Titanium alloy material, parts, heat treatment simulation method, heat treatment simulation apparatus, program, and method for manufacturing titanium alloy material.

Abstract

This invention discloses a rod-shaped or wire-shaped titanium alloy material made of an α+β type titanium alloy, which exhibits small variation in tensile properties. [Solution] The titanium alloy material of the present disclosure is a rod-shaped or wire-shaped titanium alloy material made of an α+β type titanium alloy, characterized in that in a cross section perpendicular to the longitudinal direction, it has an equiaxed α phase and a transformed β structure, the average value of the equivalent circle diameter of the equiaxed α phase is 20.0 μm or less, the standard deviation of the equivalent circle diameter of the equiaxed α phase is 8.0 μm or less, and the average value of the aspect ratio of the equiaxed α phase is 5.0 or less.

Description

Technical Field

[0001] This application discloses a titanium alloy material, parts, a heat treatment simulation method, a heat treatment simulation apparatus, a program, and a method for manufacturing a titanium alloy material.

Background Art

[0002] Titanium alloys are applied to aircraft structural materials, airframe parts such as seat rails and window frames, engine parts, parts of automobiles such as connecting rods, valves and mufflers, consumer products such as golf club heads and building materials, etc., taking advantage of their light weight and excellent corrosion resistance. In addition, due to their good biocompatibility, they are also widely used in medical applications such as implants, and in decorative items such as watches and glasses frames.

[0003] An example of the manufacturing process of a general titanium alloy material will be described. First, sponge titanium, master alloy, titanium scrap, etc. are used as melting raw materials, and an ingot is manufactured by a vacuum arc melting method, an electron beam melting method, a plasma melting method, etc. Next, in order to adjust the coarse grain structure derived from casting, the ingot is heated to the β single-phase region or the α+β two-phase region, and breakdown processing by forging or rolling is performed to obtain a hot working material such as a slab or a billet. The hot working material is subsequently hot worked into the shape of a plate or a bar. The hot worked material composed of these plates and bars may be annealed and pickled to become a product as it is, or may be further cold worked and annealed to remove strain according to the required dimensions and properties to become a product. In this application, these are referred to as titanium alloy materials.

[0004] In titanium ingots, especially large ingots, coarse crystal grains with particle sizes of several tens of millimeters are formed. Furthermore, in α+β type titanium alloys, the β⇒α transformation progresses as the temperature decreases during hot working, significantly increasing deformation resistance. Therefore, when hot working α+β type titanium alloys, the load limit of the equipment is often exceeded in general hot working equipment, making processing impossible. For these reasons, the division of α+β type titanium alloy ingots has traditionally been carried out by forging using forging equipment with a large load limit, involving repeated heating and processing. This increases costs and reduces production efficiency. On the other hand, pure titanium and α type titanium alloys, which have excellent formability, have a small amount of solid solution strengthening due to alloying elements, so the increase in deformation resistance due to the β⇒α transformation is also small. For this reason, such problems are less likely to manifest in pure titanium and α type titanium alloys.

[0005] In light of the above circumstances, in the manufacture of α+β type titanium alloy materials, methods have been proposed to omit the ingot forging process and achieve highly efficient hot working, such as heating to a predetermined temperature, inclined rolling at a cross-sectional reduction rate determined with respect to the heating temperature, followed by reheating and hot rolling again; a method that refines the microstructure by combining processing and heat treatment; and a method that performs α+β two-phase rolling after β→α transformation by reheating.

[0006] For example, Patent Document 1 discloses a manufacturing method for obtaining rods and wires with excellent surface quality and no cracks, etc., by heating a rolled titanium or titanium alloy material to a predetermined temperature, then performing inclined rolling at a predetermined cross-sectional reduction rate corresponding to the heating temperature, then reheating or holding it in a heating device, and then rolling it using die rolling.

[0007] Patent Document 2 discloses a manufacturing method in which an ingot is rapidly cooled from a temperature above the β transformation point at a cooling rate of 5°C / second or more without splitting the ingot, followed by hot working in the α+β two-phase region, and then held at a temperature within 50°C just below the β transformation point.

[0008] Patent Document 3 discloses a method for manufacturing rolled titanium alloy material, in which an α+β type titanium alloy ingot is heated to 1000-1150°C, then subjected to β single-phase region bloc rolling at 950°C or higher with a forging ratio of 1.5 or higher, and then the resulting bloc-rolled material is cooled to 800°C or lower, reheated to 850-950°C, and subjected to α+β bloc rolling with a forging ratio of 2 or higher. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 6-292906 [Patent Document 2] Japanese Patent Application Publication No. 3-120343 [Patent Document 3] Japanese Patent Application Publication No. 58-25424 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] When obtaining hot-worked α+β type titanium alloys, it is important that the ingot can be processed using a general hot-working apparatus, omitting the ingot forging process, and that stable and excellent properties can be obtained after processing. For example, it is preferable that the variation in the tensile properties of the titanium alloy rod or wire obtained after hot-working is as small as possible. (1) In the conventional technology, there is room for improvement in reducing the standard deviation of the tensile properties of α+β type titanium alloy rods or wires. (2) It cannot be said that sufficient research has been conducted on hot working conditions that allow for efficient hot working of α+β type titanium alloy ingots using general equipment, without the need for fractional forging, while also minimizing the standard deviation of the tensile properties of the hot-worked material and obtaining stable and excellent properties. For this reason, there is room to consider the use of (heat treatment) simulations based on numerous experimental results. (3) Furthermore, in the analysis of induction heating, which has a high heating rate and is therefore frequently used for reheating on manufacturing lines, magnetic field analysis is necessary in addition to FEM analysis. Since induction heating generally uses frequencies of 50 to 450 kHz, the time step for its analysis should be a maximum of 2.0 × 10⁻⁶ -9 The time step needs to be around a second. If such a time step is adopted, FEM analysis of manufacturing processes such as heat treatment and processing of ingots cannot be completed in a realistic time. In this regard, when manufacturing various metal materials such as α+β type titanium alloy materials, a new analytical method is needed that can accurately match the heat transfer analysis simulating induction heating with the actual thermal history applied to the metal material. [Means for solving the problem]

[0011] This application discloses several embodiments as means for solving each of the problems (1) to (3) above. <Aspect 1> A rod-shaped or wire-shaped titanium alloy material made of α+β type titanium alloy, In a cross-section perpendicular to the longitudinal direction, it has an equiaxed α phase and a transformed β structure. The average value of the equivalent circular diameter of the equiaxed α phase is 20.0 μm or less. The standard deviation of the equivalent circular diameter of the equiaxed α phase is 8.0 μm or less, and The average aspect ratio of the aforementioned equiaxial α phase is 5.0 or less. Titanium alloy material. <Aspect 2> A titanium alloy material according to embodiment 1, When a tensile test is performed with the longitudinal direction as the tensile direction, the standard deviation of the 0.2% proof stress is 30 MPa or less, and the standard deviation of elongation is 1.0% or less. Titanium alloy material. <Aspect 3> A titanium alloy material according to embodiment 1 or 2, In mass percent, Al: 5.5-6.75%, V: 3.5~4.5%, Fe: 0~0.40%, O: 0~0.20%, C: 0~0.08%, N: 0~0.05%, H: 0~0.015%, and Remainder: Ti and impurities Having a chemical composition consisting of, Titanium alloy material. <Aspect 4> A titanium alloy material according to embodiment 1 or 2, In mass percent, Al: 2.5-3.5% V: 2.0~3.0%, Fe: 0~0.25%, O: 0~0.15%, C: 0~0.08%, N: 0~0.05%, H: 0~0.015%, and Remainder: Ti and impurities Having a chemical composition consisting of, Titanium alloy material. <Aspect 5> A titanium alloy material according to embodiment 1 or 2, In mass percent, Al: 4.4-6.5% Fe: 0.5~2.9%, Si: 0~0.50%, O: 0~0.25%, C: 0~0.08%, N: 0~0.05%, Ni: 0~0.15%, Cr: 0~0.25%, Mn: 0~0.25%, and The remainder consists of Ti and impurities. The chemical composition has the following content of Fe, Ni, Cr, and Mn, expressed in mass percent: %Fe, %Ni, %Cr, and %Mn satisfying the condition 0.5% ≤ %Fe + %Ni + %Cr + %Mn ≤ 2.9%. Titanium alloy material. <Aspect 6> A component comprising a titanium alloy material according to embodiments 1 to 5. <Aspect 7> A heat treatment simulation method including the following steps 1-3: Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution. <Aspect 8> The heat treatment simulation method described in Embodiment 7, including steps I to III below: Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform a convergence calculation of the temperature change rates of each phase for each time and temperature. <Pattern 9> A heat treatment simulation method according to embodiment 7 or 8, including steps A to C below: Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature. <Aspect 10> A heat treatment simulation method according to embodiment 9, Based on the phase fraction of each phase obtained by the aforementioned coupled analysis calculation, the deformation resistance for each time and temperature is predicted. Heat treatment simulation method. <Aspect 11> A heat treatment simulation device, It has a first calculation unit, a second calculation unit, and a third calculation unit, The first calculation unit calculates the Joule heat distribution due to eddy currents generated in the metal material inside the coil using the magnetic field obtained by assuming the heating coil is a solenoid, The second calculation unit calculates the temperature of each element of the metal material based on an FEM model for heat transfer analysis of the metal material, The third calculation unit calculates the amount of heat generated by each element in the FEM model using the Joule heat distribution. Heat treatment simulation device. <Aspect 12> A heat treatment simulation apparatus according to embodiment 11, It has an analysis unit, a prediction unit, and a coupled analysis calculation unit. The analysis unit performs plastic deformation analysis and heat transfer analysis of the metal material when the metal material is heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. The prediction unit uses 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the processing heat generation amount to predict the temperature change rate in the heat transfer analysis. The coupled analysis calculation unit performs the coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in the analysis unit, or by repeatedly performing the analysis in the analysis unit and the prediction in the prediction unit to calculate the convergence of the temperature change rate of each phase for each time and temperature. Heat treatment simulation device. <Aspect 13> A heat treatment simulation apparatus according to embodiment 11 or 12, It has a first prediction unit, a second prediction unit, and a coupled analysis calculation unit. The first prediction unit predicts the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a preset temperature change rate, for the β / α transformation of the α+β type titanium alloy material. The second prediction unit predicts the latent heat of transformation associated with each phase for each time and temperature based on the transformation rate of each phase for each time and temperature predicted by the first prediction unit, and predicts the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation. The coupled analysis calculation unit performs the coupled analysis calculation by either introducing the temperature change rate predicted by the second prediction unit into the temperature change rate in the first prediction unit, or by repeatedly performing the predictions in the first prediction unit and the second prediction unit to perform convergence calculations for the transformation rate of each phase and the temperature change rate for each time and temperature. Heat treatment simulation device. <Aspect 14> A heat treatment simulation apparatus according to embodiment 13, It has a third prediction unit, The third prediction unit predicts the deformation resistance for each time and temperature based on the phase fraction of each phase obtained by the coupled analysis calculation unit. Heat treatment simulation device. <Aspect 15> A program that operates a computer as a heat treatment simulation device, To the aforementioned computer, Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution due to eddy currents generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution. A program that executes something. <Aspect 16> A program according to embodiment 15, To the aforementioned computer, Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform convergence calculations for the temperature change rates of each phase for each time and temperature. A program that executes something. <Aspect 17> A program according to embodiment 15 or 16, To the aforementioned computer, Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature. A program that executes something. <Aspect 18> A program according to embodiment 17, To the aforementioned computer, Based on the phase fraction of each phase obtained by the aforementioned coupled analysis calculation, the deformation resistance for each time and temperature is predicted. A program that executes something. <Aspect 19> A method for manufacturing rod-shaped or wire-shaped titanium alloy materials made of α+β type titanium alloy, To obtain an ingot made of α+β type titanium alloy, The ingot is heated in a heating furnace at a set temperature T1 for a furnace time t1, and then T β +30℃ or higher and T β Below +300℃ (where T β A first hot working process is performed at the temperature of the β transformation point (where is the β transformation point) to obtain a first intermediate material with a reduction ratio of 60% or more. Without processing the first intermediate material at a temperature above the β transformation point, T β -200℃ or higher and T β To obtain a second intermediate material by performing a second hot working process with a reduction ratio of 30% or more at a temperature below °C, and, The second intermediate material is heated in one or more of the following: an atmospheric furnace, an atmospheric furnace, and an induction heating furnace, followed by hot rolling as a third hot working process, and then heated in an induction heating furnace after the third hot working process, followed by hot rolling as a fourth hot working process, to obtain a rod-shaped or wire-shaped titanium alloy material. Includes, The temperature in the third hot working and the fourth hot working is T β -200℃ or higher and T β Below -20℃, The total reduction ratio of the third and fourth hot working processes is 70% or more. A method for manufacturing titanium alloy materials. <Aspect 20> A method for manufacturing a titanium alloy material according to embodiment 19, The shape of the cross-section of the ingot perpendicular to its longitudinal direction is rectangular. A method for manufacturing titanium alloy materials. <Aspect 21> A method for manufacturing a titanium alloy material according to aspect 19 or 20, where the ratio L / S of the perimeter L (mm) of the cross-section to the area S (mm 2 ) of the cross-section perpendicular to the longitudinal direction of the ingot is 0.005 or more, A method for manufacturing a titanium alloy material. <Aspect 22> A method for manufacturing a titanium alloy material according to any one of aspects 19 to 21, where the second hot working is performed during the latency period of the β⇒α transformation or during the transformation, A method for manufacturing a titanium alloy material. <Aspect 23> A method for manufacturing a titanium alloy material according to any one of aspects 19 to 22, where the current value and frequency of the induction heating furnace are determined based on the results obtained by any one of the heat treatment simulation methods of aspects 7 to 10, A method for manufacturing a titanium alloy material.

Advantages of the Invention

[0012] The titanium alloy material of the present disclosure has a small standard deviation of tensile properties. Further, the method for manufacturing the titanium alloy material of the present disclosure can perform hot working on an ingot of an α+β type titanium alloy using a general apparatus, omitting block forging, and can reduce the standard deviation of the tensile properties of the hot worked material. Furthermore, according to the heat treatment simulation method, apparatus, and program of the present disclosure, the accuracy of the agreement between the heat transfer analysis simulating induction heating and the actual heat history applied to the metal material can be improved. For example, it is possible to accurately determine appropriate induction heating conditions in the method for manufacturing a bar-shaped or wire-shaped titanium alloy material.

Brief Description of the Drawings

[0013] [Figure 1] An example of the metal structure constituting an α+β type titanium alloy is shown. [Figure 2]This shows the microstructure after processing a processed FM test specimen (φ8×12mm) taken from a Ti-6Al-4V ingot (Tβ=1000℃), an α+β type titanium alloy, by heating and holding it in the β single-phase region, then processing it in the α+β two-phase region at 930℃ (Tβ-70℃), and holding it for 1000 seconds. [Figure 3] This paper presents the results of investigating the hot deformation resistance under various temperature histories using a φ8 × L12 mm processed Formaster (FM) test specimen taken from a Ti-6Al-4V ingot, which is an α+β type titanium alloy. [Figure 4] This shows the relationship between temperature, stress, and microstructure in heat treatment simulations. [Figure 5] This shows the temperature dependence of the density of carbon steel and the density of α+β type titanium alloy (Ti-6Al-4V), respectively. [Figure 6] This diagram schematically shows the coordinate system used during induction heating of a round billet. [Figure 7] This graph compares the analytical values ​​and experimental values ​​of the temperature transition during induction heating. [Figure 8] The analysis results for the distance from the center of the billet and the maximum temperature reached are shown. [Figure 9] This shows the tissue observation results in the C section of the billet. [Modes for carrying out the invention]

[0014] 1. Background leading to the present invention In α+β type titanium alloys, the β⇒α transformation progresses as the temperature decreases from the β transformation point, increasing deformation resistance. Therefore, α+β type titanium alloys can become difficult to process as the temperature decreases. For this reason, the heating temperature before processing is set to the high-temperature range of the α+β two-phase system, and reheating is performed as needed using a heating device installed on the production line. Induction heating devices, which have a high heating rate, are often used for heating on the production line. To propose a processing process that is feasible within equipment constraints, we investigated methods for predicting the temperature during induction heating and methods for predicting deformation resistance considering temperature and phase fraction. The methods in this invention can also be applied to heating using atmospheric furnaces or inert gas atmosphere furnaces, in addition to induction heating devices.

[0015] Furthermore, in α+β type titanium alloys, as the temperature decreases from the β single-phase region and the β⇒α transformation occurs, grain boundary α phases are generated at the β grain boundaries and lamellar α phases are generated within the β grains. In particular, the grain boundary α phases tend to grow in the width direction. Widely grown grain boundary α phases are difficult to refine during hot working in the α+β two-phase region. When wide grain boundary α phases are present in α+β type titanium alloys, these grain boundary α phases tend to become the starting point for fracture under tension and fatigue. Specifically, stress concentrates in the wide grain boundary α phases, causing voids to form, leading to crack propagation and fracture. Therefore, suppressing the precipitation of grain boundary α phases or separating them by continuing hot working in the α+β two-phase region is considered effective in improving the properties of hot-worked materials. On the other hand, as the temperature decreases, α+β type titanium alloys undergo the β⇒α transformation, which reduces ductility, making them more susceptible to cracking and surface defects during hot working, or increasing deformation resistance, making processing impossible. Therefore, in hot working in the α+β two-phase region, processing and heating are repeated, or reheating is performed using heating equipment installed on the line. For reheating, induction heating, which has a high heating rate, is sometimes used. Compared to heating in atmospheric furnaces using air or inert atmospheres, reheating by induction heating has a shorter heating time, resulting in a large temperature difference between the surface and the center of the cross section perpendicular to the longitudinal direction. This temperature difference also changes with the transport time, and the temperature from the surface decreases as the transport time increases. A large temperature difference leads to variations in microstructure and mechanical properties. In particular, in the center, if the temperature is high, the grain boundary α phase grows broadly, or the temperature rises to the β single-phase region due to heat generation during processing, resulting in a significant decrease in mechanical properties. On the other hand, if the temperature of the surface layer is low, ductility decreases, surface defects occur, deformation resistance increases, and processing stops. Therefore, we investigated processing temperatures and processing amounts that efficiently separate the grain boundary α phase, as well as methods to reduce variations in microstructure and mechanical properties in the cross section perpendicular to the longitudinal direction.

[0016] As a result of diligent research, the inventors have discovered that the grain boundary α phase of an α+β type titanium alloy can be finely controlled by processing it during the latency period of the β⇒α transformation, and that the grain boundary α phase can be efficiently separated by controlling the processing temperature and amount of processing in the subsequent α+β two-phase region processing. Furthermore, they have found that by manufacturing a titanium alloy material in this manner, an α+β type titanium alloy material can be obtained in which, for a cross-section perpendicular to the longitudinal direction of the titanium alloy material, the average equivalent circle diameter of the equiaxed α phase in the cross-section is 20.0 μm or less, the standard deviation of the equivalent circle diameter is 8.0 μm or less, and the average aspect ratio is 5.0 or less, resulting in a material with small variations in mechanical properties within the cross-section. In addition, such a titanium alloy material is obtained by hot working an ingot under predetermined conditions to obtain an intermediate material (titanium alloy billet), and then T β -200℃ or higher and T β We found that it can be manufactured by heating at a predetermined temperature and time to below -20℃, and then performing hot working with a reduction ratio of 70% or more while reheating under predetermined conditions. Furthermore, we found that the intermediate material, the titanium alloy billet, is made by T β +30℃ or higher and T β After heating to a temperature of +300℃ or lower, a first hot working process with a surface area reduction of 60% or more is performed, T β Without processing at temperatures above, β -200℃ or higher and T β It was also found that it is preferable to perform a second hot working process at temperatures below ℃ with a reduction in surface area of ​​30% or more. The second hot working process is preferably performed during the latency period of the β→α transformation or during the transformation itself. Furthermore, to investigate these manufacturing conditions, an induction heating analysis technique was developed that can be performed in conjunction with FEM analysis.

[0017] The following describes a titanium alloy material, its manufacturing method, parts, and a heat treatment simulation method, heat treatment simulation apparatus, and program according to one embodiment.

[0018] 2. Titanium alloy material The titanium alloy material of this disclosure is a rod-shaped or wire-shaped titanium alloy material made of an α+β type titanium alloy. The titanium alloy material of this disclosure has an equiaxed α phase and a transformed β structure in a cross section perpendicular to the longitudinal direction. Here, the average value of the equivalent circle diameter of the equiaxed α phase is 20.0 μm or less, the standard deviation of the equivalent circle diameter of the equiaxed α phase is 8.0 μm or less, and the average value of the aspect ratio of the equiaxed α phase is 5.0 or less. The titanium alloy material of this disclosure has a small standard deviation of tensile properties because the average value of the equivalent circle diameter of the equiaxed α phase, the standard deviation of the equivalent circle diameter of the equiaxed α phase, and the average value of the aspect ratio of the equiaxed α phase are below a predetermined level. For example, when a tensile test is performed with the longitudinal direction as the tensile direction, the titanium alloy material of this disclosure may have a standard deviation of 30 MPa or less for the 0.2% yield strength and a standard deviation of 1.0% or less for the elongation.

[0019] 2.1 Chemical composition The chemical composition of the titanium alloy material disclosed herein may be that which is described as an α+β type titanium alloy in JIS H4600 (plates and strips), JIS H4650 (bars), JIS H4670 (wires), ASTM B265 (Strip, Sheet, and Plate), and ASTM B348 (Bars and Billets), or it may be otherwise. For example, the titanium alloy material may have a chemical composition consisting of, by mass%, Al: 5.5~6.75%, V: 3.5~4.5%, Fe: 0~0.40%, O: 0~0.20%, C: 0~0.08%, N: 0~0.05%, H: 0~0.015%, with the remainder being Ti and impurities. Alternatively, the titanium alloy material may have a chemical composition consisting of, by mass%, Al: 2.5-3.5%, V: 2.0-3.0%, Fe: 0-0.25%, O: 0-0.15%, C: 0-0.08%, N: 0-0.05%, H: 0-0.015%, with the remainder being Ti and impurities. Alternatively, the titanium alloy material may have a chemical composition consisting of, by mass%, Al: 4.4-6.5%, Fe: 0.5-2.9%, Si: 0-0.50%, O: 0-0.25%, C: 0-0.08%, N: 0-0.05%, Ni: 0-0.15%, Cr: 0-0.25%, Mn: 0-0.25%, and the remainder being Ti and impurities, where the mass% content of Fe, Ni, Cr, and Mn (%Fe, %Ni, %Cr, %Mn) satisfies the condition 0.5% ≤ %Fe + %Ni + %Cr + %Mn ≤ 2.9%. The remainder of the chemical composition of the titanium alloy material according to this embodiment may be Ti and impurities, as described above. Impurities include, but are not limited to, Cl, Na, Mg, Ca, B introduced during the refining process, and Zr, Sn, Mo, Nb, Ta, V introduced from scrap, etc. An impurity level is acceptable if the content of each element is 0.1% or less, and the total amount is 0.5% or less.

[0020] 2.2 Shape The shape of the titanium alloy material in this disclosure is rod-shaped or linear. The rod-shaped or linear titanium alloy material may have a length of, for example, 0.1m to 100m, 0.1m to 50m, or 0.1m to 10m, and the equivalent diameter of the cross-section perpendicular to its longitudinal direction may be 3mm to 50mm, 5mm to 40mm, or 8mm to 20mm. The shape of the cross-section perpendicular to the longitudinal direction of the rod-shaped or linear titanium alloy material is not particularly limited and may be, for example, circular (including elliptical and oblong shapes), angular, or other shapes. In this application, the "longitudinal direction" of the titanium alloy material means the direction that coincides with the hot rolling direction of the titanium alloy material.

[0021] 2.3 Organization Figure 1 shows an example of the microstructure of an α+β type titanium alloy. As mentioned above, when an ingot is processed in the β single-phase region and then heated and processed in the α+β two-phase region, an equiaxed α phase and a transformed β structure (a structure consisting of lamellar α phase and lamellar β phase) are obtained, as shown in Figure 1.

[0022] 2.3.1 Equiaxed α phase The equiaxed α phase is equiaxed as its name suggests when the amount of processing in the α+β two-phase region is sufficiently large, but when the amount of processing is small, it takes on an elongated form with a large aspect ratio. Here, in a cross section perpendicular to the longitudinal direction of the titanium alloy material, the strength of the titanium alloy material tends to decrease as the average value of the equivalent circle diameter of the equiaxed α phase increases. This is because dislocations during processing tend to accumulate at the grain boundaries of the equiaxed α phase, and as the equivalent circle diameter increases, the internal stress generated at the grain boundaries increases, making it easier for voids, which are the starting points for tensile and fatigue fracture, to occur. In this embodiment, the average value of the equivalent circle diameter of the equiaxed α phase is 20.0 μm or less, preferably 15.0 μm or less, and more preferably 10.0 μm or less. The lower limit of the average value of the equivalent circle diameter of the equiaxed α phase is not particularly limited and may be, for example, 1.0 μm or more, 2.0 μm or more, 4.0 μm or more, or 8.0 μm or more.

[0023] In a cross-section perpendicular to the longitudinal direction of a titanium alloy material, as the standard deviation of the equivalent circular diameter of the equiaxed α phase increases, stress concentration in coarse grains becomes more likely, and the macroscopic strength and ductility of the titanium alloy material tend to decrease. The standard deviation increases with greater temperature variation during hot working. In this embodiment, the standard deviation of the equivalent circular diameter of the equiaxed α phase is 8.0 μm or less, preferably 5.0 μm or less, and more preferably 3.0 μm or less. The lower limit of the standard deviation of the equivalent circular diameter of the equiaxed α phase is not particularly limited and may be, for example, 0.2 μm or more, 0.5 μm or more, or 1.0 μm or more.

[0024] In a cross-section perpendicular to the longitudinal direction of a titanium alloy material, the larger the average aspect ratio of the equiaxed α phase, the more likely stress concentration is to occur, leading to void formation and a decrease in ductility. Furthermore, when the average aspect ratio of the equiaxed α phase is large, voids tend to propagate along the grain boundaries of the equiaxed α phase, becoming the starting point for fracture in tension and fatigue. In this embodiment, the average aspect ratio of the equiaxed α phase is 5.0 or less, preferably 4.0 or less, and more preferably 3.0 or less. The lower limit of the average aspect ratio of the equiaxed α phase is not particularly limited, and is 1.0 or more, but may be greater than 1.0, 1.5 or more, or 2.0 or more.

[0025] Furthermore, the average value, standard deviation, and aspect ratio of the equivalent circular diameter of these equiaxial α phases are thought to interact with each other, resulting in complex characteristics.

[0026] The mean value of the equivalent circle diameter of the equiaxial α phase, the standard deviation of the equivalent circle diameter of the equiaxial α phase, and the aspect ratio of the equiaxial α phase are measured as follows. (1) Observe any nine locations on the cross section perpendicular to the longitudinal direction of the titanium alloy material using an optical microscope. For example, if the equivalent diameter of the circular cross section perpendicular to the longitudinal direction of the titanium alloy material is X mm, observe a total of nine locations on the optical microscope: four at a depth of X / 50, four at X / 4, and one at X / 2, starting from the outer edge of the cross section and moving inward. Each observation field of view should be 3 mm × 3 mm. The four observation locations at depth X / 50 are on two straight lines passing through the centroid of the cross section perpendicular to the longitudinal direction of the titanium alloy material (the approximate center of the 3 mm × 3 mm field of view is on these straight lines), and these two straight lines are orthogonal to each other (i.e., the four observation locations can be in the cardinal directions). The same applies to the four observation locations at depth X / 4. If there are overlapping areas, such as with round bars with a diameter of φ15 mm or less, the entire cross section should be the subject of observation. (2) Identify the equiaxed α phases included in the observation field and measure their major and minor axes, assuming they are ellipses. Specifically, the largest diameter of the equiaxed α phase is considered the major axis, and the largest of the line segments perpendicular to the major axis, from one point on the grain boundary of the equiaxed α phase to another point, is considered the minor axis, and an ellipse having these major and minor axes is assumed. The equivalent diameter of the circle is the geometric mean of the major and minor axes, and the aspect ratio = major axis / minor axis. For all nine fields of view described above, determine the equivalent diameter and aspect ratio for at least 80 equiaxed α phases (i.e., obtain a total of at least 720 values). Note that when measuring the major and minor axes of the equiaxed α phases, there are methods such as observing and measuring the sample after mirror polishing and etching the grain boundaries with an optical microscope, or measuring by SEM-EBSD by considering regions with an orientation difference of 3° or more from adjacent regions as equiaxed α phases, but in this application, the former method will be adopted. (3) For the 720 or more equivalent circle diameters obtained, calculate their arithmetic mean and define this as the "average value of the equivalent circle diameters of the equiaxial α phase," and calculate its standard deviation and define this as the "standard deviation of the equivalent circle diameters of the equiaxial α phase." Also, for the 720 or more aspect ratios obtained, calculate their arithmetic mean and define this as the "average value of the aspect ratios of the equiaxial α phase."

[0027] 2.3.2 Transformed β-tissue (Lamellar tissue of lamellar α-phase and lamellar β-phase) When an α+β type titanium alloy is cooled from the α+β two-phase region, lamellar α phases (side plate α phases) precipitate from the grain boundaries toward the grains in the region that was the β phase at high temperatures. When an α+β type titanium alloy is cooled from the β single-phase region, α phases (grain boundary α phases) precipitate along the grain boundaries at a higher temperature than the side plate α phases. As described above, in the titanium alloy material of this disclosure, variations in tensile properties are suppressed by controlling the equiaxed α phase, and the morphology of the lamellar α phases and lamellar β phases within the transformed β structure is not particularly limited. In the titanium alloy material of this disclosure, the lamellar α phases and lamellar β phases may have the same length and width as those in conventional hot-worked α+β type titanium alloys. For example, the length of the lamellar α phase may be between 1 μm and 10,000 μm, and the aspect ratio of the lamellar α phase may be between 1 and 100,000. Furthermore, the length of the lamellar β phase may be between 1 μm and 10,000 μm, and the aspect ratio of the lamellar β phase may be between 1 and 100,000. The lamellar α phase and lamellar β phase may constitute a layered structure. A layered structure is a structure like that shown in Figure 1, and can also be called a needle-like structure (that is, the terms "lamellar α phase" and "lamellar β phase" used in this application are concepts that include "needle-like α phase," "needle-like β phase," and "plate-like α phase" and "plate-like β phase").

[0028] 2.4 Mechanical Properties As described above, the titanium alloy material of this disclosure has good tensile properties, and in particular, the standard deviation of the tensile properties is small. For example, when a tensile test is performed on the titanium alloy material of this disclosure with the longitudinal direction as the tensile direction, the standard deviation of the 0.2% yield strength may be, for example, 30 MPa or less. Also, the standard deviation of elongation may be, for example, 1.0% or less.

[0029] 2.5 Applications (Parts) The technology disclosed herein also has aspects of a component containing the titanium alloy material described above. The type of such component is not particularly limited. For example, the component may be one of the following: aircraft frame or structural material, airframe components such as seat rails and window frames, engine components, automobile connecting rods, valves and mufflers, or decorative items such as watches and eyeglass frames. The titanium alloy material disclosed herein can be suitably used in automobile connecting rods and eyeglass frames, among other things.

[0030] 3. Manufacturing method of titanium alloy materials The technology disclosed herein also has aspects as a method for manufacturing titanium alloy materials. One embodiment describes a method for manufacturing a rod-shaped or wire-shaped titanium alloy material made of an α+β type titanium alloy, To obtain an ingot made of α+β type titanium alloy, The ingot is heated in a heating furnace at a set temperature T1 for a furnace time t1, and then T β +30℃ or higher and T β Below +300℃ (where T β A first hot working process is performed at the temperature of the β transformation point (where is the β transformation point) to obtain a first intermediate material with a reduction ratio of 60% or more. Without processing the first intermediate material at a temperature above the β transformation point, T β -200℃ or higher and T β To obtain a second intermediate material by performing a second hot working process with a reduction ratio of 30% or more at a temperature below °C, and, The second intermediate material is heated in one or more of the following: an atmospheric furnace, an atmospheric furnace, and an induction heating furnace, followed by hot rolling as a third hot working process, and then heated in an induction heating furnace after the third hot working process, followed by hot rolling as a fourth hot working process, to obtain a rod-shaped or wire-shaped titanium alloy material. This includes, The temperature in the third hot working and the fourth hot working is T β -200℃ or higher and T β Below -20℃, The combined reduction ratio of the third and fourth hot working processes is 70% or more.

[0031] In the above manufacturing method, the heating conditions in the heating furnace and the hot working conditions must be set to the optimal conditions according to the chemical composition, shape (rectangular, cylindrical), and dimensions of the ingot and intermediate material. In this case, it is preferable to predict the optimal conditions using a heat treatment simulation with analysis, and then set the conditions for actual operation based on the prediction results. That is, in the manufacturing method disclosed herein, it is preferable that the above-mentioned various conditions be determined based on the results of a predetermined heat treatment simulation method. Details of the heat treatment simulation will be described later.

[0032] 3.1 Ingot The ingot made of α+β type titanium alloy may be obtained by conventionally known methods. The chemical composition of the ingot may be the same as the chemical composition described above. The microstructure of the ingot may be the as-cast microstructure, and may have a coarse-grained cast structure such as columnar crystals or equiaxed crystals. The shape of the ingot is not particularly limited and may be any shape that allows for hot working as described later. The ingot may be, for example, an ingot, slab, bloom, or billet. The ingot is hot-worked as is without fractional forging. If the cross-sectional shape perpendicular to the longitudinal direction of the ingot is rectangular, it can be hot-worked as is by roll rolling or die rolling to process it into a rod or round bar shape. Similarly, if the cross-sectional shape perpendicular to the longitudinal direction of the ingot is circular, it can also be hot-worked as is by die rolling to process it into a rod or round bar shape. The ingot may have width, thickness, and length. In this case, the width of the ingot may be between 50 mm and 1500 mm, the thickness may be between 30 mm and 1500 mm, and the length may be between 0.1 m and 100 m. Furthermore, if the cross-sectional shape of the ingot is circular, the width and thickness of the ingot shall substantially coincide with the diameter of the circle.

[0033] In the above manufacturing method, the area S (mm²) of the cross-section (transverse plane) perpendicular to the longitudinal direction of the ingot is 2The ratio L / S of the circumference L (mm) of the cross-section to the surface is preferably 0.005 or higher. This is because a larger L / S for titanium material results in greater heat removal from the surface during cooling, thus reducing the difference in thermal history between the surface and the center of the ingot and reducing the difference in microstructure. Furthermore, the time until solidification and the cooling time after solidification are shortened, and the microstructure becomes finer, improving the mechanical properties. From the viewpoint of increasing heat removal, a larger L / S is better, so there is no particular upper limit. As mentioned above, L / S is preferably 0.005 or higher, more preferably 0.006 or higher, and even more preferably 0.008 or higher. In addition, L / S may be, for example, 0.030 or less, 0.025 or less, or 0.020 or less.

[0034] 3.2 Heating and first hot working in a heating furnace In the above manufacturing method, the above ingot is heated in a heating furnace at a set temperature T1 for a furnace time t1, and then T β +30℃ or higher and T β Below +300℃ (where T β A first hot working process is performed at a temperature (where is the β transformation point) with a reduction ratio of 60% or more. This yields a first intermediate material. The first hot working process may also be hot rolling. The first hot working process can be considered equivalent to accretion processing in the β single-phase region.

[0035] The furnace time t1 in a heating furnace is the time the ingot is heated in a heating furnace at the above-mentioned set temperature T1. When heating an ingot in a heating furnace, the furnace set temperature T1 and furnace time t1 are determined by the shape and size of the ingot, the heating method, and the alloy type (including emissivity, specific heat, thermal conductivity, and latent heat of transformation). Naturally, the heat applied to the surface of the ingot diffuses into the interior. Small ingots and rectangular ingots with a large (surface area / volume) have a shorter time t1 because the heat diffusion from the surface to the interior is greater. Also, in rectangular cross-section ingots, the time t1 is limited in the longer side, where the heating rate is slower than in the shorter side. Note that the temperature of the ingot does not need to be uniform; for example, the center of the ingot may be T β At +30℃, the surface of the ingot is T βTemperature distributions such as +200℃ are acceptable. In this case, the time it takes for the temperature of the center of the ingot to decrease to the temperature range for subsequent α+β two-phase processing (second hot working) is shortened, thus shortening the manufacturing time. The set temperature T1 and furnace time t1 should be determined so that the ingot reaches the desired temperature during the first hot working. If the set temperature T1 is too low or the furnace time t1 is too short, the ingot may not reach the desired temperature, and the α⇒β transformation may not be sufficiently promoted. On the other hand, if the set temperature T1 is too high or the furnace time t1 is too long, it may lead to a decrease in manufacturing efficiency, etc.

[0036] In the first hot working stage, the ingot is first heated to the β single-phase region for processing. This is done to refine the microstructure of the cast material, which has poor machinability, by heating it to the β single-phase region, which has relatively good machinability. If the temperature in the first hot working stage is too low, the surface layer undergoes a β-to-α transformation due to heat dissipation from contact with the processing equipment, resulting in a large difference in microstructure between the surface and the interior. On the other hand, if the temperature in the first hot working stage is too high, a thick, hard oxygen-enriched layer forms on the surface of the ingot due to reaction with oxygen in the atmosphere, reducing machinability and causing cracks and indentations during hot working, requiring additional treatment such as mechanical cutting or grinding. β +30℃ or higher and T β These problems are resolved by keeping the temperature below +300℃. Note that "temperature in the first hot working" refers to the temperature of the ingot during the first hot working. That is, in the first hot working, the temperature of both the surface and the core of the ingot is T β +30℃ or higher and T β The temperature should be kept below +300℃. The temperature of the ingot during the first hot working stage may vary depending on the set temperature T1 and time t1 in the heating furnace, as well as the time from the heating furnace to the first hot working stage.

[0037] If the reduction ratio in the first hot working is too low, the microstructure cannot be sufficiently refined. If the reduction ratio in the first hot working (total reduction ratio) is 60% or more, the microstructure can be sufficiently refined, and the tensile properties of the final titanium alloy material will be good. The reduction ratio in the first hot working may be 65% or more, or 70% or more. There is no particular upper limit to the reduction ratio. For example, the reduction ratio may be 90% or less, or 80% or less.

[0038] 3.3 Second Hot Working In the above manufacturing method, the first intermediate material obtained by the first hot working is processed without being subjected to a temperature above the β transformation point, T β -200℃ or higher and T β A second hot working process is performed at a temperature below 30°C to achieve a reduction in surface area (total reduction in surface area) of 30% or more. This yields a second intermediate material. The second hot working process may also be performed by hot rolling.

[0039] After the first hot working (blocking in the β single-phase region), T β Reasons for not processing at the above temperatures, and for performing the second hot working (α+β two-phase processing) at T β -200℃ or higher and T β The reason for performing the process at temperatures below °C will be explained. Figure 2 shows a typical α+β type titanium alloy, Ti-6Al-4V ingot (T β Using a processed FM test specimen (φ8×12mm) taken from 1000℃, after heating and holding in the β single-phase region, 930℃ (T βThis is the microstructure after processing in the α+β two-phase region at -70℃ and holding for 1000s. The latency time for the β⇒grain boundary α phase transformation at 930℃ is approximately 20 seconds, and processing was performed during this latency period. As shown in Figure 2, at a reduction ratio of 0%, a coarse grain boundary α phase with a width of approximately 25 μm was formed at the β grain boundary. On the other hand, the width of the grain boundary α phase decreased with increasing reduction ratio. Furthermore, when processing is performed after the precipitation of the grain boundary α phase, the processing strain acts as a driving force for the refinement of the grain boundary α phase. On the other hand, when processing is performed in the β single-phase region, the processing strain decreases due to recovery and recrystallization, and its contribution to the refinement of the grain boundary α phase is small. For this reason, processing in the β single-phase region, where processing strain is easily reduced by recovery and recrystallization, should be avoided, and processing should be performed where the processing strain contributes to the refinement of the grain boundary α width. β -200℃ or higher and T β The processing is performed at a temperature of less than . The second hot working is preferably performed before the phase fraction reaches equilibrium (during the latency period of the β⇒α transformation, or during the β⇒α transformation), and more preferably during the latency period of the β⇒α transformation.

[0040] Second hot working is T β -200℃ or higher and T β Let me explain another reason for performing the procedure at temperatures below [temperature]. Figure 3 shows the results of investigating the hot deformation resistance under various temperature histories using a φ8 × L12 mm processed Formaster (FM) test piece taken from a Ti-6Al-4V ingot, a typical α+β type titanium alloy. In equilibrium, Ti-6Al-4V has a phase fraction of approximately α phase:β phase = 9:1 at room temperature. The β transformation point temperature is 1000°C, and the α⇒β transformation proceeds between 800°C and 1000°C. Therefore, when a processed FM test piece is heated to the test temperature and held for 10 minutes for processing, the hot deformation resistance decreases between 800°C and 1000°C due to the rise in temperature and the increase in the β phase fraction (white square in Figure 3). βIn the β single-phase temperature range above °C, the hot deformation resistance is small and decreases with increasing temperature, but the decrease is slight. On the other hand, the hot deformation resistance (black square in Figure 3) in the thermal history simulating α+β two-phase processing after fractional processing in the β single-phase range decreased in the temperature range of 800-1000 °C where β / α transformation occurs, compared to the case of heating only (white square in Figure 3). This is because during cooling, there is a time until the start of the β⇒α transformation (latency time) and the transformation time, and the α phase fraction is lower than the equilibrium phase fraction. Thus, the second hot processing is T β If the process is carried out at temperatures below -200℃, the deformation resistance increases significantly due to the β⇒α transformation, which may exceed the upper limit of the load specifications for typical hot working equipment.

[0041] In this way, by controlling the temperature and phase fraction during hot working, the grain size and aspect ratio of the equiaxed α phase in α+β type titanium alloy can be controlled. However, if the set temperature T1 and furnace time t1 in the heating furnace, the temperature during the first hot working, and the temperature during the second hot working cannot be controlled to satisfy the above conditions, a good microstructure cannot be obtained, and problems such as warping with concave surfaces in the temperature-reducing areas with high hot deformation resistance, and processing stoppage due to load exceeding the equipment limit will occur. In particular, in the heat treatment of rectangular ingots, the longer sides of the cross-section perpendicular to the longitudinal direction are less likely to heat and cool compared to the shorter sides. Furthermore, when hot working a rectangular ingot that has sides with lower temperatures and high hot deformation resistance compared to other parts, the workability of those sides is lower than that of other sides, which can lead to surface defects such as ear cracking on those sides, reducing yield, or shape defects such as warping with concave surfaces on those sides, potentially leading to processing stoppage, as well as variations in material properties after hot working.

[0042] In the manufacturing method of the present disclosure, the above-mentioned problems can be more effectively suppressed by setting appropriate heating conditions for the first hot working and the second hot working based on the results of a heat treatment simulation. For example, in the manufacturing method of the present disclosure, the set temperature T1 and the furnace time t1 in the heating furnace may be determined based on the results of a heat treatment simulation method according to the first embodiment described later, the conditions from after heating in the heating furnace to the first hot working may be determined based on the results of a heat treatment simulation method according to the first embodiment described later, and the conditions from the first hot working to the second hot working may be determined based on the results of a heat treatment simulation method according to the first embodiment described later.

[0043] 3.4 Heat treatment simulation method related to the first embodiment As a method for appropriately selecting the set temperature T1 and furnace time t1 in a heating furnace, we investigated a method that couples and analyzes the temperature and phase fraction of an α+β type titanium alloy.

[0044] Conventional heat transfer analysis only analyzes heat conduction due to temperature gradients. Therefore, in titanium, which generates large latent heat of transformation due to β / α transformation, the calculation accuracy near the transformation point is low, and because the transformation cannot be determined, its applicability to deformation resistance and microstructure control is limited.

[0045] On the other hand, in the heat treatment analysis of steel, as shown in Figure 4, analyses that couple the temperature distribution, stress and deformation, and phase transformation of the heat-treated area have been devised and implemented. Phase transformation is considered as an isothermal transformation progressing over a small time interval, from austenite to ferrite, pearlite, bainite, and martensite. The analysis is performed using an isothermal transformation diagram and the isothermal transformation rate, and the latent heat of transformation during the phase transformation is considered in the heat transfer analysis, while the transformation strain is considered in the elastoplastic analysis. Efforts have also been made to consider the stress dependence of the transformation rate. Therefore, we considered using these methods for the heat transfer analysis of α+β type titanium alloy and designing a processing schedule using the obtained temperature history.

[0046] Figure 5 shows the temperature dependence of the density of carbon steel and α+β type titanium alloy (Ti-6Al-4V). In carbon steel, the density changes significantly at point A1 (approximately 727°C) due to α / γ transformation. Therefore, the strain caused by the transformation (transformation strain) is large, and residual stress generated during quenching from the γ region may affect the durability of the product. On the other hand, in α+β type titanium alloys, including Ti-6Al-4V, β / α transformation occurs at the β transformation point (approximately 1000°C), but no significant change in density is observed. Therefore, the transformation strain is smaller than that of steel, and its effect on the stress state is considered to be small. In other words, the effect of volume change due to transformation is small during heating as well as during cooling, and does not need to be considered, but the latent heat associated with transformation needs to be considered. By considering the latent heat of transformation, the accuracy of temperature-microstructure coupled simulations can be improved, and it is thought that it will be possible to provide α+β type titanium alloys with a stable microstructure that strongly affects material properties and manufacturing defects. Furthermore, by carefully timing the β / α transformation and performing processing at the optimal time for the β phase, which has superior processability compared to the α phase, it is possible to provide α+β type titanium with a stable structure.

[0047] The heat treatment simulation method according to the first embodiment is based on the above technical concept. That is, the heat treatment simulation method according to the first embodiment is a heat treatment simulation method for α+β type titanium alloys, The first step involves predicting the transformation start time and the transformation rate of each phase for each time and temperature of the α+β type titanium alloy when it is heated or cooled at a preset temperature change rate. In the first step, based on the predicted transformation rates of each phase for each time and temperature, the latent heat of transformation associated with the transformation is predicted for each time and temperature, and the temperature change rate of the α+β type titanium alloy and the time change rate of the phase fraction of each phase are predicted by heat transfer analysis using the predicted latent heat of transformation. A coupled analysis step is performed by either introducing the temperature change rate predicted in the second step into the temperature change rate in the first step, or by repeatedly performing the first and second steps to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature, and The method comprises the above. In the heat treatment simulation method according to the first embodiment, in the first step, the transformation start time of the β / α transformation is predicted for each of the grain boundary α phase generated on the β grain boundary and the lamellar α phase generated within the β grain, and the transformation rates of the grain boundary α phase and the lamellar α phase are also predicted. Furthermore, in the heat treatment simulation method according to the first embodiment, the heat transfer analysis is performed in the second step using a three-dimensional transient heat conduction equation. Furthermore, in the heat treatment simulation method according to the first embodiment, the deformation resistance for each time and temperature is predicted based on the phase fraction of each phase obtained by the coupled analysis calculation. Furthermore, in the heat treatment simulation method according to the first embodiment, the β grain size for each time and temperature is predicted based on the phase fraction of each phase and temperature obtained by the coupled analysis calculation.

[0048] 3.4.1 Step 1 In the first step, the transformation start time and the transformation rate of each phase for each time and temperature of the α+β type titanium alloy are predicted when it is heated or cooled at a predetermined temperature change rate. The method for predicting the transformation start time and the method for predicting the transformation rate of each phase for each time and temperature will be explained below. Note that the transformation rate of each phase may be predicted for all constituent phases that may be included in the α+β type titanium alloy, but in the following explanation, as an example, the prediction of the transformation rate of the transformation from the β phase to the α phase (β⇒α transformation) during cooling of the α+β type titanium alloy will be explained. Note that the initial value of the predetermined temperature change rate may be obtained by heat transfer analysis from the temperature distribution at the time immediately preceding. Furthermore, the prediction method below can be easily applied to the transformation from the α phase to the β phase (α⇒β transformation) during heating, and to the β / martensitic transformation during heating or cooling.

[0049] When analyzing phase transformation during heat treatment, there are two methods: using a Continuous Cooling Transformation (CCT) diagram or a Time-Temperature Transformation (TTT) diagram. Because it is difficult to control the cooling rate at both the microstructure observation location and the temperature measurement location, the CCT diagram is not a material-specific value. As the size and shape of the component change, countless CCT diagrams exist even under the same cooling conditions. On the other hand, the TTT diagram is material-specific, meaning that once the chemical composition is determined, the physical properties are uniquely determined. Therefore, in one embodiment of the method, a technique is employed to predict phase transformation during continuous cooling using the TTT diagram (predicting the CCT diagram from the TTT diagram).

[0050] As described above, when an α+β type titanium alloy is cooled from the β single-phase region, the α phase (grain boundary α phase) precipitates along the grain boundaries of the β phase, and then lamellar α phase (side plate α phase) precipitates from the grain boundaries toward the grains of the β phase. Among the lamellar α phases, clumps that are aligned in the same orientation are called colonies. Since the timing of the start of the transformation from the β phase to these grain boundary α phases and lamellar α phases differs, it is advisable to perform phase transformation analysis independently for each.

[0051] Furthermore, α+β type titanium alloys such as Ti-6Al-4V and Ti-5Al-1Fe undergo primarily diffusion transformation, although they contain some shear transformation components, even at high cooling rates (e.g., 300°C / s or higher). In actual manufacturing processes, the cooling rate is 10°C / s or less, even with air cooling using fans. Therefore, in the method disclosed herein, it is acceptable to consider the transformation from the β phase to the grain boundary α phase and the lamellar α phase as diffusion transformation for analysis purposes.

[0052] Diffusion-type transformations involve the diffusion of additive elements such as Al and V, and their onset timing depends on the temperature and time history. Scheil's additive rule, shown in equation (1), is used to determine the onset of this transformation.

[0053]

number

[0054] Here, the infinitesimal time of the i-th step in the temperature analysis is Δt i , the latency period until the start of diffusion transformation at the i-step temperature is τ i Let the contribution Δt in each calculation step be as follows. i / τ i The transformation begins when the sum of the values ​​becomes 1.

[0055] To predict the rate of diffusive transformation of the lamellar α phase (transformation rate), for example, the following equation (2), which is a modified version of the Johnson-Mehl equation, can be used.

[0056]

number

[0057] Here, f(T) and n(T) are material constants, which are functions that depend on the alloy type and temperature T. Also, ξ0 is the equilibrium phase fraction at temperature T.

[0058] The grain boundary α phase precipitates at the β grain boundary and then grows in the thickness direction. Therefore, the rate of diffusive transformation can be analyzed using the n-th power law expressed by equation (3) below, with respect to the thickness d of the grain boundary α phase.

[0059]

number

[0060] Here, d is the width of the grain boundary α phase, and nd(T) and k(T) are material constants that depend on the temperature T. The phase fraction of the grain boundary α phase can be calculated using the formula (thickness of the grain boundary α phase / 2) × β grain volume / β grain surface area = 3d / r, where r is the β grain size.

[0061] 3.4.2 Step 2 In the second step, based on the phase transformation rates for each time and temperature predicted in the first step, the latent heat of transformation associated with the transformation is predicted for each time and temperature. Then, using the predicted latent heat of transformation, a heat transfer analysis is performed to predict the temperature change rate of the α+β type or β type titanium alloy and the time change rate of the phase fraction of each phase. In the heat treatment simulation according to the first embodiment, it is preferable to couple the phase transformation analysis in the first step and the temperature analysis according to the heat conduction equation in the second step. In the second step, it is preferable to perform the heat transfer analysis using a three-dimensional transient heat conduction equation, which is commonly used in finite element methods (FEM). An example of a three-dimensional transient heat conduction equation is shown in equation (4) below.

[0062]

number

[0063] Here, ρ: density, c p : constant-pressure specific heat, k: thermal conductivity, T: temperature, t: time, Q: heat generation. Note that the heat conduction equation used in the second step is not limited to equation (4), and depending on the shape of the simulation target, transient heat conduction equations for two-dimensional, one-dimensional, or axisymmetric bodies may be used. Furthermore, on the surface of the simulation target, heat transfer from different materials considering convection, radiation, and contact resistance may be taken into account.

[0064] The heat generation Q includes Joule heating due to induction heating, processing heat generated by plastic deformation work, and latent heat of transformation associated with phase transformation. Equation (5) below describes the latent heat of transformation associated with phase transformation in α+β type titanium alloys.

[0065]

number

[0066] Here, H βα : Latent heat of transformation from β phase to α phase (grain boundary α phase, intragranular α phase), ξ i: These are the volume fractions of the β phase, grain boundary α phase, and intragranular α phase. These volume fractions of the β phase, grain boundary α phase, and intragranular α phase can be determined from the transformation rates for each temperature predicted in the first step.

[0067] Furthermore, the α+β type titanium alloy in the heat treatment process is considered to be a mixture of these three phases, and the linear mixing side is applicable to physical quantities such as specific heat and thermal conductivity. That is, the physical quantity C used in the heat transfer analysis is given by the following equation (6). C in equation (6) i is, i These are physical quantities of the single-phase state (β phase, α phase). The physical quantity C given by equation (6) is the same as ρ and C in equation (4). p This includes k.

[0068]

number

number

[0069] Using equation (6), it is possible to predict not only physical quantities but also macroscopic mechanical properties, such as deformation resistance.

[0070] 3.4.3 Coupled Analysis Step The above coupled analysis of temperature and phase transformation is applicable regardless of whether it is an explicit or implicit method. In the explicit method, the temperature change rate of the α+β type or β type titanium alloy predicted in the second step is introduced into the temperature change rate in the first step to perform the coupled analysis calculation. In the implicit method, the coupled analysis calculation is performed by repeatedly performing the first and second steps to converge the transformation rate of each phase and the temperature change rate for each time and temperature. In the heat treatment simulation method according to the first embodiment, either method may be used for the calculation. Furthermore, the simulation method according to the first embodiment is applicable not only to heat treatment but also to simulations that simultaneously consider plastic deformation.

[0071] For the heat treatment simulation related to the first form, it is possible to perform simulations not only using proprietary programs written in languages ​​such as Fortran and C, but also using the finite element method (FEM) based on the Galerkin method, where the temperature T is defined as a linear sum of the temperature vector φ at each junction and a weight function N. By performing such coupled temperature and phase fraction analysis, it is possible to predict the history of temperature and phase fraction during heat treatment with higher accuracy compared to conventional heat transfer analysis.

[0072] This coupled analysis of temperature and phase fraction allows for the prediction of the temperature and phase fraction history during heat treatment with higher accuracy compared to conventional heat transfer analysis. Below, we will further explain an example of a method for predicting β particle size using the temperature and phase fraction predicted in this way.

[0073] In the β-monophase region, β grains grow according to the following n-th power law.

[0074]

number

[0075] Here, d0 is the initial particle size, d is the particle size after holding at temperature T for t seconds, R is the gas constant, and C and Q are material constants.

[0076] Also, particle size d p From the parent phase to the particle size after transformation d s This can be predicted using the following prediction formula, which takes the grain boundary surface as the nucleation site.

[0077]

number

[0078] Here, Is: nucleation rate, and G: growth rate. In this manner, the β particle size at each time can be predicted based on the temperature and phase fraction at each time obtained by coupled analysis calculations.

[0079] Furthermore, as mentioned above, the simulation method of this disclosure is also applicable to simulations that simultaneously consider elastoplastic deformation. In such calculations, the β grain size after recrystallization can be predicted using the strain and strain rate obtained in the elastoplastic analysis. For such predictions, for example, an expression using the Z parameter has been proposed.

[0080]

number

number

[0081] Here, v: strain rate, Q β , c, and m are material constants. By considering recrystallization using equations (10) and (11), the β grain size can be predicted with higher accuracy.

[0082] As described above, in the manufacturing method of the present disclosure, the first hot working conditions and the second hot working conditions can be determined based on the results of the heat treatment simulation method according to the first embodiment described above. According to the heat treatment simulation method according to the first embodiment, by considering the latent heat of transformation, the thermal history imparted to the α+β type titanium alloy material during heating and cooling can be accurately predicted. For example, the temperature of the ingot can be accurately predicted by the heat treatment simulation method according to the first embodiment, and heating conditions in the heating furnace, such as the set temperature T1 and the furnace time t1, can be determined. Alternatively, the temperature change of the ingot from the heating furnace to the first hot working can be accurately predicted by the heat treatment simulation method according to the first embodiment, and conditions (e.g., time and cooling conditions) from after heating in the heating furnace to the first hot working can be determined. Furthermore, the temperature change of the intermediate material from the first hot working to the second hot working can be accurately predicted by the heat treatment simulation method according to the first embodiment, and conditions (e.g., time and cooling conditions) from the first hot working to the second hot working can be determined.

[0083] 3.5 Third and fourth hot working processes In the above manufacturing method, the second intermediate material obtained by the second hot working is heated in one or more of the following: an atmospheric furnace, an atmospheric furnace, and an induction heating furnace, then subjected to hot rolling as a third hot working step, and further heated in an induction heating furnace after the third hot working step, then subjected to hot rolling as a fourth hot working step to obtain a rod-shaped or wire-shaped titanium alloy material. Here, the temperature in the third and fourth hot working steps is T β -200℃ or higher and T β The temperature is below -20℃, and the total reduction ratio of the third and fourth hot working is 70% or more. In the above manufacturing method, for example, the second intermediate material (titanium alloy billet) obtained by performing the first and second hot working on the ingot is heated, transported, and then heated using a heating device set up on the line, so that the second intermediate material is T β -200℃ or higher and T β Third and fourth hot working are performed with a total cross-sectional area of ​​70% or more while reheating to a temperature below -20°C. In the above manufacturing method, after the second hot working, the second intermediate material may be cooled to room temperature, or it may be heated using one or more of the atmospheric furnace, atmospheric furnace, and induction heating furnace without cooling to room temperature, and then subjected to the third hot working. There is no particular lower limit for the cooling temperature when it is not cooled to room temperature.

[0084] In the third and fourth hot working processes, the second intermediate material is heated to the α+β two-phase region and rolled in order to break up the grain boundary α phase and lamellar α phase, which have a large aspect ratio and constitute the needle-like structure obtained by cooling from the β single-phase region, thereby reducing the aspect ratio. This breakdown occurs when strain and low-angle grain boundaries are created within these α phases during hot working, and the β phase diffuses into them. Therefore, processing in the α+β two-phase region, where the β phase fraction exceeds 50%, promotes the breakdown of the grain boundary α phase and lamellar α phase. However, if the temperature in the third and fourth hot working processes is too low, the surface temperature will drop, especially due to heat dissipation from contact with the processing equipment, resulting in insufficient ductility and surface defects such as wrinkles and scratches, requiring additional treatment by mechanical cutting or grinding. Furthermore, the β phase fraction will decrease, making it difficult for the breakdown to progress and increasing the difference in structure between the surface and the interior. On the other hand, if the temperature during the third and fourth hot working is too high, the heat generated during processing will cause the temperature to exceed the β transformation point, and during subsequent cooling, the grain boundary α phase and lamellar α phase will precipitate again, forming a needle-like structure and preventing the acquisition of an equiaxed structure. β -200℃ or higher and T β These problems are resolved by keeping the temperature below -20℃ and ensuring that the total reduction ratio of the third and fourth hot working processes is 70% or more, thereby obtaining the titanium alloy material of this disclosure.

[0085] Here, the heating device installed on the line may be an atmospheric furnace, an atmospheric furnace, or an induction heating furnace, but heating after the third hot working and before the fourth hot working is preferably performed by an induction heating furnace. The indicators for controlling the temperature of the second intermediate material in these heating devices are the furnace temperature and time in the furnace for atmospheric furnaces, and the current value and frequency for induction heating furnaces, and are determined from the transport time, pass schedule, shape and size of the second intermediate material, and alloy type (including emissivity, specific heat, thermal conductivity, and latent heat of transformation). Naturally, the longer the transport time, the greater the amount of heat removed from the surface before hot working, so the amount of heat that needs to be supplied to the second intermediate material increases. On the other hand, if the amount of heat generated is large due to the large amount of processing, it is necessary to supply enough heat so that the temperature of the entire second intermediate material does not exceed the β transformation point. Considering the above, the lower limit of the target temperature of the billet during reheating is T β The temperature is set to -200°C. On the other hand, regarding the upper temperature limit during reheating, as the temperature rises and the β phase fraction increases, the grain boundary α phase is generated and grows at the β grain boundaries during cooling, and remains with a large aspect ratio, so T β Set the temperature to -20°C.

[0086] In the manufacturing method of this disclosure, it is preferable that appropriate heating conditions for the third and fourth hot working processes be set based on the results of a heat treatment simulation. For example, in the manufacturing method of this disclosure, the furnace temperature and time spent in the atmospheric furnace may be determined based on the results of the heat treatment simulation method according to the first embodiment described above. Furthermore, in the manufacturing method of this disclosure, the current value and frequency of the induction heating furnace may be determined based on the results of the heat treatment simulation method according to the second embodiment described later.

[0087] 3.6 Heat treatment simulation method related to the second form In line-based reheating, induction heating furnaces with high heating rates are frequently used. To appropriately select the settings for these furnaces, we investigated an analytical method that facilitates coupled analysis with FEM analysis. The radial temperature distribution of the intermediate material (billet) during induction heating was analyzed using the following procedure.

[0088] Fig. 6 shows the coordinate system during the induction heating of a round billet. In an infinitely long coil (solenoid), the magnetic field is generated only in the z direction, and the magnetic flux density B inside the solenoid (x < R, R: coil radius) in the absence of a billet z is given by the following equation (12).

[0089] [Number]

[0090] Here, N: number of turns of the coil, L: coil length, μ0: magnetic permeability of vacuum, I = I0sin(ωt): current value, ω = 2πf is the angular frequency calculated from the frequency f, and t is time.

[0091] For an arbitrary point P (coordinates x; x < R b , R b is the billet radius) inside the billet, find the current value I a (x).

[0092] First, the magnetic flux Φ passing through the inside of point P is given by the following equation (13) with the relative magnetic permeability of titanium being μ r (= 1.0001).

[0093] [Number]

[0094] The electromotive force V generated in the infinitesimal region dx at point P a is given by the following equation (14) as the time change of the magnetic flux passing through the inside of the billet at point P (Faraday's law of electromagnetic induction).

[0095] [Number]

[0096] The electrical resistance R per unit length dz of this infinitesimal region a is given by the following equation (15) using the electrical resistivity ρ of the billet, so the induced current I generated at point Pa (x) is given by equation (16).

[0097]

number

number

[0098] In the above, we assumed that the magnetic field generated in the solenoid is constant. In reality, the magnetic field H generated in a solenoid of finite length is different. z (x) increases as the distance x from the central axis of the coil increases. Also, if there is a billet inside the solenoid, the induced current generated in the billet creates a magnetic field inside the billet that cancels out the magnetic field generated by the current flowing through the solenoid.Therefore, in the following, we assume that the induced current actually generated on the billet surface is equal to the product of equation (16) above and a correction value M that takes these effects into account.

[0099] In general, in induction heating, the distribution I(x) of the induced current generated inside the billet is given by the following equation (17).

[0100]

number

number

[0101] δ is called the current penetration depth. Using equation (18) above, the Joule heat Q(x) generated at point P is given by the following equation (20).

[0102]

number

[0103] The Joule heat calculated above is applicable regardless of whether it is an explicit or implicit method. Furthermore, the shape of the intermediate material may be rod-shaped, linear, circular (including elliptical and oblong shapes), angular, or any other shape. Here, the billet radius R b The equivalent radius of the circle of these cross-sections may be used. FEM analysis is applicable to simulations that simultaneously consider plastic deformation. In this case, it is advisable to use 50% to 100% of the plastic working energy generated by plastic deformation as the amount of heat generated by the processing for the heat transfer analysis. Furthermore, in α+β type titanium alloys, a large latent heat of transformation is generated with the phase transformation of the α / β phase. Therefore, in the heat transfer analysis, further accuracy improvements can be expected by calculating and coupling the phase fraction and latent heat of transformation separately from the temperature. The method for calculating and coupling the phase fraction and latent heat of transformation is as explained in the heat treatment simulation related to the first form. Regarding the heat treatment simulation method related to the second form, it is possible to perform simulations using the finite element method (FEM) based on the Galerkin method, by setting the temperature T as a linear sum of the temperature vector φ and weight function N at each junction.

[0104] As described above, according to the manufacturing method of the present disclosure, by going through the first hot working, second hot working, third hot working, and fourth hot working steps described above, it is possible to omit the ingot splitting forging process and directly perform hot working on the α+β type titanium alloy ingot using a general rolling mill, and it is also possible to reduce the standard deviation of the tensile properties of the titanium alloy material (bar or wire) after hot working.

[0105] 4. Heat treatment simulation method The technology disclosed herein also has aspects as a heat treatment simulation method. A heat treatment simulation method according to one embodiment includes the following steps 1 to 3: Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution due to eddy currents generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution.

[0106] The heat treatment simulation method of this disclosure corresponds to the heat treatment simulation according to the second embodiment described above. This heat treatment simulation may be combined with one or both of the following steps I to III and steps A to C.

[0107] In other words, the heat treatment simulation method of this disclosure may include, in addition to steps 1 to 3 above, the following steps I to III: Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform a convergence calculation of the temperature change rates of each phase for each time and temperature.

[0108] Furthermore, the heat treatment simulation method of this disclosure may include, in addition to steps 1 to 3 above, or in addition to steps 1 to 3 and steps I to III above, the following steps A to C: Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature.

[0109] Steps I to III and Steps A to C described above correspond to the first step, second step, and coupled analysis step in the thermal simulation method according to the first embodiment described above. Details are as described above, and further explanation is omitted. In addition, in the heat treatment simulation method of this disclosure, the deformation resistance for each time and temperature may be predicted based on the phase fraction of each phase obtained by the coupled analysis calculation. For example, by predicting the deformation resistance for each time and temperature and incorporating this into the hot working conditions, more appropriate hot working conditions can be determined.

[0110] 5. Heat treatment simulation device Furthermore, the technology of this disclosure also has aspects as a heat treatment simulation device. That is, the heat treatment simulation device of this disclosure has a first calculation unit, a second calculation unit, and a third calculation unit. Here, the first calculation unit calculates the Joule heat distribution due to eddy currents generated in the metal material inside the coil using a magnetic field obtained by assuming the heating coil is a solenoid, the second calculation unit calculates the temperature of each element of the metal material based on an FEM model for heat transfer analysis of the metal material, and the third calculation unit calculates the amount of heat generated by each element in the FEM model using the Joule heat distribution. That is, in the heat treatment simulation device of this disclosure, step 1 described above is performed in the first calculation unit. Step 2 described above is performed in the second calculation unit. Step 3 described above is performed in the third calculation unit.

[0111] As described above, the heat treatment simulation apparatus of this disclosure is an apparatus capable of performing the heat treatment simulation method according to the second embodiment described above. The heat treatment simulation apparatus may further have the following parts.

[0112] In other words, the heat treatment simulation apparatus of this disclosure may have an analysis unit, a prediction unit, and a coupled analysis calculation unit. The analysis unit performs plastic deformation analysis and heat transfer analysis of the metal material when the metal material is heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. The prediction unit uses 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the processing heat generation amount to predict the temperature change rate in the heat transfer analysis. The coupled analysis calculation unit may perform the coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in the analysis unit, or by repeatedly performing the analysis in the analysis unit and the prediction in the prediction unit to perform a convergence calculation of the temperature change rate of each phase for each time and temperature. That is, in the heat treatment simulation apparatus of this disclosure, step I described above may be performed in the analysis unit. Step II described above may be performed in the prediction unit. Furthermore, step III described above may be performed in the coupled analysis calculation unit.

[0113] Furthermore, the heat treatment simulation apparatus of this disclosure may also include a first prediction unit, a second prediction unit, and a coupled analysis calculation unit. The first prediction unit predicts the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a preset temperature change rate, for the β / α transformation of the α+β type titanium alloy material. The second prediction unit predicts the latent heat of transformation associated with each phase for each time and temperature based on the transformation rate of each phase for each time and temperature predicted by the first prediction unit, and predicts the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation. The coupled analysis calculation unit may perform coupled analysis calculations by either introducing the temperature change rate predicted by the second prediction unit into the temperature change rate in the first prediction unit, or by repeatedly performing the predictions in the first prediction unit and the second prediction unit to perform convergence calculations for the transformation rate of each phase and the temperature change rate for each time and temperature. That is, in the heat treatment simulation apparatus of this disclosure, step A described above may be performed in the first prediction unit. Step B described above may be performed in the second prediction unit. Furthermore, step C described above may be performed in the coupled analysis calculation unit.

[0114] Furthermore, the heat treatment simulation apparatus of this disclosure may also have a third prediction unit. The third prediction unit may predict the deformation resistance for each time and temperature based on the phase fraction of each phase obtained by the coupled analysis calculation unit.

[0115] Furthermore, the heat treatment simulation apparatus of this disclosure preferably includes at least a central computing unit as hardware, and the various calculation units, analysis units, prediction units, coupled analysis calculation units, etc., described above are preferably implemented as functions of the central computing unit.

[0116] 6. Program Furthermore, the technology disclosed herein also has an aspect as a program that operates a computer as a heat treatment simulation device. That is, the program disclosed herein operates on the computer, Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution due to eddy currents generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution. This is what causes it to execute.

[0117] As described above, the program of this disclosure causes a computer to execute the heat treatment simulation method according to the second embodiment described above. The program may also cause the computer to execute the following steps.

[0118] In other words, the program of this disclosure is provided to the computer, Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform convergence calculations for the temperature change rates of each phase for each time and temperature. It may also be something that causes the execution of [something].

[0119] Furthermore, the program of this disclosure is installed on the computer, Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature. It may also be something that causes the execution of [something].

[0120] Furthermore, the program of this disclosure is installed on the computer, Based on the phase fraction of each phase obtained by the aforementioned coupled analysis calculation, the deformation resistance for each time and temperature is predicted. It may also be something that causes the execution of [something]. [Examples]

[0121] The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples. The present invention allows for the adoption of various conditions without departing from its essence and insofar as it achieves its objective.

[0122] 1. Examination of induction heating simulations To verify the accuracy of the induction heating simulation, the surface temperature of the billet during heating was measured, and the microstructure of the round bar cross-section after heating was investigated. A 3 mm hole was machined in the side of a Ti-6Al-4V titanium alloy billet (φ200 × L450) that had been hot-worked in the α+β two-phase region, and a K-type thermocouple in a protective tube was inserted. This billet was heated to 650°C in an atmospheric furnace, and then heated at a frequency of 60 Hz and current values ​​of 5000 A and 5500 A, and the temperature was measured. After heating, the billet was allowed to cool, and the microstructure of the C-section of the billet was observed. Coupled analysis of this induction heating and heat transfer analysis was also performed. The correction value M = 0.86 was used.

[0123] Figure 7 shows a comparison of the analyzed and experimental values ​​of the temperature transition during induction heating. As shown in Figure 7, the analyzed values ​​of the temperature transition during induction heating reproduced the experimental values ​​well. Figure 8 shows the analyzed maximum temperature reached, and Figure 9 shows the microstructure observation results in the C section of the billet. In this test, a billet hot-worked in the α+β two-phase region was used, so in the region where the maximum temperature reached was below the β transformation point, a bi-modal structure as shown in Figure 9(c) was formed, and in the region above the β transformation point, a needle-like structure as shown in Figure 9(d) was formed. The analysis predicted that the entire billet would exceed the β transformation point at 5500A, and the area outside 45 mm from the center of the billet would exceed the β transformation point at 5000A, which reproduced the microstructure observation results (Figures 9(a) and (b)) well.

[0124] 2. Manufacturing and evaluation of titanium alloy materials 2.1 Preparation of the ingot Ingots were obtained by melting raw materials that had been adjusted to the chemical composition shown in Table 1 below. [Table 1]

[0125] 2.2 First hot working and second hot working The obtained ingots were subjected to first and second hot working under the conditions shown in Table 2 below to obtain titanium alloy billets as intermediate materials. In Nos. 1-5, the first hot working was performed using a box rolling mill (with appropriate rotation to introduce appropriate strain to the long and short sides of the ingot), and then the second hot working was performed without cooling to room temperature. The heating time was selected considering the rolling load, utilizing the heat treatment simulation method for the first embodiment described above. In Nos. 6-7, both the first and second hot working were performed by forging. [Table 2]

[0126] 2.3 Third and fourth hot working processes Using the obtained α+β type titanium alloy billet, it was heated to 700°C in an atmospheric furnace, then heated by induction heating, and a third hot working process (hot rolling) consisting of one stand was performed. Subsequently, it was reheated using a heating device (induction heating furnace) installed on the line, and a fourth hot working process (hot rolling) consisting of 10 stands was performed to obtain a φ20 mm titanium round bar. Table 3 below shows the heat treatment and hot working conditions. The minimum temperature, maximum temperature, and maximum deformation resistance in the fourth hot working process represent the minimum temperature, maximum temperature, and maximum deformation resistance within the cross section perpendicular to the longitudinal direction during hot working. These conditions were selected using the heat treatment simulation methods related to the first and second embodiments. The crystalline structure of the round bar thus obtained was investigated. Here, the cross-sectional deformation resistance was set to a maximum of 150 MPa, considering a safety factor of 20% at the upper limit of equipment capable of rolling with a typical rolling mill. [Table 3]

[0127] 2.4 Observation of crystal structure The crystalline structure was determined by measuring the equivalent circular diameter and aspect ratio of the equiaxed α phase in a cross section perpendicular to the longitudinal direction of the obtained φ20 mm titanium rod. This was done at a total of nine fields of view (3 mm × 3 mm) at depths of 3 mm and 5 mm from the surface (representing the east, west, north, and south directions) and at a depth of 10 mm. The mean and standard deviation were calculated for each field of view. Approximately 800 data points were measured. The results are shown in Table 4 below.

[0128] 2.5 Tensile Test Tensile tests were conducted on titanium round bars, with the longitudinal direction as the tensile direction. Measurements were taken five times each (15 data points in total) at depths of 3 mm, 5 mm, and 10 mm from the surface, and the mean and standard deviation were calculated. Tensile test specimens were taken in accordance with ASTM E8, with a parallel section of φ3 mm × L12.5 mm taken at a depth of 3 mm from the surface, and a parallel section of φ6 mm × L25 mm taken at depths of 5 mm and 10 mm from the surface. The 0.2% yield strength was tested at a strain rate of 0.015 / min, and the elongation at 0.08 / min. The results are shown in Table 4 below.

[0129] 2.6 Evaluation Results [Table 4]

[0130] The results shown in Tables 3 and 4 indicate the following: For Examples 1-7, the standard deviation of the 0.2% yield strength was 30 MPa or less, the standard deviation of the elongation was 1% or less, and hot-rolled materials with a uniform structure were obtained. This is because both the third and fourth hot working processes were performed by T β -200℃ or moreT β This is thought to be because the experiment was conducted at temperatures below -20°C, and the total reduction in surface area was above a predetermined level, causing the grain boundary α phase to be fragmented and refined into a fine, equiaxed state. In Comparative Example 8, because the frequency during induction heating was low, the center of the round bar was T in the fourth processing step. β The temperature exceeded ℃. As a result, although the standard deviation of the mechanical properties was small, needle-like structures were mixed into the center of the product, and the structure became coarser, causing the average diameter of the equiaxed α phase to exceed the target. Consequently, sufficient 0.2% yield strength and elongation could not be obtained compared to Example 4. In Comparative Example 9, the current value during induction heating was high, so the surface temperature in the third hot working stage was T β The temperature exceeded ℃. In addition, in Comparative Example 10, despite the large total reduction ratio and high heat generation during the third hot working, the induction heating current value or frequency was the same as in the other conditions, resulting in a high temperature after reheating, and the core temperature during the fourth hot working was T β The temperature exceeded ℃. Therefore, in all cases, when the temperature decreased, a grain boundary α phase with a large aspect ratio was formed at the grain boundaries of the β grains and remained even after processing. As a result, the average aspect ratio of the equiaxed α phase exceeded 5.0, resulting in large variations in tensile properties. In Comparative Example 11, the combined reduction ratio of the third and fourth hot working was small, resulting in insufficient promotion of the equiaxed α phase fragmentation, and the average aspect ratio exceeded 5.0. Consequently, there was a large variation in ductility. In Comparative Example 12, the induction heating frequency was high, and the variation in processing temperature within the cross-section was large. As a result, the diameter of the equiaxed α phase differed from part to part, increasing the standard deviation, and the average aspect ratio also exceeded 5.0. Consequently, there was a large variation in ductility. Furthermore, in the fourth hot working stage, the minimum temperature fell below the lower limit, and the maximum deformation resistance exceeded the upper limit (150 MPa) set with a safety factor of 20%. However, since the equipment upper limit (180 MPa) without a safety factor was not exceeded, the rolling process could be continued. In Comparative Example 13, the target temperature of the heating device installed on the line was low, so the surface temperature during the fourth hot working stage was T β The temperature dropped significantly below -200℃. As a result, the deformation resistance of the material increased excessively, causing the rolling process to stop.

[0131] 3. Summary Based on the above results, it can be said that rod-shaped or wire-shaped titanium alloy materials made of α+β type titanium alloy that satisfy the following conditions (1) to (4) have suppressed variations in tensile properties. (1) The titanium alloy material has an equiaxed α phase and a transformed β structure in a cross section perpendicular to the longitudinal direction. (2) The average value of the equivalent circle diameter of the equiaxed α phase is 20.0 μm or less. (3) The standard deviation of the equivalent circular diameter of the equiaxed α phase is 8.0 μm or less. (4) The average aspect ratio of the equiaxial α phase is 5.0 or less.

Claims

1. A rod-shaped or wire-shaped titanium alloy material made of α+β type titanium alloy, In a cross-section perpendicular to the longitudinal direction, it has an equiaxed α phase and a transformed β structure. The average value of the equivalent circular diameter of the equiaxed α phase is 20.0 μm or less. The standard deviation of the equivalent circular diameter of the equiaxed α phase is 8.0 μm or less, and The average aspect ratio of the equiaxial α phase is 5.0 or less. Titanium alloy material.

2. The titanium alloy material according to claim 1, When a tensile test is performed with the longitudinal direction as the tensile direction, the standard deviation of the 0.2% proof stress is 30 MPa or less, and the standard deviation of elongation is 1.0% or less. Titanium alloy material.

3. A titanium alloy material according to claim 1 or 2, In mass percent, Al: 5.5-6.75%, V: 3.5-4.5%, Fe: 0-0.40%, O: 0-0.20%, C: 0-0.08%, N: 0-0.05%, H: 0-0.015%, and Remainder: Ti and impurities Having a chemical composition consisting of, Titanium alloy material.

4. A titanium alloy material according to claim 1 or 2, In mass percent, Al: 2.5-3.5%, V: 2.0 to 3.0%, Fe: 0 to 0.25%, O: 0-0.15%, C: 0-0.08%, N: 0-0.05%, H: 0-0.015%, and Remainder: Ti and impurities Having a chemical composition consisting of, Titanium alloy material.

5. A titanium alloy material according to claim 1 or 2, In mass percent, Al: 4.4-6.5%, Fe: 0.5-2.9%, Si: 0 to 0.50%, O: 0-0.25%, C: 0-0.08%, N: 0-0.05%, Ni: 0 to 0.15%, Cr: 0-0.25%, Mn: 0-0.25%, and The remainder consists of Ti and impurities. The chemical composition has a mass percentage content of Fe, Ni, Cr, and Mn such that 0.5% ≤ %Fe + %Ni + %Cr + %Mn ≤ 2.9%. Titanium alloy material.

6. A component comprising the titanium alloy material described in claim 1 or 2.

7. A heat treatment simulation method including the following steps 1-3: Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution due to eddy currents generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution.

8. The heat treatment simulation method according to claim 7, comprising the following steps I to III: Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform a convergence calculation of the temperature change rates of each phase for each time and temperature.

9. The heat treatment simulation method according to claim 7, including steps A to C below: Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature.

10. A heat treatment simulation method according to claim 9, Based on the phase fraction of each phase obtained by the aforementioned coupled analysis calculation, the deformation resistance for each time and temperature is predicted. Heat treatment simulation method.

11. A heat treatment simulation device, It has a first calculation unit, a second calculation unit, and a third calculation unit, The first calculation unit uses the magnetic field obtained by assuming the heating coil is a solenoid to calculate the Joule heat distribution due to eddy currents generated in the metal material inside the coil, The second calculation unit calculates the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, The third calculation unit calculates the amount of heat generated by each element in the FEM model using the Joule heat distribution. Heat treatment simulation device.

12. A heat treatment simulation apparatus according to claim 11, It has an analysis unit, a prediction unit, and a coupled analysis calculation unit. The analysis unit performs plastic deformation analysis and heat transfer analysis of the metal material when the metal material is heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. The prediction unit uses 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the processing heat generation amount to predict the temperature change rate in the heat transfer analysis. The coupled analysis calculation unit performs the coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in the analysis unit, or by repeatedly performing the analysis in the analysis unit and the prediction in the prediction unit to calculate the convergence of the temperature change rates of each phase for each time and temperature. Heat treatment simulation device.

13. A heat treatment simulation apparatus according to claim 11, It has a first prediction unit, a second prediction unit, and a coupled analysis calculation unit. The first prediction unit predicts the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a preset temperature change rate, The second prediction unit predicts the latent heat of transformation associated with each phase for each time and temperature based on the transformation rate of each phase for each time and temperature predicted by the first prediction unit, and predicts the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation. The coupled analysis calculation unit performs the coupled analysis calculation by either introducing the temperature change rate predicted by the second prediction unit into the temperature change rate in the first prediction unit, or by repeatedly performing the predictions in the first prediction unit and the second prediction unit to perform convergence calculations for the transformation rate of each phase and the temperature change rate for each time and temperature. Heat treatment simulation device.

14. A heat treatment simulation apparatus according to claim 13, It has a third prediction unit, The third prediction unit predicts the deformation resistance for each time and temperature based on the phase fraction of each phase obtained by the coupled analysis calculation unit. Heat treatment simulation device.

15. A program that operates a computer as a heat treatment simulation device, To the aforementioned computer, Step 1: Using the magnetic field obtained by assuming the heating coil is a solenoid, calculate the Joule heat distribution due to eddy currents generated in the metal material inside the heating coil. Step 2: Calculate the temperature of each element of the metal material based on a FEM model for heat transfer analysis of the metal material, and Step 3: Calculate the amount of heat generated by each element in the FEM model using the Joule heat distribution. A program that executes something.

16. The L according to claim 15, To the aforementioned computer, Step I: Perform plastic deformation analysis and heat transfer analysis on a metal material after it has been heated or cooled at a predetermined temperature change rate and subjected to plastic deformation. Step II: Using 50-100% of the plastic deformation energy predicted from the plastic deformation analysis as the heat generated during processing, predict the temperature change rate in the heat transfer analysis, and Step III: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step I, or by repeatedly performing Step I and Step II to perform convergence calculations for the temperature change rates of each phase for each time and temperature. A program that executes something.

17. The L according to claim 15, To the aforementioned computer, Step A: Predict the transformation start time and the transformation rate of each phase for each time and temperature when the α+β type titanium alloy material is heated or cooled at a predetermined temperature change rate. Step B: Based on the predicted transformation rates of each phase for each time and temperature, predict the latent heat of transformation associated with the transformation for each time and temperature, and predict the temperature change rate of the α+β type titanium alloy material and the time change rate of the phase fraction of each phase by performing a heat transfer analysis using the predicted latent heat of transformation, and Step C: Perform a coupled analysis calculation by either introducing the predicted temperature change rate into the temperature change rate in Step A, or by repeatedly performing Step A and Step B to perform convergence calculations of the transformation rate of each phase and the temperature change rate for each time and temperature. A program that executes something.

18. The program according to claim 17, To the aforementioned computer, Based on the phase fraction of each phase obtained by the aforementioned coupled analysis calculation, the deformation resistance for each time and temperature is predicted. A program that executes something.

19. A method for manufacturing rod-shaped or wire-shaped titanium alloy materials made of α+β type titanium alloy, To obtain an ingot made of α+β type titanium alloy, The ingot is heated in a furnace to a set temperature T １ During the time spent in the furnace t １ After heating for a while, T β +30℃ or higher and T β Below +300℃ (here, T β A first hot working process is performed at a temperature (where is the β transformation point) with a reduction ratio of 60% or more to obtain a first intermediate material. Without processing the first intermediate material at a temperature above the β transformation point, T β -200℃ or higher and T β To obtain a second intermediate material by performing a second hot working process with a reduction ratio of 30% or more at a temperature below °C, and The second intermediate material is heated in one or more of the following: an atmospheric furnace, an atmospheric furnace, and an induction heating furnace, followed by hot rolling as a third hot working process, and then heated in an induction heating furnace after the third hot working process, followed by hot rolling as a fourth hot working process, to obtain a rod-shaped or wire-shaped titanium alloy material. Includes, The temperature in the third hot working and the fourth hot working is T β -200°C or higher and T β -20°C or lower, The total reduction ratio of the third and fourth hot working processes is 70% or more. A method for manufacturing titanium alloy materials.

20. A method for manufacturing a titanium alloy material according to claim 19, The shape of the cross-section of the ingot perpendicular to its longitudinal direction is rectangular. A method for manufacturing titanium alloy materials.

21. A method for manufacturing a titanium alloy material according to claim 19 or 20, The area S (mm²) of the cross-section perpendicular to the longitudinal direction of the ingot. ２ The ratio L / S of the circumference L (mm) of the cross-section to the given cross-section is 0.005 or more. A method for manufacturing titanium alloy materials.

22. A method for manufacturing a titanium alloy material according to claim 19 or 20, The second hot working is performed during the latency period of the β⇒α transformation, or during the transformation. A method for manufacturing titanium alloy materials.

23. A method for manufacturing a titanium alloy material according to claim 19 or 20, The current value and frequency of the induction heating furnace are determined based on the results obtained by the heat treatment simulation method described in claim 7. A method for manufacturing titanium alloy materials.

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