A super soft red copper strip and a grain refinement production process thereof

Abstract

The present application relates to a kind of extra-soft red copper strip and its grain refinement production process, belong to non-ferrous metal processing technical field, red copper casting blank is heated after homogenization and is carried out low temperature hot rolling, hot rolling strip blank is milled after surface, roughing and trimming, then, first heat treatment annealing is carried out, and after cleaning, it is rolled to finished product thickness, second heat treatment annealing is carried out, and the extra-soft red copper strip product is obtained;The average grain size of the extra-soft red copper strip is ≤30 μm;Vickers hardness HV≤50, elongation A50 after breaking A50≥45%;Electrical conductivity ≥100% IACS.The present application can solve the contradiction problem of extra-soft red copper strip in grain refinement, high electrical conductivity and extra-soft state in prior art.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal processing technology, specifically relating to an extra-soft copper strip and its grain refinement production process. Background Technology

[0002] High-purity copper (such as T2, TU1, and TU2) is widely used in electronic components, power transmission, precision instruments, and heat exchangers due to its excellent electrical and thermal conductivity, corrosion resistance, and non-magnetic properties. Many applications not only require copper to have extremely high electrical conductivity (close to the theoretical value of pure copper), but also require it to be in an extra-soft state (Vickers hardness HV≤50) and have extremely high ductility (elongation after fracture A50≥45%) to facilitate subsequent precision stamping, deep drawing, and other processing.

[0003] In traditional manufacturing processes, achieving the desired soft mechanical properties primarily relies on a final high-temperature, long-duration annealing process. However, this annealing process easily leads to abnormal grain growth, resulting in coarse grains with average sizes often exceeding 50 μm or even 100 μm. Coarse grains significantly reduce the material's strength and fatigue resistance, and are prone to causing an "orange peel" surface texture. This negatively impacts surface quality and final product yield during subsequent processing such as bending and stamping.

[0004] Introducing cold deformation during processing to refine the grains can improve strength, but it sacrifices the material's softness. Subsequent annealing at higher temperatures or for longer periods is then required to soften the grains, which exacerbates the grain coarsening problem. Furthermore, coarse grain structures are often accompanied by inhomogeneities in properties such as hardness and elongation across different parts of the material, leading to poor product reliability during subsequent processing.

[0005] Existing technologies employ methods such as intermediate annealing and adjusting rolling passes, but it remains difficult to effectively refine the grain size to below 30 μm, or even to the 15-25 μm range, while maintaining good uniformity and ensuring the achievement of an ultra-soft state (HV≤50, A50≥45%). Adding trace amounts of grain-refining elements such as Ag, Fe, and Zr can suppress grain growth, but it significantly reduces conductivity, failing to meet the requirements for high-purity, high-conductivity copper.

[0006] Therefore, developing a production process that can achieve significant grain refinement and ensure microstructure uniformity while maintaining the high purity, high conductivity and ultra-soft state of copper is of great industrial application value and an urgent technical need. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an ultra-soft copper strip and its grain refinement production process, thereby resolving the contradictions in existing ultra-soft copper strips regarding grain refinement, high conductivity, and ultra-softness, and meeting the application requirements for ultra-soft copper strips.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is: a grain refinement production process for extra-soft copper strip, wherein the copper billet is homogenized and heated and then subjected to low-temperature hot rolling, the hot-rolled strip is milled, pre-rolled and trimmed, and then subjected to a first heat treatment annealing, and after cleaning and rolling to the finished thickness, a second heat treatment annealing is performed to obtain the extra-soft copper strip product.

[0009] The temperature of the low-temperature hot rolling is 350℃-500℃, and the final rolling temperature is not lower than 350℃;

[0010] The first heat treatment annealing adopts a stepped heating and holding annealing process, including:

[0011] First stage: Increase the temperature to 240-260℃ at 80-120℃ / h and hold for 1-2 hours; Second stage: Increase the temperature to 370-390℃ at 40-60℃ / h and hold for 3-4 hours; Third stage: Decrease the temperature to 60℃ at 40-70℃ / h and air cool to room temperature after removing from the furnace.

[0012] The second heat treatment annealing is carried out in an air-cushion bright annealing furnace and adopts a high-temperature heat treatment annealing regime. The annealing process is 600℃-650℃ and the strip speed is 10-20m / min.

[0013] Its beneficial effects are: the temperature range of low-temperature hot rolling is higher than the static recrystallization temperature of copper, and the rolling deformation process and recrystallization process are partially superimposed. Compared with the traditional hot rolling process (final rolling temperature > 600℃), the resulting grains are finer and the deformation energy storage distribution is more uniform.

[0014] In the first heat treatment annealing, the first stage promotes the low-temperature recovery process, eliminates microscopic internal stress, and at the same time utilizes the relatively slow grain boundary migration rate at this temperature to form a large number of fine and uniformly distributed recrystallization nuclei; the second stage is conducive to the recrystallization temperature of copper, allowing the nuclei formed in the first stage to grow fully and complete the recrystallization process, and using a relatively low heating rate and holding temperature to control the grain growth rate, obtaining fine and uniform recrystallized grains; the third stage is the cooling stage.

[0015] The second heat treatment annealing employs an air-cushioned bright annealing furnace to avoid excessive grain growth caused by prolonged holding. This stage of heat treatment annealing involves short holding at a sufficiently softening temperature to further reduce dislocation density, bringing the material to an ultra-soft state. The temperature and speed of the air-cushion furnace are combined to minimize grain growth in the strip after rolling. After exiting the furnace, the strip can immediately enter the online cleaning process to prevent further grain growth caused by slow cooling.

[0016] Furthermore, the homogenization heating temperature is 880℃-920℃, and the temperature is maintained for 4-5 hours.

[0017] Its beneficial effects are: homogenization heating before low-temperature hot rolling eliminates casting segregation, dissolves non-equilibrium phases, fully dissolves any trace impurities that may exist, and prevents them from precipitating and hindering recrystallization in subsequent processes, thus preparing a uniform structure for subsequent hot working.

[0018] Furthermore, the low-temperature hot rolling process involves 7-11 rolling passes, with a total deformation of 90%-95%.

[0019] Furthermore, both the first and second heat treatment annealing were carried out in a protective atmosphere of decomposed ammonia, which consisted of 75% nitrogen and 25% hydrogen by volume.

[0020] Furthermore, in the first heat treatment annealing, the first stage heating rate is 100℃ / h, the holding temperature is 250℃, and the holding time is 1-2 hours.

[0021] Furthermore, in the first heat treatment annealing, the second stage heating rate is 50℃ / h, the holding temperature is 380℃, and the holding time is 3-4 hours.

[0022] Furthermore, the raw material for the copper billet is cathode copper, wherein the total mass fraction of Cu+Ag is ≥99.95%, and the oxygen content is controlled to be ≤0.0010%, the sulfur content to be ≤0.0010%, and the phosphorus content to be ≤0.0030%.

[0023] Its beneficial effects are: strictly controlling the content of impurity elements and avoiding the influence of elements such as oxygen, sulfur, and phosphorus on subsequent processing performance.

[0024] Furthermore, the casting temperature of the copper billet is controlled at 1150-1180℃, the temperature difference between the inlet and outlet cooling water of the crystallizer is controlled within 8℃, and secondary cooling water is used.

[0025] Its beneficial effects are: introducing a higher dislocation density and finer initial dendrites into the as-cast structure.

[0026] Furthermore, the extra-soft copper strip produced by this invention has the following properties: average grain size ≤30μm; Vickers hardness HV≤50; elongation after fracture A50≥45%; conductivity ≥100% IACS; uniform grain size distribution, with no abnormally large grains.

[0027] This invention also proposes an extra-soft copper strip, which is produced by the production process described above.

[0028] The technical principle of this invention is as follows: This invention introduces uniform deformation energy storage through low-temperature rolling: rolling in the temperature range of 350-500℃ (final rolling ≥350℃) combines deformation and dynamic / subdynamic recrystallization to provide uniform driving force for subsequent annealing.

[0029] This invention employs a stepped heat treatment annealing + high-temperature heat treatment annealing strategy: in the low-temperature nucleation / recovery stage, grain boundary migration is suppressed and a large number of uniform crystal nuclei are formed; in the recrystallization stage, grain growth is controlled to obtain fine grains; and in the high-temperature short-time softening stage, a soft state is achieved while minimizing grain growth.

[0030] The beneficial effects obtained by this invention are as follows: By combining the process of "high temperature homogenization + temperature-controlled hot rolling + stepped heat treatment annealing + high temperature heat treatment annealing", the contradiction of "softening must lead to coarse grains" in the traditional process is broken: (1) The average grain size of the final product can be stably controlled within the range of ≤30μm, which is much smaller than the range of 50μm or even 100μm in the traditional annealing process; (2) While obtaining a fine grain structure, the Vickers hardness HV≤50 and the elongation after fracture A50≥45% are guaranteed, which fully meets the application requirements of extra soft copper; (3) No alloying elements are added in the process, maintaining the high purity of copper and the conductivity ≥100% IACS; (4) Abnormal grain growth is avoided, the grain size distribution is concentrated, the material properties are uniform and stable, and the fine grain structure improves the strength, fatigue resistance and surface quality and yield of the material in subsequent precision processing.

[0031] Therefore, the present invention achieves significant technical effects in terms of grain refinement, significant grain refinement, excellent soft-state properties, high conductivity, good microstructure uniformity, and improved product performance through the synergistic effect of multiple steps. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the embodiments, but this should not be construed as limiting the invention in any way.

[0033] Example 1: Production of 1.5mm thick extra-soft copper strip

[0034] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95 wt%) is selected, and the cathode copper oxygen content ≤0.0010%, sulfur content ≤0.0010%, and phosphorus content ≤0.0030%. Charcoal and graphite powder are used for covering, and smelting is carried out in a reducing atmosphere. Vertical continuous casting is used to produce a 230mm thick and 620mm wide billet. The decomposed ammonia consists of 75% nitrogen and 25% hydrogen by volume. The casting temperature of the copper billet is controlled at 1150-1180℃, and the temperature difference between the inlet and outlet of the cooling water in the crystallizer is controlled within 8℃. Secondary cooling water is used to introduce a high dislocation density and fine initial dendrite structure into the as-cast structure.

[0035] The second step is homogenization heating: the billet is held at 880℃ for 5 hours, then air-cooled to 500℃ after being taken out of the furnace, and then transferred to hot rolling.

[0036] The third step is hot rolling: nine rolling passes are performed, with the rolling pass distribution being 230mm -215mm -185mm -143mm -107mm -75mm -46mm -30mm -21mm -15mm, the total deformation is 93.4%, and the final rolling temperature is 396℃, resulting in a 15mm thick strip.

[0037] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to produce 2.0mm thick rolled coils. These coils are then individually loaded into a bell-shaped furnace for stepped heat treatment annealing: the first stage involves heating at 100℃ / h to 250℃ and holding for 1 hour; the second stage involves heating at 50℃ / h to 380℃ and holding for 3 hours; and the third stage involves furnace cooling at 50℃ / h to 60℃ followed by air cooling.

[0038] The fifth step involves cleaning the product after the fourth heat treatment and rolling it to a finished thickness of 1.5mm. Then, a second heat treatment annealing is performed using an air-cushion bright annealing furnace at 650℃ and a speed of 15m / min. After exiting the furnace, the product immediately enters an online cleaning process to prevent the grains from growing further due to slow cooling.

[0039] Step 6: Sampling and testing performance and grain size: average grain size is 28μm; Vickers hardness (HV1) is 48.3; elongation after fracture (A50mm) is 46%; conductivity is 101.4% IACS; the grains are uniform and fine, with no coarse grains; the product passes the test and is then cut and packaged.

[0040] Example 2: Production of 0.8mm thick extra-soft copper strip

[0041] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95 wt%) is selected, and the cathode copper oxygen content ≤0.0010%, sulfur content ≤0.0010%, and phosphorus content ≤0.0030%. Charcoal and graphite powder are used for covering, and smelting is carried out in a reducing atmosphere. Vertical continuous casting is used to produce a 210mm thick and 620mm wide billet. The casting temperature of the copper billet is controlled at 1150-1180℃, and the temperature difference between the inlet and outlet of the cooling water in the crystallizer is controlled within 8℃. Secondary cooling water is used to introduce a high dislocation density and fine initial dendrite structure into the as-cast structure.

[0042] The second step is to homogenize the heating: hold the billet at 900℃ for 4 hours, and then air cool it to 500℃ after it is taken out of the furnace.

[0043] The third step is hot rolling: seven rolling passes are performed, with the rolling pass distribution being 210mm -194mm -156mm -116mm -76mm -43mm -25mm -15mm, the total deformation is 92.8%, and the final rolling temperature is 412℃, resulting in a 15mm thick strip.

[0044] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to produce 1.3mm thick rolled coils. Multiple rolled coils are then loaded into a bell furnace for stepped heat treatment annealing: the first stage involves heating at 120℃ / h to 260℃ and holding for 1 hour; the second stage involves heating at 60℃ / h to 390℃ and holding for 3 hours; and the third stage involves furnace cooling at 40℃ / h to 60℃ followed by air cooling.

[0045] The fifth step involves cleaning the product after the fourth heat treatment and rolling it to a finished thickness of 0.8mm. Then, a second heat treatment annealing is performed using an air-cushion bright annealing furnace at 630℃ and 10m / min. After exiting the furnace, the product immediately enters an online cleaning process to prevent the grains from growing further due to slow cooling.

[0046] Step 6: Sampling and testing performance and grain size: average grain size is 27μm; Vickers hardness (HV0.5) is 46.7; elongation after fracture (A50mm) is 48%; conductivity is 101.1% IACS; the grains are uniform and fine, with no coarse grains; the product passes the test and is then cut and packaged.

[0047] Example 3: Production of 0.3mm thick extra-soft copper strip

[0048] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95 wt%) is selected, and the cathode copper oxygen content ≤0.0010%, sulfur content ≤0.0010%, and phosphorus content ≤0.0030%. Charcoal and graphite powder are used for covering, and smelting is carried out in a reducing atmosphere. Vertical continuous casting is used to produce a 230mm thick and 620mm wide billet. The casting temperature of the copper billet is controlled at 1150-1180℃, and the temperature difference between the inlet and outlet of the cooling water in the crystallizer is controlled within 8℃. Secondary cooling water is used to introduce a high dislocation density and fine initial dendrite structure into the as-cast structure.

[0049] The second step is to homogenize the heating: hold the billet at 920℃ for 4 hours, and then air cool it to 450℃ after it is taken out of the furnace.

[0050] The third step is hot rolling: 11 rolling passes are performed, with the rolling pass distribution being 230mm -215mm -183mm -155mm -125mm -98mm -75mm -57mm -42mm -30mm -21mm -15mm, the total deformation is 93.4%, and the final rolling temperature is 367℃, to obtain a 15mm thick strip.

[0051] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to produce 0.5mm thick rolled coils. These coils are then individually loaded into a bell-shaped furnace for stepped heat treatment annealing: the first stage involves heating at 80℃ / h to 240℃ and holding for 2 hours; the second stage involves heating at 40℃ / h to 370℃ and holding for 4 hours; and the third stage involves furnace cooling at 70℃ / h to 60℃ followed by air cooling.

[0052] The fifth step involves cleaning the product after the fourth heat treatment and rolling it to a finished thickness of 0.3mm. Then, a second heat treatment annealing is performed using an air-cushion bright annealing furnace at 600℃ and 20m / min. After exiting the furnace, the product immediately enters an online cleaning process to prevent the grains from growing further due to slow cooling.

[0053] Step 6: Sampling and testing performance and grain size: average grain size is 29μm; Vickers hardness (HV0.1) is 48.3; elongation after fracture (A50mm) is 46%; conductivity is 101.2% IACS; the grains are uniform and fine, with no coarse grains; the product passes the test and is then cut and packaged.

[0054] In the above embodiments, both the first heat treatment annealing and the second heat treatment annealing are carried out in a protective atmosphere of decomposed ammonia, wherein the decomposed ammonia consists of 75% nitrogen and 25% hydrogen by volume.

[0055] The following comparative examples demonstrate the production of 1.5mm thick copper strip using a process different from that of the present invention.

[0056] Comparative Example 1

[0057] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95wt%) was selected, covered with charcoal and graphite powder, and smelted in a reducing atmosphere. Vertical continuous casting was used to produce a 230mm thick and 620mm wide billet, which was cooled with secondary cooling water to obtain a fine dendritic structure.

[0058] The second step is to homogenize the heating process: hold the billet at 890℃ for 4 hours.

[0059] The third step is to directly roll the strip in 9 passes without air cooling after it comes out of the furnace. The rolling passes are distributed as follows: 230mm-215mm-185mm-143mm-107mm-75mm-46mm-30mm-21mm-15mm. The total deformation is 93.4%, and the final rolling temperature is 642℃, resulting in a 15mm thick strip.

[0060] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to produce a 1.5mm thick rolled coil. This coil is then individually loaded into a bell furnace for conventional heat treatment annealing: the temperature is raised to 380℃ at 100℃ / h, held for 4 hours, and then furnace cooled to 60℃ at 50℃ / h before being removed from the furnace and air-cooled.

[0061] The fifth step is to clean the heat-treated product;

[0062] Step 6: Sampling and testing performance and grain size: average grain size is 85 μm; Vickers hardness (HV1) is 58.4; elongation after fracture (A50mm) is 44%; electrical conductivity is 101.1% IACS; microstructure observation: complete recrystallization, with coarse grains present. The product performance does not meet the requirements of the extra-soft copper strip described in this invention.

[0063] Comparative Example 2

[0064] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95wt%) was selected, covered with charcoal and graphite powder, and smelted in a reducing atmosphere. Vertical continuous casting was used to produce a 230mm thick and 620mm wide billet, which was cooled with secondary cooling water to obtain a fine dendritic structure.

[0065] The second step is to homogenize the heating: hold the billet at 890℃ for 4 hours, and then air cool it to 500℃ after it is taken out of the furnace.

[0066] The third step involves nine rolling passes, with the passing passes distributed as follows: 230mm - 215mm - 185mm - 143mm - 107mm - 75mm - 46mm - 30mm - 21mm - 15mm. The total deformation is 93.4%, and the final rolling temperature is 379℃, resulting in a 15mm thick strip.

[0067] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to form a 2.0mm thick rolled coil. This coil is then individually loaded into a bell furnace for conventional heat treatment annealing: the temperature is raised to 380℃ at 100℃ / h, held for 4 hours, and then furnace cooled to 60℃ at 50℃ / h before being removed from the furnace and air-cooled.

[0068] The fifth step is to clean the heat-treated product and roll it to a finished thickness of 1.5mm. Then, perform a second heat treatment annealing. The annealing process is carried out in an air-cushion bright annealing furnace at 650℃ and 15m / min.

[0069] Step 6: Sampling and testing performance and grain size: average grain size is 44μm; Vickers hardness (HV1) is 53.8; elongation after fracture (A50mm) is 40%; microstructure observation: relatively uniform, with few coarse grains. The product performance does not meet the requirements of the extra-soft copper strip described in this invention.

[0070] Comparative Example 3

[0071] The first step, raw materials and casting: T2 cathode copper (Cu+Ag≥99.95wt%) was selected, covered with charcoal and graphite powder, and smelted in a reducing atmosphere. Vertical continuous casting was used to produce a 230mm thick and 620mm wide billet, which was cooled with secondary cooling water to obtain a fine dendritic structure.

[0072] The second step is to homogenize the heating process: hold the billet at 890℃ for 4 hours.

[0073] The third step is to directly roll the strip in 9 passes without air cooling after it comes out of the furnace. The rolling passes are distributed as follows: 230mm-215mm-185mm-143mm-107mm-75mm-46mm-30mm-21mm-15mm. The total deformation is 93.4%, and the final rolling temperature is 642℃, resulting in a 15mm thick strip.

[0074] The fourth step involves milling, initial rolling, and trimming the hot-rolled strip to form a 2.0mm thick rolled coil. This coil is then individually loaded into a bell furnace and subjected to the stepped heat treatment annealing method of this invention: the first stage involves heating at 100℃ / h to 250℃ and holding for 1 hour; the second stage involves heating at 50℃ / h to 380℃ and holding for 3 hours; and the third stage involves furnace cooling at 50℃ / h to 60℃ followed by air cooling after removal from the furnace.

[0075] The fifth step is to clean the heat-treated product and roll it to a finished thickness of 1.5mm. Then, perform a second heat treatment annealing. The annealing process is carried out in an air-cushion bright annealing furnace at 650℃ and 15m / min.

[0076] Step 6: Sampling and testing performance and grain size: average grain size is 38 μm; Vickers hardness (HV1) is 47.1; elongation after fracture (A50mm) is 48%; conductivity is 101.3% IACS; microstructure observation: relatively uniform, with few coarse grains. Although the product performance does not meet the requirements of the extra-soft copper strip described in this invention in some indicators, it can still be used in scenarios where grain size requirements are not strict and product performance requirements are not high.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific implementation of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A grain refinement process for ultra-soft copper strip, characterized in that, After homogenization heating, the copper billet is hot rolled at low temperature. After milling, initial rolling and trimming, the hot rolled strip is subjected to the first heat treatment annealing. After cleaning and rolling to the finished thickness, it is subjected to the second heat treatment annealing to obtain the extra soft copper strip product. The temperature of the low-temperature hot rolling is 350℃-500℃, and the final rolling temperature is not lower than 350℃; The first heat treatment annealing adopts a stepped heating and holding annealing process, including: First stage: Increase the temperature to 240-260℃ at 80-120℃ / h and hold for 1-2 hours; Second stage: Increase the temperature to 370-390℃ at 40-60℃ / h and hold for 3-4 hours; Third stage: Decrease the temperature to 60℃ at 40-70℃ / h and air cool to room temperature after removing from the furnace. The second heat treatment annealing is carried out in an air-cushion bright annealing furnace and adopts a high-temperature heat treatment annealing regime. The annealing process is 600℃-650℃ and the strip speed is 10-20m / min.

2. The grain refinement production process for the extra-soft copper strip according to claim 1, characterized in that, The homogenization heating temperature is 880℃-920℃, and the temperature is maintained for 4-5 hours.

3. The grain refinement production process for the extra-soft copper strip according to claim 1, characterized in that, The low-temperature hot rolling process involves 7-11 rolling passes, with a total deformation of 90%-95%.

4. The grain refinement production process for the extra-soft copper strip according to claim 1, characterized in that, Both the first and second heat treatment annealing were carried out in a protective atmosphere of decomposed ammonia, which consisted of 75% nitrogen and 25% hydrogen by volume.

5. The grain refinement process for the extra-soft copper strip according to claim 1, characterized in that, In the first heat treatment annealing, the first stage heating rate is 100℃ / h, the holding temperature is 250℃, and the holding time is 1-2 hours.

6. The grain refinement production process for the extra-soft copper strip according to claim 1, characterized in that, In the first heat treatment annealing, the second stage heating rate is 50℃ / h, the holding temperature is 380℃, and the holding time is 3-4 hours.

7. The grain refinement process for the extra-soft copper strip according to claim 1, characterized in that, The raw material for the copper billet is cathode copper, wherein the total mass fraction of Cu+Ag is ≥99.95%, and the oxygen content is controlled to be ≤0.0010%, the sulfur content to be ≤0.0010%, and the phosphorus content to be ≤0.0030%.

8. The grain refinement process for ultra-soft copper strip according to claim 7, characterized in that, The casting temperature of the copper billet is controlled at 1150-1180℃, the temperature difference between the inlet and outlet cooling water of the crystallizer is controlled within 8℃, and secondary cooling water is used.

9. The grain refinement production process for the extra-soft copper strip according to claim 1, characterized in that, The produced extra-soft copper strip has the following properties: average grain size ≤30μm; Vickers hardness HV≤50; elongation after fracture A50≥45%; conductivity ≥100% IACS; small standard deviation of grain size distribution and no abnormally large grains.

10. A type of extra-soft copper strip, characterized in that, It is produced by the manufacturing process described in any one of claims 1-9.