Large-size low-grain-size 4N5 oxygen-free copper plate and preparation method thereof

Abstract

The invention discloses a large-size low-grain-size 4N5 oxygen-free copper plate and a preparation method thereof, and the preparation method comprises the steps of first-fire forging, second-fire forging, third-fire forging and heat treatment to obtain the 4N5 oxygen-free copper plate. Through multiple times of upsetting and drawing in the forging process, crystal grains in metal are repeatedly crushed and recrystallized, the crystal grains are refined, then the heat treatment process is combined, the crystal grain size of the oxygen-free copper plate is further refined, large-size crystal grains are reduced, the structure uniformity of the oxygen-free copper plate is better, and the mechanical property of the oxygen-free copper plate is higher. After the low-grain-size 4N5 oxygen-free copper plate prepared through the method is precisely machined, due to the fact that the grain size of the low-grain-size 4N5 oxygen-free copper plate is small, grain growth is not obvious, residual stress is released in the heat treatment process, and then the problem that grains of a large-specification 4N5 oxygen-free copper plate grow abnormally in the high-temperature environment is solved.

Description

Technical Field

[0001] The invention relates to the technical field of nonferrous metal processing, and in particular to a large-size low-grained 4N5 oxygen-free copper plate and a preparation method thereof. Background Art

[0002] 4N5 oxygen-free copper has the advantages of high electrical conductivity, thermal conductivity, non-magnetic properties, low hydrogen permeability and good plastic processing performance. It is widely used in medical equipment, aerospace and other fields. The oxygen-free copper in these fields mainly includes pipes, wires, rods, copper bars and copper plates. Among them, the production and preparation processes of oxygen-free copper pipes, wires, rods and copper bars include large deformation forming processes from ingot casting to extrusion, forging (cold drawing or rolling). Since the above-mentioned forming methods have a large deformation amount, the prepared copper material has a uniform metallographic structure and a small grain size (average grain size ≤80μm), which can meet the needs of most instruments and equipment, and ensure that its strength, electrical conductivity, thermal conductivity and other properties meet the requirements.

[0003] However, large-sized oxygen-free copper sheets are mainly used as vacuum chambers for medical precision instruments. They need to be turned, welded and processed before they can be used. If copper ingots are used for precision processing directly, the cast grain size will be large and the structure will be uneven, which cannot meet the use requirements. Therefore, for large-sized 4N5 oxygen-free copper sheets with a unit weight of more than 1000 Kg, the preparation method is to form large-diameter 4N5 oxygen-free copper ingots after multiple hot forging. Forging has a large deformation amount, which can not only eliminate the shrinkage and porosity defects of the blank, but also make the internal structure of the oxygen-free copper sheet reach the broken grains of the forged state, refine the large-size grains of the ingot, and make the structure of the copper plate more uniform, with an average grain size of less than 80μm. However, after forging, the oxygen-free copper sheet has the problem of abnormal grain growth after precision processing or application in a high-temperature environment (850℃), and the average grain size of the plate increases from 80μm to 200μm. The reasons for abnormal grain growth are as follows: (1) Although the precision machining processes such as grinding, lapping, and extrusion can achieve extremely high dimensional accuracy and surface quality, the large deformation will indirectly promote grain growth; (2) There is residual stress in the plate after forging. Under high temperature environment, the residual stress causes the abnormal growth of grains inside the plate. Therefore, it is urgent to improve the preparation process of large-sized oxygen-free copper plates to solve the problem of abnormal grain growth during subsequent processing and use. Summary of the invention

[0004] The present invention provides a large-sized low-grained 4N5 oxygen-free copper plate and a preparation method thereof, aiming to solve the technical problem that the large-sized oxygen-free copper plate prepared by the existing preparation method has abnormal grain growth after subsequent precision processing or application in a high-temperature environment (850°C), thereby affecting its organizational uniformity and mechanical properties.

[0005] To achieve its purpose, the present invention adopts the following technical solution: A method for preparing a large-scale low-grained 4N5 oxygen-free copper plate comprises the following steps: (1) One-fire forging: Heat the 4N5 oxygen-free copper ingot to 810-830℃, keep it warm, and then perform three upsetting and three drawing before the temperature is ≤650℃ to complete the one-fire forging; after the one-fire forging is completed, water-cool it to obtain a one-fire forging; (2) two-fire forging; heating the first-fire forging obtained in step (1) to 580-600°C, keeping the temperature, performing three upsetting and three drawing before the temperature is ≤500°C, and completing the second-fire forging; after the second-fire forging is completed, water cooling is performed to obtain the second-fire forging; (3) three-fire forging; heating the two-fire forging obtained in step (2) to 650-700°C, keeping the temperature and performing three upsetting and three drawing before the temperature is ≤600°C to complete the three-fire forging; water cooling after the three-fire forging is completed to obtain a 4N5 oxygen-free copper sheet blank; (4) Heat treatment: heating the 4N5 oxygen-free copper sheet blank obtained in step (3) until the core surface temperature of the 4N5 oxygen-free copper sheet blank reaches 300° C., and then keeping the temperature for 110-130 minutes; after the insulation is completed, water cooling is performed to obtain a 4N5 oxygen-free copper sheet.

[0006] Furthermore, the ingot used for the first fire forging in step (1) is a round 4N5 oxygen-free copper ingot of Φ300-700 mm.

[0007] Furthermore, step (1) heating the ingot, and steps (2) and (3) heating the forgings all use an electrically controlled furnace.

[0008] Furthermore, the holding time after the ingot casting in step (1) and the heating of the forging in steps (2) and (3) is 180-240 minutes.

[0009] Furthermore, in steps (1), (2) and (3), a 5500t hydraulic forging device is used for forging, wherein the single forging ratio is 3-15, and the total forging ratio of three forgings and three drawing is 10-40.

[0010] Furthermore, after water cooling in steps (1), (2) and (3), the temperature of the forgings is all less than 60°C.

[0011] Furthermore, step (4) is performed by heating in a heat treatment furnace.

[0012] Furthermore, after water cooling in step (4), the surface temperature of the 4N5 oxygen-free copper sheet blank is ≤50°C.

[0013] The large-sized low-grained 4N5 oxygen-free copper plate prepared by the above preparation method has a weight of ≥1000 Kg and an average grain size of ≤75 μm, and can be used for precision instrument processing or in a high-temperature environment above 850°C.

[0014] The beneficial effects of the present invention are as follows: The large-scale low-grained 4N5 oxygen-free copper sheet preparation method provided by the present invention is to repeatedly break and recrystallize the grains inside the metal through upsetting and drawing during the forging process, and the grains are refined. Then, the grain size of the oxygen-free copper sheet is further refined in combination with the heat treatment process, and the presence of large-size grains is reduced, so that the organization uniformity is better and the mechanical properties are higher. After the low-grained 4N5 oxygen-free copper sheet prepared by the method is precisely processed, the grain growth is not obvious due to its small grain size, and the heat treatment and the process from heat treatment to finished product machining and placement release residual stress, thereby solving the problem of abnormal grain growth of large-scale 4N5 oxygen-free copper sheet in high temperature environment. At the same time, the refined grains improve the mechanical properties such as strength and toughness of the forging synchronously, and the internal organization and performance of the metal are gradually improved through multiple upsetting and drawing deformation operations, and the generation of defects is reduced. The prepared oxygen-free copper sheet can be used as a vacuum chamber of various medical precision instruments through high temperature and precision processing processes such as turning and welding in the later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a metallographic image of the surface of the 4N5 oxygen-free copper ingot after corrosion in Example 1 of the present invention; Figure 2 This is a metallographic image of the forged state of the 4N5 oxygen-free copper plate blank after three-fire forging in Example 1 of the present invention; Figure 3 This is a metallographic image of a 4N5 oxygen-free copper plate after heat treatment in Example 1 of the present invention; Figure 4 This is a metallographic image of a 4N5 oxygen-free copper plate after high temperature experiment in Example 1 of the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with embodiments: In the following embodiments of the present invention, a desktop heating electric control furnace is used for heating forgings in one-fire forging, two-fire forging and three-fire forging. A GJWKG-3 heat treatment furnace of Xi'an Fulite Heat Treatment Co., Ltd. is used for heat treatment heating of 4N5 oxygen-free copper sheet blanks. The forging equipment is a 50MN rapid forging hydraulic unit.

[0017] Example 1 A large-size low-grained 4N5 oxygen-free copper plate and a preparation method thereof, comprising the following steps: (1) One-fire forging: A Φ440 mm round 4N5 oxygen-free copper ingot is heated to 830°C in an electric-controlled furnace. After being kept warm for 210 min, it is subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 11. The temperature of the forging is measured in real time during the forging process. The one-fire forging is completed before the temperature drops below 650°C. After the one-fire forging is completed, the forging is water-cooled to 54°C to obtain a one-fire forging. (2) Two-fire forging: The first-fire forging obtained in step (1) is heated to 600°C by an electric-controlled furnace, kept at this temperature for 210 minutes, and then subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 11. The temperature of the forging is measured in real time during the forging process, and the second-fire forging is completed before the temperature drops below 500°C. After the second-fire forging is completed, the forging is water-cooled to 55°C to obtain the second-fire forging; (3) three-fire forging; the two-fire forging obtained in step (2) is heated to 700°C by an electric-controlled furnace, kept at this temperature for 210 minutes, and then subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 11. During the forging process, the temperature of the forging is measured in real time, and the three-fire forging is completed before the temperature drops below 600°C; after the three-fire forging is completed, the forging is water-cooled to 52°C to obtain a 4N5 oxygen-free copper sheet blank; (4) Heat treatment: The 4N5 oxygen-free copper sheet blank obtained in step (3) is placed in a heat treatment furnace at a heating rate of 100°C / h for heating until the core and surface temperatures of the 4N5 oxygen-free copper sheet blank reach 300°C, and then kept warm for 120 minutes; after the insulation is completed, the 4N5 oxygen-free copper sheet blank is placed in a water tank for water cooling for 30 minutes until the surface temperature of the sheet reaches 42°C, thereby obtaining a 4N5 oxygen-free copper sheet.

[0018] The grain size of the prepared 4N5 oxygen-free copper sheet was measured under high temperature environment. The specific method is as follows: in a hydrogen atmosphere, the 4N5 oxygen-free copper sheet was first heated from room temperature to 740°C for 90 minutes; then heated from 740°C to 780°C for 45 minutes, and then kept warm for 35 minutes after reaching 780°C; then heated from 780°C to 850°C for 25 minutes; finally, kept warm at 850°C for 25 minutes. After the insulation was completed, the 4N5 oxygen-free copper sheet was cooled to room temperature with the furnace for grain size detection.

[0019] Among them, the surface metallographic structure of the as-cast Φ440mm round 4N5 oxygen-free copper ingot after corrosion is as follows Figure 1 As shown in the figure, the average grain size is 7000μm; after three-fire forging, the metallographic structure of the forged sheet is as follows Figure 2 As shown, the average grain size is measured to be 80μm; after heat treatment, the metallographic structure of the plate is as follows Figure 3 As shown in the figure, the average grain size is 75μm. After high temperature test, the metallographic structure of the plate is as follows Figure 4 As shown, the average grain size is measured to be 10 μm. Figure 1-4It can be seen that the average grain size of the 4N5 oxygen-free copper plate produced by this method is 75μm, and the grain size has been refined, meeting the requirement that the average grain size of the 4N5 oxygen-free copper plate is ≤80μm. Moreover, after the high temperature test, the average grain size of the plate is 10μm, and there is no problem of abnormal grain growth.

[0020] Example 2 A large-size low-grained 4N5 oxygen-free copper plate and a preparation method thereof, comprising the following steps: (1) One-fire forging: A Φ310 mm round 4N5 oxygen-free copper ingot is heated to 810°C in an electric-controlled furnace. After being kept warm for 180 min, it is subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 9.5. The temperature of the forging is measured in real time during the forging process. The one-fire forging is completed before the temperature drops below 650°C. After the one-fire forging is completed, the forging is water-cooled to 51°C to obtain a one-fire forging. (2) Two-fire forging: the first-fire forging obtained in step (1) is heated to 580°C by an electric-controlled furnace, kept at this temperature for 180 minutes, and then subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 9.5. During the forging process, the temperature of the forging is measured in real time, and the second-fire forging is completed before the temperature drops below 500°C. After the second-fire forging is completed, the forging is water-cooled to 53°C to obtain the second-fire forging; (3) three-fire forging; the two-fire forging obtained in step (2) is heated to 650°C by an electric-controlled furnace, kept warm for 180 minutes, and then subjected to three upsetting and three drawing under the condition that the forging ratio of the forging equipment is 9.5. During the forging process, the temperature of the forging is measured in real time, and the three-fire forging is completed before the temperature is lower than 600°C; after the three-fire forging is completed, the forging is water-cooled to 55°C to obtain a 4N5 oxygen-free copper sheet blank; (4) Heat treatment: The 4N5 oxygen-free copper sheet blank obtained in step (3) is sent to a heat treatment furnace with a heating rate of 100°C / h for heating until the core surface temperature of the 4N5 oxygen-free copper sheet blank reaches 300°C, and then kept warm for 110 minutes; after the insulation is completed, the 4N5 oxygen-free copper sheet blank is placed in a water tank for water cooling for 40 minutes until the surface temperature of the sheet is 41°C, thereby obtaining a 4N5 oxygen-free copper sheet. The average grain size is measured to be 72μm, which meets the requirement that the average grain size of the 4N5 oxygen-free copper sheet is less than 80μm.

[0021] Example 3 A large-size low-grained 4N5 oxygen-free copper plate and a preparation method thereof, comprising the following steps: (1) One-fire forging: A Φ700 mm round 4N5 oxygen-free copper ingot is heated to 820°C in an electric-controlled furnace. After being kept warm for 240 min, it is subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 10.5. The temperature of the forging is measured in real time during the forging process. The one-fire forging is completed before the temperature drops below 650°C. After the one-fire forging is completed, the forging is water-cooled to 55°C to obtain a one-fire forging. (2) Two-fire forging: the first-fire forging obtained in step (1) is heated to 600°C by an electric-controlled furnace, kept at this temperature for 240 minutes, and then subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 10.5. During the forging process, the temperature of the forging is measured in real time, and the second-fire forging is completed before the temperature drops below 500°C. After the second-fire forging is completed, the forging is water-cooled to 53°C to obtain the second-fire forging; (3) three-fire forging; the two-fire forging obtained in step (2) is heated to 700°C by an electric-controlled furnace, kept at this temperature for 240 minutes, and then subjected to three upsetting and three drawing processes under the condition that the forging ratio of the forging equipment is 10.5. During the forging process, the temperature of the forging is measured in real time, and the three-fire forging is completed before the temperature drops below 600°C; after the three-fire forging is completed, the forging is water-cooled to 57°C to obtain a 4N5 oxygen-free copper sheet blank; (4) Heat treatment: The 4N5 oxygen-free copper sheet blank obtained in step (3) is sent to a heat treatment furnace with a heating rate of 100°C / h for heating until the core surface temperature of the 4N5 oxygen-free copper sheet blank reaches 300°C, and then kept warm for 130 minutes; after the insulation is completed, the 4N5 oxygen-free copper sheet blank is placed in a water tank for water cooling for 40 minutes until the surface temperature of the sheet is 44°C, thereby obtaining a 4N5 oxygen-free copper sheet. The average grain size is measured to be 72μm, which meets the requirement that the average grain size of the 4N5 oxygen-free copper sheet is less than 80μm.

[0022] It can be seen from Examples 1-3 that the average grain size of the prepared 4N5 oxygen-free copper plates meets the requirements, and the 4N5 oxygen-free copper plates of Examples 1-3 are placed for 10 days and then subjected to ultrasonic testing and penetrant testing, and it is found that the plates have no cracks and internal defects, indicating that the 4N5 oxygen-free copper plates are qualified products.

Claims

1. A method for preparing large-scale low-grained 4N5 oxygen-free copper sheet, characterized in that: The following steps are involved: (1) One-fire forging: Heat the 4N5 oxygen-free copper ingot to 810-830℃, keep it warm, and then perform three upsetting and three drawing before the temperature is ≤650℃ to complete the one-fire forging; after the one-fire forging is completed, water-cool it to obtain a one-fire forging; (2) two-fire forging; heating the first-fire forging obtained in step (1) to 580-600°C, keeping the temperature, performing three upsetting and three drawing before the temperature is ≤500°C, and completing the second-fire forging; after the second-fire forging is completed, water cooling is performed to obtain the second-fire forging; (3) three-fire forging; heating the two-fire forging obtained in step (2) to 650-700°C, keeping the temperature and performing three upsetting and three drawing before the temperature is ≤600°C to complete the three-fire forging; water cooling after the three-fire forging is completed to obtain a 4N5 oxygen-free copper sheet blank; (4) Heat treatment: heating the 4N5 oxygen-free copper sheet blank obtained in step (3) until the core surface temperature of the 4N5 oxygen-free copper sheet blank reaches 300° C., and then keeping the temperature for 110-130 minutes; after the insulation is completed, water cooling is performed to obtain a 4N5 oxygen-free copper sheet.

2. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 1, characterized in that: The ingot used for the first-fire forging in step (1) is a round 4N5 oxygen-free copper ingot of Φ300-700 mm.

3. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 2, characterized in that: The step (1) of heating the ingot and the steps (2) and (3) of heating the forgings all use an electrically controlled furnace.

4. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 3, characterized in that: The holding time after heating of the ingot in step (1) and the forging in steps (2) and (3) is 180-240 minutes.

5. The method for preparing a large-scale low-grained 4N5 oxygen-free copper sheet according to claim 4, characterized in that: During the forging of steps (1), (2) and (3), 5500t hydraulic forging equipment is used, wherein the single forging ratio is 3-15, and the total forging ratio of three piers and three draws is 10-40.

6. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 5, characterized in that: After water cooling in steps (1), (2) and (3), the temperature of the forgings is all less than 60 °C.

7. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 6, characterized in that: Step (4) is to heat the sample in a heat treatment furnace.

8. The method for preparing a large-sized low-grained 4N5 oxygen-free copper sheet according to claim 7, characterized in that: After water cooling in step (4), the surface temperature of the 4N5 oxygen-free copper sheet blank is ≤50°C.

9. A large-size low-grained 4N5 oxygen-free copper sheet prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The 4N5 oxygen-free copper plate has a weight of ≥1000 Kg and an average grain size of ≤75 μm, and can be used for precision instrument processing or in a high temperature environment above 850° C.

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