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

Update: 25-04-2021

Titanium rods and titanium alloys are an important meta […]

Titanium rods and titanium alloys are an important metal structure material that emerged in the 1950s. Among them, TC4 alloy is a widely used a+ Lu type titanium alloy at home and abroad, due to its high specific strength, good corrosion resistance and superior comprehensive performance. Features, widely used in aerospace, chemical machinery, medical engineering and other industries. Common defects of titanium rod manufacturer TC4 alloy include segregation of alloying elements and inclusions, residual casting structure, embrittlement layer, hydrogen embrittlement, brittleness and forging cracks.
A certain unit found a 4.3mmX0.68mm crack on the surface when machining the TC4 titanium alloy bar 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. The forging material is formed into a cake, and the cake material is flared into a ring. The defects may be caused by cracks caused by improper forging process, or it may be a bar material. There are metallurgical defects such as inclusions, segregation, pores, etc., and cracks are caused by metallurgical defects in the subsequent reforming process.
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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. The sponge titanium is weakly oxidized and melted to form a low-density segregation defect area, and the sponge titanium is severely oxidized and melted to form oxygen-rich inclusions. 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 the brittle phase T^Al will be formed. During the hot forging process, the deformation ability and deformation coordination ability of this area are very poor. Coarse flakes and bright blocks are difficult to break, and the structure is easy to appear as coarse, and cracks are also easy to occur, which are defects that are relatively harmful to materials.
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 be oxidized and insufficiently melted, 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.