Brass for cold heading and preparation method thereof

Abstract

The present invention discloses a brass for cold heading. The brass comprises the following components by weight: Cu: 64.0-67.0 wt%, Fe: 0.01-0.07 wt%, As: 0.005-0.03 wt%, Pb <0.01 wt%, with the remainder being Zn and unavoidable impurity elements. The microstructure of the brass for cold heading is a single α phase with an average size of 30-50 μm. The brass for cold heading exhibits both good mechanical properties and good compression properties, making it suitable for cold heading processes to produce products with complex shapes. The present invention also discloses a method for preparing the brass for cold heading.

Description

Technical Field

[0001] The invention belongs to the technical field of copper alloy materials, and particularly relates to brass for cold heading and a preparation method thereof. Background Art

[0002] Brass is a widely used material in metalworking, offering excellent corrosion resistance and processing properties. It is therefore widely used in numerous fields. Brass is divided into ordinary brass and complex brass. The main alloying elements of ordinary brass are Cu and Zn. Ordinary brass H65 has properties between H68 and H62, with higher strength and ductility, better ductility than H62, and cheaper than H68. It is the most suitable brass material for cold heading and is widely used in the manufacture of structural parts such as bolts, nuts, washers, and springs.

[0003] Cold heading is a process in which an external force is applied to metal at room temperature to form it in a predetermined mold. The blank is placed in the mold of the cold heading machine, pressure is applied to the mold, and the relative movement of the upper and lower molds is used to deform the blank in the mold cavity, thereby forming the required part or blank. Since there is tangential tensile stress on the side surface of the blank during cold heading, longitudinal surface cracks are easily generated. Therefore, the material used for cold heading must have a low deformation resistance and be able to withstand a large degree of deformation without cracking. The elongation and yield strength can reflect the quality of the material's cold heading performance. The greater the elongation and the lower the yield strength, the better the material's cold heading performance. However, from the perspective of part use, higher strength is required to maintain deformation under external force. Therefore, the yield strength and elongation of the material used for cold heading must be controlled within an appropriate range. The upsetting test can reflect the material's cold heading performance. The larger the compression degree εc value, the better the material's cold heading performance.

[0004] The room-temperature microstructure of brass varies with the Zn content. According to the Cu-Zn phase diagram, there are three types of room-temperature microstructures for brass: Brass with a Zn content below 35% has a room-temperature microstructure consisting solely of the α phase, known as α brass (single-phase brass); brass with a Zn content between 36% and 46% has a room-temperature microstructure consisting solely of the (α+β) phase, known as (α+β) brass (two-phase brass); and brass with a Zn content between 46% and 50% has a room-temperature microstructure consisting solely of the β phase, known as β brass. The Cu content of H65 brass, as specified in national standard GB5231, ranges from 63% to 68.5%. When the Cu content approaches the lower limit, a small amount of β phase appears. Above 64%, the microstructure becomes a single α phase.

[0005] There are two mainstream production methods for H65 brass: "horizontal continuous casting rod billet - stretching" and "horizontal continuous casting ingot - extrusion - stretching". The former cannot eliminate the structural defects brought by the as-cast structure, such as micro-porosity, dendritic segregation, pores, and uneven grains. When cold heading complex parts, cracking problems often occur, and its application range is limited. The latter completely eliminates the defects of the as-cast structure through hot extrusion, and the grain size is uniform, making it suitable for cold heading complex parts.

[0006] However, the "horizontal continuous casting ingot-extrusion-stretching" method is not suitable for producing H65 brass. After the standard wire coil is stretched, intermittent transverse cracking often occurs on the surface, and the yield rate is extremely low, which cannot meet the market demand for H65 large-size extruded coil wire. At present, the industry can only adopt the method of increasing the Cu content, that is, replacing H65 with H68 or even H70. Although this method can avoid the cracking problem, the increase in Cu content will increase the cost, so it is a method that is adopted out of necessity. Summary of the Invention

[0007] The invention provides a brass for cold heading, which has good mechanical properties and good compression properties, can be well used in a cold heading process to prepare products with complex shapes, and has a high yield.

[0008] A specific embodiment of the present invention provides a brass for cold heading, wherein the mass percentages of the components of the brass for cold heading are: Cu: 64.0-67.0wt%, Fe: 0.01-0.07wt%, As: 0.005-0.03wt%, Pb < 0.01wt%, and the balance is Zn and unavoidable impurity elements;

[0009] The microstructure of the brass for cold heading is a single α phase, and the average size of the α phase is 30-50 μm.

[0010] The Cu content provided by the present invention can affect the ratio of α phase to β phase in the brass structure. When the Cu content is lower than 64.0wt%, the brittle β phase begins to appear in the H65 room-temperature structure, which easily causes cold heading cracking. When the Cu content exceeds 67%, on the one hand, the Cu content overlaps with the lower limit of the H68 national standard range (67.0-70.0%). Since copper is a precious metal element, the higher the Cu content, the higher the raw material cost. On the other hand, the α phase has poor high-temperature plasticity and high resistance to hot extrusion deformation. The extrusion temperature needs to reach a higher temperature to complete the extrusion of the alloy, which affects the life of tooling dies such as extrusion dies and extrusion barrels.

[0011] The trace amount of Fe provided by the present invention can increase the recrystallization temperature in brass and inhibit the growth of α and β phases. Since the national standard of H65 brass requires the upper limit of Fe content not to exceed 0.07wt%, the Fe content of the brass of the present invention is controlled at 0.01-0.07wt%.

[0012] The trace amount of As provided by the present invention can combine with Cu atoms and trace amounts of O and H atoms in the brass melt to form high-melting-point AsCuH3O4 (copper arsenate). At high temperatures above 600°C, the concentration of O and H atoms in the β phase is higher than that in the α phase. Therefore, AsCuH3O4 is primarily present in the β phase, significantly inhibiting the β phase from developing into elongated strips and blocks, resulting in fine, dispersed β phases with an average spacing of ≥20 μm between β phases. This allows for a single α phase at room temperature. The inhibitory effect weakens as the volume fraction of the β phase in the brass increases. When the As content exceeds 0.03wt%, the excess As easily forms brittle compounds Cu3As and CuZnAs with Cu and Zn, embrittled grain boundaries. Therefore, the As content in the brass of the present invention is controlled to 0.005-0.03wt%.

[0013] The solubility of Pb provided by the present invention in α brass is extremely low, and the melting point of Pb is only 327°C. When the Pb content in single-phase brass such as H65 exceeds 0.01wt%, the Pb on the grain boundary changes from solid to liquid, and cracking is likely to occur during hot extrusion.

[0014] The microstructure of the brass for cold heading of the present invention consists of a single α phase. This is because the α phase has excellent cold deformation properties. Compared with α+β dual-phase brass, single α phase brass is easier to cold head.

[0015] The average size of the α phase provided by the present invention is 30-50 μm. This is because the cold heading deformation of the metal occurs due to the slip of the grains and the deformation of the grains themselves. Reducing the grain size will inevitably increase the number of grains, and the deformation can be more evenly distributed to each grain, which is not easy to form stress concentration, and thus has a small tendency to crack. However, the smaller the grains and the greater the number of grains, the greater the deformation resistance reflected to the outside, which will make cold heading deformation difficult and increase the risk of cracking.

[0016] Furthermore, the internal texture of the brass for cold heading consists of a recrystallized texture and a wire texture.

[0017] More preferably, having <111> The volume fraction of the recrystallized texture in the direction is 55-70%, with <100> The volume fraction of the recrystallized texture in the direction is 12-20%; <111> The volume fraction of the silk texture in the direction is 8-15%, with <100> The volume fraction of the silk texture in the direction is ≤7%.

[0018] Compared with the wire texture, the recrystallized texture has lower cold heading deformation resistance and is easier to cold head, but the presence of wire texture can improve the mechanical properties of brass. <111> Directional texture is the most favorable texture for cold heading, followed by <100> The recrystallization texture in the direction of <100> The wire texture in the direction is the most unfavorable texture for cold heading, but it has higher mechanical properties. <111> The silk texture in the direction is second, so the present invention provides a suitable ratio of <111> Recrystallization texture and <100> The wire texture in the direction makes the brass for cold heading provided by the present invention have good compression performance, suitable for cold heading, and also have good mechanical properties.

[0019] The present invention also provides a method for preparing the brass for cold heading. The technical route of the preparation method is smelting → horizontal continuous casting → extrusion → tempering → finished product stretching → inspection, and the specific steps are:

[0020] (1) preparing the brass for cold heading according to the mass percentage of each component, smelting and horizontally continuous casting to obtain an ingot;

[0021] (2) Extruding the ingot obtained in step (1) to obtain an extruded blank, wherein the extrusion process is as follows: an extrusion temperature of 600-660° C., an extrusion ratio of 20-150, and an extrusion speed of 8-15 mm / s;

[0022] (3) tempering the extruded blank obtained in step (2) at 450-600° C.;

[0023] (4) The tempered extruded blank obtained in step (3) is subjected to finished product stretching to obtain brass for cold heading, and the processing rate of the finished product stretching is 2-8%.

[0024] The brass of the present invention needs to be extruded at a temperature lower than the phase transformation temperature of H65 brass, that is, the extrusion temperature is controlled at 600-660°C. Due to the high deformation resistance of low-temperature extrusion, a small extrusion ratio of 20-150 and a fast extrusion process of 8-15 mm / s are required. The purpose is to control the β phase morphology during H65 hot extrusion to be fine granular, with an average diameter of ≤5 μm and a volume fraction of ≤3%. This is because during H65 hot extrusion, the alloy structure undergoes not only recrystallization but also an α→α+β phase transformation. The lattice constant of the α phase ranges from 3.608 to 3.693 Å, and the lattice constant of the β phase ranges from 2.942 to 2.949 Å. This difference in lattice constants can lead to stress concentration at the phase interface. When the β phase precipitated from the α phase is dendritic, the stress concentration phenomenon is most serious. Crack sources will initiate at the intersection of the dendritic β phases, causing cracks on the outer ring surface of the extruded billet due to the superimposed bending shear stress during coiling. The high-temperature microstructure of H65 is closely related to the extrusion temperature. At low extrusion temperatures, the β phase precipitates from the α phase in fine particles, and even no β phase appears because the phase transition temperature has not been reached. As the extrusion temperature increases, the β phase morphology develops into a dendritic structure, and the stress concentration caused by the phase transition begins to intensify. The extrusion temperature of the brass of the present invention should not exceed 660°C. When the extrusion temperature exceeds 780°C, the β phase morphology appears in a blocky form, and the stress concentration phenomenon gradually weakens. When the extrusion temperature is too low, below 600°C, H65 extrusion becomes very difficult. Therefore, the extrusion temperature of the brass of the present invention is controlled between 600-660°C.

[0025] The tempering temperature provided by the present invention is below 450°C, which is far away from the brass phase transformation temperature point of around 474°C. The β phase cannot obtain a single α phase structure through the α+β→α phase transformation; when the tempering temperature exceeds 600°C, it is very easy to cause coarse structure.

[0026] The present invention adopts a low processing rate stretching process, and the processing rate is controlled at 2-8%, the purpose of which is to limit the tensile deformation and increase the volume fraction of the silk texture. When the processing rate is less than 2%, <111> The volume fraction of the silk texture in the direction is less than 8%, the strength of the parts processed by cold heading is low and does not meet the use requirements. Moreover, due to the small elongation, the surface quality of the finished product is poor. When the processing rate exceeds 8%, <111> and <100> The volume fraction of directional silk texture increases, exceeding the upper limit of the required range.

[0027] Furthermore, the tempering temperature is preferably selected in the range of 510-560℃. If the tempering temperature is below 510℃, the secondary recrystallization driving force during the tempering process is small because the extruded billet is already a recrystallized structure. <111> and <100> It is difficult to reduce the volume fraction of the directional silk texture, and it is difficult to ensure the quality of the finished product. <111> The volume fraction of directional recrystallization texture reaches more than 50%; after the tempering temperature exceeds 560℃, when the holding time is long, the α phase tends to become coarse.

[0028] Furthermore, in step (1), the smelting temperature is 1020-1150° C. At this smelting temperature, the metal provided by the present invention can be completely melted.

[0029] Furthermore, in step (1), the horizontal continuous casting process is: the ingot specification is The casting temperature is 1060-1100℃, the pulling speed is 40-80mm / min, the cooling water pressure is 0.30-0.55Mpa, the inlet and outlet water temperature difference is 20-40℃, and the cooling water flow rate is 30-90L / min.

[0030] Furthermore, in step (2), the extrusion flow number is 1-2.

[0031] Furthermore, in step (2), the wire winding method after extrusion is coiling, and the extruded blank is cooled naturally in the air.

[0032] Furthermore, the extruded blank after tempering is pickled to remove oxide scale on the surface of the extruded blank, and the volume ratio of the pickling solution is nitric acid: sulfuric acid: water = 1:12:32.

[0033] Furthermore, the pickled extruded blank is stretched into a finished product, the processing rate is controlled at 2-8%, and a polycrystalline mold is used as the mold.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention provides an appropriate mass percentage of As element, thereby suppressing the development of the β phase into long strips and blocks at high temperature, and thus obtaining a brass for cold heading with a single α phase of appropriate size at room temperature. Due to the single α phase of appropriate size, the brass for cold heading provided by the present invention has good compression properties, tensile properties and tensile strength, and provides a suitable mass ratio of Cu content, so that the cost is low.

[0036] (2) The present invention is achieved by <111> and <100> By regulating the directional recrystallization texture, the volume fraction of the filament texture and the size of the α phase, the excellent mechanical properties of H65 brass are obtained: tensile strength: 360-420 MPa, yield strength: 280-350 MPa, elongation A: 28-40%, and hardness HV5: 110-140. This solves the problems of surface wrinkles, incomplete filling and surface cracking that are common in H65 brass cold heading.

[0037] (3) When preparing brass wire for large diameter cold heading, the present invention controls the morphology, size, and volume fraction of the high-temperature microstructure of the extruded blank by providing a suitable extrusion process and tempering process, thereby reducing the generation of crack sources and solving the problem of intermittent cracks on the surface of the wire during the coiling process when producing H65 brass using the current process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a microstructure photograph of the extruded blank prepared in Example 1 of the present invention;

[0039] Figure 2 This is a microstructure photograph of the extruded blank prepared in Comparative Example 3 of the present invention;

[0040] Figure 3 This is a microstructure photograph of the brass for cold heading prepared in Example 1 of the present invention;

[0041] Figure 4 This is a microstructure photograph of the brass for cold heading prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0043] The present invention provides 5 embodiments and 6 comparative examples, and the specific compositions are shown in Table 1.

[0044] Example 1

[0045] One specification is The brass wire preparation method is as follows:

[0046] 1) Melting: Prepare the materials according to the required ingredients, and then melt them in an industrial frequency melting furnace at a melting temperature of 1040-1110℃. After all the metals are melted and the test results are qualified, pour them into the industrial frequency furnace for insulation.

[0047] 2) Horizontal continuous casting: Ingot specifications: Casting temperature: 1060-1080℃, pulling speed: 58mm / min, cooling water pressure: 0.55Mpa, inlet and outlet water temperature difference: 38℃, cooling water flow rate: 66L / min.

[0048] 3) Extrusion: Extrusion temperature: 640℃, extrusion flow number: 1, extrusion blank specifications: Extrusion ratio: 133, extrusion speed: 13mm / s, winding method is coiling, cooling method is natural cooling in the air. Figure 1 As shown, the microstructure characteristics of the obtained extruded blank are as follows: the β phase is fine granular, with an average diameter of 3.8 μm and a volume fraction of 2.6%.

[0049] 4) Tempering: Tempering temperature: 520℃, heating from room temperature, heating time: 40min, after reaching the set temperature, holding time: 240min, the extruded blank after tempering is pickled to remove the surface oxide scale, the pickling solution volume ratio: nitric acid: sulfuric acid: water = 1:12:32.

[0050] 5) Finished product stretching: after pickling Extruded blanks are stretched into coils and finished products Processing rate: 4.5%, the mold is polycrystalline mold. Figure 3 As shown, the microstructure characteristics of the finished product are: the α phase area accounts for 100%, the α phase size is 36μm, <111> The volume fraction of the recrystallized texture in the direction is 68.3%. <100> The volume fraction of the recrystallized texture in the direction is 14.2%. <111> The volume fraction of the silk texture in the direction is 12.8%. <100> The volume fraction of the silk texture in the direction is 4.7%.

[0051] 6) Inspection.

[0052] Example 2

[0053] One specification is The brass wire preparation method is as follows:

[0054] 1) Melting: Prepare the materials according to the required ingredients, and then melt them in an industrial frequency melting furnace at a melting temperature of 1040-1130℃. After all the metals are melted and the test results are qualified, pour them into the industrial frequency furnace for insulation.

[0055] 2) Horizontal continuous casting: Ingot specifications: Casting temperature: 1050-1070℃, pulling speed: 64mm / min, cooling water pressure: 0.45Mpa, inlet and outlet water temperature difference: 31℃, cooling water flow: 52L / min.

[0056] 3) Extrusion: Extrusion temperature: 600℃, extrusion flow number: 1, extrusion blank specifications: Extrusion ratio: 39.5, extrusion speed: 8mm / s, winding method is coiling, and cooling method is natural cooling in the air.

[0057] 4) Tempering: Tempering temperature: 560℃, heating from room temperature, heating time: 90min, after reaching the set temperature, holding time: 270min, the extruded blank after tempering is pickled to remove the surface oxide scale, the pickling solution volume ratio: nitric acid: sulfuric acid: water = 1:12:32.

[0058] 5) Finished product stretching: after pickling Extruded blanks are stretched into coils and finished products The processing rate is controlled at 6.3%, and the mold is a polycrystalline mold.

[0059] 6) Inspection.

[0060] Example 3

[0061] One specification is The brass wire preparation method is as follows:

[0062] 1) Melting: Prepare the materials according to the required ingredients, and then melt them in an industrial frequency melting furnace at a melting temperature of 1035-1140℃. After all the metals are melted and the test results are qualified, pour them into the industrial frequency furnace for insulation.

[0063] 2) Horizontal continuous casting: Ingot specifications: Casting temperature: 1045-1070℃, pulling speed: 80mm / min, cooling water pressure: 0.30Mpa, inlet and outlet water temperature difference: 26℃, cooling water flow rate: 39L / min.

[0064] 3) Extrusion: Extrusion temperature: 660℃, extrusion flow number: 2, extrusion blank specifications: Extrusion ratio: 97, extrusion speed: 12.5mm / s, winding method is coiling, and cooling method is natural cooling in the air.

[0065] 4) Tempering: Tempering temperature: 510℃, heating from room temperature, heating time: 30min, after reaching the set temperature, holding time: 300min, the extruded blank after tempering is pickled to remove the surface oxide scale, the pickling solution volume ratio: nitric acid: sulfuric acid: water = 1:12:32.

[0066] 5) Finished product stretching: after pickling Extruded blanks are stretched into coils and finished products Processing rate: 7.5%, the mold is a polycrystalline mold.

[0067] 6) Inspection.

[0068] Example 4

[0069] One specification is The brass wire preparation method is as follows:

[0070] 1) Melting: Prepare the materials according to the required ingredients, and then melt them in an industrial frequency melting furnace at a melting temperature of 1030-1090℃. After all the metals are melted and the components are tested to be qualified, pour them into the industrial frequency furnace for insulation.

[0071] 2) Horizontal continuous casting: Ingot specifications: Casting temperature: 1045-1065℃, pulling speed: 72mm / min, cooling water pressure: 0.40Mpa, inlet and outlet water temperature difference: 31℃, cooling water flow rate: 43L / min.

[0072] 3) Extrusion: Extrusion temperature: 630℃, extrusion flow number: 1, extrusion blank specifications: Extrusion ratio: 118, extrusion speed: 10mm / s, winding method is coiling, cooling method is natural cooling in air.

[0073] 4) Tempering: Tempering temperature: 540℃, heating from room temperature, heating time: 50min, after reaching the set temperature, holding time: 180min, the extruded blank after tempering is pickled to remove the surface oxide scale, the pickling solution volume ratio: nitric acid: sulfuric acid: water = 1:12:32.

[0074] 5) Finished product stretching: after pickling Extruded blanks are stretched into coils and finished products Processing rate: 6.1%, the mold is a polycrystalline mold.

[0075] 6) Inspection.

[0076] Example 5

[0077] One specification is The brass wire preparation method is as follows:

[0078] 1) Melting: Prepare the materials according to the required ingredients, and then melt them in an industrial frequency melting furnace at a melting temperature of 1040-1100℃. After all the metals are melted and tested to meet the requirements, pour them into the industrial frequency furnace for heat preservation.

[0079] 2) Horizontal continuous casting: Ingot specifications: Casting temperature: 1065-1080℃, pulling speed: 45mm / min, cooling water pressure: 0.50Mpa, inlet and outlet water temperature difference: 36℃, cooling water flow: 60L / min.

[0080] 3) Extrusion: Extrusion temperature: 620℃, extrusion flow number: 1, extrusion blank specifications: Extrusion ratio: 84, extrusion speed: 10.8 mm / s, winding method is coiling, and cooling method is natural cooling in the air.

[0081] 4) Tempering: Tempering temperature: 530℃, heating from room temperature, heating time: 50min, after reaching the set temperature, holding time: 240min, the extruded blank after tempering is pickled to remove the surface oxide scale, the pickling solution volume ratio: nitric acid: sulfuric acid: water = 1:12:32.

[0082] 5) Finished product stretching: after pickling Extruded blanks are stretched into coils and finished products Processing rate: 5.2%, the mold is a polycrystalline mold.

[0083] 6) Inspection.

[0084] Comparative Example 1

[0085] The Cu content is 63.08 wt %, and the rest is the same as in Example 1. The purpose is to compare the effect of adding Cu content on the extruded structure and coil drawing of H65 brass.

[0086] Comparative Example 2

[0087] No As element was added, As < 0.001 wt %, and the rest was the same as in Example 1. The purpose was to compare the effect of added As content on the extruded structure and coiling of H65 brass.

[0088] Comparative Example 3

[0089] The extrusion temperature is 720℃, and the rest is the same as in Example 1. The purpose is to compare the effect of extrusion temperature on the extrusion structure and coiling of H65 brass. Figure 2 As shown, its microstructure morphology is characterized by: the β phase morphology is dendritic, and the finished product is as shown Figure 4 The microstructure characteristics of the finished product are as follows: the α phase area accounts for 100%, the α phase size is 55μm, <111> The volume fraction of the recrystallized texture in the direction is 48.3%. <100> The volume fraction of the recrystallized texture in the direction is 28.2%. <111> The volume fraction of the silk texture in the direction is 8.0%. <100> The volume fraction of the silk texture in the direction is 15.5%.

[0090] Comparative Example 4

[0091] The extruded blank was not tempered at 510-560°C, and the rest was the same as in Example 1. The purpose was to compare the effects of tempering of the extruded blank on the H65 structure and coiling.

[0092] Comparative Example 5

[0093] The extruded blank was tempered at 650°C, and the rest was the same as in Example 1. The purpose was to compare the effects of high-temperature tempering of the extruded blank on the H65 microstructure, coil drawing and cold heading properties.

[0094] Comparative Example 6

[0095] The extruded blank was tempered at 400°C, and the rest was the same as in Example 1. The purpose was to compare the effects of low-temperature tempering of the extruded blank on the H65 microstructure, coil drawing and cold heading properties.

[0096] Comparative Example 7

[0097] The processing rate of the extruded blank to the finished product is 15%, and the rest is the same as in Example 1. The purpose is to compare the effect of the processing rate on the cold heading performance.

[0098] The microstructures of 5 examples and 7 comparative examples were tested, and the results are recorded in Table 2.

[0099] Phase area ratio, size, and quantity: observed under a scanning electron microscope.

[0100] Grain size (α phase size): Metallographic specimens were prepared in accordance with GB / T 13298. Grain size was measured using the comparison method specified in GB / T 6394-2017 (Method for determination of average grain size of metals), i.e., the grain size was assessed by comparison with a standard rating chart.

[0101] Texture: The texture was observed and measured using a scanning electron microscope backscattered electron diffraction (EBSD) device.

[0102] The following performance tests were performed on the five embodiments and seven comparative examples, and the results are recorded in Table 3.

[0103] From Table 3 we can see that:

[0104] 1) The Cu content of Comparative Example 1 is 63.08 wt %, which is lower than the lower limit of the Cu content range of the embodiment. β phase also appears in the room temperature structure of the alloy. Since the structure affects the performance, the tensile strength, yield strength, and hardness of Comparative Example 1 are higher than those of the embodiment, while the elongation and compression indexes are lower than those of Example 1. This shows that the Cu content affects the ratio and texture distribution of the α phase and β phase in the brass structure, thereby affecting the cold heading performance of the brass.

[0105] 2) Comparative Example 2 does not add As. Since As can improve the β-phase morphology and processing performance in the brass extrusion structure, the tensile strength and yield strength of Comparative Example 2 are lower than those of Example 1, but the elongation is lower than that of Example 1. The alloy compression index is lower than that of Example 1, and the cold heading performance deteriorates.

[0106] 3) In Comparative Example 3, the extrusion temperature was 720°C, which exceeded the upper limit of the temperature range of the embodiment. Since the high extrusion temperature causes the alloy's extruded dynamically recrystallized grains to become coarser, the strength of the brass increases, the elongation decreases, and the degree of compression decreases, thus deteriorating the cold heading performance of the brass.

[0107] 4) The extruded blank obtained in Comparative Example 4 was not tempered at 510-560°C, because tempering can reduce the <111> and <100> Directional silk texture volume fraction, improve <111> The volume fraction of the directional recrystallized texture is increased, and the mechanical properties of the brass are improved, thereby obtaining good cold heading performance. Therefore, the tensile strength, yield strength, and hardness of the brass prepared in Comparative Example 4 are higher than those in Example 1, while the elongation and compression indexes are lower than those in Example 1, and the cold heading performance of the brass deteriorates.

[0108] 5) The extruded blank prepared in Comparative Example 5 was subjected to high-temperature tempering treatment at 650°C, and the α phase became coarser. Compared with Example 1, the brass elongation and compression degree of Comparative Example 5 decreased, and the cold heading performance deteriorated.

[0109] 6) The extruded blank prepared in Comparative Example 6 was subjected to a low-temperature tempering treatment at 400°C, which was far away from the brass phase transition temperature of approximately 474°C. The β phase could not obtain a single α phase structure through the α+β→α phase transformation. As a result, the tensile strength, yield strength, and hardness of the brass prepared in Comparative Example 6 were higher than those of the brass prepared in Example 1, while the elongation and compression indexes were lower than those of the brass prepared in Example 1, resulting in poor cold heading performance of the brass.

[0110] 7) The processing rate of the extruded blank of Comparative Example 7 is 15%, which exceeds the upper limit of the range of 2-8%, so that the brass obtained in Comparative Example 7 is <111> and <100> The volume fraction of the directional wire texture increases, resulting in the brass prepared in Comparative Example 7 having much higher tensile strength, yield strength, and hardness than the brass prepared in Example 1, while the elongation and compression indexes are much lower than those of the brass prepared in Example 1, and the cold heading performance of the brass deteriorates.

[0111] Tensile strength, yield strength Rp0.2 and cross-sectional reduction rate: tested in accordance with GB / T228.1-2021 "Tensile test of metallic materials Part 1: Room temperature test method".

[0112] Hardness HV5: Tested according to GB / T4340.1-2009 "Vickers hardness test for metallic materials - Part 1: Test method".

[0113] Upsetting test: The sample is made into a cylindrical shape with a height of 1.5 times the original diameter of the sample, and then flattened on a hydraulic press until the first crack visible to the naked eye appears on the surface of the sample. The degree of compression (H0: original height of cylindrical specimen, H k : The height of the sample when the first visible crack appears on the side during flattening). The larger the εc value, the better the forgeability of the sample.

[0114] Table 1 Chemical composition of Examples and Comparative Examples

[0115] serial number Cu Fe As Pb Zn Example 1 64.20 0.028 0.015 0.0065 margin Example 2 63.78 0.012 0.0060 0.0080 margin Example 3 66.59 0.062 0.022 0.039 margin Example 4 65.44 0.040 0.028 0.054 margin Example 5 66.92 0.036 0.0096 0.023 margin Comparative Example 1 63.08 0.025 0.015 0.0059 margin Comparative Example 2 64.20 0.028 ＜0.001 0.0065 margin Comparative Example 3 64.20 0.028 0.015 0.0065 margin Comparative Example 4 64.20 0.028 0.015 0.0065 margin Comparative Example 5 64.20 0.028 0.015 0.0065 margin Comparative Example 6 64.20 0.028 0.015 0.0065 margin Comparative Example 7 64.20 0.028 0.015 0.0065 margin

[0116] Table 2 Microstructure test data of Examples and Comparative Examples

[0117]

[0118]

[0119] Table 3 Mechanical properties and cold heading properties of the embodiments of the present invention and the comparative examples

[0120]

Claims

1. A brass for cold heading, characterized in that: The mass percentages of the components of the brass for cold heading are: Cu: 64.0-67.0wt%, Fe: 0.01-0.07wt%, As: 0.005-0.03wt%, Pb < 0.01wt%, and the balance is Zn and unavoidable impurity elements; The microstructure of the brass for cold heading is a single α phase, and the average size of the α phase is 30-50 μm.

2. The brass for cold heading according to claim 1, characterized in that: The internal texture of the brass for cold heading consists of a recrystallized texture and a wire texture.

3. The brass for cold heading according to claim 2, characterized in that: have <111> The volume fraction of the recrystallized texture in the direction is 55-70%, with <100> The volume fraction of the recrystallized texture in the direction is 12-20%; <111> The volume fraction of the silk texture in the direction is 8-15%, with <100> The volume fraction of the silk texture in the direction is ≤7%.

4. A method for preparing brass for cold heading according to any one of claims 1 to 3, characterized in that: include: (1) preparing the brass for cold heading in accordance with the mass percentage of each component according to any one of claims 1 to 3, smelting and horizontally continuous casting to obtain an ingot; (2) Extruding the ingot obtained in step (1) to obtain an extruded blank, wherein the extrusion process is as follows: an extrusion temperature of 600-660° C., an extrusion ratio of 20-150, and an extrusion speed of 8-15 mm / s; (3) tempering the extruded blank obtained in step (2) at 450-600° C.; (4) The tempered extruded blank obtained in step (3) is subjected to finished product stretching to obtain brass for cold heading, wherein the processing rate of the finished product stretching is 2-8%.

5. The method for preparing brass for cold heading according to claim 4, characterized in that: In step (2), the tempering temperature is 510-560°C.

6. The method for preparing brass for cold heading according to claim 4, characterized in that: In step (1), the smelting temperature is 1020-1150°C.

7. The method for preparing brass for cold heading according to claim 4, characterized in that: In step (1), the horizontal continuous casting process is as follows: ingot specification is φ140-260mm, casting temperature is 1060-1100℃, pulling speed is 40-80mm / min, cooling water pressure is 0.30-0.55MPa, inlet and outlet water temperature difference is 20-40℃, and cooling water flow rate is 30-90L / min.

8. The method for preparing brass for cold heading according to claim 4, characterized in that: In step (2), the extrusion flow number is 1-2.

9. The method for preparing brass for cold heading according to claim 4, characterized in that: In step (2), the wire winding method after extrusion is coiling, and the extruded blank is cooled naturally in the air.

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