β TYPE TITANIUM ALLOY AND THERMAL MECHANICAL TREATMENT METHOD OF THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a β type titanium alloy that can be used in various mechanical engineering regions to produce a half-finished product and a component from a β( beta) type titanium alloy by thermal mechanical treatment accompanying with change of a material property, and is used in an engineering manner in which strength and a fatigue characteristic of a β type titanium alloy are improved.;SOLUTION: A β type titanium alloy has a fine grain structure, and is characterized in that an average grain diameter of a β grain is at most 0.5 μm, an average grain diameter of a spherical type α phase precipitate is at most 0.5 μm, and a volume fraction in a composition is at least 40%. Moreover, a thermal mechanical treatment method of a β type titanium alloy includes strong strain working and a heat treatment process, before working, continuation heating is performed for at least one minute per billet diameter 1 mm to (β transus+5 to β transus+15)°C, performed by water hardening, then by an equal channel angle extrusion method, in that change of a deformation direction after respective working steps is 90°, and under the temperature of (β transus-200 to β transus-150)°C, strong strain working is performed until accumulation strain becomes at least 3.5, and continuously water hardening is performed.;COPYRIGHT: (C)2014,JPO&INPIT