A method for improving the edge quality of H65 brass strip

Abstract

The present invention belongs to the field of copper and copper alloy processing, and relates to the quality control of the edges of H65 brass, and is specifically a method for improving the edge quality of H65 brass strips. This method effectively improves the edge quality of H65 brass strips and avoids the decrease in product yield due to cutting edges. The present invention solves the problem of cracking of the hot-rolled edges that often occurs in the hot-rolling process of H65 brass by adopting the above-mentioned composition ratio adjustment, heating temperature, heating time, atmosphere control, hot rolling passes, adding roller water isolation devices, slow cooling and other schemes. Through the above scheme, the temperature drop can be greatly reduced during the hot rolling process while ensuring the qualified composition of the ingot, and the β phase ratio of H65 brass can be controlled to more than 20%, thereby achieving the beneficial effect of smooth edges of H65 brass after hot rolling, uniform grain structure and no obvious defects, and ultimately improving the yield of the finished product.

Description

Technical Field

[0001] The invention belongs to the field of copper and copper alloy processing, relates to H65 brass edge quality control, and specifically provides a method for improving the edge quality of an H65 brass strip. Background Art

[0002] Brass H65 products are widely used in electrical, hardware, electronic communications, machine manufacturing, computer connectors, building decoration and other industries due to their good processability, mechanical properties, corrosion resistance, electrical conductivity and thermal conductivity. Figure 4 The edge cracking phenomenon is very obvious after hot rolling, and there are obvious cracks at the grain boundaries. To prevent the strip from breaking during subsequent processing, the cracked edge part must be trimmed cleanly, but trimming the cracked edge part will reduce the product yield. Summary of the Invention

[0003] The invention provides a method for improving the edge quality of an H65 brass strip and avoiding a decrease in product yield due to cutting the edge.

[0004] The present invention is achieved by adopting the following technical solution: a method for improving the edge quality of H65 brass strip, comprising the steps of batching, melting, heating the ingot, hot rolling, and cooling; during batching, the copper content ratio is controlled to be 63.5wt%-64.5wt%;

[0005] When heating the ingot, the H65 brass ingot is dynamically moved and heated in a gas heating furnace. During the heating process, the heating temperature is controlled at 880℃~890℃, the heating time is 2.5~3.5h, the atmosphere in the furnace is slightly oxidizing, and the air-fuel ratio is controlled at 10.5-11.5;

[0006] During hot rolling, the heated H65 brass ingot is hot rolled using a two-roll reversible rolling mill. The hot rolling passes are set to 9. Except for the first two passes which are slow, the remaining passes are rolled at a high speed of 4 m / s. At the same time, a water barrier is used to prevent the cooling water of the upper roll from flowing into the material surface, ensuring that most of the processing is completed before the high shaping temperature of 750-780℃ is reached.

[0007] After rolling is completed, the billet is air-cooled to below 400°C at room temperature, and then the spray is turned on for water cooling.

[0008] In the present invention, when H65 brass is melted and cast, the copper content ratio is controlled within 63.5 wt %-64.5 wt %, thereby increasing the volume content of the β phase, improving high-temperature plasticity, and reducing hot-rolling cracking.

[0009] The H65 brass ingot is then subjected to dynamic, mobile heating in a gas-fired furnace to reduce uneven heating within the ingot and improve heating uniformity. During the heating process, the temperature is controlled between 880°C and 890°C for 2.5 to 3.5 hours. The furnace atmosphere is slightly oxidizing, and the air-fuel ratio is controlled between 10.5 and 11.5 to ensure sufficient heating of the ingot and a relatively high volume content of β phase within the ingot's internal structure.

[0010] The heated H65 brass ingot is hot rolled in a two-roll reversing mill. The hot rolling process is repeated nine times. The first two passes are slow, while the remaining passes are rolled at a high speed of 4 m / s. This minimizes the temperature drop during the process and ensures that the majority of the work is completed before the high shaping temperature of 750-780°C is reached. This nine-pass rolling process achieves an ideal final rolling temperature.

[0011] Then, the brass H65 strip is slowly cooled to ensure that the β phase continuously transforms into the α phase, thereby reducing the volume content of the β phase at low temperature and facilitating subsequent cold working deformation treatment.

[0012] Beneficial effects of the present invention: The present invention solves the problem of hot-rolled edge cracking that often occurs in H65 brass during hot rolling by adopting the above-mentioned composition ratio adjustment, heating temperature, heating time, atmosphere control, hot rolling passes, adding a water-isolating device for the rolls, and slow cooling. Through the above-mentioned solution, the temperature drop can be greatly reduced during the hot rolling process while ensuring the ingot composition is qualified, and the β phase ratio of H65 brass can be controlled to be above 20%, thereby achieving the following: Figure 5 The H65 brass shown has a smooth edge after hot rolling, uniform grain structure and no obvious defects, which ultimately has the beneficial effect of improving the yield rate of finished products. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the degree of ingot deformation.

[0014] Figure 2 Schematic diagram of water barrier device.

[0015] Figure 3 for Figure 2 Top view of .

[0016] Figure 4 Schematic diagram of cracked grains at the hot-rolled edge of H65 brass in the prior art (magnified 200 times under a microscope).

[0017] Figure 5 The H65 brass of the present invention has smooth grains on the hot-rolled edges (magnified 200 times under a microscope).

[0018] 1-Ingot, 2-Top rod, 3-Roller, 4-Spray pipeline, 5-Collecting tank. DETAILED DESCRIPTION

[0019] The present invention will now be further described in conjunction with a specific embodiment. The process is exemplified by processing an H65 brass ingot with dimensions of 160mm*300mm*6000mm (thickness*width*length). The specific production method is as follows:

[0020] (1) Adjust the H65 brass casting ratio

[0021] The copper content of brass H65 is controlled at 63.5-64.5%, and it is melted and cast into an ingot of 160mm*300mm*6000mm (thickness*width*length) in the conventional way. After it reaches room temperature, the defective parts at the head and tail are sawed off, generally 300mm-400mm at the head and tail.

[0022] (2) Heating the ingot

[0023] Place the sawn rectangular H65 brass ingot into the gas heating furnace for heating. The distance between adjacent ingots in the furnace should be controlled at 100mm. Figure 1 The push rod shown in the figure pushes the ingot once, and the pushing distance each time is 350mm.

[0024] During the heating process, the heating temperature is controlled at 880℃~890℃, the heating time is 2.5~3.5h, the atmosphere in the furnace is slightly oxidizing, and the air-fuel ratio is controlled at 10.5-11.5.

[0025] When the ingots are stepped to the furnace outlet (to prevent the ingot temperature from dropping, ensure that the ingots are 1.5 meters away from the front furnace door), in order to prevent over-burning, the deformation degree of the ingots in the furnace is observed through the fire viewing hole. When the deformation of 3-4 batches of ingots reaches 20mm / m, the following occurs: Figure 1 When the ingots reach the deformation degree shown, they can be taken out of the furnace and hot rolling can begin. The time interval between two adjacent batches of ingots being taken out of the furnace is 10-15 minutes.

[0026] (3) Hot rolling

[0027] The heated ingot is hot rolled using a two-roll reversible rolling mill. The rolling process is performed in 9 passes, with the rolling passes being: 160→134→109→82→61.5→46→34.5→26→20→16.5+0.50 (unit: mm).

[0028] The upper roll of the two-roll reversing mill can be increased as follows Figure 2The water barrier shown prevents roller cooling water from flowing into the billet surface, reducing the billet temperature and ensuring that the ingot remains in a temperature range with optimal plasticity during rolling, thereby reducing cracking and facilitating rolling. The finishing temperature is ultimately controlled above 700°C through the combined effects of rolling passes, rapid rolling, and the water barrier. The water barrier consists of a collection trough located close to the roller surface and below the spray line. This collects all the sprayed water and directs it out through the appropriate pipeline.

[0029] (4) Cooling

[0030] After rolling is completed, the billet is air-cooled to below 400°C at room temperature, and then the spray is turned on for water cooling.

[0031] Brass H65 has an α single-phase structure at room temperature and a dual-phase structure (α+β) at high temperature. During the rolling temperature drop process, a phase transformation β→α occurs. Since the α phase (face-centered cubic) and the β phase (body-centered cubic) belong to two different crystal structures, the transformation process causes a volume change (the β phase is small and the α phase is large), which generates huge phase change stress.

[0032] Compared with the α phase, the β phase has lower tensile strength and better plasticity in the high temperature state. In order to obtain easily controllable high temperature plasticity of brass H65, the volume content of the β phase in the alloy must be strictly controlled. Only when the volume content of the β phase is greater than 20% can its high temperature plasticity be guaranteed.

[0033] Controlling the copper content of H65 brass ingots to 63.5-64.5wt% makes it easier to obtain a β-phase content exceeding 20% ​​during the heating process. Heating temperatures of 880°C-890°C for 2.5-3.5 hours, using a slightly oxidizing furnace atmosphere, also ensures that the β-phase maintains a high volume fraction even after the temperature decreases after exiting the furnace. During hot rolling, the β-phase content changes very little above 780°C. From 780-690°C, in just 90°C (due to faster heat dissipation at the edges of the billet), the β-phase content drops rapidly from 25% to 5%. During this drastic phase transformation, phase transition stresses are noticeable, which, combined with rolling deformation stresses, can easily cause cracks. Therefore, hot rolling is performed at a relatively fast rate to minimize the temperature drop during the process, ensuring that the majority of the processing is completed before the high forming temperature of 750-780°C, thereby reducing the adverse effects of phase transition stresses.

[0034] At room temperature, the β phase has extremely poor plasticity. After hot rolling, it should be cooled slowly to allow the β phase structure to fully transform into the α phase structure, which is conducive to subsequent cold processing.

Claims

1. A method for improving the edge quality of H65 brass strip, comprising the steps of batching, melting, heating the ingot, hot rolling, and cooling; characterized in that: When mixing the ingredients, the copper content ratio is controlled at 63.5wt%-64.5wt%; When heating the ingots, the H65 brass ingots are subjected to dynamic mobile heating in a gas-fired heating furnace. The dynamic mobile heating means that the spacing between adjacent ingots in the furnace is controlled at 100±10mm. From the time the ingots enter the heating zone, the ingots are advanced once every 10-15 minutes with a push rod, and each advancement distance is 350mm. When the ingots step into the furnace outlet, in order to prevent overburning, the degree of deformation of the ingots in the furnace is observed through the fire viewing hole. When the deformation of 3-4 batches of ingots reaches 20mm / m, they can be removed from the furnace and hot rolling can begin. The time interval between the removal of two batches of ingots from the furnace is 10-15 minutes. During the heating process, the heating temperature is controlled at 880℃~890℃, the heating time is 2.5~3.5h, the atmosphere in the furnace is slightly oxidizing, and the air-fuel ratio is controlled at 10.5-11.

5. During hot rolling, the heated H65 brass ingot is hot rolled using a two-roll reversible rolling mill. The hot rolling passes are set to 9. Except for the first two passes which are slow, the remaining passes are rolled at a high speed of 4 m / s. At the same time, a water barrier is used on the upper roll to prevent the cooling water from flowing into the material surface, ensuring that most of the processing is completed before the high shaping temperature of 750-780℃ is reached. After rolling is completed, the billet is air-cooled to below 400°C at room temperature, and then the spray is turned on for water cooling.

2. A method for improving the edge quality of H65 brass strip according to claim 1, characterized in that: After the ingredients are prepared, the raw materials are melted and cast into ingots of 160mm*300mm*6000m. After the ingot reaches room temperature, the defective parts at the head and tail are sawed off, with the head and tail each being sawed off 300mm-400mm.

3. A method for improving the edge quality of H65 brass strip according to claim 1, characterized in that: The furnace outlet position refers to the ingot being 1.5 meters away from the front furnace door.

4. A method for improving the edge quality of H65 brass strip according to claim 1, characterized in that: During hot rolling, the rolling passes are: 160→134→109→82→61.5→46→34.5→26→20→16.5+0.50, unit: mm.

5. A method for improving the edge quality of H65 brass strip according to claim 4, characterized in that: A water-isolating device is used to prevent the cooling water of the upper rolling roller from flowing into the material surface, thereby avoiding lowering the temperature of the billet and ensuring that the ingot is in a temperature range with good plasticity during the rolling process. Through the combined effects of rolling passes, rapid rolling and the water-isolating device, the final rolling temperature is ultimately controlled above 700°C.

6. A method for improving the edge quality of H65 brass strip according to claim 5, characterized in that: The water isolation device is a collecting tank, which is arranged below the spray pipeline and close to the surface of the upper roller.

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