A copper alloy bar and a preparation method thereof

Abstract

The present invention discloses a copper alloy bar, which is characterized in that: the mass percentage composition of the copper alloy is Si: 4.0 - 4.5 wt%, Ni: 16 - 18 wt%, Mn: 3.0 - 4.0 wt%, Fe: 0.1 - 0.3 wt%, and the balance is Cu and inevitable impurities. By adding Si, Ni, Mn, and Fe to the copper matrix and controlling the addition amounts of Si, Ni, Mn, and Fe, the average grain size is 0.015 - 0.01 mm. Through solution strengthening and aging strengthening, the tensile strength of the copper alloy is finally ≥650 MPa, the high-temperature softening resistance temperature is ≥650 °C, the friction coefficient is 0.12 - 0.15, the corrosion-resistant weight loss is ≤1.2 mg / cm2, and the fatigue strength is ≥360 MPa. While meeting the mechanical property requirements of the bearing cage, it has good cold working performance and can withstand complex stamping deformation.

Description

Technical Field

[0001] The present invention belongs to the technical field of copper alloys, and particularly relates to a copper alloy bar and a preparation method thereof. Background Art

[0002] When a rolling bearing is working, especially when the load is complex and it rotates at a high speed, the bearing cage has to bear a great centrifugal force, impact and vibration. There is a large sliding friction between the cage and the rolling elements, and a large amount of heat is generated. The combined action of force and heat will cause cage failure. In severe cases, it will cause cage burning and fracture, resulting in the abnormal operation of the bearing. Therefore, it is required that the material of the cage has a certain strength, and also needs to meet the requirements of high temperature resistance, small friction coefficient, good wear resistance and high impact toughness. In addition, since the cage is formed by stamping and undergoes complex stamping deformation, it is also required that the material has good cold working properties.

[0003] Silicon bronze (QSi1-3) is a traditional material used to manufacture bearing cages. Its tensile strength is about 490 MPa and its elongation is about 10%. It has certain wear resistance, high temperature resistance and fatigue resistance. Since the heat treatment phase region range of silicon bronze is relatively narrow, the process parameters such as extrusion temperature and speed are relatively demanding. If the extrusion parameters do not match well, microcracks are likely to appear after extrusion. Therefore, the current domestic production process is horizontal continuous casting → wire drawing → pickling → drawing → hot forging. The advantages are that the process flow is relatively short. The disadvantages are: 1. If hot forging is not carried out, the properties of the material itself cannot meet the requirements of the strength, wear resistance, corrosion resistance and other properties of the bearing cage in high-end fields. 2. Hot forging requires heating the material to a temperature above the recrystallization temperature for forging. During the forging process, grain growth is likely to occur, and there is a large difference in the grain size between the middle part and the edge part of the material. The grain structure at the edge is coarse, resulting in non-uniform properties of the material. When preparing the bearing cage subsequently, due to the coarse and non-uniform grain structure, it is easy to crack after long-term use. 3. Its upsetting ratio of the forging billet is also small, the forging efficiency is low, and the dimensional accuracy of the material after hot forging is not high. Summary of the Invention

[0004] The first technical problem to be solved by the present invention is to provide a copper alloy bar with excellent comprehensive properties such as strength, plasticity, high temperature softening resistance, fatigue resistance, wear resistance, etc. and stable properties.

[0005] The second technical problem to be solved by the present invention is to provide a preparation method of the copper alloy bar.

[0006] The technical solution adopted by the present invention to solve the first technical problem is: a copper alloy bar, characterized in that the mass percentage composition of the copper alloy is: Si: 4.0 - 4.5 wt%, Ni: 16 - 18 wt%, Mn: 3.0 - 4.0 wt%, Fe: 0.1 - 0.3 wt%, and the balance is Cu and unavoidable impurities.

[0007] The present invention adds 16-18 wt% of Ni. By introducing the Ni element, the α solid solution is further strengthened, improving the corrosion resistance, high-temperature resistance, ductility, tensile strength, and fatigue resistance of the alloy, etc. If the Ni content is less than 16%, more Mn 2 Si phases will be formed, and the material is prone to cracking. If the Ni content is higher than 18%, too much Ni will dissolve into the matrix, and during subsequent aging, not all of the Ni dissolved in the matrix can be precipitated. Although the strength of the material will increase, it will cause a large lattice distortion in the matrix, reducing the plasticity of the material.

[0008] The present invention adds 4.0-4.5 wt% of Si. The mass ratio of Si to Ni is close to 1:4, forming Ni 2 Si phases in the material. It is a kind of age-hardening phase, showing a coherent and semi-coherent relationship with the matrix, causing resistance to the cutting of dislocations, and improving the strength, high-temperature resistance, corrosion resistance, and wear resistance of the alloy, etc. If the Si content is greater than 4.5 wt%, the plasticity of the material will be reduced, and part of it will precipitate as Mn 2 Si phases. The more the precipitated Mn 2 Si phases, the greater the tendency of self-cracking. If the Si content is less than 4.0 wt%, the quantity of Ni 2 Si phases is insufficient, unable to meet the quantity of coherent and semi-coherent with the matrix, resulting in a weakened age-hardening effect and reducing the strength, wear resistance, corrosion resistance, fatigue resistance, and high-temperature softening resistance of the material.

[0009] The present invention adds 3.0-4.0 wt% of Mn. Mn can produce solid solution and age-hardening. Mn dissolved in the copper matrix causes lattice distortion. The lattice distortion increases the resistance to dislocation movement, making slip difficult to occur, thereby improving the strength and corrosion resistance of the material. After aging precipitation, Mn exists in the form of single substance and Mn 2 Si and is evenly distributed in the copper matrix, increasing the wear resistance of the material, hindering the slip of dislocations and the growth of grains, and improving the strength and corrosion resistance of the material. However, when the Mn content is greater than 4.0 wt%, the precipitated Mn 2 Si phases increase, and the tendency of self-cracking becomes greater.

[0010] The present invention adds 0.1-0.3 wt% of Fe. At 1050 °C, the solubility of the Fe element in copper is 3.5%. As the temperature drops sharply, it will all precipitate and be evenly distributed in the matrix in the form of hard particles, hindering the grain growth and dislocation slip of the material, and improving the strength and hardness of the alloy. Since Fe exists in the matrix in the form of hard particles, the corrosion resistance and wear resistance of the alloy are increased. However, when the Fe content is greater than 0.3 wt%, free α-Fe phases and FeSi compounds will appear, and the appearance of the two will reduce the corrosion resistance of the alloy.

[0011] Preferably, it also includes RE: 0.01 to 0.05 wt%.

[0012] In the present invention, 0.01 to 0.05 wt% of RE is added. First, it improves the as-cast structure of the material, forming more equiaxed crystals. Rare earth has a strong affinity for oxygen and sulfur, forming rare earth compounds with higher melting points, strong thermal stability, and smaller specific gravities, thus achieving the functions of desulfurization and deoxidation. Also, rare earth elements easily react with atomic hydrogen to generate RH 2 or RH 3 type stable hydrides (R represents rare earth metal), and these hydrides dissolve in the copper alloy in the form of solid solution, thus eliminating the harmful effects of hydrogen. It reduces or eliminates columnar crystals and expands the equiaxed crystal zone. Second, it refines the grains, improves strength and plasticity. Rare earth can act as nucleation sites in the as-cast structure, forming new crystal nuclei and inhibiting grain growth. Also, from the perspective of solidification principle and thermodynamics, due to the large aggregation of rare earth in the liquid phase in front of the solid-liquid interface, the compositional supercooling of the alloy increases during solidification, and it solidifies and grows in a dendritic manner. At the same time, necks and fusions occur at the branching nodes, increasing the number of crystallization nuclei, thus refining the grains. Third, it improves wear resistance. Rare earth and copper elements can form metal intermetallic compounds with higher hardness and uniform distribution, and these compounds become the resistance to dislocation movement. Moreover, rare earth can effectively improve the existence form and distribution of inclusions, reduce the possibility of weakening the grain boundaries, and reduce the probability of cracking along the grain boundaries when bearing loads, thus improving wear resistance. Fourth, it improves corrosion resistance. First, the purification effect of rare earth forms high-melting-point compounds with impurity elements and discharges them in the form of slag, eliminating impurities in the copper matrix. Second, a dense oxide layer is formed on the alloy surface, preventing the outward diffusion of matrix atoms and the inward diffusion of external atoms. In addition, it increases the corrosion potential of the alloy. Cerium and / or lanthanum are preferred.

[0013] Preferably, the phase structure of the copper alloy includes an α matrix phase and a second phase, and the second phase includes Ni 2 Si phase, Mn 2 Si phase, and the area content of the Ni 2 Si phase accounts for 10 to 20% of the total phase structure, and the area content of the Mn 2 Si phase accounts for less than 1% of the total phase structure. The Ni 2 Si phase is a precipitation strengthening phase during aging, which improves the strength, corrosion resistance, high-temperature resistance, wear resistance, fatigue resistance and other properties of the material. If the area ratio is less than 10%, the strengthening phase is insufficient and in the under-aged state, and the performance of the material will be lower. When the area of the Ni 2 Si strengthening phase is greater than 20%, it proves that the strengthening phase has grown and destroyed the coherent relationship with the matrix, becoming a non-coherent relationship with the matrix, reducing the plasticity of the material. When Mn 2When the Si phase content area is greater than 1%, its quantity is large and it is a brittle phase itself. A smaller quantity can strengthen the matrix and improve the performance, but conversely increases the risk of material cracking.

[0014] Preferably, the Ni 2 The size of Si phase is between 20nm and 100nm, among which Ni 2 The amount of Si phase coherent with the matrix accounts for the proportion of Ni 2 More than 50% of the total amount of Si phase, Ni 2 The amount of Si phase semi-coherent with the matrix accounts for the proportion of Ni 2 Si phase accounts for more than 30% of the total amount, Ni 2 The amount of Si phase incoherent with the matrix accounts for the proportion of Ni 2 The Si phase accounts for less than 20% of the total amount. 2 The amount of semi-coherent Si phase and matrix is ​​≥50%, because in the case of coherent, the atoms of the two phases match well and there is almost no distortion. This phase boundary has the lowest energy and can improve the strength while improving the plasticity of the material. 2 The amount of incoherence between the Si phase and the matrix is ​​≤20%. In the incoherent case, the atomic arrangements on both sides of the interface are quite different, and the elastic distortion energy is large, thereby increasing the energy of the phase boundary. Although it can significantly improve the strength of the material, it does not significantly improve the plasticity of the material.

[0015] The technical solution adopted by the present invention to solve the second technical problem is: a method for preparing a copper alloy bar, characterized in that it includes the following preparation steps:

[0016] 1) Melting: prepare the ingredients according to the required ingredients, melting temperature: 1320~1360℃;

[0017] 2) Horizontal continuous casting: introduce molten copper into the holding furnace, use the crystallizer to lead out the ingot, casting temperature: 1230-1260°C, pressure in the crystallizer: 26KPa-130KPa, pulling speed: 4-7mm / s;

[0018] 3) Intermediate stretching: stretch the ingot to form a rod, with a stretching processing rate of ≥30%;

[0019] 4) Solution treatment: Solution treatment of the rod blank, solution treatment temperature: 900-950°C, solution treatment time: 30-60min, quenching after solution treatment, cooling rate: 80-120°C / s;

[0020] 5) Finished product stretching: stretch the rod blank to the finished product specification, with a stretching processing rate of 15-40%;

[0021] 6) Finished product aging: The rods are aged and protected by protective gas, the aging temperature is 420-460°C, and the time is 3-5h.

[0022] Pressure inside the mold: 26 KPa - 130 KPa. When the melt inside the mold solidifies, it is not easy to appear loose in structure, the copper water compensates for shrinkage in time, and it is not easy to cause surface cracking of the bar.

[0023] The intermediate drawing reduction rate ≥ 30%. First: reduce the size of the billet. Second: after drawing, the deformation storage energy of the material will increase, and the energy required for the long strip grains to become equiaxed grains will decrease, so the solution temperature will be reduced to prevent grain growth.

[0024] Solution treatment dissolves the second phase generated during melting into the matrix to form a uniform solid solution. After the alloy is rapidly cooled, the second phase dissolved in the matrix remains in the matrix as a supersaturated solid solution, which can improve the ductility and toughness of the alloy and create conditions for further precipitation hardening treatment. Solution temperature: 900 - 950 °C, solution time: 30 - 60 min. When the solution temperature is higher than 950 °C and the time is greater than 60 min, the material is prone to grain growth and the material properties will be reduced. When the solution temperature is lower than 900 °C and the time is less than 30 min, the second phase in the material cannot completely enter the matrix, which will weaken the strengthening effect of the subsequent aging process and reduce the material properties.

[0025] Final aging causes the precipitation of Ni 2 Si phase, which is dispersed in the matrix, resulting in precipitation hardening and improving the strength, high-temperature softening resistance, wear resistance, fatigue resistance and corrosion resistance of the material. Aging temperature: 420 - 460 °C, time: 3 - 5 h. When the aging temperature > 460 °C and the time > 5 h, the material will be in an over-aged state. As the second phase gradually grows, the difference from the matrix becomes larger and larger, and the generated distortion energy becomes larger and larger, resulting in the interface relationship with the matrix changing from coherent → semi-coherent → incoherent. In addition, the grains of the material also grow, reducing the material properties. If the aging temperature < 420 °C and the time < 3 h, the material is in an under-aged state, and the number of the second phase dissolved in the matrix is relatively large, resulting in a sharp decrease in the number of the second phase that is coherent and semi-coherent with the matrix, weakening the aging strengthening effect and seriously reducing the material properties.

[0026] Preferably, in step 2), electromagnetic stirring is performed on the copper water in the mold, current frequency: 3 - 9 HZ, current intensity: 300 - 350 A, the area content ratio of equiaxed grains ≥ 95%, equiaxed grain size: 0.005 - 0.02 mm.

[0027] Through the generated electromagnetic force, the superheat of the copper water in the mold is improved and eliminated, and the copper water is constantly tumbling, breaking the dendrites in the melt. The broken dendrites can act as new nucleation sites, making the grains of the billet refined and obtaining as much equiaxed grain structure as possible.

[0028] Compared with the prior art, the advantages of the present invention are: adding Si, Ni, Mn and Fe into the copper matrix and controlling the addition amount of Si, Ni, Mn and Fe, the average grain size is 0.015-0.01 mm, and the tensile strength of the copper alloy is finally achieved by solid solution strengthening and aging strengthening, which is ≥650 MPa, the high temperature softening temperature is ≥650°C, the friction coefficient is 0.12-0.15, and the corrosion resistance weight loss is ≤1.2 mg / cm 2 , fatigue strength ≥360MPa. While meeting the mechanical performance requirements of the bearing cage, it has good cold processing performance and can withstand complex stamping deformation. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the embodiments.

[0030] The present invention provides three examples and one comparative example, and the specific components are shown in Table 1. The examples are prepared according to the preparation method of the present invention.

[0031] The preparation steps of the copper alloy rod in Example 1 are as follows:

[0032] 1) Melting: prepare the ingredients according to the required ingredients, melting temperature: 1350℃;

[0033] 2) Horizontal continuous casting: introduce molten copper into the holding furnace, use the crystallizer to lead out the ingot, casting temperature: 1250℃, pressure in the crystallizer: 50KPa, pulling speed: 5mm / s; electromagnetic stirring is performed on the molten copper in the crystallizer, current frequency: 5HZ, current intensity: 320A. The specification of the ingot is Φ20mm.

[0034] 3) Intermediate stretching: The ingot is stretched to form a rod with a specification of Φ16mm.

[0035] 4) Solution treatment: Solution treatment of the rod blank, solution treatment temperature: 920°C, solution treatment time: 40 min, quenching after solution treatment, cooling rate: 100°C / s.

[0036] 5) Finished product stretching: The rod blank is stretched to the finished product specification, the finished product specification is Φ15mm.

[0037] 6) Finished product aging: The bars are aged and protected with nitrogen, aging temperature: 420°C, time: 4h.

[0038] The preparation steps of the copper alloy rod in Example 2 are as follows:

[0039] 1) Melting: prepare the ingredients according to the required ingredients, melting temperature: 1340℃;

[0040] 2) Horizontal continuous casting: Introduce molten copper into the holding furnace, and use a mold to draw out the billet. Casting temperature: 1240 °C, pressure inside the mold: 60 KPa, drawing speed: 6 mm / s; Electromagnetic stirring is carried out on the molten copper in the mold, current frequency: 6 HZ, current intensity: 330 A. The billet specification is Φ20 mm.

[0041] 3) Intermediate drawing: Draw the billet to form a rod billet, and the rod billet specification is Φ16 mm.

[0042] 4) Solution treatment: Solution-treat the rod billet, solution treatment temperature: 930 °C, solution treatment time: 35 min, and perform quenching after solution treatment, with a cooling rate of 100 °C / s.

[0043] 5) Final drawing: Draw the rod billet to the final product specification, and the final product specification is Φ15 mm.

[0044] 6) Final aging: Age the rod and protect it with nitrogen. Aging temperature: 430 °C, time: 4 h.

[0045] The preparation steps of the copper alloy rod in Example 3 are as follows:

[0046] 1) Melting: Charge according to the required composition, melting temperature: 1350 °C;

[0047] 2) Horizontal continuous casting: Introduce molten copper into the holding furnace, and use a mold to draw out the billet. Casting temperature: 1250 °C, pressure inside the mold: 70 KPa, drawing speed: 4 mm / s; Electromagnetic stirring is carried out on the molten copper in the mold, current frequency: 7 HZ, current intensity: 310 A. The billet specification is Φ20 mm.

[0048] 3) Intermediate drawing: Draw the billet to form a rod billet, and the rod billet specification is Φ16 mm.

[0049] 4) Solution treatment: Solution-treat the rod billet, solution treatment temperature: 940 °C, solution treatment time: 30 min, and perform quenching after solution treatment, with a cooling rate of 100 °C / s.

[0050] 5) Final drawing: Draw the rod billet to the final product specification, and the final product specification is Φ15 mm.

[0051] 6) Final aging: Age the rod and protect it with nitrogen. Aging temperature: 450 °C, time: 3.5 h.

[0052] The comparative example is QSi1-3, a commercially available forging, with a specification of Φ15 mm.

[0053] Detect the phase structure of the obtained examples, and the specific detection results are shown in Table 2.

[0054] The phase ratio, phase size, and number of phase distributions were observed using a transmission electron microscope. Among them, A: the ratio of the number of Ni 2 Si phases coherent with the matrix to the total number of Ni 2 Si phases; B: the ratio of the number of Ni 2 Si phases semi-coherent with the matrix to the total number of Ni 2 Si phases; C: the ratio of the number of Ni 2 Si phases non-coherent with the matrix to the total number of Ni 2 Si phases.

[0055] The obtained examples and comparative examples were subjected to performance testing. The specific test results are shown in Table 3.

[0056] Tensile strength Rm, yield strength Rp0.2, and elongation A100: were tested in accordance with GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature". For each example, 10 samples were randomly selected for performance testing, and the final performance was averaged.

[0057] Corrosion resistance: The test standard is GB / T10125-2012. It is the test standard or test method.

[0058] High-temperature softening resistance: The sample was placed in a muffle furnace and held at a certain temperature for 1 h, followed by air cooling. When the hardness decreased by 15%, this temperature was called the softening temperature of the material. It is the test standard or test method.

[0059] Coefficient of friction: A large-load friction and wear testing machine was used. Under the condition of a load of 100 KN, the temperature was 25 °C, the friction speed was 200 r / min, and the friction mode was dry friction. It is the test standard or test method.

[0060] Fatigue strength: At room temperature of 25 °C, the maximum stress when the material withstands 10 8 cycles of alternating load without fracture.

[0061] Table 1 Compositions of examples and comparative examples of the present invention / wt%

[0062]

[0063] Table 2 Phase structure of examples of the present invention

[0064]

[0065] Table 3 Mechanical properties of examples and comparative examples of the present invention

[0066]

Claims

1. A copper alloy bar, characterized in that: The mass percentage composition of the copper alloy is: Si: 4.0 - 4.5 wt%, Ni: 16 - 18 wt%, Mn: 3.0 - 4.0 wt%, Fe: 0.1 - 0.3 wt%, RE: 0.01 - 0.05 wt%, and the balance is Cu and unavoidable impurities; The phase structure of the copper alloy includes an α matrix phase and a second phase, and the second phase includes Ni 2 Si phase, Mn 2 Si phase, and the area content of the Ni 2 Si phase accounts for 10-20% of the total phase structure, and the area content of the Mn 2 Si phase accounts for less than 1% of the total phase structure; The Ni 2 size of the Si phase is from 20 nm to 100 nm. Among them, the number of Ni 2 Si phases coherent with the matrix accounts for more than 50% of the total number of Ni 2 Si phases, the number of Ni 2 Si phases semi-coherent with the matrix accounts for more than 30% of the total number of Ni 2 Si phases, and the number of Ni 2 Si phases non-coherent with the matrix accounts for 20% or less of the total number of Ni 2 Si phases.

2. A preparation method of the copper alloy bar according to claim 1, characterized in that it includes the following preparation steps: 1) Melting: Charge according to the required components, melting temperature: 1320 - 1360 °C; 2) Horizontal continuous casting: Introduce the molten copper into the holding furnace, and use a mold to draw out the billet. Casting temperature: 1230 - 1260 °C, pressure in the mold: 26 kPa - 130 kPa, drawing speed: 4 - 7 mm / s; 3) Intermediate drawing: Draw the billet to form a bar blank, and the drawing reduction rate ≥ 30%; 4) Solution treatment: Solution-treat the bar blank, solution temperature: 900 - 950 °C, solution time: 30 - 60 min. After solution treatment, perform quenching, and the cooling rate is 80 - 120 °C / s; 5) Final drawing: Draw the bar blank to the finished product specification, and the drawing reduction rate is 15 - 40%; 6) Final aging: Age the bar and protect it with a protective gas. Aging temperature: 420 - 460 °C, time: 3 - 5 h.

3. According to the preparation method of the copper alloy bar described in claim 2, characterized in that: In the step 2), electromagnetic stirring is performed on the molten copper in the mold, current frequency: 3 - 9 Hz, current intensity: 300 - 350 A, the area content ratio of equiaxed grains ≥ 95%, and the equiaxed grain size: 0.005 - 0.02 mm.

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