Metallographic structure and mechanical properties of GR5 titanium slab

With the upgrading of domestic aerospace products, the demand for Ti6Al4V titanium alloy titanium plates is increasing, which also places higher and higher requirements on its various mechanical properties and formability. High-quality, large-size titanium slabs are the key to successfully preparing large-size titanium plates of Ti6Al4V titanium alloy. The researchers mainly study the microstructural differences in different deformation zones of wide slabs, aiming to improve the preparation maturity and mass production stability of Ti6Al4V titanium alloy fine-grained slabs, and prepare for the subsequent rolling of high-quality fine-grained wide slabs. . Width titanium plates lay the foundation of the organization.

Ti6Al4V titanium alloy (domestic grade GR5) has moderate room temperature and high temperature strength, good creep resistance and thermal stability, high fatigue performance and resistance to crack growth (in seawater), as well as good fracture toughness and thermal stability. Salt stress corrosion resistance, suitable for molding using various pressure processing methods, and using various welding and mechanical processing methods. As a general material, Ti6Al4V titanium alloy has been widely used in the aerospace industry and civil industry. Industrially produced large-size ingots of Ti6Al4V titanium alloy were selected for the test. Smelted 3 times in a vacuum consumable arc furnace. After peeling, samples were taken from the upper, middle and lower parts of the ingot to test for chemical composition. The average value of the measurement data of the three samples is (mass fraction, %): Al6.42, V4.09, Fe0.02, O0.20, Ti balance. It can be seen that the main component elements Al and V and the impurity elements Fe and O in the Ti6Al4V titanium alloy industrial-grade large-size ingot have good content uniformity and no segregation, meeting the composition uniformity requirements of high alloy steel. High-quality, large-format boards.
The steel ingot is forged into a slab using a multi-fire upsetting free forging process. The forging equipment is a 45MN fast forging machine. The size of the finished slab after forging is 150mm×1060mm×1500mm. Cut the plate along the cross section about 100mm from the edge of the plate, observe the lateral low-magnification structure of the plate, and grade it according to the GJB2505A-2008 standard. Take metallographic samples and tensile samples from different positions of the titanium slab as required. The metallographic structure is inspected and graded according to GJB1538A-2008 standard. The cut tensile specimen blanks were heat treated. The heat treatment process is 810℃/1.5h/AC. The heat treatment samples comply with the GB/T228-2008 standard.

(1) The room temperature tensile properties of different parts of the titanium slab meet the index requirements and are relatively rich. The tensile strength is more than 100MPa higher than the standard requirements, the yield strength is more than 87MPa higher than the standard value, and the elongation and area shrinkage also have a certain margin. The measured data of strength index has the smallest dispersion and the difference of elongation index is small, indicating that the forging process achieves good control over the uniformity of slab forming.
(2) The transverse low-magnification structure of the titanium slab is fuzzy crystal, indicating that the forging has good forging permeability, the grains are fully broken, and the degree of structural refinement is high.
(3) The transverse microstructure of the titanium slab is mainly equiaxed α structure, and the average size of primary α in the center of the slab is slightly larger than that of other parts. The reason for the structural difference is that the deformation of the core of the slab is lower than that of other parts, and the degree of grain fragmentation is relatively low. The longitudinal microstructure of the titanium slab is dominated by long strips of primary α. The metal streamlines along the deformation and elongation directions are obvious, the grains are fine and uniform, and the structure consistency at each sampling position is good.