α+β type titanium alloy, a titanium alloy strip, coil-rolling process of titanium alloy, and process for producing a cold-rolled titanium alloy strip

Abstract

A high strength and ductility α+β type titanium alloy, comprising at least one isomorphous β stabilizing element in a Mo equivalence of 2.0-4.5 mass %, at least one eutectic β stabilizing element in an Fe equivalence of 0.3-2.0 mass %, and Si in an amount of 0.1-1.5 mass %, and optionally comprising C in an amount of 0.01-0.15% mass.

What is claimed:  
     
       1. An α+β titanium alloy comprising: 
       at least one isomorphous β stabilizing element in a Mo equivalence of 2.0-4.5 mass %,  
       at least one eutectic β stabilizing element in an Fe equivalence of 0.3-2.0 mass %,  
       Si in an amount of 0.1-1.5 mass %, and  
       C in an amount of 0.01-0.15 mass %, and  
       
         an Al equivalence of more than  3  mass % and not more than  5 . 5  mass %.  
       
     
     
       2. The α+β titanium alloy according to  claim 1 , wherein the alloy further comprises an Al equivalence of more than 3 mass % and less than 6.5 mass %. 
     
     
       3. A titanium alloy strip comprising the titanium alloy of  claim 1 , wherein the strip has a tensile strength of 900 MPa or more, an elongation of 4% or more, and a ratio of a longitudinal elongation in a coil-rolling direction to a transverse elongation in a direction perpendicular to the coil-rolling direction of form 0.4 to 1.0. 
     
     
       4. A process for using a titanium alloy, the process comprising 
       forming a titanium alloy strip from the titanium alloy of  claim 1 ,  
       annealing the titanium alloy strip at a temperature T satisfying the following inequality: (β transus−270° C.)≦T≦(βtransus−50° C.), and  
       then coil-rolling the annealed strip.  
     
     
       5. The process according to  claim 4 , wherein the titanium alloy strip is coil-rolled at a rolling reduction of 20% or more while a tension-roll of 49-392 MPa is applied to the strip. 
     
     
       6. The process according to  claim 4 , wherein the coil-rolling is performed plural times in a manner that an annealing step in an α+β temperature range intervenes therebetween. 
     
     
       7. A process for using a titanium alloy, the process comprising annealing the titanium alloy of  claim 1  at a temperature not less than a temperature for relieving work-hardening during coil-rolling and not more than the β transus. 
     
     
       8. A titanium alloy strip comprising the titanium alloy of  claim 2 , wherein the strip has a tensile strength of 900 MPa or more, an elongation of 4% or more, and a ratio of a longitudinal elongation in a coil-rolling direction to a transverse elongation in a direction perpendicular to the coil-rolling direction of from 0.4 to 1.0.