Titanium allotropic transformation temperature
The specific temperature threshold at which titanium transforms from the hexagonal close-packed alpha phase into the body-centered cubic beta phase.
At room temperature, titanium has a hexagonal lattice (alpha phase). When it gets strongly heated during welding, it transforms above the transformation temperature into a body-centered cubic lattice (beta phase). On cooling, the structure must cleanly transform back into the alpha phase. If this happens too quickly or uncontrolled, hard, brittle microstructural constituents form, which can lead to cracks. Therefore, when welding you need to control the heat input and let the part cool slowly and evenly. The transformation temperature is not a value you need to actively set, but a material property you need to consider during cooling.