High-strength low-alloy titanium alloy and production method for same

Abstract

To provide a titanium alloy which is a high-strength low-alloy with a 750 MPa or more in terms of tensile strength. A production method is capable of producing the titanium alloy by using a low-priced, low-grade sponge titanium as a raw material. This high-strength low-alloy titanium alloy has an alloy composition containing O of from 0.2 to 0.8%, C of from 0.01 to 0.15%, N of from 0.01 to 0.07%, Fe of from 0.3 to 1.0% and the balance being substantially Ti. At the time of production, a low-grade sponge Ti containing N of 0.01% or more and Fe of 0.2% or more is used in at least a portion of raw materials to allow it to be a source of the aforementioned Ni and Fe components.

What is claimed is:  
     
         1 . A high-strength low-alloy titanium alloy composition comprising O of from 0.2 to 0.8%, C of from 0.01 to 0.15%, N of from 0.01 to 0.07%, Fe of from 0.3 to 1.0% and the balance being substantially Ti and, also, having a tensile strength of 750 MPa or more.  
     
     
         2 . The high-strength low-alloy titanium alloy composition according to  claim 1 , and further comprising at least one of Cr and Ni such that an entire content inclusive of Fe comes to be Fe %+Cr %+Ni %:1.2% or less, and satisfying a relation of O %+2N %+0.9%+0.1(Fe %+Cr %+Ni %): 1.0% or less.  
     
     
         3 . A method for producing a high-strength low-alloy titanium alloy composition comprising: 
 selecting O of from 0.2 to 0.8%;    selecting C of from 0.01 to 0.15%;    selecting N of from 0.01 to 0.07%;    selecting Fe of from 0.3 to 1.0%; and    providing a balance being substantially Ti for forming a high-strength low-alloy titanium alloy with a tensile strength of 750 MPa or more.    
     
     
         4 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 3 , wherein the Ti is a low-grade sponge Ti containing N of 0.01% or more and Fe of 0.2% or more in at least a portion of raw materials to allow it to be a source of Ni and the aforementioned Fe components.  
     
     
         5 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 1 , and further including the steps of: 
 selecting at least one of Cr and Ni such that an entire content inclusive of Fe comes to be Fe %+Cr %+Ni %:1.2% or less, and satisfying a relation of O %+2N %+0.9%+0.1 (Fe %+Cr %+Ni %):1.0% or less.    
     
     
         6 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 5 , wherein the Ti is a low-grade sponge Ti containing N of 0.01% or more and Fe of 0.2% or more in at least a portion of raw materials to allow it to be a source of the aforementioned Ni and Fe components.  
     
     
         7 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 3 , and including the step of subjecting the titanium alloy to finish forming at a forging ratio of 3 or more in the temperature range of from 600 to 900° C.  
     
     
         8 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 4 , and including the step of subjecting the titanium alloy to finish forming at a forging ratio of 3 or more in the temperature range of from 600 to 900° C.  
     
     
         9 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 5 , and including the step of subjecting the titanium alloy to finish forming at a forging ratio of 3 or more in the temperature range of from 600 to 900° C.  
     
     
         10 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 6 , and including the step of subjecting the titanium alloy to finish forming at a forging ratio of 3 or more in the temperature range of from 600 to 900° C.  
     
     
         11 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 3 , and including the steps of: 
 subjecting the titanium alloy to finish forming at a forging ratio of 3 or more; and    annealing in the temperature range of from 650 to 900° C.    
     
     
         12 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 4 , and including the steps of: 
 subjecting the titanium alloy to finish forming at a forging ratio of 3 or more; and    annealing in the temperature range of from 650 to 900° C.    
     
     
         13 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 5 , and including the steps of: 
 subjecting the titanium alloy to finish forming at a forging ratio of 3 or more; and    annealing in the temperature range of from 650 to 900° C.    
     
     
         14 . The method for producing the high-strength low-alloy titanium alloy as set forth in  claim 6 , and including the steps of: 
 subjecting the titanium alloy to finish forming at a forging ratio of 3 or more; and    annealing in the temperature range of from 650 to 900° C.