To stably produce a titanium seamless tubular material free from the generation of reluctant surface patterns, in a ring rolling method, by specifying the working degree in forging after rapid cooling in the process of forging and the working degree by ring rolling.
At the time of forming the ingot of an α type titanium alloy into a perforated stock by forging and forming the same into a seamless tubular material by a ring rolling method, the heating temp. in the forging and ring rolling is suppressed to less than the β transformation point, furthermore, in the process of the forging process, it is passed through the transformation point at a cooling rate of 1000°C/h and is subjected to heat treatment, and moreover, treatment after the cooling is executed in the temp. range of lower than the β transformation point. At this time, in the forging stage after the rapid cooling executed in the process of the forging, the forging is executed in such a manner that the draft per one heating is secured to ≥18%, and furthermore, the ring rolling is executed while the draft per one heating is secured to ≥50%. Thus, randomization into he crystal orientation of the stock is promoted to attain the refining of the crystalline grains, by which the titanium seamless tubular material free from the generation of wrinkle or white cloud-shaped ground patterns can be obtd.
ISHIYAMA SHIGEJI
KANIE MAKOTO
NANBA KIYOMI
