WORKING HEAT TREATMENT OF ALPHA+BETA TYPE TITANIUM ALLOY

摘要

PURPOSE:To permit production of an alloy having the strength and ductility equiv. to the strength and ductility of alpha+beta worked material without executing working in an alpha+beta region by working an alpha+beta type Ti alloy at a high temp. above the betatransformation point and at a specific reduction of area and specifying the subsequent cooling and aging conditions. CONSTITUTION:The alpha+beta type Ti alloy is subjected to the working to increase the reduction of area to >=80% by one time of heating at the temp. above the beta transformation point and is then quickly cooled at >=5 deg.C/sec rate; thereafter, the alloy is subjected to aging for 0.5-8hr at 500-750 deg.C. The beta single phase having good workability is obtd. if the working temp. is specified to the beta transformation point or above. The working is then easy and high strain working is possible with one time of heating. If the reduction of area is increased to >=80%, the formation of the finer beta crystal grains is achieved by the formation of the hypocrystal grains as a result of the working. The above-mentioned hypocrystal grains are annihilated and the proeutectoid alphaphase is precipitated at the beta grain boundary if the cooling rate after the working is <=5 deg.C/sec. The ductility is then greatly degraded. The precipitation of the beta phase is not enough if the aging treatment temp. and time are below the lower limit. The coarser beta phase is formed and the increase in yield point is not obtainable if said temp. and time are above the upper limit.