It is generally believed that high hydrogen content or poor microstructure uniformity in GR5 titanium alloy rods will reduce its room temperature notch stress rupture performance. The upper limit of this type of GR5 titanium alloy rod specification in the relevant domestic technical standards is >220mm. At present, there are no public reports at home and abroad on the research on the preparation process of GR5 titanium alloy rods that require notch stress fracture performance. In industrial mass production, it is common that the notch stress fracture performance of such rods is unqualified due to improper processes.
GR5 (Ti-6Al-4V) titanium alloy was successfully developed in 1954 and has now developed into a common titanium alloy in the world. It is a typical two-phase titanium alloy, and its small-sized rods are widely used in aviation, aerospace, Power station, oil field, medical treatment, automobiles, and other fields B-4. Rolling is one of the main means of producing small-sized titanium alloy rods. The continuous rolling high-speed wire rod production method is widely used in steel production and is suitable for the production of products with large quantities and few varieties. Titanium alloy bar products have the characteristics of small batches and multi-variety demand. The production cost of continuous rolling high-speed wire rod production is relatively high. At present, titanium alloy bar production mainly adopts a three-high transverse rolling mill. Therefore, for the transverse rolling mill Research on the deformation process is very necessary. As one of the important factors of rolling deformation, rolling deformation has an important impact on the final product performance of rolled bars, so the research on rolling deformation is of great significance.
Low-magnification microstructures of forged GR5 titanium alloy rods less than 50mm prepared by two processes. The low-magnification uniformity of the GR5 titanium rod prepared by process 1 is poor, showing a gradual transition from the fuzzy crystal at the edge to the semi-clear crystal in the center; the low-magnification uniformity of the rod prepared by process 2 is good, The whole sample is in fuzzy crystal state. This shows that the core structure of the ingot and the intermediate billet is not sufficiently broken and refined by the forging process 1, which is directly related to the small total deformation. The volume of the billet is large, and it is difficult to ensure that the core of the billet is fully deformed even if it is deformed in a straight line. And process 2 makes full use of the large-tonnage forging pressure of the 4500t fast forging machine, so that the large-sized billet undergoes upsetting and drawing deformation in the two-phase area, ensuring the forgeability of the billet, and using the anvil drawing length to reduce the "dead zone" of billet deformation, so that different parts of the billet are fully deformed, and a structure with good crushing, refinement, and good consistency is obtained.
(1) By adopting the forging process of billet opening in the p-phase area and upsetting and drawing + direct drawing in the two-phase area, apricot 350mm large-scale GR5 titanium alloy rods with structure, performance, and flaw detection level meeting the technical requirements of supply can be prepared.
(2) The primary a-phase microstructure with good racialization is conducive to improving the notch stress fracture performance at room temperature, and the short rod-like a-phase microstructure with strong direction consistency will reduce the notch stress fracture performance.
On the 50mm GR5 titanium alloy rod forged by the two processes, the rods with a length of 75 mm were cut longitudinally and subjected to ordinary annealing at two temperatures. The annealing systems were Ml (720 x2h/AC) and M2 (790t: x2h/AC). The low-magnification structure of the forged bar was observed with the naked eye; metallographic samples were cut along the transverse direction at 1/2 radius on the forged and annealed bar linings, and the microstructure was observed with an 0LMPUS optical microscope. Cut the sample blank along the longitudinal line at 1/2 radius of the annealed bar, and machine it into a test sample that meets the standard room temperature tensile and notch stress fracture properties. The tensile testing machine is used to test the mechanical properties of the sample and observe the microstructure of the notch area of the notch stress fracture sample. The S0NIC-138VFD ultrasonic flaw detector was used to conduct ultrasonic nondestructive flaw detection on the GR5 titanium alloy finished bars obtained by forging with two processes.
