In order to choose the right annealing process, we first observe the effects of heating and cooling temperature on microstructure and mechanical properties of GR5 Titanium Alloy.
Test materials 920 ℃ GR5 titanium alloy hot-rolled bar, hot-rolled total distortion rate of about 80%, a + β / β transformation point is 980 ~ 990 ℃. The sample was 1000 ℃, 950 ℃, 930 ℃, 830 ℃ heat insulation were air-cooled, water-cooled furnace cooling and 1 hour. Different ways annealing on the microstructure and mechanical properties are affected.
Wherein the cooling rate have a significant impact on the microstructure and mechanical properties of the four temperature microstructure. When cooled, 1000 ℃, 950 ℃ and 930 ℃ in equilibrium β phase ingredients are to martensite transformation, β phase transformation to martensite a` needle. At 1000 ℃ showed significant Wilcoxon organization whose mechanical properties of 1000 ℃ air-cooled data fairly. And the water-cooled sample 950 ℃ and 930 ℃, air cooling microstructure and characteristics similar, but equiaxed β + martensite a` is a primary needle between the phases. In this case corresponds to the highest overall performance, but also better than air cooling tissue creep resistance. 830 ℃ when the heat balance of the β-phase component has not touch the M line, but after cooling in intergranular β phase also found a very fine needle transformation products, distinguishable only with an electron microscope. But the structure has not yet been measured needles. In this case the tensile strength and reduction of area are very low. As for the furnace cooling, since the sample was cooled slowly at high temperatures to stay a long time, fully polymorphic transitions of all of a phases are coarsened. After 1000 ℃ furnace cooling, a bulky piece of β phase and a photo in the original β grain boundary phase formation as well as a strip of thick network within the original β grain, commonly known as basket-like tissue. 950 ℃, 930 ℃ and 830 ℃ after furnace cooling, since a phase tend to a primary interface with raw nucleation, growth, a microstructure are equiaxed and intergranular β phase. Tensile strength after 1000 ℃ furnace cooling than air-cooled and water-cooled low tensile ductility is higher. Overall performance after temperature furnace other than cold water and air are low.
In summary, in order to get the best GR5 titanium alloy strength and ductility overall performance, while there are good creep resistance and fracture toughness, can be incubated for 1 hour at 950 ℃ air cooling (or water) annealing process. In order to facilitate subsequent processing, metallurgical plant at the factory, GR5 titanium alloys are used in the 700 ~ 800 ℃ temperature for 1 hour and air cooling technology. For some large-sized forgings, in order to ensure uniformity of performance, sometimes using furnace cooling process.