傾斜圧延法によるTi-6Al-4V合金継目無管の製造条件検討

概要

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Manufacturing conditions for Ti-6Al-4V alloy seamless pipes by inclined rolling process were investigated on laboratory scale. Elevated temperature torsion tests and piercing tests were carried out on Ti-6Al-4V alloy ingot and forged materials after various conditions. A portion of the pierced shell were hot rolled and annealed to predict microstructure and tensile properties of products by the inclined rolling process. The results were as follows. (1) Grain size affects deformability at elevated temperatures. Material with finer grain size possesses higher deformability as well as wider temperature range of high deformability in alpha+beta temperature region. (2) The material forged in beta region with coarse grain size possesses sufficient deformabilities for the piercing operation. There is no effect of the forging conditions on tensile properties after piercing operation. (3) The microstructure on the final products consists of fine acicular structure and their tensile properties satisfy the specification for Ti-6Al-4V seamless pipes. (4) Piercing temperature at 1373K and reheating temperature at 1223K are recommended for the inclined rolling process to avoid formation of grain boundary alpha phase which detoriorates ductility of the products.