Method for determining microstructure of titanium alloy and method for producing titanium alloy

Abstract

A method for determining a microstructure of a titanium alloy includes determining a microstructure morphology of a titanium alloy based on a relational expression including a mechanical property parameter relating to a mechanical property of the titanium alloy, a microstructure parameter relating to a microstructure of the titanium alloy, and a composition parameter relating to a composition of the titanium alloy.

1 . A method for determining a microstructure of a titanium alloy, comprising
 determining a microstructure morphology of a titanium alloy based on a relational expression including a mechanical property parameter relating to a mechanical property of the titanium alloy, a microstructure parameter relating to a microstructure of the titanium alloy, and a composition parameter relating to a composition of the titanium alloy.   
     
     
         2 . The method for determining a microstructure of a titanium alloy according to  claim 1 ,
 wherein the mechanical property parameter includes a parameter relating to a fatigue property, and a parameter relating to at least one of toughness or creep strength,   wherein the microstructure parameter includes a parameter relating to equiaxed α phase area ratio, and a parameter relating to lamellar layer spacing, and   wherein the composition parameter includes at least a parameter relating to aluminum content.   
     
     
         3 . The method for determining a microstructure of a titanium alloy according to  claim 2 ,
 wherein the composition parameter further includes at least one of a parameter relating to nitrogen content, a parameter relating to iron content, or a parameter relating to hydrogen content.   
     
     
         4 . The method for determining a microstructure of a titanium alloy according to  claim 3 ,
 wherein when the parameter relating to creep strength is YS [MPa],
 the parameter relating to toughness is KIC [MPa√m], 
 the parameter relating to the fatigue property is σw [MPa], 
 the parameter relating to equiaxed α phase area ratio is Vα [%], 
 the parameter relating to lamellar layer spacing is DL [μm], 
 the parameter relating to aluminum content is Al [mass %], 
 the parameter relating to nitrogen content is N [mass %], 
 the parameter relating to iron content is Fe [mass %], 
 the parameter relating to hydrogen content is H [mass %]. 
 a first constant is Const 1 , and 
 a 1 , a 2 , b 1 , b 2 , b 3 , c 1 , c 2 , c 3 , and c 4  each represent a coefficient, 
   the relational expression is represented by the following expression (1):
     a 1× DL−a 2× Vα=b 1× YS+b 2×σ w+b 3× KIC+c 1×Al− c 2×N− c 3×Fe+ c 4×H−Const1   (1), and
 
   wherein the coefficient a 1  is 30 or more and 300 or less,
 the coefficient a 2  is 1 or more and 10 or less, 
 the coefficient b 1  is 0.5 or more and 5 or less, 
 the coefficient b 2  is 0.1 or more and 2 or less, 
 the coefficient b 3  is 5 or more and 50 or less, 
 the coefficient c 1  is 100 or more and 150 or less, 
 the coefficient c 2  is 1000 or more and 20000 or less, 
 the coefficient c 3  is 400 or more and 5000 or less, 
 the coefficient c 4  is 500 or more and 5000 or less, and 
 the first constant Const 1  is 1000 or more and 20000 or less. 
   
     
     
         5 . The method for determining a microstructure of a titanium alloy according to  claim 3 ,
 wherein the composition parameter further includes at least one of a parameter relating to carbon content or a parameter relating to vanadium content.   
     
     
         6 . The method for determining a microstructure of a titanium alloy according to  claim 5 ,
 wherein when the parameter relating to creep strength is YS [MPa],
 the parameter relating to toughness is KIC [MPa√m], 
 the parameter relating to the fatigue property is σw [MPa], 
 the parameter relating to equiaxed α phase area ratio is Vα [%], 
 the parameter relating to lamellar layer spacing is DL [μm], 
 the parameter relating to aluminum content is Al [mass %], 
 the parameter relating to nitrogen content is N [mass %], 
 the parameter relating to iron content is Fe [mass %], 
 the parameter relating to hydrogen content is H [mass %], 
 the parameter relating to carbon content is C [mass %], 
 the parameter relating to vanadium content is V [mass %], 
 a second constant is Const 2 , and 
 a 1 , a 2 , b 1 , b 2 , b 3 , c 1 , c 2 , c 3 , c 4 , c 5 , and c 6  each represent a coefficient, 
   the relational expression is represented by the following expression (2):
     a 1× DL−a 2× Vα=b 1× YS+b 2×σ w+b 3× KIC+c 1×Al− c 2×N− c 3×Fe' c 4×H− c 5×C+ c 6×V−Const2   (2), and
 
   wherein the coefficient a 1  is 30 or more and 300 or less,
 the coefficient a 2  is 1 or more and 10 or less, 
 the coefficient b 1  is 0.5 or more and 5 or less, 
 the coefficient b 2  is 0.1 or more and 2 or less, 
 the coefficient b 3  is 5 or more and 50 or less, 
 the coefficient c 1  is 100 or more and 150 or less, 
 the coefficient c 2  is 1000 or more and 20000 or less, 
 the coefficient c 3  is 400 or more and 5000 or less, 
 the coefficient c 4  is 500 or more and 5000 or less, 
 the coefficient c 5  is 500 or more and 5000 or less. 
 the coefficient c 6  is 10 or more and 200 or less, and 
 the second constant Const 2  is 1000 or more and 20000 or less. 
   
     
     
         7 . A method for producing a titanium alloy, comprising
 a step of calculating a condition which the microstructure parameter has to meet, based on the relational expression according to  claim 1 ,   a step of determining a value of the microstructure parameter, based on the condition,   a step of setting a heat treatment condition for achieving the determined value of the microstructure parameter, and   a step of performing heat treatment under the set heat treatment condition.   
     
     
         8 . The method for producing a titanium alloy according to  claim 7 ,
 wherein the microstructure parameter includes a parameter relating to equiaxed α phase area ratio, and a parameter relating to lamellar layer spacing, and   wherein the step of determining the value of the microstructure parameter includes:
 a first determination step of determining a value of one parameter of the parameter relating to equiaxed α phase area ratio or the parameter relating to lamellar layer spacing, and 
 a second determination step of determining a value of the other parameter of the parameter relating to equiaxed α phase area ratio or the parameter relating to lamellar layer spacing, based on the value of the one parameter determined in the first determination step and the condition. 
   
     
     
         9 . The method for producing a titanium alloy according to  claim 8 ,
 wherein the first determination step includes determining the parameter relating to equiaxed α phase area ratio, and   wherein the second determination step includes determining the parameter relating to lamellar layer spacing.   
     
     
         10 . The method for producing a titanium alloy according to  claim 8 ,
 wherein the first determination step includes determining the parameter relating to lamellar layer spacing, and   wherein the second determination step includes determining the parameter relating to equiaxed α phase area ratio.   
     
     
         11 . The method for producing a titanium alloy according to  claim 7 , further comprising:
 a step of preparing a specimen by performing heat treatment under the set heat treatment condition;   a step of evaluating a mechanical property of the specimen;   a step of determining whether the microstructure parameter determined in the step of determining the value of the microstructure parameter is appropriate, based on an evaluation result in the step of evaluating the mechanical property of the specimen; and   a step of modifying at least one of the value of the microstructure parameter or a value of the composition parameter if it is determined that the value of the microstructure parameter is not appropriate in the step of determining whether the microstructure parameter is appropriate.   
     
     
         12 . The method for producing a titanium alloy according to  claim 8 , further comprising:
 a step of preparing a specimen by performing heat treatment under the set heat treatment condition;   a step of evaluating a mechanical property of the specimen;   a step of determining whether the microstructure parameter determined in the step of determining the value of the microstructure parameter is appropriate, based on an evaluation result in the step of evaluating the mechanical property of the specimen; and   a step of modifying at least one of the value of the microstructure parameter or a value of the composition parameter if it is determined that the value of the microstructure parameter is not appropriate in the step of determining whether the microstructure parameter is appropriate.   
     
     
         13 . The method for producing a titanium alloy according to  claim 9 , further comprising:
 a step of preparing a specimen by performing heat treatment under the set heat treatment condition;   a step of evaluating a mechanical property of the specimen;   a step of determining whether the microstructure parameter determined in the step of determining the value of the microstructure parameter is appropriate, based on an evaluation result in the step of evaluating the mechanical property of the specimen; and   a step of modifying at least one of the value of the microstructure parameter or a value of the composition parameter if it is determined that the value of the microstructure parameter is not appropriate in the step of determining whether the microstructure parameter is appropriate.   
     
     
         14 . The method for producing a titanium alloy according to  claim 10 , further comprising:
 a step of preparing a specimen by performing heat treatment under the set heat treatment condition;   a step of evaluating a mechanical property of the specimen;   a step of determining whether the microstructure parameter determined in the step of determining the value of the microstructure parameter is appropriate, based on an evaluation result in the step of evaluating the mechanical property of the specimen; and   a step of modifying at least one of the value of the microstructure parameter or a value of the composition parameter if it is determined that the value of the microstructure parameter is not appropriate in the step of determining whether the microstructure parameter is appropriate.