging CP line of the present invention is based on the following principles:

[0023] C: Carbon determines the strength and plasticity of hot-rolled wire rod. In the cold-drawn state, as the carbon content increases, the strength of the steel wire increases and the plasticity decreases. At the same time, the higher the carbon content, the higher the strain aging performance. Therefore, ultra-low carbon steel is used. Considering its strain aging performance stability, C is set to 0.0010~0.0030%, preferably 0.0010~0.0020%.

[0024] Si: Silicon destroys the cold formability of steel and is also an important source of inclusions. The presence of silicon affects the electrical conductivity of steel. The higher the silicon content, the lower the electrical conductivity of steel. Considering the castability of molten steel, Si is set to 0.005-0.010%, preferably 0.005-0.008%.

[0025] Mn: Manganese can improve the strength of wire rod and is also a good deoxidizer in steelmaking. Manganese combines with sulfur to form MnS, which can alleviate the harmful effects of sulfur. However, it has a strong correlation with the electrical conductivity of steel and its presence affects the electrical conductivity of steel. Therefore, the Mn content is set to 0.025-0.070%, preferably 0.030-0.055%.

[0026] Phosphorus (P) is a harmful impurity element that reduces the plasticity and toughness of steel and sharply increases its brittle transition temperature, increasing its cold brittleness (low-temperature brittleness). The presence of phosphorus affects the electrical conductivity of steel; the higher the phosphorus content, the lower the conductivity. Therefore, P should be ≤ 0.008%.

[0027] Sulfur (S): Sulfur is a key indicator of molten steel cleanliness and significantly limits the performance of steel. Its greatest hazard is cracking during hot working, leading to hot brittleness. High sulfur content in steel increases the presence of sulfide inclusions, reducing the steel's plasticity and toughness. Therefore, S should be ≤ 0.005%.

[0028] N: Nitrogen is an important element that causes aging in low carbon steel. It will increase the brittleness of the steel and deteriorate the elongation and conductivity of the drawn steel wire. Therefore, N≤0.0025%.

[0029] Alt: Aluminum is a deoxidizing element, which partially forms Al2O3 inclusions and partially dissolves. During heating and cooling, it forms dispersed and fine AlN second phase particles, which fix nitrogen and prevent the growth of austenite grains, affecting the conductivity of the steel. Therefore, Alt is set to 0.0008~0.0030%, preferably 0.0008~0.0015%.

[0030] Cu+Cr: can improve the cold working hardening ability of steel, especially low carbon steel, promote the formation of dispersed precipitate phase, and increase the tensile strength and hardness of steel, which is not conducive to the drawing performance of steel wire, and reduces the purity of steel wire and affects the conductivity of steel. Therefore, Cu+Cr≤0.03%, preferably Cu+Cr≤0.025%.

[0031] (Al+Ti+V+Nb) / N: Al+Ti+V+Nb has a great affinity with N. After combining with N, it reduces the work hardening of the drawn steel wire by solute N. However, its presence increases the nitrogen absorption capacity of molten steel, increases the strain aging of the steel wire, and deteriorates the elongation performance of the steel wire. Therefore, (Al+Ti+V+Nb) / N is controlled to 5-15, preferably 5-10.

[0032] C+Si+Mn+P+S: The total content of conventional solute elements in steel can reduce the electrical conductivity of steel. The higher the content, the greater the reduction. Therefore, C+Si+Mn+P+S is controlled to be ≤ 0.09%, preferably C+Si+Mn+P+S ≤ 0.08%.

[0033] The design concept of the method for producing hot-rolled wire rod for low-strain aging CP line of the present invention is as follows:

[0034] The hot-rolled wire rod for CP line of the present invention belongs to ultra-low carbon steel. In order to ensure uniform coarsening of ferrite grains of wire rod and achieve high conductivity, low strength and low strain aging performance requirements, the steel billet is preheated at 600-800℃ to ensure that the temperature inside and outside the steel billet is quickly consistent in the low temperature section, and then heated at 1150-1230℃ to obtain uniform coarsened austenite structure. If the heating temperature is too low (<1150℃), the austenite grains of the steel billet are fine, resulting in fine ferrite grains of wire rod, reduced conductivity, increased tensile strength, and increased strain aging during drawing; if the heating temperature is too high (>1230℃), it will cause This causes overheating of the steel billet, intergranular oxidation and excessively coarse austenite grains. The rolling process is prone to obvious local second phase pinning, which reduces the elongation performance of the wire rod. Subsequently, high-speed wire rolling is carried out, and there is no water tank cooling in the rough, medium and finishing rolling processes. Only the high-temperature rolling process with water cooling between rolling mills is combined to achieve uniform coarsening of the austenite recrystallization rolling. The controlled cooling adopts the combination of high-temperature wire drawing (930-950℃) and the fan-free insulation and slow cooling (0.5-2.5℃ / s) process during the phase transformation process of the Stelmor wire to obtain low tensile strength, high elongation and high conductivity of the wire rod, and finally the CP wire finished wire has good low strain aging performance.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention addresses the problems that existing hot-rolled wire rods for CP lines cannot take into account both mechanical properties and electrical conductivity, especially the problem of drawing fracture, reduced elongation after aging, and failure to meet user requirements. A low-strain aging hot-rolled wire rod for CP lines and a production method thereof are developed. By optimizing the chemical composition and the heating and controlled rolling and cooling processes during the production process, the tensile strength of the hot-rolled wire rod is 280-310 MPa, the elongation is ≥45%, and the electrical conductivity is ≥16.5%, taking into account the requirements of high conductivity and low strain aging, ensuring that the elongation of the CP line finished wire is ≥18%, and there is no significant decrease in elongation after aging, meeting the latest needs of applications in industries such as electronic communications. DETAILED DESCRIPTION

[0037] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0038] In the following examples, the chemical composition and mass percentage of the hot-rolled wire rod for the low strain aging CP line are as follows: C: 0.0010-0.0030%, Si: 0.005-0.010%, Mn: 0.025-0.070%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008-0.0030%, Cu+Cr≤0.030%, 5≤(Al+Ti+V+Nb) / N≤15, C+Si+Mn+P+S≤0.09%, with the remainder being Fe and unavoidable impurities. The specific components used in each example are shown in Table 1.

[0039] Table 1 Chemical composition of hot-rolled wire rods in Examples and Comparative Examples (wt%)

[0040]

[0041] In the following embodiments, the production method of hot-rolled wire rod for low strain aging CP line includes the following steps:

[0042] 1) Smelting ingots: smelting molten steel according to the composition in Table 1 and continuously casting into ingots;

[0043] 2) Billet heating: including preheating section, heating section, soaking section; the billet enters the furnace at a temperature of 20-400°C and is preheated to 600-800°C in the preheating section; if the heating section is a one-stage heating, the heating temperature is 1150-1230°C and the heating time is 80-100 minutes; if the heating section is a two-stage heating, the heating temperatures of the two sections are 1100-1180°C and 1150-1230°C, and the heating times are 40-50 minutes and 30-40 minutes respectively; the temperature of the soaking section is 1160-1200°C, and the soaking time is 20-30 minutes;

[0044] 3) High-speed wire rolling: The starting rolling temperature of high-speed wire rolling is 1060-1100℃. The whole rolling process is cooled by water in the rolling mill, and the temperature of the wire entering the finishing rolling is controlled at 970-1000℃. The temperature of the wire entering the sizing unit is 960-990℃. The wire-laying unit is cooled by water tanks from the sizing unit to the laying head, and the laying head temperature is controlled at 930-950℃.

[0045] 4) Cooling: Cooling is carried out in the Stelmor air cooling line, using a delayed cooling mode, with the insulation cover fully covered and slowly cooled at a speed of 0.5-2.5℃ / s; there are 12 sections of air-cooled rollers, the speed of the first section is 0.12-0.20m / s, and the speed of the latter section is increased by a multiple of 1.04-1.09 on the basis of the previous section. The overlap point of the wire rod is not fixed to reduce the difference in the same circle of the wire rod; there are 16 fans in total, and only the last fan is turned on. The rated air volume of this fan is 100,000m 3 / h, air volume is opened at 30-50%;

[0046] 5) Coiling: The coiling temperature is 630-670℃.

[0047] The specific process parameters used in each embodiment and each comparative example are shown in Tables 2 to 4.

[0048] Table 2 Process parameters for heating the slab in the embodiments and comparative examples

[0049]

[0050] Table 3 Process parameters of high-speed wire rolling in the embodiment and comparative example

[0051]

[0052] Table 4 Process parameters for cooling and coiling in the examples and comparative examples

[0053]

[0054] The hot-rolled wire rods prepared in each embodiment and each comparative example were used to prepare a CP line. The specific application method is as follows:

[0055] A 6.5mm diameter hot-rolled wire rod was drawn to a diameter of 1.3-2.0mm to form the core wire. This wire was then heat-treated at 650-720°C to obtain an annealed wire with a tensile strength of 280-320 MPa. This wire was then copper-plated and further drawn before being tin-plated to produce a 0.2mm diameter low-strain aged CP wire. Table 5 compares the relevant application parameters and performance.

[0056] Table 5 Application parameters and performance comparison of hot rolled wire rods in the embodiment and comparative example

[0057]

[0058] By optimizing the chemical composition and the heating and controlled rolling and cooling processes during the production process, the present invention ensures that the tensile strength of the hot-rolled wire rod is 280-310 MPa, the elongation is ≥45%, and the conductivity is ≥16.5%. This takes into account both the high conductivity and low strain aging requirements, ensuring that the elongation of the CP wire finished product is ≥18%, and there is no significant decrease in elongation after aging (the reduction rate is ≤1%), thus meeting the latest needs of applications in industries such as electronic communications.

[0059] The above embodiments are merely examples for clarification and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here, and any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A hot rolled wire rod for low strain aging CP line, characterized in that: Its chemical composition and mass percentage content are: C: 0.0010~0.0030%, Si: 0.005~0.010%, Mn: 0.025~0.070%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008~0.0030%, Cu+Cr≤0.030%, 5≤(Al+Ti+V+Nb) / N≤15, C+Si+Mn+P+S≤0.09%, and the rest are Fe and unavoidable impurities; The production method of the hot-rolled wire rod for the low-strain aging CP line comprises the following steps: 1) Smelting of ingots: smelting molten steel and continuously casting into ingots; 2) Slab heating: including preheating section, heating section and soaking section; if the heating section is a one-stage heating, the heating temperature is 1150-1230℃ and the heating time is 80-100min; if the heating section is a two-stage heating, the heating temperature of the first section is 1100-1180℃ and the second section is 1150-1230℃ respectively, and the heating time is 40-50min and 30-40min respectively; 3) High-speed wire rolling: The starting rolling temperature of high-speed wire rolling is 1060~1100℃. The whole rolling process is cooled by water in the rolling mill. The section from the sizing unit to the laying head adopts water tank cooling, and the laying head temperature is controlled at 930~950℃. 4) Cooling: Cooling is carried out in the Stelmore air cooling line, using a delayed cooling mode, with the insulation cover fully covered and cooling slowly at a rate of 0.5~2.5℃ / s; 5) Coiling: Coiling temperature is 630~670℃; The hot-rolled wire rod for the low-strain aging CP line has a tensile strength of 280-310 MPa, an elongation of ≥45%, and a conductivity of ≥16.5%.

2. The hot-rolled wire rod for low strain aging CP line according to claim 1, characterized in that: Its chemical composition and mass percentage content are: C: 0.0010~0.0020%, Si: 0.005~0.008%, Mn: 0.030~0.055%, P≤0.008%, S≤0.005%, N≤0.0025%, Alt: 0.0008~0.0015%, Cu+Cr≤0.025%, 5≤(Al+Ti+V+Nb) / N≤10, C+Si+Mn+P+S≤0.08%, and the rest are Fe and unavoidable impurities.

3. The hot rolled wire rod for low strain aging CP line according to claim 1, characterized in that: The diameter of the hot-rolled wire rod for the low strain aging CP line is 6.5-14.0 mm.

4. The method for producing a hot-rolled wire rod for a low strain aging CP line according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Smelting of ingots: smelting molten steel and continuously casting into ingots; 2) Slab heating: including preheating section, heating section and soaking section; if the heating section is a one-stage heating, the heating temperature is 1150-1230℃ and the heating time is 80-100min; if the heating section is a two-stage heating, the heating temperature of the first section is 1100-1180℃ and the second section is 1150-1230℃ respectively, and the heating time is 40-50min and 30-40min respectively; 3) High-speed wire rolling: The starting rolling temperature of high-speed wire rolling is 1060~1100℃. The whole rolling process is cooled by water in the rolling mill. The section from the sizing unit to the laying head adopts water tank cooling, and the laying head temperature is controlled at 930~950℃. 4) Cooling: Cooling is carried out in the Stelmore air cooling line, using a delayed cooling mode, with the insulation cover fully covered and cooling slowly at a rate of 0.5~2.5℃ / s; 5) Coiling: The coiling temperature is 630~670℃.

5. The method for producing a hot-rolled wire rod for a low strain aging CP line according to claim 4, characterized in that: The casting billet is preheated to 600-800°C when entering the furnace at the preheating section, and the temperature is 20-400°C.

6. The method for producing a hot-rolled wire rod for a low strain aging CP line according to claim 4, characterized in that: The temperature of the soaking section is 1160-1200° C., and the soaking time is 20-30 minutes.

7. The method for producing a hot-rolled wire rod for a low strain aging CP line according to claim 4, characterized in that: The high-speed wire rolling is controlled to have a finishing temperature of 970-1000°C and a sizing temperature of 960-990°C.

8. The method for producing a hot-rolled wire rod for a low strain aging CP line according to claim 4, characterized in that: The Stelmor air-cooling line has a total of 10 to 16 sections of air-cooling rollers. The speed of the first section of rollers is 0.12 to 0.20 m / s, and the speed of the latter section of rollers increases by a multiple of 1.04 to 1.09 based on the speed of the previous section of rollers. The overlap point of the wire rods is not fixed, which reduces the difference in the same circle of the wire rods.

9. The method for producing a hot-rolled wire rod for a low strain aging CP line according to claim 4, characterized in that: The Stelmor air cooling line only turns on the last fan, which has a rated air volume of 100,000~120,000m 3 / h, air volume is opened at 30~50%.

10. Use of the hot-rolled wire rod for low strain aging CP line according to any one of claims 1 to 3 in a low strain aging CP line, characterized in that: The elongation of the low-strain aged CP line is ≥18%, and the elongation reduction rate after 7 days of aging is ≤1%.

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