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    Analysis of the causes of forging defects in titanium alloy materials such as titanium rods and tita

    2020-10-29 11:47:14

    Titanium rods and titanium alloys are an important metal structural material that emerged in the 1950s. Among them, TC4 alloy is a widely used a + Lu type titanium alloy at home and abroad, because of its high specific strength, good corrosion resistance and superior comprehensive performance. Features, widely used in aerospace, chemical machinery, medical engineering and other industries. The common defects of TC4 alloy of titanium rod manufacturers include segregation of alloying elements and inclusions, residual casting structure, embrittlement layer, hydrogen embrittlement, brittleness and forging cracks.


    A certain company found a 4.3mmX0.68mm crack on the surface of the product processed by TC4 titanium alloy bar when machining the product. In order to analyze the cause of the defect and avoid the occurrence of similar defects, various physical and chemical tests were used Means analyzed the TC4 titanium alloy product.


    The process of changing TC4 rod to forging ring parts is to heat twice at 950°C, and the forging material is formed into a cake, and the cake material is expanded into a ring material. The defects may be caused by cracks caused by improper reforming forging process, or bar material. There are metallurgical defects such as inclusions, segregation, pores, etc., and cracks are caused by metallurgical defects in the subsequent reforming process.


     Through theoretical calculations, it is concluded that the design of this set of special fixtures for computerized flat knitting knitting machines fully meets the theoretical design requirements. So the author made this set of fixtures and installed it on the worktable of the Vcentei-70 high-precision CNC machining center for actual processing verification. Then put the finished flat knitting machine flyover parts into a three-coordinate measuring machine for precise accuracy measurement, and the angle error of the two included angles is within the range of 0.2° to 0.6°, which meets the technical requirements. Since this set of fixtures can quickly and easily realize the processing and positioning of flyover parts, without the need for alignment by other means, it is suitable for mass production of flyover parts.


    Combining the left and right characteristics of the defect, it can be judged that this defect is formed by the oxidized sponge titanium during the smelting process. After the sponge titanium is weakly oxidized and melted, a low-density segregation defect area is formed. The defect is a metallurgical defect. The oxygen-rich, carbon-containing and small amount of nitrogen in the defect area will increase the hardness and brittleness of this area, and sometimes form a brittle phase T^Al. In the hot forging process, the deformation ability and deformation coordination ability of this area are very poor. Coarse flake a and bright block are difficult to break, the structure is easy to appear as coarse, and cracks are easy to occur, which is a relatively large defect to the material.


    According to the smelting process, such defects are easy to appear at the bottom of the ingot. When melting and starting the arc, the instability of the arcing current will cause the sponge titanium spread on the bottom to oxidize and melt insufficiently, forming inclusions and segregation areas, which are not easy to find during flaw detection. . In order to prevent this defect from harming the product, the bottom of the ingot should be sawed to cut off the length of 6% to 8% of the nominal diameter.


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