Beryllium bronze is a typical precipitation strengthening type alloy, having high elasticity, high strength, high conductivity, corrosion resistance, fatigue resistance, elastic hysteresis is small, non-magnetic, does not produce sparks upon impact a series of advantages, is Widely used in aerospace, aviation, electronics, telecommunications, machinery, petroleum , chemical, automotive and home appliance industries, has broad application prospects.
As a conventional product with more applications, é“Bronze bar has gradually increased its application in recent years, especially in the field of oil drilling applications. In addition, beryllium bronze is also used as a special material in aerospace, aerospace and other important fields, and its internal organization and performance requirements are far higher than conventional products. In order to meet the needs of different customers and further improve the quality of bars, the paper studies the production status of Φ30～120mm bars by two kinds of hot processing methods, such as extrusion and forging, and studies the extrusion and forging process on the bronze brazing rods. The influence of material organization and properties.
First, the test part
(1) Test materials
The test uses medium-frequency induction smelting and semi-continuous casting of ingot as raw materials, which are mined, sawn and flattened, and the ingot size is Φ175×300mm. The chemical composition is determined by ICP full-spectrum direct reading spectrometer. The analysis results are shown in Table 1. A macroscopic examination of the cross section of the ingot was carried out, and the photo of the organization is shown in Fig. 1. It can be seen from Fig. 1 that the cross section of the ingot is a small equiaxed crystal, the middle part is a coarse equiaxed crystal, and the two equiaxed crystals are radial columnar crystals, and the columnar crystals are relatively developed. The extrusion and forging of the ingot must be such that the coarse equiaxed grains and the columnar structure are sufficiently refined to improve the internal structure and properties of the material. Therefore, the study of the hot working process of the ingot has a great influence on the microstructure of the beryllium bronze bar. .
Table 1 Chemical composition of beryllium bronze ingots %
element | Be | Co | Ni | Fe | Al | Si | Pb | Cu |
QBe2.0 standard value | 1.8 to 2.1 | - | 0.2 to 0.5 | ≤0.15 | ≤0.15 | ≤0.15 | ≤0.005 | margin |
content | 1.910 | 0.150 | 0.320 | 0.074 | 0.056 | 0.065 | 0.004 | margin |
Fig.1 Macroscopic structure of the cross section of beryllium bronze ingot
(2) Test methods
The microstructure and properties of hot-processed Φ50mm bar were analyzed and studied by extrusion, forging and forging and extrusion. The specific process is as follows: (1) ingot → heating → extrusion → solution treatment → ultrasonic flaw detection → suede → inspection; (2) ingot → heating → forging → solution treatment → ultrasonic flaw detection → suede → inspection; ) Ingot → heating → forging → trimming → heating → extrusion → solution treatment → ultrasonic flaw detection → suede → inspection.
The test uses a 1t air hammer and a 16.3MN horizontal extruder to forge and extrude the beryllium bronze ingot, and 780±10°C×70-85min solution treatment. The metallographic examination is in accordance with the “QJ2337-92é“ bronze gold. The phase test method was observed by MM6 metallographic microscope, and the tensile properties were tested according to GB/T228-2002 Metallic Room Tensile Test Method. The internal tissue defect inspection of the bar uses two methods: fracture test and ultrasonic flaw detection. Fracture performance testing using the naked eye and the stereo microscope according to "YS/T336 copper, nickel and its alloy pipe and bar fracture test method" for fracture observation, ultrasonic flaw detection according to "GB/T3310 copper alloy bar ultrasonic flaw detection method" on the bar Non-destructive testing.
Second, the results and discussion
(1) The influence of processing methods on the microstructure of bars
Since beryllium bronze has high deformation resistance at normal temperature, it is usually hot extrusion and hot forging. Compared to other thermal processing methods, extruded articles are characterized by a non-uniform distribution in length and length. In general, the grain at the front end is coarse along the length of the product, and the grain at the back end is fine along the radial direction of the section. The front end portion is often insufficiently deformed, and particularly when the extrusion ratio is small (R < 5), a certain degree of cast structure is often retained. The microstructure of the bars of different processing techniques is shown in Figure 2. Figures 2(a) and (b) show the microstructure of the Φ50mm beryllium bronze extruded bar along the radial upper edge and center of the section. It can be seen from Fig. 2 that the edge grains of the alloy are fine and uniform, the central crystal grains are large, and there are long large crystal grains, and the structure is extremely uneven. The unevenness of the structure is mainly caused by the difference in the degree of metal deformation of the outer metal and the central portion. This uneven deformation in the radial direction inevitably leads to uneven structure of the metal, that is, the degree of fracture of the outer metal. It is more intense than the central part. Forging processing is more uniform in length and section at the same processing rate compared with ordinary extrusion. Figures 2(c) and (d) are Φ50mm beryllium bronze forged bars along the radial upper edge and center of the section. microstructure. From the comparative analysis in the figure, it can be found that the microstructure of the forged bar along the radial direction of the section is slightly larger than that of the edge, but it is relatively uniform with respect to the extruded structure, and there is no particularly large elongated grain in the center. Figures 2(e) and (f) show the microstructure of the cross-section edge and center of a Φ50mm beryllium bronze bar processed by a forging + extrusion process. The microstructure of the bar processed by the process is finer and evener. The main reason is that the ingot is first upset in the forging of the blank, so that the longitudinal and near-longitudinal columnar grains are effectively broken. Moreover, the radial columnar grains and the coarse equiaxed crystals in the center are effectively crushed and refined, and the internal structure of the forged blank is much more uniform than the internal structure of the original ingot, and in this case, the extrusion is further performed. The extruded structure will of course be relatively uniform and finer and more uniform than the directly forged tissue.
Figure 2 Bar microstructure of different processing techniques
(II) Effect of processing methods on mechanical properties of bars
Deformation and tissue inhomogeneity of the extruded article necessarily cause a non-uniformity in mechanical properties. In general, the core and the front end of a solid product (without heat treatment) have low strength and high elongation, while the outer layer and the rear end have high strength and low elongation. Moreover, since there is a certain degree of difference in the internal organization of the bars produced by the three processes, it is necessary to select a reasonable sampling position of the tensile specimen. The tensile specimen sampling position of the test was determined to be 1/2 of the radius of the cross section of the middle portion of the bar. The tensile properties of the three test processes are shown in Table 2. It can be seen from the test data in Table 2 that the strength of the extruded bar is higher than that of the forged bar, but the elongation is slightly lower, and the strength and elongation of the bar produced by the forging + extrusion process are both higher than the former two. High, indicating that the mechanical synthesis performance of the third process is the best. From the analysis of the results of mechanical properties, the performance difference between the three processes is consistent with the difference in its organization. The center structure of the extruded bar is extremely uneven, and there is a certain degree of large grain and strip or fibrous structure. However, although the forged structure is larger than the edge structure, the forged structure is mostly equiaxed grains, so The tensile strength of extruded bars is higher than that of forged bars, while the elongation is slightly lower. Since the bar of the forging + extrusion process is fine and relatively uniform, the tensile strength and the elongation are both high, that is, the comprehensive mechanical properties are the best.
Table 2 Bar tensile properties of different processing processes
Processing methods | Specification ∕mm | status | Tensile strength Rm∕MPa | Elongation A∕% |
extrusion | Φ50 | M | 520.6 | 41.2 |
forging | Φ50 | M | 495.4 | 46.6 |
Forging + extrusion | Φ50 | M | 526.5 | 50.0 |
(3) The effect of different processing methods on the improvement of internal tissue defects of bars
The ingot can be effectively improved by internal processing such as extrusion and forging, and the defects inside the material can be eliminated and reduced to some extent. For example, loose and shrinkage holes can be welded under the interaction of heat and compressive stress, and the inclusions can be broken and refined to reduce the damage to the material properties. However, the pores are difficult to eliminate due to the presence of a certain degree of gas pressure inside. The internal tissue defect inspection of beryllium bronze bar can be tested separately or comprehensively by two methods: fracture test and ultrasonic flaw detection. Figures 3 to 5 show the results of macro-fracture inspection and ultrasonic flaw detection of bars produced by extrusion, forging and extrusion + forging processes, respectively. It can be seen from the figure that the macroscopic fractures in Fig. 3 and Fig. 4 have some defects such as loose pores and pores visible to the naked eye. The macroscopic fractures in Fig. 5 are relatively dense, and there are substantially no defects such as shrinkage cavities and pores visible to the naked eye. Moreover, the results of the fracture test are basically consistent with the results of the ultrasonic flaw detection. The defect wave in Fig. 3 is the highest and the clutter is the most, and Fig. 4 is second. The defect wave in Fig. 5 is the lowest and almost no clutter. The comprehensive comparison shows that there are many internal structural defects of the extruded bar, but most of them can meet the standard requirements, and the forged bar is second, while the forging + extrusion process produces the best internal structure of the bar, and the internal ingot is deficient. The improvement is most obvious.
Fig. 3 Macroscopic fracture morphology and ultrasonic flaw detection waveform of extruded bar
Fig. 4 Macroscopic fracture morphology and ultrasonic flaw detection waveform of forged bar
Figure 5: Macroscopic fracture morphology and ultrasonic flaw detection waveform of extrusion + forging
Third, the conclusion
The hot working process can effectively break the coarse grains of the beryllium bronze ingot, improve the internal structure of the material, and reduce the structural defects. Under the same processing rate, the forging + extrusion process is the most obvious improvement on the bar structure, and the microstructure is small. Uniform, the comprehensive mechanical properties are the best, the forging process is second, the extrusion process is not as good as the former two, the microstructure is not uniform, but the mechanical properties are equivalent to the forging process.
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