Wire rod for high-conductivity cable and low-wire-fracture-rate production process of wire rod

Abstract

The invention discloses a wire rod for a cable with low wire fracture rate and high conductivity. The wire rod comprises the following main chemical components in percentage by mass: less than or equal to 0.0010% of C, less than or equal to 0.008% of Si, less than or equal to 0.015% of Mn, less than or equal to 0.006% of P, less than or equal to 0.003% of S, less than or equal to 0.004% of N, less than or equal to 0.015% of Cu + Ni + Cr + Mo + Alt, less than or equal to 0.01% of Alt and less than or equal to 180ppm of [O]. And 25 < = (Cu + Ni + Cr + Mo) / Alt < = 50. By optimizing steel components and strictly controlling heating, rolling and cooling processes, precise control of austenite grain size and ferrite grain size is achieved, the technical problem that an existing cable steel preparation process is difficult to consider high conductivity and easy-drawing performance at the same time can be effectively solved, 0.035-0.045 mm ultra-fine drawing is met, the conductivity is larger than or equal to 17.0%, and the tensile strength is larger than or equal to 9.0%. The wire breakage rate is less than or equal to 0.2 times / ton, and the applicability is wide.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a wire rod for a high-conductivity cable and a production process thereof with a low wire breakage rate. Background Art

[0002] Cable steel, also known as copper-clad steel, is high-quality ultra-low carbon steel (carbon content ≤ 0.002%). As the base of bimetallic composite wire, its deep processing process requires a series of processes such as multiple drawing, heat treatment, and copper plating. Bimetallic wire combines the strength and toughness of steel with the conductivity and high-frequency characteristics of copper. It has the advantages of saving copper and reducing costs. It is widely used in the core wires of parallel dual-core telephone user communications, connectors of various electronic components, etc. The diameter of copper-clad steel wire is often very small, so cable steel needs to be subjected to a large drawing deformation (diameter before drawing ≥ 6.5mm, diameter after drawing is 0.04-0.12mm). To ensure that the wire is not broken or less broken during the wire drawing process is the basis and key to the quality of cable steel products.

[0003] Patent CN108062992 provides a steel wire for copper-clad steel composite shielded wire with excellent drawing performance and electrical conductivity. The chemical composition and mass percentage of the steel wire are C≤0.010%, Si≤0.010%, Mn≤0.07%, P≤0.010%, S≤0.010%, Al≤0.004%, Ti≤0.003%, B: 0.0060-0.0120%, and the balance is Fe and unavoidable impurities; the production method includes billet smelting, billet heating, wire rolling and wire cooling processes; wherein the heating process adopts continuous casting billet heating and hot rolling billet secondary heating, and the wire cooling process adopts a slow cooling process, which can achieve drawing to 0.08mm without breaking the wire, and the conductivity can reach more than 16.3%; but the corresponding drawing and conductivity indicators currently cannot meet the requirements of high-quality cable steel. Patent application CN107236902A discloses a semi-hard cable steel, the mass percentage of the chemical composition of the semi-hard cable steel is: C≤0.02%, Si≤0.02%, Mn 0.05-0.1%, P≤0.020%, S≤0.015%, Als 0.005-0.01%, the rest is Fe and inevitable impurities, and the above elements satisfy Cu+Ni+Cr+Mo≤0.030%, Mn / S≥10; its production method includes: hot metal desulfurization, converter smelting, argon blowing, RH furnace treatment, continuous casting, billet heating, high-speed wire rolling, and Stelmor controlled cooling. The cable steel produced by this patent has low conductivity and high work hardening rate after drawing, which is not conducive to drawing and needs high-temperature annealing after drawing, and the user's production cost is high.

[0004] Further exploration of the preparation process of cable wire rods with both high conductivity and low wire breakage rate has important research and application significance. Summary of the invention

[0005] The main purpose of the present invention is to provide a wire rod production process for cables with low wire breakage rate and high conductivity in view of the problems and shortcomings of the existing ultra-fine drawing process for cable steel. On the basis of ensuring that the conductivity is ≥17.0%, it can meet the ultra-fine drawing of 0.035-0.045mm and the wire breakage rate is ≤0.2 times / ton, meeting the latest needs of the electronic communication industry.

[0006] To achieve the above solution, the technical solution adopted by the present invention is:

[0007] A wire rod for a high-conductivity cable, the chemical composition of which is calculated by weight percentage: C≤0.0010%, Si≤0.008%, Mn≤0.015%, P≤0.006%, S≤0.003%, N≤0.004%, Cu+Ni+Cr+Mo+Alt≤0.015%, Alt≤0.01%, [O]≤180ppm, and the rest is Fe and unavoidable impurities.

[0008] Furthermore, the chemical composition of the wire rod for the cable with low broken wire rate and high conductivity is as follows by weight percentage: C 0.0005-0.0008%, Si 0.002-0.005%, Mn 0.005-0.010%, P≤0.004%, S≤0.003%, N≤0.004%, Cu+Ni+Cr+Mo+Alt 0.0045-0.010%, [O] 100-140ppm, and the rest is Fe and unavoidable impurities.

[0009] Furthermore, 25≤(Cu+Ni+Cr+Mo) / Alt≤50.

[0010] Preferably, in the wire rod for high conductivity cable, the Cu content is 0.001-0.003%, the Ni content is 0.0005-0.0010%, the Cr content is 0.002-0.004%, and the Mo content is 0.001-0.002%.

[0011] In the above scheme, the electrical conductivity of the cable wire rod can reach 17.5-17.9%, which can meet the requirements of 0.035-0.045 mm ultra-fine drawing, and the wire breakage rate is ≤0.2 times / ton.

[0012] The above-mentioned method for preparing wire rod for cables with low wire breakage rate and high conductivity includes molten iron desulfurization, converter or electric furnace, RH treatment, continuous casting and high-speed wire rolling steps, wherein the high-speed wire rolling step adopts a controlled rolling and controlled cooling process, and the key control requirements include: 1) extending the heating time of the heating furnace, increasing the rolling start temperature, and regulating the finishing rolling temperature, the sizing temperature and the wire laying temperature; 2) fully opening the Stelmor line insulation cover to regulate the roller speed and the coiling temperature.

[0013] Furthermore, in the controlled rolling and controlled cooling process, the heating time in the heating furnace is ≥ 120 min, the starting rolling temperature is 1150 - 1250 °C, the temperature entering the finishing mill is 910 - 930 °C, the temperature entering the reducing and sizing mill is 900 - 920 °C, the wire laying temperature is 880 - 900 °C, all the heat preservation covers on the Stelmor line are fully opened, the roller table speed is 0.10 - 0.20 m / s, and the temperature entering the coiling reel is ≥ 500 °C.

[0014] Preferably, the heating time in the heating furnace is 120 - 200 min, and the starting rolling temperature is 1200 - 1250 °C.

[0015] Preferably, the temperature entering the coiling reel is 500 - 700 °C.

[0016] In the above solution, the original austenite grain size is coarsened by heating at high temperature for a long time. During the subsequent rolling process, austenite recrystallization and refinement are achieved through controlled rolling temperature, avoiding mixed grains caused by rolling in the two-phase region. And the phase transformation and grain growth behavior on the Stelmor line are controlled according to the delayed cooling mode, promoting the final obtaining of wire rods for cables with a low wire breakage rate and high conductivity.

[0017] The principle of the present invention includes:

[0018] 1. Composition design

[0019] The functions of each element in the steel are as follows:

[0020] C: It is the most important constituent element in the steel. The carbon content directly determines its strength and plasticity. In the cold-drawn state, the tensile strength of the steel continuously increases with the increase of the carbon content, and the plasticity decreases with the increase of the carbon content. Generally, ultra-low carbon steel is selected as the raw material for making copper-clad steel because ultra-low carbon steel has good deformability and meets the deformation requirements of copper-clad steel. In this application, C ≤ 0.0010%, and the preferred content is 0.0005 - 0.0008%.

[0021] Si: It is used as a control element. This element destroys the cold formability of the steel, improves the elastic limit of the steel wire, and is also an important source of inclusions. The presence of silicon will affect the conductivity of the steel. The higher the silicon content, the lower the conductivity of the steel. Therefore, Si ≤ 0.008%, and the preferred content is 0.002 - 0.005%.

[0022] Mn: It can improve the strength of the wire rod and is a good deoxidizer for steelmaking. Manganese combines with sulfur to form MnS, which can reduce the harmful effects of sulfur, but there is a strong correlation with the electrical conductivity of the steel. Its presence affects the conductivity of the steel. At the same time, a low manganese content can shift the carbon content range of the peritectic reaction point to the left. Therefore, Mn ≤ 0.015%, and the preferred content is 0.005 - 0.010%.

[0023] P: It is a harmful impurity element that reduces the plasticity and toughness of steel, and sharply raises the brittle transition temperature of steel, that is, it increases the cold brittleness (becoming brittle at low temperatures) of steel. The presence of phosphorus will affect the electrical conductivity of steel. The higher the phosphorus content, the lower the electrical conductivity of steel. Therefore, P≤0.006%, preferably P≤0.004%.

[0024] S: It is one of the important indicators for measuring the cleanliness of molten steel, and greatly restricts the improvement of the properties of steel. Its greatest harm is cracking during hot working, resulting in hot brittleness. A high sulfur content in steel increases the content of sulfide inclusions, leading to a decrease in the plasticity and toughness of steel. Therefore, S≤0.003%.

[0025] N: Nitrogen will increase the brittleness of steel and often forms second-phase particles with Al, V, Ti, etc. to refine the grain size, thus deteriorating the electrical conductivity of cable steel. Therefore, N≤0.004%.

[0026] Cu+Ni+Cr+Mo+Alt: Metal elements will reduce the electrical conductivity of cable steel, but appropriate addition can stabilize the grain size and facilitate the wire rod drawing. Therefore, Cu+Ni+Cr+Mo+Alt is controlled to be ≤0.015%, preferably 0.005 - 0.010%; and at the same time, 25≤(Cu+Ni+Cr+Mo) / Alt≤50 is controlled; which is beneficial to ensuring and improving the electrical conductivity of the obtained wire rod, and further combined with the optimized high-speed wire rolling process, realizing the control of the grain size of cable steel, and can effectively balance the high electrical conductivity and extremely fine drawing performance of wire rods for cables, etc.

[0027] [O]: Oxygen in steel will lead to an increase in inclusions, deteriorate the purity of steel quality and then affect the electrical conductivity, and too high oxygen content will lead to defects such as surface bubbles of the continuous casting billet. Therefore, [O]≤180ppm, preferably the [O] content is 100 - 140ppm.

[0028] 2. Process improvement

[0029] Principle of controlled rolling and controlled cooling process: The composition of cable steel is close to that of industrial pure iron. In the present invention, high-temperature and long-time heating is first carried out to coarsen the size of the original austenite grain size, and then during the subsequent rolling process, austenite recrystallization and refinement are achieved through temperature-controlled rolling, avoiding mixed grains caused by rolling in the two-phase region, and controlling the phase transformation and grain growth behavior on the Stelmor line according to the delayed cooling mode to ensure obtaining wire rods for cables with a low wire breakage rate and high conductivity.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1) By optimizing the components of steel and strictly controlling the heating, rolling, and cooling processes, the present invention realizes the precise control of the austenite grain size and ferrite grain size, and can effectively overcome the technical problem that it is difficult to balance the high electrical conductivity and easy drawability in the existing cable steel preparation process;

[0032] 2) On the basis of ensuring that the conductivity ≥ 17.0%, the wire rod production process for cables of the present invention can meet the requirements of ultra-fine drawing with a wire diameter of 0.035 - 0.045 mm, the wire breakage rate ≤ 0.2 times / ton, and has a wide applicability.

[0033] 3) The production process involved in the present invention is relatively simple and easy to operate. Under the existing equipment and technology conditions, it can achieve the efficient preparation of wire rods for cables with a low wire breakage rate and high conductivity, and is suitable for popularization and application. Detailed Embodiments

[0034] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The key process control steps of each embodiment of the present invention are as follows:

[0036] (1) Produce billets according to the conventional cable steel smelting process. The process flow is: desulfurization → converter or electric furnace → RH treatment → continuous casting, and produce billets with qualified compositions. The chemical compositions are calculated by weight percentage as follows: C ≤ 0.0010%, Si ≤ 0.008%, Mn ≤ 0.015%, P ≤ 0.006%, S ≤ 0.003%, N ≤ 0.004%, Cu + Ni + Cr + Mo + Alt ≤ 0.015%, Alt ≤ 0.01%, [O] ≤ 180 ppm, and the rest is Fe and unavoidable impurities; and 25 ≤ (Cu + Ni + Cr + Mo) / Alt ≤ 50.

[0037] (2) After the billets, enter the high-speed wire rolling: the heating time in the heating furnace ≥ 120 min, the heating temperature is 1250 - 1350 °C, the starting rolling temperature is 1150 - 1250 °C, the entry temperature into the finishing mill is 920 ± 10 °C, the entry temperature into the sizing mill is 910 ± 10 °C, the wire laying temperature is 890 ± 10 °C, all the heat preservation covers on the Stelmor line are fully open (40 heat preservation covers), the roller table speed is 0.10 - 0.20 m / s, and the entry temperature into the coiler is ≥ 500 °C.

[0038] Table 1 Chemical compositions of the cable steel in the examples and comparative examples, wt%

[0039]

[0040]

[0041] Table 2 Process parameters in the steel rolling process of the examples and comparative examples

[0042]

[0043]

[0044] Table 3 Comparison of quality indexes of wire rods in examples and comparative examples

[0045]

[0046] The production process of wire rods for cables with low wire breakage rate and high conductivity has been developed in this invention of patent. On the basis of ensuring the conductivity ≥ 17.0%, it can meet the extremely fine wire drawing with a wire diameter of 0.035 - 0.045 mm, and the wire breakage rate ≤ 0.2 times / ton, meeting the latest requirements of the electronic communication industry, effectively reducing the thickness of the outer copper layer of copper clad steel, improving the wire drawing performance of steel wires, reducing the wire breakage rate during cold drawing, and thus reducing the production and manufacturing costs.

[0047] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A wire rod for a high-conductivity cable, characterized in that, Its chemical composition by mass percentage is: C ≤ 0.0010%, Si ≤ 0.008%, Mn ≤ 0.015%, P ≤ 0.006%, S ≤ 0.003%, N ≤ 0.004%, Cu + Ni + Cr + Mo + Alt ≤ 0.015%, Alt ≤ 0.01%, [O] ≤ 180 ppm, and the balance is Fe and unavoidable impurities; and 25 ≤ (Cu + Ni + Cr + Mo) / Alt ≤ 50.

2. The wire rod for high-conductivity cable according to claim 1, characterized in that, Its chemical composition by weight percentage is: C 0.0005 - 0.0008%, Si 0.002 - 0.005%, Mn 0.005 - 0.010%, P ≤ 0.004%, S ≤ 0.003%, N ≤ 0.004%, Cu + Ni + Cr + Mo + Alt 0.0045 - 0.010%, [O] 100 - 140 ppm, and the balance is Fe and unavoidable impurities.

3. The wire rod for high-conductivity cable according to claim 1, characterized in that, The electrical conductivity of the wire rod for cables reaches 17.5 - 17.9%; the diameter of the wire rod is 0.035 - 0.045 mm, and the wire breakage rate during drawing is ≤ 0.2 times / ton.

4. The low wire breakage rate production process of the wire rod for high conductivity cables according to any one of claims 1 to 3, characterized in that, It includes steps of hot metal desulfurization, converter or electric furnace, RH treatment, continuous casting and high-speed wire rolling. Among them, the high-speed wire rolling step adopts a controlled rolling and controlled cooling process. The key control requirements include: 1) extending the heating time in the heating furnace, increasing the rolling start temperature, and regulating the temperature entering the finishing mill, the temperature entering the sizing mill and the spinning temperature; 2) fully opening the insulation covers on the Stelmor line, and regulating the roller table speed and the temperature entering the coiling reel.

5. The low wire breakage rate production process according to claim 4, characterized in that, The rolling start temperature is increased to 1150 - 1250 °C.

6. The low wire breakage rate production process according to claim 4, characterized in that, In the controlled rolling and controlled cooling process, the heating time in the heating furnace is ≥ 120 min, the temperature entering the finishing mill is 910 - 930 °C, the temperature entering the sizing mill is 900 - 920 °C, and the spinning temperature is 880 - 900 °C.

7. The low wire breakage rate production process according to claim 6, characterized in that, The heating time in the heating furnace is 120 - 200 min; the rolling start temperature is 1200 - 1250 °C.

8. The low wire breakage rate production process according to claim 4, characterized in that The roller table speed is controlled to be 0.10 - 0.20 m / s, and the temperature entering the coiling reel is ≥ 500 °C.

9. The low wire breakage rate production process according to claim 8, characterized in that, The temperature entering the coiling reel is 500 - 700 °C.

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