Process for improving tin segregation in copper-nickel-tin alloy rods

Abstract

The application discloses a process method for improving tin segregation of copper-nickel-tin alloy rod, relates to the field of non-ferrous metal smelting and processing technology, and the mass percentage composition of the copper-nickel-tin alloy is as follows: Ni 3.5%-15.5%, Sn 1.8%-8.5%, Ti 0.08%-0.3%, and the balance is Cu and inevitable impurities; and the preparation method comprises the following steps: after raw materials are melted, copper-titanium intermediate alloy is added to perform intermittent stop-pulling casting to obtain a cast ingot; a car body is sequentially subjected to axial microforging, first-stage two-level homogenizing annealing, forging and second-stage two-level homogenizing annealing; and finally, the cast ingot is sent into a preheated extruding machine to perform extrusion, so as to obtain a copper-nickel-tin alloy extruded rod. The copper-nickel-tin alloy extruded rod produced by adopting the process method has uniform end surface composition, and the tin content difference from the edge to the center of the end surface is not more than 0.3wt%; and the rod has uniform and dense structure.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting and processing technology, and in particular to a process method for improving tin segregation in copper-nickel-tin alloy rods. Background Technology

[0002] With the rapid development of key sectors and increasingly demanding service conditions, the demand for copper alloy components in terms of "high load-bearing capacity, high stability, and high strength" is increasing. Copper-nickel-tin alloys, due to their high strength and elasticity, good resistance to stress relaxation, and excellent wear and corrosion resistance, have become copper alloy structural materials with significant application value in the fields of friction reduction and wear resistance. From their initial application in elastic elements in precision instruments and the electrical industry, they have gradually expanded to applications in aircraft landing gear, heavy-duty engineering machinery, and other fields, including friction-reducing and wear-resistant bearing bushings, as well as key structural components in oil drilling.

[0003] However, due to the presence of low-melting-point tin (Sn), copper-nickel-tin alloys have a wide crystallization temperature range, leading to macroscopic anti-segregation and microscopic dendritic segregation of Sn during solidification. In regions with severe segregation, such as grain boundaries, coarse, brittle low-melting-point eutectic phases form. During subsequent hot working, these brittle phases at the grain boundaries melt or crack, becoming stress concentration crack initiation points, severely degrading the alloy's hot working plasticity and final toughness, resulting in a decline in overall material properties and a low yield rate in industrial production. These problems have become bottlenecks restricting the manufacturing and widespread application of this alloy. Therefore, achieving homogeneous control of the alloy composition is fundamental to obtaining copper-nickel-tin alloys that possess both high strength and excellent plasticity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a process method to improve tin segregation in copper-nickel-tin alloy rods, which can effectively reduce tin segregation during solidification and produce copper-nickel-tin alloy rods with more uniform composition.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a process method for improving tin segregation in copper-nickel-tin alloy rods, wherein the mass percentage composition of the copper-nickel-tin alloy is Ni 3.5%~15.5%, Sn 1.8%~8.5%, Ti 0.08%~0.3%, and the balance is Cu and unavoidable impurities; The preparation steps include the following: S1. After melting the required raw materials, add copper-titanium master alloy and cast to obtain an ingot; S2. The ingot obtained in S1 is surface-machined and micro-forged along the ingot axis to further reduce the ingot diameter by 2~6mm, forming a pre-deformed layer on the surface of the ingot. S3. The ingot after S2 micro-forging is subjected to the first homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours; the second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S4. The ingot after the first homogenization annealing in S3 is subjected to three-stage forging, with the deformation amount controlled at 5%~20% for each stage. S5. The ingot forged in S4 is subjected to a second homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours. The second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S6. The ingot after the second homogenization annealing in S5 is fed into a preheated extruder for extrusion at a speed of 1~10mm / s to finally obtain copper-nickel-tin alloy extruded bars.

[0006] In step S2, the formation of a pre-deformed layer on the surface of the ingot works synergistically with the first homogenization annealing in step S3, giving the tin atoms in the pre-deformed layer greater diffusion motive force. During the first homogenization annealing process, the tin atoms diffuse into the interior of the ingot, thereby achieving the homogenization of the overall tin content of the ingot.

[0007] In step S3, the first stage of homogenization annealing is a low-temperature, long-time annealing. This eliminates the processing stress generated by the micro-forging in step S2 while gradually dissolving the tin-rich, low-melting-point eutectic at the grain boundaries, achieving solid-state diffusion of tin and avoiding grain boundary overheating, liquefaction, and grain growth caused by direct high-temperature, long-time heating. The second stage of annealing is a high-temperature, short-time annealing, accelerating the bulk diffusion of nickel and tin atoms and further improving tin segregation and the high-temperature properties of the alloy. The first homogenization annealing can control the number of coarse grains and improve the uniformity of the microstructure, ensuring smooth forging and improving the uniformity of the alloy's properties.

[0008] In step S4, a three-stage forging process is used. During the forging process, the ingot deforms in different directions, which promotes the uniform diffusion of tin elements during the deformation process.

[0009] The second homogenization annealing before extrusion still uses the same stepped two-stage annealing process. With the support of forging deformation, the tin element obtains stronger diffusion power, thereby extruding a more uniform bar.

[0010] Further, in step S1, the specific steps for adding the copper-titanium master alloy are as follows: 0.08% to 0.3% of the total weight of the copper liquid is added 15 to 20 minutes before casting; the casting adopts an intermittent stop-casting process, specifically, the casting is carried out in an alternating casting method with a stop time of 3 seconds and a casting time of 3 seconds, and the casting temperature is 1200℃ to 1380℃.

[0011] When copper-nickel-tin raw materials are smelted, 0.08% to 0.3% trace amounts of titanium are added. Titanium and nickel form the Ni3Ti phase. This phase acts as a strong nucleation point, which can refine the casting grains and thus reduce tin segregation during solidification. At the same time, the Ni3Ti phase does not dissolve during solid solution, which can effectively suppress discontinuous precipitation (DP). Through grain boundary pinning, it refines the grains and improves the strength and toughness of the material.

[0012] When the casting process is stopped, there is no relative movement between the ingot and the crystallizer. The first cooling causes the thickness of the solidified shell to increase rapidly, and the alloy crystallization speed is accelerated, thereby reducing the flow of low-melting-point tin to the surface. When the casting process is started, the solidified shell quickly leaves the crystallizer wall and moves downward. This sudden movement causes the melt to vibrate slightly, which promotes the redistribution of alloying elements in the micro-region, which helps to reduce tin segregation and promote compositional uniformity.

[0013] Furthermore, in step S2, the amount of the surface skin is 2~6mm.

[0014] Furthermore, in step S6, the extruder is preheated before extrusion, wherein the preheating temperature of the extrusion die and extrusion pad is 300℃~400℃, and the preheating temperature of the extrusion cylinder is 380℃~450℃.

[0015] Further, in step S6, after extrusion by the extruder, 300-500mm is cut off from the tail of the extruded bar and 100-200mm is cut off from the head; the bar after cutting off the head and tail is pickled to remove the surface oxide scale.

[0016] Furthermore, the deviation of the Sn element content from the edge to the center of the end face of the copper-nickel-tin alloy rod does not exceed 0.3wt%.

[0017] According to the above technical solution, the beneficial effects of the present invention are: This invention employs a "titanium grain refinement and stop casting" method to reduce tin segregation during solidification. Before bar extrusion, the ingot undergoes a series of processes: "ingot finishing, micro-forging, first homogenization annealing, forging, and second homogenization annealing" to homogenize the tin content. Specifically, the micro-forging before the first step-homogenization annealing significantly homogenizes the high tin content near the ingot surface. The two step-homogenization annealing processes ensure homogenization while maintaining fine alloy grains, thus improving alloy performance.

[0018] The bars produced using the above process have uniform end-face composition, with the tin content difference from the edge to the center of the end face not exceeding 0.3 wt%; the bar structure is uniform and dense. The machining process reduces the introduction of ingot surface defects into the extruded bars, and the homogenization annealing and forging processes further eliminate microscopic defects in the as-cast state, resulting in good performance consistency between the edge and center of the bar. Attached Figure Description

[0019] Figure 1 This is a high-magnification microstructure image of the end face edge of the copper-nickel-tin alloy rod prepared according to the present invention; Figure 2 This is a high-magnification microstructure image of the center of the end face of the copper-nickel-tin alloy rod prepared according to the present invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] A process for improving tin segregation in copper-nickel-tin alloy rods, wherein the mass percentage composition of the copper-nickel-tin alloy is Ni 3.5%~15.5%, Sn 1.8%~8.5%, Ti 0.08%~0.3%, with the balance being Cu and unavoidable impurities; The preparation steps include the following: S1. After melting the required raw materials, add 0.08%~0.3% of copper-titanium master alloy by weight of the copper liquid, and then cast the ingot. The casting adopts an intermittent stop casting process with alternating casting times of 3 seconds and 3 seconds, and the casting temperature is 1200℃~1380℃. It should be noted that the copper-titanium master alloy is added 15~20 minutes before casting.

[0022] S2. The ingot obtained in S1 is surface-machined with a machining allowance of 2-6 mm. Then, it is micro-forged along the ingot axis to further reduce the ingot diameter by 2-6 mm, forming a pre-deformed layer on the ingot surface. S3. The ingot after S2 micro-forging is subjected to the first homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours; the second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S4. The ingot after the first homogenization annealing in S3 is subjected to three-stage forging, with the deformation amount controlled at 5%~20% for each stage. S5. The ingot forged in S4 is subjected to a second homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours. The second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S6. The ingot after the second homogenization annealing in S5 is fed into a preheated extruder for extrusion at a speed of 1~10 mm / s. Specifically, the extruder is preheated before extrusion, with the extrusion die and extrusion pad preheated at 300℃~400℃ and the extrusion cylinder preheated at 380℃~450℃. After extrusion, 300~500 mm is cut off the tail of the extruded bar and 100~200 mm is cut off the head. The bar after head and tail removal is pickled to remove the surface oxide scale, and finally copper-nickel-tin alloy extruded bar is obtained.

[0023] The Sn content in the copper-nickel-tin alloy rod produced by the process of this invention has a deviation of no more than 0.3 wt% from the edge to the center of the end face. See the high-magnification microstructure image. Figure 1-2 .

[0024] Example 1: Preparation of C72700 alloy rods with a diameter of 60mm. The mass percentage composition of copper, nickel and tin is Ni 8.5%~9.5%, Sn 5.5%~6.5%, Ti 0.09%, with the balance being Cu and unavoidable impurities.

[0025] The preparation steps are as follows: S1. Add a certain proportion of electrolytic copper plates and nickel plates to the melting furnace, heat to melt the electrolytic copper plates, then add pure tin. After melting, adjust the composition to the qualified range. Add copper-titanium master alloy 15-20 minutes before casting to obtain the melt. Flow the melt into the crystallizer for casting, using an intermittent stop-start casting process. This casting process is an alternating casting method with a stop-start time of 3 seconds and a casting time of 3 seconds. The casting temperature is 1200℃~1280℃ to obtain the ingot. S2. After sawing the ingot obtained in S1 to the specified length, surface finishing is performed. The finishing amount is 2.5mm. After finishing, micro-forging is performed along the ingot axis on a forging machine to further reduce the ingot diameter by 2mm, forming a pre-deformed layer on the ingot surface. S3. The ingot after S2 micro-forging is sent into a heating furnace for the first homogenization annealing. A two-stage stepped annealing process is adopted. The first annealing temperature is 800℃ and the holding time is 8 hours. The second annealing temperature is 860℃ and the holding time is 3 hours. S4. The ingot after the first homogenization annealing in S3 is subjected to three-stage forging with three pulls. The deformation amount of each pull is controlled between 5% and 8.4%, with an average of 5.6%. S5. The ingot forged in S4 is subjected to a second homogenization annealing process using a stepped two-stage annealing process. The first stage annealing temperature is 800℃ and the holding time is 8 hours; the second stage annealing temperature is 860℃ and the holding time is 3 hours. S6. The ingot after the second homogenization annealing in S5 is fed into a preheated extruder for extrusion at a speed of 5 mm / s. The extruder is preheated before extrusion, with the extrusion die and extrusion pad preheated at 354℃ and the extrusion cylinder preheated at 388℃. After extrusion, 300 mm is cut off from the tail and 150 mm is cut off from the head of the extruded bar. The bar after head and tail removal is pickled to remove the surface oxide scale, and finally copper-nickel-tin alloy extruded bar is obtained.

[0026] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 5.76 wt%, while the Sn content at the center was 5.64 wt%, with a difference of 0.12 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0027] Example 2: Preparation of C72900 alloy rods with a diameter of Φ70mm. The mass percentage composition of copper, nickel and tin is Ni 14.5%~15.5%, Sn 7.5%~8.5%, Ti 0.2%, with the balance being Cu and unavoidable impurities.

[0028] The preparation steps are as follows: S1. Add a certain proportion of electrolytic copper plates and nickel plates to the melting furnace, heat to melt the electrolytic copper plates, then add pure tin. After melting, adjust the composition to the qualified range. Add copper-titanium master alloy 15-20 minutes before casting to obtain the melt. Flow the melt into the crystallizer for casting, using an intermittent stop-start casting process. This casting process is an alternating casting method with a stop-start time of 3 seconds and a casting time of 3 seconds. The casting temperature is 1278℃~1350℃ to obtain the ingot. S2. After sawing the ingot obtained in S1 to the specified length, surface finishing is performed with a finishing allowance of 5mm. After finishing, the ingot is micro-forged along the ingot axis on a forging machine to further reduce the ingot diameter by 4mm, forming a pre-deformed layer on the ingot surface. S3. The ingot after S2 micro-forging is sent into a heating furnace for the first homogenization annealing. A two-stage stepped annealing process is adopted. The first stage annealing temperature is 820℃ and the holding time is 6 hours. The second stage annealing temperature is 860℃ and the holding time is 3 hours. S4. The ingot after the first homogenization annealing in S3 is subjected to three-stage forging with three pulls. The deformation amount of each pull is controlled at 8%~15%, with an average of 12.3%. S5. The ingot forged in S4 is subjected to a second homogenization annealing process using a stepped two-stage annealing process. The first stage annealing temperature is 820℃ and the holding time is 6 hours; the second stage annealing temperature is 860℃ and the holding time is 3 hours. S6. The ingot after the second homogenization annealing in S5 is fed into a preheated extruder for extrusion at a speed of 5 mm / s. The extruder is preheated before extrusion, with the extrusion die and extrusion pad preheated to 360℃ and the extrusion cylinder preheated to 408℃. After extrusion, 300 mm is cut off from the tail and 150 mm is cut off from the head of the extruded bar. The bar after head and tail removal is pickled to remove the surface oxide scale, and finally copper-nickel-tin alloy extruded bar is obtained.

[0029] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 7.71 wt%, while the Sn content at the center was 7.48 wt%, with a difference of 0.23 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0030] Example 3: C72900 alloy rods with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 14.5%~15.5%, Sn 7.5%~8.5%, Ti 0.17%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.17% of the total weight of the molten copper; the ingot diameter was further reduced by 3.5mm through micro-forging; the two-stage stepped annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 820℃, held for 5 hours; the second stage annealing temperature was 850℃, held for 3 hours; the ingot after the first homogenization annealing was subjected to three-stage forging with the deformation controlled at 14%~22% each time, with an average of 19.1%.

[0031] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 8.11 wt%, while the Sn content at the center was 7.96 wt%, with a difference of 0.15 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0032] Example 4: Preparation of C72900 alloy bars with a diameter of Φ70mm. The mass percentage composition of copper, nickel, and tin was Ni 14.5%~15.5%, Sn 7.5%~8.5%, Ti 0.3%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.3% of the total weight of the molten copper; the surface finishing was 4mm; the ingot diameter was further reduced by 6mm through micro-forging; the two-stage stepped annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 810℃, held for 7.5 hours; the second stage annealing temperature was 830℃, held for 3 hours; the ingot after the first homogenization annealing was subjected to three-stage forging with the deformation controlled at 11%~19.3% each time, with an average of 18.0%.

[0033] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 7.98 wt%, while the Sn content at the center was 7.77 wt%, with a difference of 0.21 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0034] Example 5: Preparation of C72600 alloy bars with a diameter of Φ70mm. The mass percentage composition of copper, nickel, and tin was Ni 3.5%~4.5%, Sn 3.5%~4.5%, Ti 0.12%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.12% of the total weight of the molten copper; the surface finishing thickness was 2.5mm; the ingot diameter was further reduced by 5mm through micro-forging; the two-stage stepped annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 820℃, held for 3 hours; the second stage annealing temperature was 850℃, held for 1 hour; the ingot after the first homogenization annealing was subjected to three-stage forging with the deformation controlled at 8%~12% each time, with an average of 9.5%.

[0035] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 3.86 wt%, and the Sn content at the center was 3.80 wt%, with a difference of 0.06 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0036] Example 6: Preparation of C72500 alloy bars with a diameter of Φ65mm. The mass percentage composition of copper, nickel, and tin was Ni 8.5%~10.5%, Sn 1.8%~2.8%, Ti 0.08%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.08% of the total weight of the molten copper; the surface finishing was 5mm; the ingot diameter was further reduced by 2.8mm through micro-forging; the two-stage stepped annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 820℃, held for 3.5 hours; the second stage annealing temperature was 840℃, held for 2.5 hours; the ingot after the first homogenization annealing was subjected to three-stage forging with the deformation controlled at 11%~18.3% each time, with an average of 15.6%.

[0037] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 2.43 wt%, while the Sn content at the center was 2.38 wt%, with a difference of 0.05 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0038] Comparative Example 1: C72500 alloy bars with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 8.5%~10.5%, Sn 1.8%~2.8%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: no copper-titanium master alloy was added, i.e., the amount of copper-titanium master alloy added was 0; continuous casting was used for casting; the ingots were not subjected to machining or micro-forging, but were subjected to a single homogenization annealing. The first annealing temperature was 800℃, held for 8 hours; the second annealing temperature was 860℃, held for 3 hours, and then fed into an extruder for extrusion.

[0039] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 2.12 wt%, while the Sn content at the center was 1.78 wt%, with a difference of 0.34 wt%. Tissue density test: Flaws were found to be loose.

[0040] Comparative Example 2: C72900 alloy bars with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 14.5%~15.5%, Sn 7.5%~8.5%, Ti 0.17%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.17% of the total weight of the molten copper; the ingot surface was not machined; the ingot diameter was further reduced by 5mm through micro-forging; the stepped two-stage annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 810℃, held for 8 hours; the second stage annealing temperature was 830℃, held for 3 hours; the ingot after the first homogenization annealing was subjected to three-stage forging with the deformation controlled at 18%~20% for each stage, with an average of 19.7%.

[0041] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 7.89 wt%, while the Sn content at the center was 7.45 wt%, with a difference of 0.44 wt%. Organizational density test: Defects on the surface of the ingot were introduced into the alloy bar. After flaw detection, the tail of the bar was twice as long as normal; there were no internal defects.

[0042] Comparative Example 3: C72900 alloy bars with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 14.5%~15.5%, Sn 7.5%~8.5%, Ti 0.12%, with the balance being Cu and unavoidable impurities. The preparation steps were roughly the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.12% of the total weight of the copper liquid; the surface finishing layer was 5mm thick, followed by two-stage stepped annealing processes without micro-forging. The first-stage annealing temperature was 820℃, held for 3 hours; the second-stage annealing temperature was 860℃, held for 3 hours; the ingot after the first homogenization annealing was subjected to three-stage forging, with the deformation amount of each forging controlled at 12%~18.2%, averaging 15.9%.

[0043] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 8.26 wt%, while the Sn content at the center was 7.69 wt%, with a difference of 0.57 wt%. Organizational density test: No material defects such as porosity were found during flaw detection.

[0044] Comparative Example 4: C72900 alloy bars with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 14.5%~15.5%, Sn 7.5%~8.5%, with the balance being Cu and unavoidable impurities. The preparation steps were roughly the same as in Example 2, except that: no copper-titanium master alloy was added, i.e., the amount of copper-titanium master alloy added was 0; continuous casting was used for casting; the surface finishing layer was 4.5mm; the ingot diameter was further reduced by 3.5mm through micro-forging; the stepped two-stage annealing process after micro-forging and before extrusion was as follows: the first stage annealing temperature was 820℃, held for 3 hours; the second stage annealing temperature was 860℃, held for 3 hours; the ingot after the first homogenization annealing was subjected to three-stage forging, with the deformation amount of each stage controlled at 8.3%~16.0%, with an average of 10.7%.

[0045] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 7.90 wt%, while the Sn content at the center was 7.56 wt%, with a difference of 0.34 wt%. Organizational density test: No casting defects such as porosity or looseness were found during flaw detection.

[0046] Comparative Example 5: C72600 alloy rods with a diameter of Φ70mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 3.5%~4.5%, Sn 3.5%~4.5%, Ti 0.12%, with the balance being Cu and unavoidable impurities. The preparation steps were largely the same as in Example 2, except that: the amount of copper-titanium master alloy added accounted for 0.12% of the total weight of the molten copper; the surface finishing layer was 5mm; the ingot diameter was further reduced by 5mm through micro-forging; and after micro-forging, the ingot was subjected to heated extrusion at a temperature of 860℃ for 8 hours.

[0047] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 4.12 wt%, while the Sn content at the center was 3.71 wt%, with a difference of 0.41 wt%. Tissue density test: Minor porosity defects were found during flaw detection.

[0048] Comparative Example 6: C72700 alloy bars with a diameter of Φ60mm were prepared. The mass percentage composition of copper, nickel, and tin was Ni 8.5%~9.5%, Sn 5.5%~6.5%, Ti 0.21%, with the balance being Cu and unavoidable impurities. The preparation steps were roughly the same as in Example 1, except that: the amount of copper-titanium master alloy added accounted for 0.21% of the total weight of copper liquid; the surface finishing was 3mm; the ingot diameter was further reduced by 4mm through micro-forging; the stepped two-stage annealing process after micro-forging was as follows: the first stage annealing temperature was 780℃, held for 8 hours; the second stage annealing temperature was 850℃, held for 3 hours; then the ingot was cast using a three-stage forging process, with the deformation amount of each stage controlled at 5%~7.5%, averaging 6.8%; pre-extrusion heating was performed at 860℃ for 4 hours.

[0049] The obtained copper-nickel-tin alloy extruded bars were subjected to a series of tests, including composition, performance, and flaw detection. The test results are as follows: Sn segregation detection in alloy composition: Compositional analysis was performed on the end face of the alloy bar. The Sn content at the edge was 6.32 wt%, while the Sn content at the center was 5.93 wt%, with a difference of 0.39 wt%. Organizational density test: No casting defects such as porosity or looseness were found during flaw detection.

[0050] Table 1. Flaw detection defects and microstructure characteristics of ingots in embodiments and comparative examples of the present invention. Table 1 shows the defects and microstructure characteristics of the ingots in Examples 1-6 and Comparative Examples 1-6 of this invention. As shown in Table 1, adding trace amounts of titanium during the casting process and employing an intermittent stop-casting process effectively reduced tin segregation during solidification. Before hot extrusion, the ingots were sequentially subjected to machining (removing the high-tin surface layer and defects), micro-forging, a first two-stage stepped annealing process, forging, and a second two-stage stepped annealing process, allowing tin to diffuse sufficiently and significantly improving tin segregation. The copper-nickel-tin rods prepared using the above process exhibited uniform end-face composition, with a tin content difference from the edge to the center not exceeding 0.3 wt%, and a dense and uniform microstructure.

[0051] In Comparative Example 1, although the C72500 bar directly extruded from the ingot had a low tin content (1.8-2.8%), the segregation problem was still quite prominent due to severe tin segregation in the ingot and only one homogenization annealing. In Comparative Example 2, the C72900 ingot was not machined, and the high-tin segregation layer on the surface was not removed. Despite two homogenization annealing treatments, the diffusion effect was limited, and the segregation on the end face of the bar was still obvious. Furthermore, due to surface defects, the extruded bar showed abnormal tail length during flaw detection. In Comparative Example 3, the C72900 ingot was not micro-forged before homogenization, resulting in insufficient atomic diffusion motive force, which significantly weakened the segregation improvement effect. In Comparative Example 4, no titanium was added during the C72900 ingot casting process, and continuous casting was used. The ingot grains were coarse, and tin segregation was aggravated. The effects of subsequent machined casting and homogenization annealing treatments were weakened, and the segregation improvement effect was not as good as the examples. In Comparative Example 5, the C72600 ingot only underwent machining and micro-forging, but did not undergo homogenization annealing after micro-forging. Direct high-temperature heating was used before extrusion, which improved tin homogenization to some extent, but was far from ideal. In Comparative Example 6, the C72700 ingot had a high titanium content, which made the material harder. In addition, the homogenization annealing temperature before forging was too low, resulting in slow tin diffusion. Direct high-temperature heating was used before extrusion, leading to grain inhomogeneity and unsatisfactory segregation improvement.

[0052] In summary, the preparation method of the present invention is feasible for improving the uniformity of tin composition in copper-nickel-tin rods.

[0053] It should be noted that the above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A process for improving tin segregation in copper-nickel-tin alloy rod, characterized by: The copper-nickel-tin composition by mass percentage is Ni 3.5%~15.5%, Sn 1.8%~8.5%, Ti 0.08%~0.3%, with the balance being Cu and unavoidable impurities; The preparation steps include the following: S1. After melting the required raw materials, add copper-titanium master alloy and cast to obtain an ingot; wherein, the casting adopts an intermittent stop-start casting process, specifically, the casting stop time is 3 seconds and the casting time is 3 seconds, and the casting temperature is 1200℃~1380℃. S2. The ingot obtained in S1 is surface-machined and micro-forged along the ingot axis to further reduce the ingot diameter by 2~6mm and form a pre-deformed layer on the surface of the ingot. S3. The ingot after S2 micro-forging is subjected to the first homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours; the second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S4. The ingot after the first homogenization annealing in S3 is subjected to three-stage forging, with the deformation amount controlled at 5%~20% for each stage. S5. The ingot forged in S4 is subjected to a second homogenization annealing. The homogenization annealing adopts a two-stage stepped annealing process. The first stage annealing temperature is 800℃~820℃, and the holding time is 3~8 hours. The second stage annealing temperature is 830℃~860℃, and the holding time is 1~3 hours. S6. The ingot after the second homogenization annealing in S5 is fed into a preheated extrusion press for extrusion at a speed of 1~10mm / s to finally obtain copper-nickel-tin alloy extruded bars. The extrusion press is preheated before extrusion, with the extrusion die and extrusion pad preheated at 300℃~400℃ and the extrusion cylinder preheated at 380℃~450℃. The deviation of the Sn element content from the edge to the center of the end face of the copper-nickel-tin alloy rod shall not exceed 0.3 wt%.

2. The process for improving tin segregation in copper nickel tin alloy rod as claimed in claim 1 wherein: In step S1, the specific steps for adding the copper-titanium master alloy are as follows: 0.015% to 0.2% of the total weight of the copper liquid is added 15 to 20 minutes before casting.

3. The process method for improving tin segregation in copper-nickel-tin alloy rods according to claim 1, characterized in that: In step S2, the thickness of the surface skin is 2~6mm.

4. The process for improving tin segregation in copper-nickel-tin alloy rods according to claim 1, characterized in that: In step S6, after extrusion by the extruder, 300-500mm is cut off from the tail of the extruded bar and 100-200mm is cut off from the head; the bar after head and tail removal is pickled to remove the surface oxide scale.

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