A method for preparing fine-grained H70 brass rods

Abstract

This invention provides a method for preparing fine-grained H70 brass rods, belonging to the field of brass rod preparation technology. It solves the problems of insufficient precision and cracking caused by dimensional deviations and coarse grains in existing brass rod preparation methods. This invention involves heating sawn brass ingots in a medium-frequency induction furnace; extruding the heated ingots into billet coils using an extruder; cooling the extruded coils using a combination of spraying and water baths; stretching the billet coils; annealing the stretched brass rods to obtain finished rods; and sampling the finished rods after annealing for microstructure analysis and mechanical property testing. This invention, through hot extrusion, EJP finishing and stretching, and annealing processes, prepares brass rods with high dimensional accuracy, uniform structure, and fine grains. The obtained rods exhibit good deep-drawing performance and adaptability to large deformation cold working, meeting the requirements of subsequent high-precision forming and processing.

Description

Technical Field

[0001] This invention belongs to the field of brass rod preparation technology, specifically relating to a method for preparing fine-grained H70 brass rods. Background Technology

[0002] H70 brass is an industrial brass with copper and zinc as the main alloying elements, widely used in heat sinks, mechanical parts, and electronic components. This alloy possesses good plasticity, cold and hot working properties, and high tensile strength, making it particularly suitable for cold stamping processes. However, when conventional H70 brass bars undergo high-strength, deep-drawing deformation, insufficient dimensional accuracy and inherent tolerances in the stamping dies can easily lead to die damage and material waste, thus increasing production costs. Furthermore, if the grain size of the H70 material used is too large, cracking is prone to occur during cold deformation under residual stress.

[0003] Therefore, the present invention aims to provide a method for preparing H70 brass rods with high dimensional accuracy (deviation range of -0.08-0mm) and uniform and fine grains, so as to solve the problems of insufficient accuracy and cracking caused by dimensional deviation and coarse grains during subsequent cold working. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing fine-grained H70 brass rods, so as to solve the problems of insufficient precision and cracking caused by dimensional deviations and coarse grains in existing brass rod preparation methods.

[0005] The technical solution of this invention is: a method for preparing fine-grained H70 brass rods, comprising the following steps: Step 1: According to the required size and weight, the H70 brass ingot billet is sawn and cut into pieces, and the sawn brass ingot is placed in a medium frequency induction furnace for heating; Step 2: The heated brass ingot is extruded into billet coils using an extrusion press; the extruded coils are then cooled using a combination of spraying and water bath cooling. Step 3: Use an EJP finishing continuous drawing machine to stretch the billet coil into finished product. Use an H13 die during the stretching process and control the dimensional accuracy within 70-80% of the product tolerance range. Step 4: The stretched brass rods are annealed within 24 hours, otherwise bending under stress will occur. The stretched rods are placed in an annealing furnace and held at 460-480℃ for 100-120 minutes. During the annealing process, a mixture of 4% H2 and N2 gas is introduced as a protective atmosphere to obtain the finished rods. Step 5: After annealing, samples of the finished bar stock are taken for microstructure analysis and mechanical property testing. Microstructure analysis includes OM and SEM analysis, and mechanical property testing includes tensile testing and hardness testing.

[0006] As a further improvement of the present invention, in step one, the diameter of the H70 brass ingot billet is Φ260mm.

[0007] As a further improvement of the present invention, in step one, the sawn brass ingot is subjected to a low-temperature rapid heating process, with a heating temperature of 670-720°C and a heating time of 20-30 minutes, in order to suppress excessive grain growth.

[0008] As a further improvement of the present invention, in step two, the extrusion die is made of H13 steel and the extrusion die is lubricated with a mixed lubricant consisting of 80% asphalt and 20% graphite.

[0009] As a further improvement of the present invention, in step two, the cooling time is 3-5 minutes, the spray water temperature is controlled within the range of 20-50℃, and the cooling water is a dynamic circulation system.

[0010] As a further improvement of the present invention, in step three, the finishing and drawing process is carried out on an EJP type dual-cam drawing machine, model D-0932, with a drawing force range of 200 / 150kN.

[0011] As a further improvement of the present invention, in step four, the finished bar is made of H70 brass with a diameter range of 15-40mm and an allowable deviation of -0.08-0mm; the length of the bar is between 1500-4000mm, the hardness range is 55-65HV, and the grain size is controlled at 35-60μm.

[0012] The performance testing and microstructure analysis of the H70 brass rods prepared according to the method of the present invention were performed according to the following steps: The tensile property test samples were processed into dumbbell-shaped specimens according to the national standards GB / T4423 and GB / T34505. The sampling location was arbitrary, and the tensile strength, yield strength and elongation after fracture of the bar were determined. The strain rate during the tensile process was 0.4 mm / s. Specimens with a thickness of 10-15 mm were cut from any part of the bar for metallographic observation and hardness testing. After grinding and polishing, the metallographic samples were etched with an etching solution prepared by 3g FeCl3 and 100ml anhydrous ethanol for 20-40 seconds, and then their microstructure was observed under an optical microscope.

[0013] The beneficial effects of this invention are as follows: This invention addresses the shortcomings of existing H70 brass bars in terms of dimensional accuracy control and grain uniformity. It provides an improved preparation method, which uses H70 ingots as raw materials. After heating in a medium-frequency induction furnace, the ingots are processed into stretch billets (i.e., brass coils) by an extrusion press. The stretch billets are then drawn into finished bars using an EJP finishing and stretching machine. Finally, annealing is performed to eliminate stress and achieve uniform grain refinement, thereby comprehensively improving the cold working performance of the bars.

[0014] In step one of this invention, a low-temperature rapid heating process of 670-720℃ for 20-30 minutes is employed. Compared to traditional high-temperature, long-duration heating, this method ensures that the H70 brass ingot is uniformly heated to the plastic state required for extrusion. Furthermore, by shortening the heating cycle and controlling the upper limit of the heating temperature, excessive grain growth within the ingot is suppressed, laying the foundation for grain refinement in subsequent extrusion and annealing processes. Simultaneously, this invention is well-matched with the high-efficiency heating characteristics of a medium-frequency induction furnace, reducing energy consumption, improving production efficiency, and ensuring uniform heating to prevent localized performance differences in the ingot, thus guaranteeing the stability of subsequent processing.

[0015] In step two of this invention, an H13 steel extrusion die is selected. Its high hardness and wear resistance ensure the stability of the die cavity dimensions during extrusion, preventing dimensional deviations in the billet due to die wear. A mixed lubricant of 80% asphalt and 20% graphite effectively reduces the coefficient of friction between the billet and the die, minimizing surface defects such as sticking and scratches, and improving the surface quality of the billet. Combined with 3-5 minutes of spray and water bath cooling, this rapidly inhibits secondary grain growth in the billet after extrusion and ensures uniform cooling through dynamic circulating cooling water, preventing uneven cooling that could generate internal stress. This seamlessly integrates with the subsequent stretching process, providing high-quality billets for precise dimensional control of the finished product.

[0016] In step three of this invention, a D-0932 type EJP dual-cam drawing machine is used. Its continuous and stable tensile force output characteristics reduce the cumulative dimensional errors of traditional step-by-step drawing. Combined with an H13 high-precision die, the dimensional accuracy is controlled within 70-80% of the product tolerance range, ultimately achieving an allowable deviation of -0.08-0mm for the finished bar stock. This significantly reduces die damage and material waste caused by dimensional deviations during subsequent cold working. This invention works synergistically with the preceding extrusion and cooling processes, achieving a step-by-step improvement in dimensional accuracy through "bill quality assurance + precise drawing and shaping control."

[0017] Step four of this invention requires annealing to be completed within 24 hours after stretching, avoiding bar bending caused by residual stress and ensuring product straightness. Annealing parameters of 460-480℃ and 100-120 minutes precisely eliminate work hardening and internal stress during stretching, while promoting uniform grain refinement to 35-60μm, improving bar plasticity and cold working adaptability. The mixed protective atmosphere of 4% H2 and N2 prevents surface oxidation during annealing, ensuring surface quality; furthermore, the reducing properties of N2 remove trace oxide films from the surface, further optimizing processing performance. This process, in conjunction with the previous "fine grain foundation + precise shape control," ultimately achieves comprehensive compliance in bar dimensional accuracy, microstructure uniformity, and mechanical properties.

[0018] The above-mentioned process links are interconnected and work together to form a complete quality control chain from raw material heating to finished product annealing. This not only solves the core problems of dimensional deviation and coarse grains in traditional processes, but also achieves a balance between production efficiency and product performance through precise matching of process parameters.

[0019] This invention achieves high dimensional accuracy and uniform grain refinement of H70 brass rods through optimized extrusion, stretching and annealing processes, effectively solving the problems of insufficient accuracy and cracking caused by dimensional deviation and coarse grains during cold working of rods, and improving yield and processing stability. Attached Figure Description

[0020] Figure 1 Metallographic image of the brass rod core obtained in Example 1 of this invention; Figure 2 Metallographic image of the brass rod core obtained in Example 2 of this invention; Figure 3 This is a metallographic image of the brass rod core obtained in Example 3 of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the embodiments.

[0022] Example 1 Step 1: According to the required size and weight, the Φ260mm×800mm H70 brass ingot blank is sawn and cut. The sawn brass ingot is placed in a medium frequency induction furnace for heating. The low temperature rapid heating process is adopted, the heating temperature is 670℃, and the heating time is 20 minutes. Step 2: The heated brass ingot is extruded into billet coils using an extrusion press. The extrusion die is made of H13 steel and lubricated with a mixed lubricant consisting of 80% asphalt and 20% graphite. The extruded coils are cooled by a combination of spraying and water bath for 3 minutes. The temperature of the spray water is controlled within 20°C, and the cooling water is a dynamic circulation system. Step 3: The billet coil is stretched into a finished product using an EJP type dual-tandem cam drawing machine. The equipment model is D-0932, the tensile force range is 200 / 150kN, H13 dies are used during the stretching process, and the dimensional accuracy is controlled within 70% of the product tolerance range. Step 4: The stretched brass rods are annealed within 24 hours, otherwise bending under stress will occur. The stretched rods are placed in an annealing furnace and held at 460°C for 100 minutes. During the annealing process, a mixture of 4% H2 and N2 gas is introduced as a protective atmosphere to obtain the finished rods. The finished bar stock is made of H70 brass with a diameter of 15mm and an allowable deviation of -0.08-0mm; the bar stock length is 1500mm, the hardness is 55HV, and the grain size is 35μm.

[0023] Step 5: After annealing, samples of the finished bar stock are taken for microstructure analysis and mechanical property testing. Microstructure analysis includes OM and SEM analysis, and mechanical property testing includes tensile testing and hardness testing.

[0024] Its performance testing and organizational analysis are performed according to the following steps: The tensile property test samples were processed into dumbbell-shaped specimens according to the national standards GB / T4423 and GB / T34505. The sampling location was arbitrary, and the tensile strength, yield strength and elongation after fracture of the bar were determined. The strain rate during the tensile process was 0.4 mm / s. A 10 mm thick specimen was cut from any part of the bar for metallographic observation and hardness testing. After grinding and polishing, the metallographic sample was etched with an etching solution prepared by 3 g FeCl3 and 100 ml anhydrous ethanol for 20 seconds. The microstructure was then observed under an optical microscope.

[0025] The actual dimensional test results of the finished bar stock obtained in Example 1 are shown in Table 1. The metallographic features of the core of the finished bar stock are as follows: Figure 1 As shown in Table 2, the mechanical performance data test data are as follows.

[0026]

[0027]

[0028] Example 2 Step 1: According to the required size and weight, the Φ260mm×800mm H70 brass ingot blank is sawn and cut. The sawn brass ingot is placed in a medium frequency induction furnace for heating. The low temperature rapid heating process is adopted, the heating temperature is 695℃, and the heating time is 25 minutes. Step 2: The heated brass ingot is extruded into billet coils using an extrusion press. The extrusion die is made of H13 steel and lubricated with a mixed lubricant consisting of 80% asphalt and 20% graphite. The extruded coils are cooled by a combination of spraying and water bath for 4 minutes. The spray water temperature is controlled within 35°C and the cooling water is a dynamic circulation system. Step 3: The billet coil is stretched into a finished product using an EJP type dual-cam drawing machine unit for finishing and continuous drawing. The equipment model is D-0932, the tensile force range is 200 / 150kN, H13 dies are used during the stretching process, and the dimensional accuracy is controlled within 75% of the product tolerance range. Step 4: The stretched brass rods are annealed within 24 hours, otherwise bending under stress will occur. The stretched rods are placed in an annealing furnace and held at 470°C for 110 minutes. During the annealing process, a mixture of 4% H2 and N2 gas is introduced as a protective atmosphere to obtain the finished rods. The finished bar stock is made of H70 brass with a diameter of 27mm and an allowable deviation of -0.08-0mm; the bar stock length is 2700mm, the hardness is 60HV, and the grain size is 47μm.

[0029] Step 5: After annealing, samples of the finished bar stock are taken for microstructure analysis and mechanical property testing. Microstructure analysis includes OM and SEM analysis, and mechanical property testing includes tensile testing and hardness testing.

[0030] Its performance testing and organizational analysis are performed according to the following steps: The tensile property test samples were processed into dumbbell-shaped specimens according to the national standards GB / T4423 and GB / T34505. The sampling location was arbitrary, and the tensile strength, yield strength and elongation after fracture of the bar were determined. The strain rate during the tensile process was 0.4 mm / s. A 13 mm thick specimen was cut from any part of the bar for metallographic observation and hardness testing. After grinding and polishing, the metallographic sample was etched with an etching solution prepared by 3 g FeCl3 and 100 ml anhydrous ethanol for 30 seconds. The microstructure was then observed under an optical microscope.

[0031] The actual dimensional test results of the finished bar stock obtained in Example 2 are shown in Table 3. The metallographic features of the core of the finished bar stock are as follows: Figure 2 As shown in Table 4, the mechanical property test data are as follows.

[0032]

[0033]

[0034] Example 3 Step 1: According to the required size and weight, the Φ260mm×800mm H70 brass ingot blank is sawn and cut. The sawn brass ingot is placed in a medium frequency induction furnace for heating. The low temperature rapid heating process is adopted, the heating temperature is 720℃, and the heating time is 30 minutes. Step 2: The heated brass ingot is extruded into billet coils using an extrusion press. The extrusion die is made of H13 steel and lubricated with a mixed lubricant consisting of 80% asphalt and 20% graphite. The extruded coils are cooled by a combination of spraying and water bath for 5 minutes. The spray water temperature is controlled within 50°C and the cooling water is a dynamic circulation system. Step 3: The billet coil is stretched into a finished product using an EJP type dual-tandem cam drawing machine. The equipment model is D-0932, the tensile force range is 200 / 150kN, H13 dies are used during the stretching process, and the dimensional accuracy is controlled within 80% of the product tolerance range. Step 4: The stretched brass rods are annealed within 24 hours, otherwise bending under stress will occur. The stretched rods are placed in an annealing furnace and held at 480°C for 120 minutes. During the annealing process, a mixture of 4% H2 and N2 gas is introduced as a protective atmosphere to obtain the finished rods. The finished bar stock is made of H70 brass with a diameter of 40mm and an allowable deviation of -0.08-0mm; the bar stock length is 4000mm, the hardness is 65HV, and the grain size is 60μm.

[0035] Step 5: After annealing, samples of the finished bar stock are taken for microstructure analysis and mechanical property testing. Microstructure analysis includes OM and SEM analysis, and mechanical property testing includes tensile testing and hardness testing.

[0036] Its performance testing and organizational analysis are performed according to the following steps: The tensile property test samples were processed into dumbbell-shaped specimens according to the national standards GB / T4423 and GB / T34505. The sampling location was arbitrary, and the tensile strength, yield strength and elongation after fracture of the bar were determined. The strain rate during the tensile process was 0.4 mm / s. A 15 mm thick specimen was cut from any part of the bar for metallographic observation and hardness testing. After grinding and polishing, the metallographic sample was etched with an etching solution prepared by 3 g FeCl3 and 100 ml anhydrous ethanol for 40 seconds. The microstructure was then observed under an optical microscope.

[0037] The actual dimensional test results of the finished bar stock obtained in Example 3 are shown in Table 5. The metallographic features of the core of the finished bar stock are as follows: Figure 3 As shown in Table 6, the mechanical performance data and test data are as follows.

[0038]

[0039]

[0040] This method successfully prepared high-performance fine-grained H70 brass rods through a synergistic process of "low-temperature rapid heating - extrusion composite cooling - EJP finishing and continuous drawing - timely annealing". The test results of Examples 1-3 show that the finished rods have diameters of 15-40 mm and lengths of 1500-4000 mm, with measured dimensions controlled within the allowable deviation range of -0.08-0 mm, meeting the high-requirement processing requirements. The grain size is refined to 35-60 μm, with good metallographic uniformity. The mechanical properties are stable, with tensile strength of 315-327 MPa, yield strength of 160-167 MPa, elongation of 68-71%, and hardness of 55-65 HV, exhibiting excellent deep-drawing performance and adaptability to large deformation cold working.

[0041] This method effectively solves the problems of machining cracking and mold wear caused by dimensional deviation and coarse grains in traditional H70 brass bars, improves the yield and processing stability, and can be widely used in high-precision machining scenarios in fields such as heat sinks, mechanical parts and electronic components.

Claims

1. A method for preparing fine-grained H70 brass rods, characterized in that: Includes the following steps: Step 1: According to the required size and weight, the H70 brass ingot billet is sawn and cut into pieces, and the sawn brass ingot is placed in a medium frequency induction furnace for heating; Step 2: The heated brass ingot is extruded into billet coils using an extrusion press; the extruded coils are then cooled using a combination of spraying and water bath cooling. Step 3: Use an EJP finishing continuous drawing machine to stretch the billet coil into finished product. Use an H13 die during the stretching process and control the dimensional accuracy within 70-80% of the product tolerance range. Step 4: The stretched brass rods are annealed within 24 hours. The stretched rods are placed in an annealing furnace and held at 460-480℃ for 100-120 minutes. During the annealing process, a mixture of 4% H2 and N2 gas is introduced as a protective atmosphere to obtain the finished rods. Step 5: After annealing, samples of the finished bar stock are taken for microstructure analysis and mechanical property testing. Microstructure analysis includes OM and SEM analysis, and mechanical property testing includes tensile testing and hardness testing.

2. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step one, the diameter of the H70 brass ingot billet is Φ260mm.

3. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step one, the sawn brass ingots are subjected to a low-temperature rapid heating process, with a heating temperature of 670-720℃ and a heating time of 20-30 minutes.

4. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step two, the extrusion die is made of H13 steel and is lubricated with a mixed lubricant consisting of 80% asphalt and 20% graphite.

5. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step two, the cooling time is 3-5 minutes, the spray water temperature is controlled within the range of 20-50℃, and the cooling water is a dynamic circulation system.

6. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step three, the finishing and drawing process is carried out on an EJP type dual-cam drawing machine, model D-0932, with a drawing force range of 200 / 150kN.

7. The method for preparing a fine-grained H70 brass rod according to claim 1, characterized in that: In step four, the finished bar is made of H70 brass with a diameter ranging from 15 to 40 mm and an allowable deviation of -0.08 to 0 mm; the bar length is between 1500 and 4000 mm, the hardness range is 55 to 65 HV, and the grain size is controlled between 35 and 60 μm.

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