Titanium rods and titanium alloys are an important metal structural material that emerged in the 1950s. Among them, TC4 alloy is a + Lu type titanium alloy widely used at home and abroad. Due to its high specific strength, good corrosion resistance and superior comprehensive performance, etc. Characteristics, widely used in aerospace, chemical machinery, pharmaceutical engineering and other industries. Common defects of titanium rod manufacturer TC4 alloy include segregation and inclusions of alloy elements, residual of cast structure, embrittlement layer, hydrogen embrittlement, brittleness and forging cracks.
A unit found a crack of about 4.3mmX0.68mm on its surface when machining the TC4 titanium alloy bar products. In order to analyze the cause of the defect and avoid the occurrence of similar defects, various physical and chemical tests were used. Means, the TC4 titanium alloy product was analyzed.
The process of changing the forging ring of TC4 bar is heating at two fires at 950 ° C, and the forging causes the cake material, and the cake material expands into a ring material. The defect may be caused by improper reforging process and may also be a bar material. There are metallurgical defects such as inclusions, segregation, pores, etc. in the subsequent reforging process caused by metallurgical defects.
Through theoretical calculations, it is concluded that the design of this set of special clamps for computerized flat knitting machines is in full compliance with the theoretical design requirements. So the author made this set of fixtures and installed them on the worktable of the Vcentei-70 high-precision CNC machining center for actual processing verification. Then put the finished product of the flat knitting machine flybridge into the three-coordinate measuring machine for accurate precision measurement, and the angle error between the two included angles is in the range of 0.2 ° ~ 0.6 °, which meets the technical requirements. Because this set of fixtures can realize the processing and positioning of the flyover parts very conveniently and quickly, and there is no need to find the alignment by other methods, it is suitable for mass production of flyover parts.
The left and right characteristics of the comprehensive defect can be judged that this defect is due to the formation of oxidized sponge titanium during the smelting process. The sponge titanium is weakly oxidized to form a low-density segregation defect area. The sponge titanium is severely oxidized and melted to form oxygen-rich inclusions Defects are metallurgical defects. The oxygen-rich carbon and a small amount of nitrogen in the defect area will increase the hardness and become brittle in this area, and sometimes form brittle phase T ^ Al. During the hot forging process, the deformation ability and deformation coordination ability of this area are very poor. Coarse flakes a and bright blocks are difficult to break, and the structure tends to appear coarse, and it is also prone to cracks, which is a defect that is relatively harmful to the material.
According to the smelting process, such defects are likely to appear at the bottom of the ingot. When the arc is melted, the arc current is unstable. It is easy to make the sponge titanium spread at the bottom insufficiently oxidized and melted, forming inclusions and segregation areas, which are not easy to find during flaw detection. . In order to prevent the damage caused by this defect to the product, the bottom of the ingot should be sawed off the length of 6% -8% of the nominal diameter.