| 摘要 |
PURPOSE: To eliminate the dispersion of fracture toughness value due to a difference in draft in a forged product and to improve homogeneity in strength by performing prescribed finish forging in aβ-phase region and then rapid cooling, at the time of producing a forged product of near beta titanium alloy with complicated shape. CONSTITUTION: At the time of forging, finish forging is carried out at 30-50% draft in theβ-phase region higher by 30 deg.C thanβ-transus temp., followed by rapid cooling. As compared with an alpha plus beta alloy, a near beta titanium alloy has large beta crystalline grain size and the degree of flatness of the crystalline grain is greatly changed with the change in finish draft. Simultaneously, with the increase in draft, the degree of flatness in increased and also the beta crystalline grain boundaries being flat in a direction perpendicular to working direction have continuity andα-phases are liable to precipitate. Accordingly, in this treatment, finish forging draft is limited in order to refine crystalline grains and also to inhibit the precipitation and growth of theα-phases precipitated in grain boundaries, and further, rapid cooling is carried out from the temp. after forging.
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