Method for producing a horizontal continuous casting free-cutting brass bar

Abstract

This invention discloses a method for preparing a horizontally continuously cast free-machining brass rod. The rod's composition, by weight percentage, consists of Cu, 61.0~63.0 wt%, B4C, 0.1~0.6 wt%, Bi, 0.7~1.5 wt%, Pb ≤0.08 wt%, total unavoidable impurities ≤0.3 wt%, and the balance Zn. The method involves sequential steps of raw material proportioning, melting in an inert gas environment, horizontal continuous casting, ink-forming annealing, finishing, and finished product inspection. The core principle is to suppress melt oxidation and reduce gas inclusions in an inert gas environment, combined with the ink-forming annealing process to release fine carbon particles from B4C, synergistically improving machinability and tensile strength with Bi. The resulting free-machining brass rod has a tensile strength of not less than 500 MPa, an elongation of not less than 4.5%, an alloy hardness of not less than 150 HV, an electrical conductivity of not less than 20% IACS, and machinability comparable to leaded brass, preventing cutting entanglement and tool damage, with the cutting particle length consistently controlled within 5 mm. It can meet the application requirements of high-end equipment, electronics and electrical, mechanical hardware and other fields, and has good environmental protection and practicality.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal material casting and processing technology, specifically a method and product for preparing horizontally continuous casting free-cutting brass bars under inert gas protection. Background Technology

[0002] Free-machining brass bars are widely used in high-end equipment, electronics, machinery, sanitary ware, hardware, and other fields due to their excellent machinability, tensile strength, hardness, and corrosion resistance. Traditionally, lead (Pb) is added to brass bars to improve machinability, with a lead content of no less than 2%. However, lead is toxic. With increasingly stringent global environmental requirements, reducing lead content and improving the machinability and mechanical properties of free-machining brass bars through the addition of other environmentally friendly alloying elements has become an inevitable trend in the industry.

[0003] Currently, the preparation of free-cutting brass mostly adopts traditional semi-continuous casting or pouring processes, which have problems such as uneven alloy composition, many internal defects (such as porosity and inclusions), and large anisotropy in machinability and mechanical properties. At the same time, existing free-cutting brass often improves machinability by adding a single element, making it difficult to balance machinability and mechanical properties. As a result, it is difficult to meet the needs of high-end equipment, electronics and electrical, and precision machinery fields, thus limiting its application range. Moreover, some products are prone to tool entanglement and tool damage during the cutting process, and the size of the cutting particles is unstable, which affects processing efficiency and product quality.

[0004] Horizontal continuous casting under inert gas protection offers advantages such as oxidation prevention, continuity, cooling, and adjustable traction rate, effectively improving the quality of brass bars. Boron carbide (B4C), as a novel additive phase, releases carbon particles after specific graphitization annealing treatment, dispersing them throughout the copper matrix. Combined with Bi, it significantly improves machinability while compensating for the shortcomings of single-element additives, thus balancing the material's mechanical, electrical, and machinability properties. Therefore, developing a method for preparing free-machining brass bars based on horizontal continuous casting under inert gas protection, incorporating a composite additive of B4C and Bi, and meeting specific performance indicators, has significant practical implications and application value. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing horizontally continuously cast free-cutting brass rods, which can improve the problem of poor performance of free-cutting brass rods.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a free-cutting brass alloy, wherein the raw materials for preparing the free-cutting brass include the following components: The chemical composition, by weight percentage, is as follows: Cu, 61.0~63.0 wt% B4C, 0.1~0.6wt%; Bi, 0.7~1.5wt%; Pb, ≤0.08wt%; Total unavoidable impurities ≤0.3wt%; The balance is Zn.

[0007] In some embodiments, the raw materials for preparing the copper alloy include the following components: Cu, 60.0~63.0 wt%; B4C, 0.1~0.6wt%; Bi, 0.7~1.5wt%; Pb, ≤0.08wt%; Total unavoidable impurities ≤0.3wt%; The balance is Zn.

[0008] Secondly, this application provides a method for preparing a horizontally continuously cast free-cutting brass rod, the method comprising: The components of the above-mentioned free-cutting brass rod are provided, and the components are smelted in an inert gas environment to obtain a copper alloy melt; The copper alloy melt is introduced into a continuous casting mold for horizontal continuous casting. The mold adopts an oblique slit structure to ensure uniform magnetic field distribution. During the continuous casting process, an inert gas with a pressure of one atmosphere is used for protection to obtain a cast rod. The cast rod is subjected to ink annealing treatment. The cast rod is placed in an annealing furnace and heated to 900~1000℃ under the protection of reducing gas. It is held for 1~2 hours and then cooled to room temperature to allow B4C to release carbon and form fine carbon particles, which are dispersed in the copper matrix to improve the machinability and obtain ink annealed cast rod. The ink-annealed casting rod is hot-rolled by feeding the casting rod into a hot rolling mill and performing multiple hot rolling passes to obtain the hot-rolled casting rod. The hot-rolled casting rod is subjected to solution treatment, and then placed in a heat treatment furnace. The solution-treated casting rod is subjected to multiple cold drawing processes, and an intermediate annealing process is performed after each drawing process to obtain a semi-finished copper alloy. The semi-finished copper alloy is subjected to low-temperature stress-relief annealing to obtain the finished copper alloy.

[0009] In some embodiments, the process of melting the components in an inert gas environment to obtain a copper alloy melt includes: The proportioned Cu, Zn, Bi, B4C and other alloy raw materials are put into a vacuum melting furnace. After closing the furnace door, the vacuum is drawn to the set vacuum level, and then argon gas is introduced to atmospheric pressure. The temperature is raised to the melting temperature and kept constant. During this period, the raw materials are continuously stirred to fully melt them. Simultaneously, online degassing and slag removal are completed to obtain a copper alloy melt with uniform composition and high purity.

[0010] In some embodiments, the process of feeding the proportioned raw materials into a vacuum melting furnace, evacuating it, introducing argon gas to atmospheric pressure, and heating it to obtain a copper alloy melt includes: The proportioned raw materials are put into the melting furnace of the vacuum horizontal continuous casting unit. After the furnace door is closed, the vacuum is drawn to 0.001~0.005 MPa, and argon gas is introduced to atmospheric pressure. Medium-frequency induction heating is used to raise the temperature to 1200~1280℃ and hold it for 30~60 minutes to completely melt the raw materials. During this period, the material is stirred with a graphite rod 2~3 times, each time for 5~8 minutes. At the same time, argon gas is purged and graphite filtration is used to remove gas and slag. The argon gas purging flow rate is 5~10 L / min to obtain copper alloy melt.

[0011] In some embodiments, the step of introducing molten copper alloy into a continuous casting mold for horizontal continuous casting in an inert gas environment to obtain a cast rod includes: The qualified copper alloy melt is introduced into a continuous casting crystallizer with an oblique slit structure. The crystallizer temperature is controlled at 700~780℃ and the cooling rate is ≥100℃ / s. The argon gas in the furnace is maintained at one atmosphere. A "pull-stop-push" billet pulling method driven by a servo motor is adopted. The continuous casting speed is set to 0.8~1.5 m / min and the traction accuracy is ±0.02mm to prepare casting rods with a diameter of 15~120mm. And / or, the crystallizer adopts a two-section structure, with the upper section being a high-permeability magnetic copper alloy and the lower section being a high-thermal-conductivity copper alloy. An external water cooling system is provided, using deionized water at 20~30℃ for cooling, to ensure uniform magnetic field and cooling effect.

[0012] In some embodiments, the hot rolling process of the copper alloy casting to obtain a hot-rolled billet includes: The cast rod obtained by continuous casting is fed into a hot rolling mill, and multiple hot rolling passes are carried out while controlling the total deformation to ≥60%. The final rolling temperature is controlled at 650~700℃ throughout the process. After hot rolling, the billet is naturally cooled to room temperature to obtain a denser, finer-grained hot-rolled billet.

[0013] In some embodiments, the solution treatment of the hot-rolled ingot includes: The hot-rolled billet is placed in a heat treatment furnace, heated to 720~750℃ and held for 1~3 hours to allow the alloying elements to fully dissolve and diffuse. Subsequently, it was rapidly water-quenched to room temperature at a cooling rate of ≥80℃ / s to suppress the tendency of dezincification and retain a uniform α+β dual-phase structure; And / or, the process of performing multiple cold drawing operations on the solution-treated billet to obtain a semi-finished copper alloy includes: performing multiple cold drawing operations on the solution-quenched billet, controlling the total deformation to 40%~60%, and performing intermediate annealing after each drawing operation. The intermediate annealing temperature is controlled at 450~500℃ and held for 1~2 hours to alleviate work hardening and avoid cracks and fractures during the drawing process, thus obtaining semi-finished copper alloy rods with precise dimensions.

[0014] In some embodiments, the process of subjecting the semi-finished copper alloy to low-temperature stress-relief annealing to obtain the finished copper alloy includes: The cold-drawn semi-finished bar is placed in an annealing furnace, heated to 250~300℃ and held for 2~4 hours to fully release the residual internal stress generated during the processing. The product is then slowly cooled to room temperature in the furnace to stabilize its microstructure and dimensional accuracy. The annealed bars are then subjected to sequential tests for composition, mechanical properties, and appearance. Once the tests are passed, the bars are packaged to obtain finished free-machining brass bars produced by continuous casting in an inert gas environment. Beneficial effects

[0015] 1. The free-machining brass prepared in this application uses 61.0~63.0wt% Cu with the balance zinc to construct an α+β dual-phase matrix, balancing basic strength, plasticity, and electrical conductivity; 0.7~1.5wt% Bi can significantly reduce cutting resistance, improve cutting surface quality, and avoid tool entanglement damage; 0.1~0.6wt% B4C releases fine carbon particles through graphitization annealing, which synergistically improves cutting performance, refines grains, and stabilizes cutting particle size with Bi; the lead addition is limited to ≤0.08wt%, which meets environmental standards while eliminating the toxicity hazards of traditional lead; the total unavoidable impurities are ≤0.3wt%, further ensuring the purity of the alloy composition and the overall stability of mechanical, electrical, and cutting properties; 2. This application also provides a method for preparing free-machining brass bars by horizontal continuous casting. The method involves horizontal continuous casting in an inert gas environment, coupled with a slanted kerf crystallizer, and stable melting pressure control to purify the copper alloy melt, create a uniform magnetic field and solidification structure, and reduce porosity, inclusions, and segregation defects. Then, multiple hot rolling passes are used to break up coarse grains in the as-cast state, densify the internal structure, and solidify the basic mechanical properties. Subsequently, solution treatment is performed to achieve full solid-solution diffusion of alloying elements, optimize the matrix phase structure, and eliminate hot rolling stress. Combined with multiple cold drawing passes and intermediate annealing, the dimensional accuracy and surface quality of the profile are precisely controlled, the grains are refined, and work hardening is alleviated, ensuring continuous processing. Finally, low-temperature stress-relief annealing is performed to completely release residual internal stress, stabilize the finished product's structure and dimensions, and prevent later deformation and cracking, ultimately obtaining a free-machining copper alloy product with uniform structure, stable performance, and excellent processing quality. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of the copper alloy preparation method provided in the embodiments of this application; Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0020] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0021] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0024] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0025] In related technologies, brass alloys are the most widely used non-ferrous metal structural materials, possessing excellent electrical and thermal conductivity and machinability, occupying an irreplaceable position in fields such as electronics, electrical engineering, mechanical hardware, sanitary ware, and precision connectors. To meet the demands of efficient machining, traditional brass commonly incorporates lead to improve chip-breaking performance, making it suitable for various structural and functional components such as high-end equipment, automatic lathe machining parts, precision bushings, terminals, and valve fittings. However, lead is toxic, and with increasingly stringent global environmental requirements, lead content control is becoming more stringent. Although elements such as bismuth are used to replace some lead, the limited alloy composition and crude casting process control make it difficult to achieve the same level of machinability as leaded brass. During cutting, issues such as tool entanglement, tool sticking, and poor chip breaking easily occur, resulting in unstable chip size and severely impacting machining efficiency and surface quality. Furthermore, conventional non-vacuum casting is prone to internal defects such as oxide inclusions, porosity, and looseness, leading to large fluctuations in mechanical properties and uneven microstructure, making it difficult to meet the requirements of high strength and high dimensional accuracy. In addition, existing brass generally suffers from poor strength-ductility matching and low electrical conductivity, making it unsuitable for high-end applications such as vacuum, precision, and high-speed cutting, thus limiting its widespread application in fields such as electronics, electrical engineering, and precision machinery.

[0026] Based on this, in order to improve the problems of insufficient machinability and numerous internal defects of free-machining brass in related technologies, the embodiments of this application provide the following solutions.

[0027] This application provides a method for preparing a free-cutting brass rod, the method comprising: S100 provides a method for preparing a horizontally continuously cast free-cutting brass bar, wherein the free-cutting brass component is smelted in an inert gas environment to obtain a copper alloy melt; S200: The copper alloy melt is introduced into the continuous casting crystallizer for horizontal continuous casting in an inert gas environment to obtain copper alloy casting rods. S300, copper alloy casting rods are subjected to ink-annealing treatment to obtain ink-annealed copper alloy casting rods; S400 involves hot rolling a graphitized annealed copper alloy casting rod to obtain a hot-rolled copper alloy rod. S500 involves solution treatment of hot-rolled copper alloy bars to obtain solution-treated copper alloy bars. S600, the solid solution copper alloy rod is subjected to multiple cold drawing and intermediate annealing to obtain a semi-finished brass rod; S700 involves low-temperature stress-relief annealing of semi-finished brass rods to obtain finished free-machining brass rods.

[0028] As can be seen from the above, the method for preparing free-cutting brass rods provided in this application involves melting the components in an inert gas environment. This inert gas environment inhibits melt oxidation and reduces gas inclusions. Combined with stirring and degassing / slag removal, this ensures the copper alloy melt has uniform composition and high purity, laying a high-quality matrix foundation for subsequent casting. Horizontal continuous casting in an inert gas environment, relying on a slanted kerf crystallizer and precise billet pulling process, achieves rapid and stable solidification of the melt, refines grains, and avoids casting defects, resulting in a dense, uniformly sized copper alloy rod. The rod undergoes graphitization annealing, which promotes the release of carbon from B4C and the formation of fine carbon particles that are dispersed throughout the copper matrix, significantly improving subsequent cutting performance while preventing surface oxidation. The annealed rod is then subjected to multi-pass hot rolling, followed by high-temperature, large-deformation crushing. The process begins with coarse grains, a dense internal structure, and the elimination of casting porosity, improving the alloy's basic mechanical properties and machinability. Subsequent solution treatment allows for full diffusion of alloying elements, optimizes the α+β dual-phase structure distribution, suppresses dezincification tendency, eliminates hot rolling stress, and retains a uniform matrix structure. The solution-treated bar undergoes multiple cold drawing passes combined with intermediate annealing. Work hardening is utilized to enhance strength and dimensional accuracy, while annealing alleviates work hardening, restores plasticity, and prevents cracking and fracture during drawing, resulting in a semi-finished brass bar with good formability. Finally, low-temperature stress-relief annealing completely releases residual internal stress generated by cold working, stabilizes the alloy structure and product dimensions, and prevents deformation and performance degradation during later use. The final product is a free-machining brass bar with excellent machinability, stable mechanical properties, and compliance with environmental standards.

[0029] In some embodiments, in step S100, the components are smelted in an inert gas environment to obtain a copper alloy melt, including: S110: The proportioned components are put into a vacuum melting furnace, vacuumed, argon gas is introduced to atmospheric pressure and heated to melt, and the initial state of copper alloy melt is obtained. S120 involves heat preservation and stirring of the initial copper alloy melt, followed by online degassing and slag removal to obtain a copper alloy melt.

[0030] This setup, through heating and melting in an inert gas environment, effectively isolates air, inhibits the high-temperature oxidation of elements such as Cu and Zn, and reduces the formation of oxide inclusions. Subsequent heat preservation and stirring provide sufficient time for the diffusion of alloying elements, allowing each element to be evenly distributed in the melt and avoiding local component segregation. At the same time, online degassing and slag removal processes remove gases and non-metallic inclusions from the melt, further improving the purity of the melt and ensuring the uniformity of the microstructure and the stability of the performance of the subsequent cast rods.

[0031] Optionally, in some embodiments, in step S110, the proportioned components are put into a vacuum melting furnace, vacuumed, argon gas is introduced, and the furnace is heated and melted to obtain a preliminary copper alloy melt. This includes: putting the proportioned Cu, Zn, Bi, B4C, and other components into a hydraulic tilting melting furnace of a vacuum horizontal continuous casting unit, closing the furnace door, evacuating the furnace to a vacuum level of 0.001~0.005 MPa, introducing argon gas to 0.103 MPa, using medium-frequency induction heating to raise the temperature to 1200~1280℃, and holding the temperature for 30~60 minutes to completely melt all components to obtain a preliminary copper alloy melt.

[0032] This setup, employing a hydraulic tilting melting furnace and medium-frequency induction heating, ensures rapid and uniform heating, allowing for quick and complete fusion of all components and preventing localized overheating or incomplete melting. Inert gas (argon) purging maximizes the removal of air from the furnace and dissolved gases from the melt, effectively preventing hydrogen and oxygen absorption and reducing defects such as porosity and pinholes in the cast rods. A melting temperature of 1200~1280℃ and a holding time of 30~60 minutes balance melt fluidity and element diffusion efficiency, ensuring uniform alloy composition and providing a high-quality melt for subsequent molding.

[0033] Optionally, in some embodiments, in step S120, the initial copper alloy melt is subjected to heat preservation stirring and online degassing and slag removal to obtain a copper alloy melt, including: stirring the initial copper alloy melt with a graphite rod 2 to 3 times during the heat preservation process, each stirring for 5 to 8 minutes, while purging with inert gas at an argon flow rate of 5 to 10 L / min, and combining graphite filtration for online degassing and slag removal, and obtaining a copper alloy melt with uniform composition and purity after the heat preservation is completed.

[0034] This setup allows the graphite rod stirring to break up the component stratification of the melt, promoting thorough mixing of various alloying elements and ensuring that trace elements such as Bi and B4C are evenly distributed in the Cu-Zn matrix, thus optimizing the phase structure of the subsequent alloy. The degassing and slag removal method, combining argon purging with graphite filtration, utilizes the adsorption effect of argon bubbles to remove gases such as hydrogen and nitrogen from the melt, while the graphite filter intercepts oxides and inclusions in the melt, further improving the purity of the melt. An argon purging flow rate of 5~10 L / min ensures effective degassing while avoiding excessive flow that could cause melt splashing and component segregation, ultimately yielding a copper alloy melt that meets the requirements of continuous casting.

[0035] In some embodiments, in step S200, the copper alloy melt is introduced into a continuous casting mold for horizontal continuous casting in an inert gas environment to obtain a copper alloy casting rod. The temperature of the mold is controlled at 700~780℃, the cooling rate is ≥100℃ / s, the "pull-stop-push" casting method is adopted, the continuous casting speed is 0.8~1.5 m / min, and the traction accuracy is controlled within ±0.02mm.

[0036] This setup, with a crystallizer temperature of 700~780℃ and a rapid cooling rate of ≥100℃ / s, enables rapid solidification of the melt, refines the as-cast grains, suppresses dendritic segregation, and promotes uniform distribution of the α+β dual phases, thereby enhancing the basic strength of the cast rod. A continuous casting speed of 0.8~1.5 m / min and a "pull-stop-push" casting method, combined with high-precision traction of ±0.02mm, effectively control the dimensional accuracy of the cast rod, avoiding defects such as surface oscillation marks, cracks, and shrinkage cavities, ensuring a smooth surface and uniform dimensions. Maintaining an inert gas environment at one atmosphere throughout the process further prevents the melt from re-oxidizing during solidification, resulting in a dense, inclusion-free copper alloy cast rod.

[0037] Optionally, in some embodiments, the crystallizer adopts a two-section structure with oblique slits, the upper section being a high-permeability magnetic copper alloy and the lower section being a high-thermal-conductivity copper alloy. A water-cooling system is provided outside the crystallizer, using deionized water at 20~30℃ for cooling.

[0038] This design ensures a uniform magnetic field distribution within the crystallizer, allowing the melt to further refine grains and homogenize composition under electromagnetic stirring. The two-section structure balances magnetic permeability and thermal conductivity; the upper section, made of high-magnetic-permeability copper alloy, enhances electromagnetic induction and promotes melt flow and mixing, while the lower section, made of high-thermal-conductivity copper alloy, improves cooling efficiency and ensures rapid solidification. The 20-30°C deionized water cooling system provides stable cooling and avoids contamination from ordinary cooling water, while precisely controlling the cooling rate to prevent internal stress cracks in the cast rod due to excessively rapid cooling.

[0039] In some embodiments, in step S300, the copper alloy casting rod is subjected to a graphitization annealing treatment to obtain a graphitization annealed copper alloy casting rod, which includes: heating to 900~1000°C under a reducing gas protection, holding at that temperature for 1~2 hours, and then cooling to room temperature, so that B4C releases carbon and forms fine carbon particles, which are dispersed in the copper matrix to improve the machinability, thereby obtaining a graphitization annealed copper alloy casting rod.

[0040] This setup, with a blackening annealing temperature of 900~1000℃ and a holding time of 1~2 hours, allows for the full decomposition of B4C in the cast rod and the release of carbon elements, forming fine and uniform carbon particles that are dispersed throughout the copper matrix. This significantly improves the subsequent machinability of the brass rod and avoids problems such as tool entanglement and wear during the cutting process. The reducing gas protection effectively isolates the rod from air, preventing oxidation and discoloration of the cast rod surface and ensuring the surface quality of the rod. The furnace cooling method allows the cast rod to cool down slowly, reducing thermal stress and preventing structural cracking, thus laying a good foundation for subsequent hot rolling processes.

[0041] Optionally, in some embodiments, the reducing gas is hydrogen, with a flow rate controlled at 3~8 L / min, and the purity of the atmosphere in the annealing furnace is ≥99.99%.

[0042] This setup ensures that hydrogen does not react with the copper alloy, effectively isolating it from air and preventing oxidation of the cast rod surface. A flow rate of 3~8L / min ensures that the air inside the furnace is fully replaced while avoiding excessive flow that could lead to energy waste and temperature fluctuations. An atmosphere purity of ≥99.99% further reduces the impact of impurity gases on the annealing process, ensuring effective ink-forming annealing, uniform carbon particle precipitation, and improved alloy machinability.

[0043] In some embodiments, in step S400, the ink-annealed copper alloy casting is hot-rolled to obtain a hot-rolled copper alloy casting, which includes: feeding the ink-annealed copper alloy casting into a hot rolling mill for multi-pass hot rolling, controlling the total hot rolling deformation to be ≥60%, maintaining the final rolling temperature at 650~700℃, and naturally cooling to room temperature after hot rolling to obtain a hot-rolled copper alloy casting.

[0044] With this setup, hot rolling with a large deformation of ≥60% can effectively break up the coarse grains in the as-cast structure, forming fine and uniform equiaxed grains through dynamic recrystallization. At the same time, it compacts the porosity and voids inside the cast rod, improving the alloy's density and mechanical properties. The final rolling temperature of 650~700℃ is within the optimal temperature range for hot working of the alloy. This ensures that the alloy has good plasticity, avoids cracking and peeling during hot rolling, and prevents excessively high final rolling temperatures from causing grain growth, thus ensuring the refinement of the microstructure after hot rolling. Natural cooling allows the alloy to cool down slowly, reducing thermal stress and preventing microstructure cracking, laying a good foundation for subsequent solution treatment.

[0045] In some embodiments, in step S500, the hot-rolled copper alloy bar is subjected to solution treatment to obtain a solution-treated copper alloy bar, which includes: placing the hot-rolled copper alloy bar in a heat treatment furnace, heating it to 720~750°C and holding it at that temperature for 1~3 hours, and then water quenching it to room temperature at a cooling rate of ≥80°C / s to obtain a solution-treated copper alloy bar.

[0046] With this setup, the solution treatment temperature of 720~750℃ and the holding time of 1~3 hours allow elements such as Bi and B4C in the alloy to fully dissolve into the Cu-Zn matrix, forming a supersaturated solid solution, optimizing the ratio and distribution of the α+β dual phases, while eliminating residual stress generated during hot rolling and improving the uniformity of the alloy microstructure. Rapid water quenching at ≥80℃ / s can suppress the decomposition of the supersaturated solid solution and the precipitation of the dezincified phase, retaining the uniform microstructure at high temperature to room temperature, effectively improving the alloy's resistance to dezincification corrosion, while ensuring that the alloy has good plasticity and subsequent cold working performance.

[0047] In some embodiments, in step S600, the solution-treated copper alloy rod is subjected to multiple cold drawing passes combined with intermediate annealing to obtain a semi-finished brass rod, including: cold drawing the solution-treated copper alloy rod, controlling the total deformation to be 40%~60%, after each drawing pass, placing the rod in a heat treatment furnace, holding it at 450~500°C for 1~2 hours for intermediate annealing, and then naturally cooling it to room temperature after annealing. After completing all drawing and intermediate annealing processes, a semi-finished brass rod is obtained.

[0048] With this setup, 40% to 60% of the total cold drawing deformation significantly improves the alloy's strength, hardness, and dimensional accuracy through work hardening, allowing the brass rod to reach the required dimensions while also improving surface finish. The intermediate annealing after each drawing pass, using a temperature of 450 to 500°C and a holding time of 1 to 2 hours, effectively eliminates work hardening and residual internal stress generated during cold drawing, promotes partial recrystallization, restores the alloy's plasticity, and avoids defects such as cracks and fractures during subsequent drawing processes, ensuring the continuity of the cold drawing process. Natural cooling after annealing avoids thermal stress generated by rapid cooling, further improving the rod's machinability.

[0049] In some embodiments, in step S700, the semi-finished brass rod is subjected to low-temperature stress-relief annealing to obtain a finished free-cutting brass rod, including: placing the semi-finished brass rod in an annealing furnace, heating it to 250~300°C and holding it at that temperature for 2~4 hours, then slowly cooling it to room temperature with the furnace, and packaging it after it passes the finished product inspection to obtain the finished free-cutting brass rod.

[0050] This setup allows for low-temperature stress-relief annealing at 250-300℃, which, without altering the already formed strengthened microstructure and mechanical properties of the alloy, fully releases the residual internal stress generated during cold drawing. This effectively prevents deformation and cracking of the brass rods during subsequent processing or use, ensuring stable product dimensional accuracy. The 2-4 hour holding time provides ample time for stress release, guaranteeing the stress-relief effect. Slow furnace cooling avoids sudden temperature changes that could generate new thermal stress, further stabilizing the alloy microstructure. Finally, the finished product inspection ensures strict quality control, guaranteeing that the composition, machinability, mechanical properties, and appearance of the finished brass rods all meet the standard requirements.

[0051] The following description is based on specific embodiments.

[0052] Example 1 A free-machining brass bar continuously cast in an inert gas environment has the following chemical composition by weight percentage: Cu, 61.0 wt%; B4C, 0.1wt%; Bi, 0.7wt%; Pb, 0.05wt%; Total unavoidable impurities, 0.2 wt%; The balance is Zn.

[0053] The preparation method is as follows: 1) Weigh Cu, Zn, Bi, and B4C raw materials precisely according to the above chemical composition weight percentages. The purity of all raw materials shall not be less than 99.9%, and the total amount of unavoidable impurities shall be ≤0.3wt%. Mix them evenly and set aside. 2) The proportioned raw materials are put into the melting furnace of the vacuum horizontal continuous casting unit. After closing the furnace door, a vacuum is drawn to make the vacuum degree inside the furnace reach 0.001MPa and argon gas is introduced to the standard atmospheric pressure. Then, the temperature is heated to 1200℃ and held for 30 minutes to completely melt the raw materials. During this period, the material is stirred twice with a graphite rod for 5 minutes each time to ensure that the composition of the melt is uniform. At the same time, online degassing and slag removal treatment is carried out (using argon gas purging combined with graphite filtration) to remove gas and impurities from the melt. After heat treatment, copper alloy melt is obtained. 3) The qualified melt is introduced into the continuous casting mold. The mold adopts an oblique slit structure to ensure uniform magnetic field distribution. The temperature of the mold is controlled at 700℃ and the cooling rate is 100℃ / s. The "pull-stop-push" casting method is adopted. The continuous casting speed is 0.8m / min. During the continuous casting process, the pressure inside the furnace is kept stable at one atmosphere to obtain a casting bar with a diameter of 15mm. The length is controlled according to production requirements. 4) Ink-forming annealing: The cast rod is placed in an annealing furnace and heated to 900~1000℃ under the protection of reducing gas. It is held for 1~2 hours and then cooled to room temperature to allow B4C to release carbon and form fine carbon particles, which are dispersed in the copper matrix to improve machinability. 5) Finishing: The annealed casting rods are straightened, ground, and cut to ensure that the straightness of the rods is ≤0.5mm / m, and the surface oxide scale and defects are removed to obtain the preliminary finished product; 6) Finished product inspection and packaging: The finished bars are subjected to mechanical property testing, cutting performance testing, electrical conductivity testing and appearance inspection. The test results are as follows: tensile strength 505MPa, elongation 4.8%, hardness of hard alloy 152HV, electrical conductivity 20.5%IACS, cutting performance reaches the same index as leaded brass, no entanglement or damage to the cutting tool, and average cutting particle length 4.2mm. After passing the test, the bars are packaged to obtain the finished product. Example 2

[0054] A free-machining brass bar continuously cast in an inert gas environment has the following chemical composition by weight percentage: Cu, 62.0 wt%; B4C, 0.3wt%; Bi, 1.1 wt%; Pb, 0.07wt%; Total unavoidable impurities: 0.25 wt%; The balance is Zn.

[0055] The preparation method is as follows: 1) Raw material ratio: Weigh Cu, Zn, Bi and B4C raw materials accurately according to the above chemical composition weight percentages. The purity of all raw materials shall not be less than 99.9%, and the total amount of unavoidable impurities shall be ≤0.3wt%. Mix them evenly and set aside. 2) Inert gas environment smelting: The proportioned raw materials are put into the smelting furnace of the vacuum horizontal continuous casting unit. After the furnace door is closed, a vacuum is drawn to make the vacuum degree inside the furnace reach 0.003MPa and argon gas is introduced to the standard atmospheric pressure. Then, it is heated to 1240℃ and held for 45 minutes to completely melt the raw materials. During this period, the material is stirred three times with a graphite rod for 6 minutes each time to ensure that the composition of the melt is uniform. At the same time, online degassing and slag removal treatment is carried out (using argon gas purging combined with graphite filtration) to remove gases and impurities from the melt. 3) Horizontal continuous casting in an inert gas environment: The qualified melt is introduced into the continuous casting mold. The mold adopts an oblique slit structure to ensure uniform magnetic field distribution. The mold temperature is controlled at 740℃ and the cooling rate is 120℃ / s. The "pull-stop-push" casting method is adopted. The continuous casting speed is 1.2m / min. During the continuous casting process, the argon pressure in the furnace is kept stable at one atmosphere to obtain a casting bar with a diameter of 60mm. The length is controlled according to production requirements. 4) Ink-forming annealing: The cast rod is placed in an annealing furnace and heated to 900~1000℃ under the protection of reducing gas. It is held for 1~2 hours and then cooled to room temperature to allow B4C to release carbon and form fine carbon particles, which are dispersed in the copper matrix to improve machinability. 5) Finishing: The annealed casting rods are straightened, ground, and cut to ensure that the straightness of the rods is ≤0.5mm / m, and the surface oxide scale and defects are removed to obtain the preliminary finished product; 6) Finished product inspection and packaging: The finished bars are subjected to composition testing, mechanical property testing, cutting performance testing, electrical conductivity testing and appearance inspection. The test results are as follows: tensile strength 530MPa, elongation 5.2%, hard alloy hardness 160HV, electrical conductivity 22%IACS, cutting performance reaches the same index as leaded brass, cutting without tangling or damaging the tool, and the average length of the cut particles is 3.0mm. After passing the test, the bars are packaged to obtain the finished product. Example 3

[0056] A free-machining brass bar continuously cast in an inert gas environment has the following chemical composition by weight percentage: Cu, 63.0 wt% B4C, 0.5 wt% Bi, 1.5 wt%; Pb, 0.08 wt% Total unavoidable impurities: 0.3 wt%; The balance is Zn.

[0057] The preparation method is as follows: 1) Raw material ratio: Weigh Cu, Zn, Bi and B4C raw materials accurately according to the above chemical composition weight percentages. The purity of all raw materials shall not be less than 99.9%, and the total amount of unavoidable impurities shall be ≤0.3wt%. Mix them evenly and set aside. 2) Inert gas environment smelting: The proportioned raw materials are put into the smelting furnace of the vacuum horizontal continuous casting unit. After the furnace door is closed, a vacuum is drawn to make the vacuum degree inside the furnace reach 0.005MPa and argon gas is introduced to the standard atmospheric pressure. Then, it is heated to 1280℃ and held for 60 minutes to completely melt the raw materials. During this period, the material is stirred three times with a graphite rod for 8 minutes each time to ensure that the composition of the melt is uniform. At the same time, online degassing and slag removal treatment is carried out (using argon gas purging combined with graphite filtration) to remove gases and impurities from the melt. 3) Horizontal continuous casting in an inert gas environment: The qualified melt is introduced into the continuous casting mold. The mold adopts an oblique slit structure to ensure uniform magnetic field distribution. The mold temperature is controlled at 780℃ and the cooling rate is 150℃ / s. The "pull-stop-push" casting method is adopted. The continuous casting speed is 1.5m / min. During the continuous casting process, the pressure inside the furnace is kept stable at one atmosphere to obtain a casting bar with a diameter of 120mm. The length is controlled according to production requirements. 4) Ink-forming annealing: The cast rod is placed in an annealing furnace and heated to 900~1000℃ under the protection of reducing gas. It is held for 1~2 hours and then cooled to room temperature to allow B4C to release carbon and form fine carbon particles, which are dispersed in the copper matrix to improve machinability. 5) Finishing: The annealed casting rods are straightened, ground, and cut to ensure that the straightness of the rods is ≤0.5mm / m, and the surface oxide scale and defects are removed to obtain the preliminary finished product; 6) Finished product inspection and packaging: The finished bars are subjected to composition testing, mechanical property testing, cutting performance testing, electrical conductivity testing and appearance inspection. The test results are as follows: tensile strength 550MPa, elongation 4.6%, hard alloy hardness 165HV, electrical conductivity 21%IACS, cutting performance reaches the same index as leaded brass, cutting without tangling or damaging the tool, and the average length of the cut particles is 4.8mm. After passing the test, the bars are packaged to obtain the finished product.

[0058] A brass rod, with the following chemical composition by weight percentage: Cu, 61.0 wt% B4C, 0.1wt% Bi, 0.5 wt% (lower than the 0.7~1.5 wt% specified in claim 1); Pb, 0.05 wt% Total unavoidable impurities: 0.2 wt%; The balance is Zn.

[0059] The preparation method is completely consistent with that in Example 1.

[0060] Finished product test results: tensile strength 480MPa (<500MPa), elongation 4.3% (<4.5%), hardness of hard alloy 145HV (<150HV), electrical conductivity 20.2% IACS. Tool entanglement occurred during cutting, and the average length of the cut particles was 6.5mm (>5mm). The cutting performance did not meet the same standards as leaded brass and did not meet the stated performance indicators. Therefore, the product is unqualified.

[0061] A brass rod, with the following chemical composition by weight percentage: Cu, 62.0 wt% B4C, 0.3wt% Bi, 1.1 wt% Pb, 0.07 wt% Total unavoidable impurities: 0.25 wt%; The balance is Zn.

[0062] Preparation method: Except for the absence of the ink annealing step, the other steps (raw material ratio, vacuum melting, horizontal continuous casting in an inert gas environment, finishing treatment, finished product testing and packaging) are completely consistent with Example 2.

[0063] Finished product test results: tensile strength 510MPa, elongation 4.7%, hardness of hard alloy 155HV, electrical conductivity 21.8%IACS. Due to the lack of ink annealing, B4C did not release carbon particles, resulting in poor machinability. The cutting tool wore out severely during cutting, with an average cutting particle length of 5.8mm (>5mm). This does not meet the same machinability as leaded brass and does not conform to the stated performance indicators. Therefore, the product is unqualified.

[0064] A brass rod, with the following chemical composition by weight percentage: Cu, 63.0 wt% B4C, 0.5 wt% Bi, 1.5 wt%; Pb, 0.08 wt% Total unavoidable impurities: 0.3 wt%; The balance is Zn.

[0065] Preparation method: Except for the inert gas environment melting and horizontal continuous casting process, and the furnace vacuum degree controlled at 0.01MPa (higher than the limit of 0.001~0.005MPa), the other steps and parameters are completely consistent with those in Example 3.

[0066] Finished product test results: tensile strength 520MPa, elongation 4.5%, hardness of hard alloy 160HV, electrical conductivity 19.5%IACS (<20%IACS). Due to substandard vacuum, a small amount of air inclusions were present in the melt, resulting in micropores on the surface of the bar. Chipping occurred during the cutting process, and the length of the cut particles was uneven (2.1~6.2mm). These results do not meet the stated performance indicators, and the product is unqualified.

[0067] The mechanical properties (tensile strength, elongation), machinability (average cutting particle length), and hardness (HV) of the finished brass rods prepared in all the above embodiments and comparative examples were tested. The testing methods are as follows: 1. Tensile strength and elongation: tested using an electronic universal testing machine according to GB / T 228.1 standard; 2. Machining Performance: A CNC lathe was used for cutting tests. The cutting parameters were set as follows: cutting speed 100 m / min, feed rate 0.2 mm / r, depth of cut 1.0 mm, and a carbide-coated turning tool (model YT15). Cutting particles (chips) were collected during the cutting process. The chips were placed on a flat table, and their lengths were measured individually using calipers. At least 10 chip samples were randomly selected from each group for statistical analysis, and the arithmetic mean was taken as the average chip length (unit: mm) for the material. A shorter average chip length indicates better chip breaking performance and superior machinability. 3. Brinell hardness (HB): Tested using a Brinell hardness tester according to GB / T 231.1 standard.

[0068] The test results are shown in Table 1 below: Example 1 505 4.2 152 Example 2 530 3.0 160 Example 3 550 4.8 165 Comparative Example 1 480 6.5 145 Comparative Example 2 510 5.8 155 Comparative Example 3 520 2.1~6.2 (heterogeneous) 160 According to the test data in Table 1, the finished brass rods prepared by the free-cutting brass composition ratio and the horizontal continuous casting method in an inert gas environment of this application have a tensile strength of 505~550MPa, an average cutting particle length of 3.0mm~4.8mm, and a hardness (HV) of 152~165. All properties are well-balanced and excellent, and fully meet the performance indicators required for production.

[0069] Compared to the comparative examples, the brass rods prepared in this application have significant advantages: Comparative Example 1, with insufficient Bi content, failed to meet the standards for both machinability and mechanical properties; Comparative Example 2, which did not undergo ink annealing, failed to release carbon particles from B4C, resulting in poor machinability; and Comparative Example 3, with insufficient vacuum, had numerous inclusions in the melt, and the cutting particle length did not meet the requirements. This demonstrates that the core composition of 61.0~63.0 wt% Cu, 0.1~0.6 wt% B4C, and 0.7~1.5 wt% Bi specified in this application, combined with the complete process of inert gas environment melting, inert gas environment horizontal continuous casting, ink annealing, and finishing, can achieve synergistic optimization of machinability and mechanical properties while maintaining environmental friendliness, meeting the stringent requirements of the electronics, electrical, and precision machinery industries for high-precision, high-performance brass rods.

[0070] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A horizontally continuously cast free-machining brass bar, characterized in that, By weight percentage, it consists of the following components composition: Cu, 61.0~63.0 wt% B4C, 0.1~0.6wt%; Bi, 0.7~1.5wt%; Pb, ≤0.08wt%; Total unavoidable impurities ≤0.3wt%; The balance is Zn; The performance indicators of the free-cutting brass rod are as follows: tensile strength ≥500MPa, elongation ≥4.5%, hardness of hard alloy ≥150HV, electrical conductivity ≥20%IACS, cutting performance equal to that of leaded brass, no entanglement or damage to the cutting tool, and cutting particle length ≤5mm.

2. A method for preparing a horizontally continuously cast free-machining brass bar, characterized in that, Includes the following steps: Step 1 Raw material ratio: Weigh Cu, Zn, Bi and B4C raw materials accurately according to the above weight percentages. The purity of the raw materials is not less than 99.9%, and ensure that the total amount of unavoidable impurities is ≤0.3wt%. Mix them evenly and set aside. Step 2 Inert Gas Melting: The proportioned raw materials are put into the melting furnace of the horizontal continuous casting unit. After closing the furnace door, a vacuum is drawn to make the vacuum degree inside the furnace reach 0.001~0.005 MPa. Inert gas is introduced to near atmospheric pressure and heated under constant pressure until the raw materials are completely melted. Then, the mixture is stirred 2~3 times with a graphite rod, each time for 5~8 minutes, to ensure that the composition of the melt is uniform. During the process, inert gas is continuously introduced for online degassing and slag removal. The residual oxygen and volatile gas impurities in the melt and furnace are removed through a one-way valve. Step 3: Horizontal continuous casting in an inert gas environment: The qualified melt is introduced into the continuous casting crystallizer. The crystallizer adopts an oblique slit structure to ensure uniform magnetic field distribution. The crystallizer temperature is controlled at 700~780℃, the cooling rate is ≥100℃ / s, and the "pull-stop-push" casting method is adopted. The continuous casting speed is 0.8~1.5 m / min. During the continuous casting process, the argon gas in the furnace is kept stable at atmospheric pressure. The diameter of the casting rod is 12~120mm, and the length is controlled according to production requirements. Step 4: Inkling Annealing: Place the cast rod into an annealing furnace, heat it to 900~1000℃ under the protection of reducing gas, hold it for 1~2 hours, and then cool it to room temperature to allow B4C to release carbon and form fine carbon particles, which are dispersed in the copper matrix to improve machinability. Step 5 Finishing: Straighten, grind, and cut the annealed casting rod to ensure that the straightness of the rod is ≤0.5mm / m, remove the surface oxide scale and defects, and obtain the preliminary finished product; Step 6: Finished Product Inspection and Packaging: The finished bars are subjected to composition testing, mechanical property testing, cutting performance testing, electrical conductivity testing, and appearance inspection to ensure that the product meets the performance indicators. After passing the inspection, the product is packaged to obtain the finished free-cutting brass bars.

3. The preparation method according to claim 2, characterized in that, In step 1, the raw materials are weighed using an electronic balance with a weighing accuracy of ±0.01g. The mixing is done using mechanical stirring at a speed of 200-300r / min for 10-15min to ensure uniform mixing of the raw materials.

4. The preparation method according to claim 2, characterized in that, In step 2, the inert gas smelting adopts a hydraulic tilting smelting furnace, the heating method is medium frequency induction heating, and the degassing and slag removal adopts the method of inert gas purging combined with graphite filtration. Argon is selected as the inert gas, and the purging flow rate is 5~10 L / min.

5. The preparation method according to claim 2, characterized in that, In step 3, the crystallizer adopts a two-section structure. The upper section is made of high-permeability magnetic copper alloy, and the lower section is made of high-thermal-conductivity copper alloy. A water cooling system is installed outside the crystallizer, and the cooling water is deionized water with the water temperature controlled at 20~30℃.

6. The preparation method according to claim 2, characterized in that, In step 3, during the continuous casting process, a servo motor is used to drive the traction mechanism, and the traction accuracy is controlled within ±0.02mm to ensure that the casting rod is uniform in size and free from vibration marks and cracks on the surface.

7. The preparation method according to claim 2, characterized in that, In step 4, the reducing gas is hydrogen, and the gas flow rate is 0.5~1.0 L / min. The fine carbon particles formed after ink annealing have a particle size of 1~5 μm and are dispersed in the copper matrix.

8. The preparation method according to claim 2, characterized in that, The specific testing items in step 6 include: mechanical property testing, including tensile strength, elongation, and hardness testing; and cutting performance testing, including cutting particle length measurement and tool wear observation.

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