High-strength, highly formable titanium alloy using molybdenum and ferrochrome, and method for manufacturing the same.

Abstract

This invention discloses a high-strength, highly formable titanium alloy using molybdenum and ferrochrome, and a method for producing the same. In the method for producing the titanium alloy according to the invention, ferrochrome containing Cr, Fe, Si, and C is added to an alloy or mixture of Ti and Mo, which is melted and cooled to form a titanium alloy base material, and the formed titanium alloy base material is then hot-formed. At this time, 1 to 15 wt% of Mo and less than 4 wt% of ferrochrome are added.

Description

Technical Field

[0001] The present invention relates to titanium and a method for producing the same. More specifically, the present invention relates to a titanium alloy having high strength and high formability using molybdenum and ferrochrome and a method for producing the same.

Background Art

[0002] Titanium and its alloys are widely used in a wide range of industrial fields such as aerospace, defense, energy industries, medical, and consumer goods due to their high strength, high corrosion resistance, and high biocompatibility.

[0003] Generally, the types of titanium alloys are classified into pure titanium, α alloys, α-β alloys, and β alloys based on their stability at room temperature. Among these, α alloys are excellent in creep strength and weldability, and in the case of β alloys, it is known that the workability increases.

[0004] So far, in the case of titanium alloys, pure titanium for general industrial use and the α-β alloy Ti-6Al-4V alloy for aerospace and defense have been mainly used, and some Ti-Zr alloys, Ti-Nb alloys, and Ti-Mo alloys that can obtain a low elastic modulus and high strength in medical and consumer goods have been used, and research for improving the low elastic modulus and high strength has been continuously conducted. However, due to the limitations of the characteristics of these alloys, their use has not expanded.

[0005] Pure titanium is cheaper than other titanium alloys in terms of cost, and while it has excellent formability, weldability, workability, and corrosion resistance, its low strength limits its application fields. Ti-6Al-4V, an α-β titanium alloy, has high strength, but is expensive and tends to have inferior properties in all aspects except strength compared to pure titanium. Furthermore, while β alloys can achieve desired properties by controlling the elements added to the alloy, they have the disadvantage of being considerably more expensive than both pure titanium and Ti-6Al-4V alloys. In particular, medical implants and eyeglass frames require excellent biocompatibility, low elastic modulus, and high strength. In these cases, achieving these properties together necessitates the addition of large amounts of expensive metallic elements such as Nb and Ta to titanium, leading to problems.

[0006] Therefore, there is a need for the development of titanium alloys made from relatively inexpensive elements and methods for manufacturing them, which can control properties such as excellent strength, formability, weldability, machinability, corrosion resistance, biocompatibility, and low elastic modulus, while minimizing cost increases. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The problem that this invention aims to solve is to provide a high-strength, highly formable titanium alloy using molybdenum and ferrochrome.

[0008] Furthermore, the problem that this invention aims to solve is to provide a method for producing a high-strength, highly formable titanium alloy that is advantageous not only in terms of reducing the manufacturing cost of titanium alloys by using ferrochrome as an alloy additive, but also in terms of ensuring strength and elongation.

[0009] The problems addressed by the present invention are not limited to those mentioned above. Other problems and advantages of the present invention not mentioned can be understood from the following description and will become even clearer from the embodiments of the present invention. Furthermore, it will be readily apparent that the problems and advantages of the present invention can be achieved by the means and combinations thereof shown in the claims. [Means for solving the problem]

[0010] To solve the aforementioned problems, the titanium alloy according to the embodiment of the present invention is characterized by containing molybdenum (Mo): 1.0 to 15.0% by weight, chromium (Cr): 0.1 to 3.0% by weight, iron (Fe): 0.1 to 1.0% by weight, silicon (Si): 0.01 to 0.1% by weight, oxygen (O): 0.4% by weight or less, with the remainder being titanium (Ti) and unavoidable impurities.

[0011] A titanium alloy according to a preferred embodiment of the present invention contains molybdenum (Mo): 1.0-15.0% by weight, chromium (Cr): 0.33 It contains approximately 1.98% by weight of iron (Fe), 0.1-0.93% by weight of silicon (Si), and 0.4% by weight or less of oxygen (O), but the chromium (Cr) content is even greater than the iron (Fe) content, with the remainder being titanium (Ti) and unavoidable impurities. the law of nature, It is characterized by having a tensile strength of 1109 to 1510 MPa.

[0012] The chromium content may be 1.7 to 4 times the iron content.

[0013] The titanium alloy may have a molybdenum equivalent ([Mo]eq.) represented by the following formula 1, which is 5.5 to 20, and a β transformation point of 670 to 815°C (where [] in formula 1 represents the weight %) of the component).

[0014] [Formula 1] [Mo]eq.=[Mo]+0.2[Ta]+0.28[Nb]+0.4[W]+0.67[V]+1.25[Cr]+1.25[Ni]+1.7[Mn]+1.7[Co]+2.5[Fe]

[0015] The titanium alloy may have a tensile strength of 750 to 1510 MPa, a yield strength of 545 to 1420 MPa, and a Young's modulus of 80 to 110 GPa.

[0016] To solve the aforementioned problems, a method for producing a titanium alloy according to an embodiment of the present invention comprises the steps of: (a) adding ferrochrome containing chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or mixture of titanium (Ti) and molybdenum; (b) melting the result of step (a) and then cooling it to form a titanium alloy base material; and (c) hot forming the titanium alloy base material, characterized in that 1 to 15% by weight of molybdenum and less than 4% by weight of ferrochrome are added relative to the total weight of the titanium alloy.

[0017] A preferred embodiment of the present invention provides a method for producing a titanium alloy, comprising the steps of (a) adding ferrochrome containing chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or mixture of titanium (Ti) and molybdenum; (b) melting the result of step (a) and then cooling it to form a titanium alloy base material; and (c) hot forming the titanium alloy base material, wherein the ferrochrome contains iron (Fe): 20-35% by weight, silicon (Si): 1-4% by weight, carbon (C): 0.15% by weight or less, with the remainder being chromium (Cr) and unavoidable impurities, and is characterized by adding 1-15% by weight of molybdenum and less than 4% by weight of ferrochrome relative to the total weight of the titanium alloy. In this case, the titanium alloy produced contains molybdenum (Mo): 1.0-15.0% by weight, chromium (Cr): 0.33 It contains approximately 1.98% by weight of iron (Fe), 0.1-0.93% by weight of silicon (Si), and 0.01-0.09% by weight of oxygen (O), with the remainder being titanium (Ti) and unavoidable impurities. the law of nature,It has a tensile strength of 1109 to 1510 MPa.

[0018] It is more preferable to add 0.5 to 2% by weight of the ferrochrome based on the weight of the entire titanium alloy.

[0019] It may contain 0.4% by weight or less of oxygen (O) based on the weight of the entire titanium alloy.

[0020] The ferrochrome may contain 20 to 35% by weight of iron (Fe), 1 to 4% by weight of silicon (Si), 0.15% by weight or less of carbon (C), and the balance is composed of chromium (Cr) and unavoidable impurities.

[0021] The hot forming can be carried out at 800 to 850 °C with a maximum forming rate of 90%.

Advantages of the Invention

[0022] According to the method for producing a high-strength and high-formability titanium alloy of the present invention, by utilizing low-carbon ferrochrome composed of elements harmless to the human body (such as Cr, Fe, Si, etc.) as an additive for a titanium-molybdenum alloy material, compared with adding to individual elements such as Cr, Fe, Si, etc., the cost can be reduced from the aspect of raw material cost and also from the aspect of the process.

[0023] Further, the high-strength and high-formability titanium alloy according to the present invention can provide excellent formability together with excellent strength by controlling the content of ferrochrome.

[0024] The above-described advantages and the specific advantages of the present invention will be described and described while explaining the embodiments for carrying out the following invention.

Brief Description of the Drawings

[0025] [Figure 1a] It is a diagram showing the phase fraction of a specimen obtained by adding 5% by weight of molybdenum to titanium. [Figure 1b] This figure shows the phase fractions of specimens in which 5% by weight of molybdenum and 4.0% by weight of ferrochrome were added to titanium. [Figure 1c] This figure shows the phase fractions of specimens in which 5% by weight of molybdenum and 0.5% by weight of ferrochrome were added to titanium. [Figure 2a] This figure shows the phase fraction of a specimen in which 9.5% by weight of molybdenum was added to titanium. [Figure 2b] This figure shows the phase fractions of specimens in which 9.5% by weight of molybdenum and 4.0% by weight of ferrochrome were added to titanium. [Figure 2c] This figure shows the phase fractions of specimens in which 9.5 wt% molybdenum and 0.5 wt% ferrochrome were added to titanium. [Figure 3a] This figure shows the phase fraction of a specimen in which 15% by weight of molybdenum was added to titanium. [Figure 3b] This figure shows the phase fractions of specimens in which 15% by weight of molybdenum and 4.0% by weight of ferrochrome were added to titanium. [Figure 3c] This figure shows the phase fractions of specimens in which 15% by weight of molybdenum and 0.5% by weight of ferrochrome were added to titanium. [Figure 4a] This figure shows the mechanical properties of comparative specimens 1 and 4 and specimens 1 to 4 of the example. [Figure 4b] This figure shows the mechanical properties of comparative specimens 2 and 5 and examples 5 to 8. [Figure 4c] This figure shows the mechanical properties of comparative specimens 3 and 6 and examples 9 to 12. [Modes for carrying out the invention]

[0026] The aforementioned objectives, features, and advantages will be described in detail below, so that a person with ordinary skill in the art to which the present invention pertains can easily implement the technical idea of ​​the present invention. In describing the present invention, if it is determined that a specific description of known technology according to the present invention would obscure the gist of the present invention, the detailed description will be omitted. Hereafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

[0027] The following describes several embodiments of the present invention, including a high-strength, highly formable titanium alloy using molybdenum and ferrochrome, and a method for producing the same.

[0028] Methods for increasing the strength of pure titanium include adding alloying elements to enhance its strength, and reducing the size of the internal crystal grains through plastic deformation and heat treatment. However, these methods involve adding alloying elements and a separate process for refining the crystal grains, which increases costs. Furthermore, the method of refining the crystal grains through plastic deformation and heat treatment can result in significant changes in the mechanical properties of the titanium alloy produced depending on the process, potentially leading to processes that are difficult to directly apply to actual production processes.

[0029] Therefore, adding alloying elements is more advantageous than refining the crystal grains through plastic deformation and heat treatment. In particular, selecting inexpensive alloying elements for alloying is the most preferable method for minimizing cost increases while increasing strength. Furthermore, to ensure biostability, it is preferable not to add toxic elements such as Co, Cu, Ni, and V. The titanium alloy according to the present invention does not contain these elements, although they may be unavoidably present as impurities in exceptional cases.

[0030] As a result of extensive research, the inventors selected Mo (Mo), an inexpensive and non-toxic element that forms a complete solid solution (a system exhibiting complete solubility between the liquid and solid phases) with titanium (such as Mo, V, and Nb), and chose a Ti-Mo alloy as the base. They also selected Fe and Cr as alloying elements that have a greater influence on the Mo equivalent (Mo equivalent greater than 1), are relatively inexpensive, and are non-toxic. Furthermore, to overcome the disadvantage of difficulty in achieving a uniform composition due to volatilization during melting when adding alloying elements such as Fe and Cr individually, they developed a method of alloying by adding ferrochrome, which contains Fe, Cr, and Si. In particular, in the case of Si, an element contained in ferrochrome, it is expected that the grains of the molten ingot will be refined by providing nucleation sites during melting. As a result, the inventors have developed a new Ti-Mo-Cr-Fe-Si alloy based on a titanium-molybdenum (Ti-Mo) alloy.

[0031] The following section will provide a more detailed explanation of the manufacturing method for high-strength titanium alloys using molybdenum and ferrochrome.

[0032] The method for producing a high-strength titanium alloy according to the present invention includes the steps of: adding ferrochrome containing chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or mixture of titanium (Ti) and molybdenum (Mo); melting the titanium and ferrochrome and then cooling them to form a titanium alloy base material; and hot forming the titanium alloy base material.

[0033] The melting of titanium, molybdenum, and ferrochrome can be carried out using various known methods such as vacuum melting, electron beam melting, plasma arc melting, non-consumable electrode arc melting, or induction skull melting. Hot forming can be carried out by methods such as hot rolling or hot forging. Hot forming can be carried out at 800-850°C with a forming ratio of 90% or less. In the case of rolling, the forming ratio can be expressed as the reduction ratio. In the present invention, as described below, by adding 1-15% by weight of molybdenum and less than 4% by weight of ferrochrome, it is possible to provide the effect that cracks do not occur even when forming is carried out at 800-850°C with a forming ratio of 90%.

[0034] After hot forming, various cooling methods can be used, such as water cooling, air cooling, or furnace cooling. The cooling method may be determined by whether or not further hot working processes are performed after hot forming. For example, if no further hot working processes are performed, water cooling can be used after hot forming. After hot forming, further heat treatments such as homogenization, solution treatment, and aging treatment can be performed.

[0035] One characteristic of ferrochrome's melting point is that it melts at a significantly lower temperature than chromium, iron, or silicon when melting them individually, and is similar to the melting point of titanium. This allows ferrochrome to melt together with titanium at a relatively low temperature, thereby reducing the manufacturing cost of titanium alloys.

[0036] In this invention, the amount of ferrochrome added is preferably less than 4% by weight of the total weight of the titanium alloy. More preferably, it is 3% by weight or less, and most preferably, 0.5 to 2% by weight. Adding ferrochrome can increase the strength compared to titanium alloys without ferrochrome. However, if the amount of ferrochrome added is 4% by weight or more, the elongation rate will be very low, and there is a risk of cracking.

[0037] Ferrochrome may contain iron (Fe): 20-35% by weight, silicon (Si): 1-4% by weight, carbon (C): 0.15% by weight or less, with the remainder being chromium (Cr) and unavoidable impurities. A characteristic of ferrochrome is that the Cr content is even higher than the Fe content. The Cr content in ferrochrome may be 1.7-4 times, for example, 2-4 times, the Fe content.

[0038] When the ferrochrome content is less than 4% by weight, the preferred range of chromium, iron, and silicon content in the titanium alloy can be met as described above.

[0039] By the method described above, the present invention provides molybdenum (Mo): 1.0~15.0% by weight, chromium (Cr): 0.33 It contains approximately 1.98% by weight of iron (Fe), 0.1-0.93% by weight of silicon (Si), and 0.4% by weight or less of oxygen (O), but the chromium (Cr) content is even greater than the iron (Fe) content, with the remainder being titanium (Ti) and unavoidable impurities. Ruko We provide a titanium alloy characterized by the following.

[0040] Molybdenum (Mo) is a non-toxic β-phase stabilizing element. Molybdenum increases strength through solid solution strengthening. However, adding more than 15% by weight of molybdenum can significantly increase the elastic modulus of the alloy, which is a problem.

[0041] Chromium (Cr) is a non-toxic element and a more effective β-phase stabilizing element than molybdenum (Mo) in titanium alloys. Adding chromium to titanium can increase its strength due to solid solution strengthening. For these effects, it is necessary to add chromium at a concentration of 0.1% by weight or more. However, if chromium is added at a concentration exceeding 3.0% by weight, there is a high possibility of fracture during the molding process due to the formation of the Laves Phase (TiCr2) phase. Therefore, the chromium content is preferably 3.0% by weight or less, and more preferably 1.98% by weight or less.

[0042] Iron (Fe), like chromium (Cr), is non-toxic and a more effective β-phase stabilizing element than molybdenum. Adding iron to titanium can increase its strength due to solid solution strengthening. For these reasons, it is necessary to add at least 0.1% by weight of iron. However, when melting a titanium alloy with more than 1.0% by weight of iron added, macro or micro segregation can be induced, and when heat-treated at a constant temperature, a very weak TiFe phase can be formed. Therefore, the iron content is preferably 1.0% by weight or less, and more preferably 0.9% by weight or less.

[0043] Silicon (Si) is a non-toxic element that, when melting titanium alloys, forms many nucleation sites, inducing grain refinement. Furthermore, silicon contributes to increasing the static strength of titanium alloys. Due to these effects, it is necessary to add at least 0.01% by weight of silicon. However, if the silicon content exceeds 0.1% by weight, the formation of brittle silicides can promote crack formation. Therefore, the silicon content is preferably 0.1% by weight or less, and more preferably 0.09% by weight or less.

[0044] The Cr, Fe, and Si content in the titanium alloy according to the present invention is determined by the amount of ferrochrome added. The above-mentioned Cr, Fe, and Si content can be achieved by adding less than 4% by weight, more preferably 3.0% by weight or less, and most preferably 0.5 to 2.0% by weight of ferrochrome.

[0045] The titanium alloy according to the present invention may contain oxygen (O) in an amount of 0.4% by weight or less relative to the total weight of the titanium alloy. Oxygen is an interstitial element that does not significantly affect corrosion resistance and is a solid solution strengthening alloying element that strengthens the lattice. However, if the oxygen content exceeds 0.4% by weight, the impact resistance can be drastically reduced by suppressing twin deformation at low temperatures.

[0046] As can be seen from the examples described later, the titanium alloy according to the present invention may have a molybdenum equivalent ([Mo]eq.) represented by the following formula 1 of 5.5 to 20 (where [] in formula 1 is the weight %) of the component).

[0047] [Formula 1] [Mo]eq.=[Mo]+0.2[Ta]+0.28[Nb]+0.4[W]+0.67[V]+1.25[Cr]+1.25[Ni]+1.7[Mn]+1.7[Co]+2.5[Fe]

[0048] Furthermore, the high-strength titanium alloy according to the present invention may have a β-transformation point of 670 to 815°C.

[0049] Furthermore, experimental results show that the high-strength titanium alloy according to the present invention may more preferably have a tensile strength of 1109 to 1510 MPa, a yield strength of 545 to 1420 MPa, and a Young's modulus of 80 to 110 GPa, considering the elongation rate in the examples described below.

[0050] Examples The configuration and operation of the present invention will be described in more detail below by preferred embodiments of the present invention. However, these are given as preferred examples of the present invention and should not be construed as limiting the present invention in any sense. Matters not described in the following embodiments can be sufficiently inferred by a person skilled in the art, and therefore their explanation will be omitted.

[0051] 1. Analysis of ferrochrome The following chemical analysis was performed on three ferrochrome specimens. EDS analysis was performed three times on each of the three locations (Left, Center, and Right) of each 10mm x 10mm specimen, and the results are shown in Table 1.

[0052] [Table 1]

[0053] All three samples contained approximately 66% by weight of Cr, approximately 31% of Fe, and approximately 3% by weight of Si, indicating that the differences in component content were not significant.

[0054] In the following experiment, we used ferrochrome specimen #1.

[0055] After removing the surface oxide layer from ferrochrome specimen #1, O, N was removed by EDS. 、C The results of the content analysis are shown in Table 2.

[0056] [Table 2]

[0057] Ferrochrome is classified into low-carbon ferrochrome, medium-carbon ferrochrome, and high-carbon ferrochrome based on its carbon content. Low-carbon ferrochrome means that the carbon content is 0.2% by weight or less, or 0.15% by weight or less. In the case of ferrochrome sample #1 analyzed above, the carbon content is approximately 0.1% by weight and the chromium content is approximately 67%, which corresponds to low-carbon ferrochrome.

[0058] The melting points of Cr, Fe, and Si are 1907°C, 1538°C, and 1414°C, respectively. However, the melting point of low-carbon ferrochrome, which has a carbon content of 0.15% by weight or less, is known to be approximately 1620°C. The melting point of titanium is 1668°C.

[0059] In titanium, elements such as O, N, C, and H are the main elements that reduce fracture ductility and require special control. In pure titanium, these elements must be controlled to below the weight percentages shown in Table 3 (there are slight differences in permissible values ​​between countries). In particular, H reduces fracture ductility even with small additions, and therefore requires special control compared to other elements.

[0060] [Table 3]

[0061] In the case of ferrochrome specimen #1 analyzed above, it is a low-carbon ferrochrome that satisfies the maximum weight percentage of elements such as O, N, C, and H listed in Table 3.

[0062] Manufacturing of titanium alloy specimens Titanium (Ti-0.02O) and molybdenum and ferrochrome in the amounts listed in Table 4 were melted in an induction skull melting furnace to form a titanium alloy, which was then cooled to produce an ingot measuring 10 mm in width, 30 mm in length, and 10 mm in thickness.

[0063] Titanium alloy specimens according to Comparative Examples 1-3 and Examples 1-12 were produced by forming the ingots at 830°C ± 20°C with a forming ratio of approximately 90% as shown in Table 4, followed by water cooling.

[0064] Table 4 shows the Mo equivalent and β transformation point for titanium alloy specimens produced according to Comparative Examples 1-3 and Examples 1-12, depending on the ferrochrome content. Table 5 shows the Cr, Fe, and Si content of titanium alloy specimens according to Examples 1-12, depending on the ferrochrome added.

[0065] [Table 4]

[0066] [Table 5]

[0067] Figure 1a shows the phase fraction of a specimen in which 5% by weight of molybdenum was added to titanium. Figure 1b shows the phase fraction of a specimen in which 5% by weight of molybdenum and 4.0% by weight of ferrochrome were added to titanium. Figure 1c shows the phase fraction of a specimen in which 5% by weight of molybdenum and 0.5% by weight of ferrochrome were added to titanium.

[0068] Referring to Figures 1a to 1c, it can be seen that while specimens with 5% by weight of molybdenum added to titanium and specimens with 5% by weight of molybdenum and 0.5% by weight of ferrochrome added to titanium show almost no TiCr2 precipitate phase, specimens with 5% by weight of molybdenum and 4.0% by weight of ferrochrome add approximately 5.63% by weight of TiCr2 precipitate phase. As mentioned above, too much TiCr2 can cause fracture during the molding process, so the amount of ferrochrome added should be less than 4.0% by weight, more preferably 3.0% by weight or less, and even more preferably 0.5 to 2.0% by weight.

[0069] Figure 2a shows the phase fraction of a specimen to which 9.5 wt% molybdenum was added to titanium. Figure 2b shows the phase fraction of a specimen to which 9.5 wt% molybdenum and 4.0 wt% ferrochrome were added to titanium. Figure 2c shows the phase fraction of a specimen to which 9.5 wt% molybdenum and 0.5 wt% ferrochrome were added to titanium.

[0070] Referring to Figures 2a to 2c, it can be seen that while specimens with 9.5 wt% molybdenum added to titanium and specimens with 9.5 wt% molybdenum and 0.5 wt% ferrochrome added to titanium show almost no TiCr2 precipitate phase, specimens with 9.5 wt% molybdenum and 4.0 wt% ferrochrome added to titanium show approximately 5.63 wt% TiCr2 precipitate phase.

[0071] Figure 3a shows the phase fraction of a specimen in which 15% by weight of molybdenum was added to titanium. Figure 3b shows the phase fraction of a specimen in which 15% by weight of molybdenum and 4.0% by weight of ferrochrome were added to titanium. Figure 3c shows the phase fraction of a specimen in which 15% by weight of molybdenum and 0.5% by weight of ferrochrome were added to titanium.

[0072] Referring to Figures 3a to 3c, it can be seen that while specimens with 15 wt% molybdenum added to titanium and specimens with 15 wt% molybdenum and 0.5 wt% ferrochrome added to titanium show almost no TiCr2 precipitate phase, specimens with 15 wt% molybdenum and 4.0 wt% ferrochrome added to titanium show approximately 5.63 wt% TiCr2 precipitate phase.

[0073] Figures 4a to 4c show comparative examples 1 to 6. 、 Sample 1 of the example 3 and Reference Examples: Samples 1-9 This shows the mechanical properties. Specifically, Figure 4a shows comparative example specimens 1 and 4, which have a molybdenum content of 5.0% by weight. 、 Reference example test specimen 1 and Sample 1 of the example 3 The mechanical properties are shown, and Figure 4b shows comparative examples 2 and 5 with a molybdenum content of 9.5% by weight. reference The sample in question 2~5 The mechanical properties are shown, and Figure 4c shows comparative specimens 3 and 6 with a molybdenum content of 15% by weight. reference The sample in question 6~9 This shows the mechanical properties for [the material].

[0074] The specimens in Comparative Example 4 are titanium alloy specimens manufactured by adding 5.0% by weight of molybdenum and 4% by weight of ferrochrome, the specimens in Comparative Example 5 are titanium alloy specimens manufactured by adding 9.5% by weight of molybdenum and 4% by weight of ferrochrome, and titanium alloy specimens manufactured by adding 15% by weight of molybdenum and 4% by weight of ferrochrome.

[0075] The mechanical properties were obtained by performing tensile tests on each titanium alloy specimen at room temperature with a deformation rate of 1.5 mm / min.

[0076] Table 6 shows the mechanical properties of comparative specimens 1-3 and example specimens 1-12.

[0077] [Table 6]

[0078] Referring to Table 6, it can be seen that the titanium-molybdenum alloy specimens from Comparative Examples 1-3, which do not contain ferrochrome, exhibit a tensile strength of 786-1064 MPa and a yield strength of 712-855 MPa. In contrast, the titanium alloy specimens manufactured by adding 3.0% by weight or less of ferrochrome to the titanium-molybdenum alloy showed an increase in tensile strength to a maximum of 1510 MPa and a yield strength to a maximum of 1420 MPa. In other words, it can be seen that titanium alloys manufactured with ferrochrome added exhibit increased strength compared to titanium alloys without ferrochrome.

[0079] In particular, referring to Table 6, it can be seen that in Examples 2 to 4, the tensile strength is 1109 to 1510 MPa and the elongation is good.

[0080] Table 7 shows the specimens from Comparative Examples 4-6 and Example 1- 3 and Reference Examples 1-9 This shows the measurement results of the elongation rate of the specimens and the observation results of crack initiation.

[0081] [Table 7]

[0082] Referring to Figures 4a to 4c and Table 7, in Comparative Examples 4 to 6, when 4.0% by weight of ferrochrome was added to titanium alloys containing 5 to 15% by weight of molybdenum, the elongation rate decreased sharply to 1.4 to 2.3%. In contrast, in Example 1 to 3 and Reference Examples 1-9 In this case, when less than 4.0% by weight of ferrochrome is added to a titanium alloy to which 5-15% by weight of molybdenum has been added, the elongation range is expressed as 2.4-49% without a sharp decrease in elongation. Furthermore, when the amount of ferrochrome added is 0.5-2.0% by weight, an even higher elongation is observed. Considering both strength and elongation, it can be said that the most preferable amount of ferrochrome added is 0.5-2.0% by weight.

[0083] Furthermore, referring to Table 7, cracks occurred in the titanium alloy specimens of Comparative Examples 4 and 6, but Examples 1- 3 and Reference Examples 1-9 In the case of titanium alloy specimens, it can be seen that no cracks have occurred.

[0084] As described above, the present invention has been explained with reference to the illustrative drawings, but it is clear that the present invention is not limited to the embodiments and drawings disclosed herein, and that various modifications can be made by an ordinary person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention are not explicitly described and explained while embodiments of the present invention have been described above, it is natural to acknowledge that predictable effects can be obtained from such configurations.

Claims

1. Although it contains molybdenum (Mo): 1.0–15.0 wt%, chromium (Cr): 0.33–1.98 wt%, iron (Fe): 0.1–0.93 wt%, silicon (Si): 0.01–0.09 wt%, and oxygen (O): 0.4 wt% or less, the chromium (Cr) content is even greater than the iron (Fe) content, and the remainder consists of titanium (Ti) and unavoidable impurities. It is characterized by having a tensile strength of 1109 to 1510 MPa. Titanium alloy.

2. The chromium content is characterized by being 1.7 to 4 times the iron content. The titanium alloy according to claim 1.

3. The titanium alloy is characterized by having a molybdenum equivalent ([Mo]eq.) represented by the following formula 1 of 5.5 to 20, and a β transformation point of 670 to 815°C. The titanium alloy according to claim 1. [Formula 1] [Mo]eq. = [Mo] + 0.2 [Ta] + 0.28 [Nb] + 0.4 [W] + 0.67 [V] + 1.25 [Cr] + 1.25 [Ni] + 1.7 [Mn] + 1.7 [Co] + 2.5 [Fe]

4. The titanium alloy is characterized by having a yield strength of 545 to 1420 MPa and a Young's modulus of 80 to 110 GPa. The titanium alloy according to claim 1.

5. (a) Adding ferrochrome containing chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or mixture of titanium (Ti) and molybdenum, (b) A step of melting the result of step (a) above and then cooling it to form a titanium alloy base material, (c) The stage of hot forming the titanium alloy base material, Includes, The ferrochrome contains iron (Fe): 20-35% by weight, silicon (Si): 1-4% by weight, carbon (C): 0.15% by weight or less, with the remainder being chromium (Cr) and unavoidable impurities. The process involves adding 1 to 15% by weight of molybdenum and less than 4% by weight of ferrochrome relative to the total weight of the titanium alloy, The titanium alloy produced is characterized by containing molybdenum (Mo): 1.0 to 15.0% by weight, chromium (Cr): 0.33 to 1.98% by weight, iron (Fe): 0.1 to 0.93% by weight, silicon (Si): 0.01 to 0.09% by weight, oxygen (O): 0.4% by weight or less, with the remainder being titanium (Ti) and unavoidable impurities, and having a tensile strength of 1109 to 1510 MPa. A method for manufacturing titanium alloys.

6. The method is characterized by adding 0.5 to 2% by weight of ferrochrome relative to the total weight of the titanium alloy. A method for producing a titanium alloy according to claim 5.

7. The hot forming described above is characterized by being carried out at 800 to 850°C with a forming rate of 90% or less. A method for producing a titanium alloy according to claim 5.

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