Patent Application
20250129454
The present disclosure relates to titanium and a method for preparing the same. More specifically, the present disclosure relates to a titanium alloy with high-strength and high-formability using molybdenum and ferrochrome and a method for preparing the same.
Titanium and an alloy thereof are widely used in a wide range of industries, including aerospace, national defense, energy industry, medical care, and consumer staples, because of high strength, high corrosion resistance, and high biocompatibility thereof.
In general, titanium alloys are classified into pure titanium, an alpha (a) alloy, an alpha-beta (a-B) alloy, and a beta (B) alloy based on a stable phase at a room temperature. Among those, the alpha alloy is known to have excellent creep strength, weldability, and the like, while the beta alloy is known to increase machinability.
So far, in the case of titanium alloy, pure titanium for general industry and a Ti-6Al-4V alloy, which is the alpha-beta alloy for aviation and defense, have been mainly used. Further, some Ti—Zr alloys, Ti—Nb alloys, and Ti—Mo alloys that may obtain low elastic modulus and high strength have been used in the medical care and the consumer staples. In addition, research is continuously being conducted to achieve lower elastic modulus and higher strength. However, use of such alloys has not been expanded because of limitations in properties thereof.
Pure titanium is cheaper than other titanium alloys in terms of price, and has excellent formability, weldability, machinability, and corrosion resistance, but has limitations in fields of application because of low strength thereof. Further, Ti-6Al-4V, which is the alpha-beta titanium alloy, has high strength, but is expensive and tends to be inferior in all properties except the strength compared to pure titanium. In addition, the beta alloy is able to achieve desired properties via control of alloy-added elements, but is significantly more expensive than the Ti-6Al-4V alloy as well as pure titanium. In particular, a medical implant, an eyeglass frame, and the like require excellent biocompatibility, low-elastic modulus, and high-strength properties. In this case, a great amount of expensive metal elements such as Nb and Ta should be added to titanium to achieve such properties together.
Therefore, a development of a titanium alloy composed of relatively inexpensive elements that may control properties such as excellent strength, formability, weldability, machinability, corrosion resistance, biocompatibility, and low elastic modulus while minimizing a price increase, and a method for preparing the same is required.
The present disclosure is to provide a high-strength and high-formability titanium alloy using molybdenum and ferrochrome.
In addition, the present disclosure is to provide a high-strength and high-formability titanium alloy that not only lowers a preparation cost of the titanium alloy using ferrochrome as an alloy additive, but is also advantageous in terms of securing strength and elongation.
Purposes according to the present disclosure are not limited to the above-mentioned purpose. Other purposes and advantages according to the present disclosure that are not mentioned may be understood based on following descriptions, and may be more clearly understood based on embodiments according to the present disclosure. Further, it will be easily understood that the purposes and advantages according to the present disclosure may be realized using means shown in the claims and combinations thereof.
A titanium alloy according to an embodiment of the present disclosure to solve the above problems includes (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, and oxygen (O): equal to or smaller than 0.4% by weight, with a remainder composed of titanium (Ti) and inevitable impurities.
A titanium alloy according to a preferred embodiment of the present disclosure includes molybdenum (Mo): 1.0 to 15.0% by weight, chromium (Cr): 0.1 to 1.98% by weight, iron (Fe): 0.1 to 0.93% by weight, silicon (Si): 0.01 to 0.09% by weight, and oxygen (O): equal to or smaller than 0.4% by weight, the content of chromium (Cr) is greater than the content of iron (Fe), the titanium alloy also includes a remainder composed of titanium (Ti) and inevitable impurities, and the titanium alloy has a tensile strength in a range of 1109 to 1510 MPa.
The content of chromium may be 1.7 to 4 times the content of iron.
The titanium alloy may have a molybdenum equivalent ([Mo]eq.), expressed in Equation 1 below, in a range of 5.5 to 20 and may have a beta transformation point in a range of 670 to 815° C. ([ ] in Equation 1 is a % by weight of a corresponding component).
[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] [Equation 1]
The titanium alloy may have a yield strength in a range of 545 to 1420 MPa and a Young's modulus in a range of 80 to 110 GPa.
A method for preparing a titanium alloy to solve the above problems includes (a) adding ferrochrome including chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or a mixture of titanium (Ti) and molybdenum, (b) melting a result of the (a) and then cooling the result to form a titanium alloy base material, and (c) hot forming the titanium alloy base material, and molybdenum is added in an amount in a range of 1 to 15% by weight and the ferrochrome is added in an amount smaller than 4% by weight with respect to a total weight of the titanium alloy.
A method for preparing a titanium alloy according to a preferred embodiment of the present disclosure includes (a) adding ferrochrome including chromium (Cr), iron (Fe), silicon (Si), and carbon (C) to an alloy or a mixture of titanium (Ti) and molybdenum, (b) melting a result of the (a) and then cooling the result to form a titanium alloy base material, and (c) hot forming the titanium alloy base material, the ferrochrome includes iron (Fe): 20 to 35% by weight, silicon (Si): 1 to 4% by weight, and carbon (C): equal to or smaller than 0.15% by weight, with a remainder composed of chromium (Cr) and inevitable impurities, and molybdenum is added in an amount in a range of 1 to 15% by weight and the ferrochrome is added in an amount smaller than 4% by weight with respect to a total weight of the titanium alloy. In this case, the prepared titanium alloy may include molybdenum (Mo): 1.0 to 15.0% by weight, chromium (Cr): 0.1 to 1.98% by weight, iron (Fe): 0.1 to 0.93% by weight, silicon (Si): 0.01 to 0.09% by weight, and oxygen (O): equal to or smaller than 0.4% by weight, with a remainder composed of titanium (Ti) and inevitable impurities, and the titanium alloy may have a tensile strength in a range of 1109 to 1510 MPa.
The ferrochrome may be added in an amount in a range of 0.5 to 2% by weight with respect to the total weight of the titanium alloy.
Oxygen (O) may be added in an amount equal to or smaller than 0.4% by weight with respect to the total weight of the titanium alloy.
The ferrochrome may include iron (Fe): 20 to 35% by weight, silicon (Si): 1 to 4% by weight, and carbon (C): equal to or smaller than 0.15% by weight, with a remainder composed of chromium (Cr) and inevitable impurities.
The hot forming may be performed in a temperature range of 800 to 850° C. with a forming ratio equal to or lower than 90%.
According to the method for preparing the high-strength and high-formability titanium alloy according to the present disclosure, using low-carbon ferrochrome, which is composed of the elements (Cr, Fe, Si, and the like) harmless to the human body, as the additive material to the titanium-molybdenum alloy may lower the cost in terms of a raw material price and a process, compared to adding Cr, Fe, Si, and the like as individual elements.
In addition, the high-strength and high-formability titanium alloy according to the present disclosure may provide the excellent formability as well as the excellent strength via the control of the content of ferrochrome.
In addition to the above-described effects, specific effects of the present disclosure will be described together while describing specific details for carrying out the disclosure below.
The above-mentioned purposes, features, and advantages will be described in detail later, so that a person skilled in the art in the technical field to which the present disclosure belongs will be able to easily implement the technical ideas of the present disclosure. In describing the present disclosure, when it is determined that a detailed description of the publicly known technology related to the present disclosure may unnecessarily obscure the gist of the present disclosure, the detailed description will be omitted. Hereinafter, a preferred embodiment according to the present disclosure will be described in detail with reference to the attached drawings.
Hereinafter, a high-strength and high-formability titanium alloy using molybdenum and ferrochrome, and a method for preparing the same according to some embodiments of the present disclosure will be described.
As methods to increase a strength of pure titanium, there are a method to increase the strength by adding alloy elements, and a method to increase the strength by reducing a size of internal grains via plastic working and heat treatment. However, such methods cause an increase in price because the alloy elements are added and the separate grain size reduction process is added. In addition, in the case of the method of reducing the size of the grains via the plastic working and the heat treatment, mechanical properties of the titanium alloy prepared based on the process may change significantly, and thus a process that is difficult to be directly applied to an actual production process may be derived.
Therefore, the method of adding the alloy elements may be considered more advantageous than the method of reducing the size of the grains via the plastic working and the heat treatment. In particular, selecting inexpensive alloy elements and alloying them may be considered the most desirable method in minimizing the price increase and increase the strength. Furthermore, to ensure biostability, it is desirable not to add toxic elements such as Co, Cu, Ni, V, and the like. The titanium alloy according to the present disclosure does not include such elements. However, as an exception, such elements may be unavoidably included as impurities.
As a result of long-term research, the inventors of the present disclosure selected Mo, which is inexpensive and non-toxic, among elements (Mo, V, Nb, and the like) that form a complete solid solution (a system that shows complete solubility in liquid and solid phases) with titanium, selected a Ti—Mo alloy as a base, and selected Fe and Cr as the alloy elements that have a greater influence (a Mo equivalent weight greater than 1) on a Mo equivalent weight than Mo, are relatively inexpensive, and are non-toxic. In addition, to overcome a disadvantage that it is difficult to achieve a uniform composition because of volatilization or the like during melting when adding the alloy elements such as Fe and Cr individually, a method of alloying titanium by adding ferrochrome including Fe, Cr, Si, and the like was developed. In particular, Si, the element included in ferrochrome, may be expected to have additional feature of providing the nucleation site during the melting and reducing a size of grains of a melted ingot. Accordingly, the inventors of the present disclosure developed a new Ti—Cr—Fe—Si alloy with the titanium-moly (Ti—Mo) alloy as the base.
Hereinafter, a method for preparing a high-strength titanium alloy using molybdenum and ferrochrome will be described in more detail.
The method for preparing the high-strength titanium alloy according to the present disclosure includes adding ferrochrome including chromium (Cr), iron (Fe), silicon (Si), and carbon (C) in an alloy or a mixture of titanium (Ti) and molybdenum (Mo), melting and then cooling titanium and ferrochrome to form a titanium alloy base material, and hot forming the titanium alloy base material.
For melting titanium, molybdenum, and ferrochrome, various known methods such as a vacuum melting method, an electron beam melting method, a plasma arc melting method, a non-consumable electrode arc melting method, an induction skull melting method, or the like may be used. The hot forming may be performed by methods such as hot rolling and hot forging. The hot forming may be performed in a temperature range of 800 to 850° C. with a forming ratio of 90% or lower. The forming ratio may be expressed as a reduction rate in the case of rolling. In the case of the present disclosure, as will be described below, molybdenum is added in an amount in a range of 1 to 15% by weight and ferrochrome is added in an amount smaller than 4% by weight. As a result, cracks may not occur even when the forming is performed in the temperature range of 800 to 850° C. with the forming ratio of 90%.
For the cooling after the hot forming, various methods such as water cooling, air cooling, and furnace cooling may be used. The cooling method may be determined depending on presence or absence of an additional hot process after the hot forming. For example, when the additional hot process does not exist, the water cooling may be performed after the hot forming. After the hot forming, an additional heat treatment such as homogenization treatment, solution heat treatment, and aging treatment may be performed.
One characteristic regarding the melting of ferrochrome is that a temperature when melting ferrochrome is significantly lower than a temperature when melting chromium, iron, silicon, and the like individually, and is similar to a melting point of titanium. Accordingly, ferrochrome may be melted with pure titanium at a relatively low temperature, thereby reducing a cost of preparing titanium alloy.
In the present disclosure, it is desirable that an amount of ferrochrome added is smaller than 4% by weight with respect to a total weight of titanium alloy. More preferably, the added amount may be equal to or smaller than 3% by weight, and most preferably, may be in a range of 0.5 to 2% by weight. The addition of ferrochrome may increase strength compared to that of titanium with no ferrochrome added. However, when the amount of ferrochrome added is equal to or greater than 4% by weight, an elongation is very low and there is a risk of the occurrence of the cracks.
Ferrochrome may include iron (Fe): 20 to 35% by weight, silicon (Si): 1 to 4% by weight, and carbon (C): equal to or smaller than 0.15% by weight, with a remainder composed of chromium (Cr) and inevitable impurities. A characteristic of ferrochrome is that the Cr content is much greater than the Fe content. In ferrochrome, the Cr content may be 1.7 to 4 times, for example, 2 to 4 times, the Fe content.
When the ferrochrome content is smaller than 4% by weight, the above desirable content ranges for chromium, iron, and silicon may be met in the titanium alloy.
With the above method, the present disclosure may provide a titanium alloy composed of 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, and oxygen (O): equal to or smaller than 0.4% by weight, with a remainder composed of titanium (Ti) and inevitable impurities. More preferably, the present disclosure may provide a titanium alloy composed of molybdenum (Mo): 1.0 to 15.0% by weight, chromium (Cr): 0.1 to 1.98% by weight, iron (Fe): 0.1 to 0.93% by weight, silicon (Si): 0.01 to 0.09% by weight, and oxygen (O): equal to or smaller than 0.4% by weight, wherein the chromium (Cr) content is greater than the iron (Fe) content, wherein the titanium alloy also includes a remainder composed of titanium (Ti) and inevitable impurities.
Molybdenum (Mo) is a non-toxic beta phase stabilizing element. Molybdenum plays a role in increasing the strength because of a solid solution strengthening effect. However, when molybdenum is added excessively, exceeding 15% by weight, the elastic modulus of the alloy greatly increases.
Chromium (Cr), as a non-toxic element and is the beta phase stabilizing element more effective than molybdenum (Mo) in the titanium alloy. Adding chromium to titanium may increase the strength because of the solid solution strengthening effect. For such effect, chromium needs to be added in an amount equal to or greater than 0.1% by weight. However, when chromium is added excessively, exceeding 3.0% by weight, there is a high possibility of fracture during the forming process because of formation of a Laves Phase (TiCr2). Therefore, the chromium content is preferably equal to or smaller than 3.0% by weight, and more preferably, equal to or smaller than 1.98% by weight.
Iron (Fe), like chromium (Cr), is not toxic and is the beta phase stabilizing element more effective than molybdenum. Adding iron to pure titanium may increase the strength because of the solid solution strengthening effect. For such effect, iron needs to be added in an amount equal to or greater than 0.1% by weight. However, when melting a titanium alloy with 1.0% by weight or a greater amount of iron added, macro or micro segregation may be induced. Further, when the titanium alloy with 1.0% by weight or the greater amount of iron added is heat treated at a certain temperature, a TiFe phase, a fairly fragile phase, may be formed. Therefore, the iron content is preferably equal to or smaller than 1.0% by weight, and more preferably, equal to or smaller than 0.9% by weight.
Silicon (Si), as a non-toxic element, forms many nucleation sites and induces the grain size reduction when melting the titanium alloy. Further, silicon contributes to increasing static strength of the titanium alloy. For such effect, silicon needs to be added in an amount equal to or greater than 0.01% by weight. However, when the silicon content exceeds 0.1% by weight, the crack occurrence may be promoted because of formation of highly brittle silicide. Therefore, the silicon content is preferably equal to or smaller than 0.1% by weight, and more preferably, equal to or smaller than 0.09% by weight.
The contents of Cr, Fe, and Si in the titanium alloy according to the present disclosure may be determined based on the amount of ferrochrome added, and the above Cr, Fe and Si contents may be met as the amount of ferrochrome added is smaller than 4% by weight, more preferably, equal to or smaller than 3.0% by weight, and most preferably, in a range of 0.5 to 2.0% by weight.
The titanium alloy according to the present disclosure may include oxygen (O) in an amount equal to or smaller than 0.4% by weight with respect to the total weight of the titanium alloy. Oxygen, as an interstitial element, is a solid solution strengthening alloying element that strengthens a lattice without significantly affecting corrosion resistance. However, when oxygen is excessively included, exceeding 0.4% by weight, impact resistance may be drastically reduced by suppressing twin deformation at a low temperature.
As may be seen in Present Examples to be described below, the titanium alloy according to the present disclosure may have a molybdenum equivalent weight ([Mo] eq.) in a range of 5.5 to 20, expressed in Equation 1 below ([ ] in Equation 1 is a % by weight of a corresponding component).
Additionally, the high-strength titanium alloy according to the present disclosure may have a beta transformation point in a range of 670 to 815° C.
Furthermore, as a result of the experiment, the high-strength titanium alloy according to the present disclosure may have a tensile strength in a range of 750 to 1510 MPa, and more preferably, in a range of 1109 to 1510 MPa when also considering the elongation according to Present Examples below, a yield strength in a range of 545 to 1420 MPa and a Young's modulus in a range of 80 to 110 GPa.
Hereinafter, a composition and an operation of the present disclosure will be described in more detail with preferred present examples of the present disclosure. However, these are presented as desirable examples of the present disclosure and are not able to be interpreted as limiting the present disclosure in any way. Contents not described in the following present examples may be sufficiently inferred technically by anyone skilled in the art, so that description thereof will be omitted.
Compositions of three ferrochrome specimens were analyzed as follows. EDS analysis was performed three times respectively at three positions (left, center, and right) of each specimen of 10 mm×10 mm size, and results are shown in Table 1.
It may be seen that all the three specimens include about 66% by weight of Cr, about 31% by weight of Fe, and about 3% by weight of Si, and differences in the contents of the components are not great.
Hereinafter, an experiment was conducted on a ferrochrome specimen #1.
After removing a surface oxide layer of the ferrochrome specimen #1, results of analyzing contents of O, N, H, and C using the EDS are shown in Table 2.
Depending on a carbon content, ferrochrome is classified into low-carbon ferrochrome, medium-carbon ferrochrome, and high-carbon ferrochrome. Among those, low-carbon ferrochrome means that the carbon content is equal to or smaller than 0.2% by weight or equal to or smaller than 0.15% by weight. The ferrochrome specimen #1 analyzed above corresponds to low-carbon ferrochrome as the carbon content is about 0.1% by weight and the chromium content is about 67%.
Melting points of Cr, Fe, and Si are 1907° C., 1538° C., and 1414° C., respectively, but a melting point of low-carbon ferrochrome with the carbon content equal to or smaller than 0.15% by weight is known to be about 1620° C. Additionally, a melting point of titanium is 1668° C.
In titanium, O, N, C, H, and the like are major elements that reduce ductility and require special management. In the titanium alloy, such elements should be managed to have contents equal to or smaller than percentages by weight shown in Table 3 (there are very small differences in allowable values by country). In particular, H reduces the ductility even when added in small amounts, so that special management is required compared to other elements.
The ferrochrome specimen #1 analyzed above is a low-carbon ferrochrome and complies with maximum percentage by weight limits for the elements such as O, N, C, H, and the like in Table 3.
Titanium (Ti-0.02 O), and molybdenum and ferrochrome with contents shown in Table 4 were melted in an induction skull melting furnace to form titanium alloys, and then the titanium alloys were cooled to produce ingots with width 10 mm×length 30 mm×thickness 10 mm.
The ingots were formed at 830° C.±20° C. at a forming ratio of about 90% shown in Table 4 and then water-cooled to prepare titanium alloy specimens according to Comparative Examples 1 to 3 and Present Examples 1 to 12.
Table 4 shows a Mo equivalent weight and a beta transformation point based on the ferrochrome content in each of the titanium alloy specimens prepared according to Comparative Examples 1 to 3 and Present Examples 1 to 12. Further, Table 5 shows contents of Cr, Fe, and Si based on ferrochrome added in the titanium alloy specimens according to Present Examples 1 to 12.
Referring to
Referring to
Referring to
The specimen according to Comparative Example 4 is a titanium alloy specimen prepared by adding 5.0% by weight of molybdenum and 4% by weight of ferrochrome, the specimen according to Comparative Example 5 is a titanium alloy specimen prepared by adding 9.5% by weight of molybdenum and 4% by weight of ferrochrome, and the specimen according to Comparative Example 6 is a titanium alloy specimen prepared by adding 15% by weight of molybdenum and 4% by weight of ferrochrome.
The mechanical properties were obtained by performing a tensile test on each titanium alloy specimen at a room temperature and a strain rate of 1.5 mm/min.
The mechanical properties for specimens according to Comparative Examples 1 to 3 and specimens according to Present Examples 1 to 12 are shown in Table 6.
Referring to Table 6, it may be seen that the titanium-molybdenum alloy specimens according to Comparative Examples 1 to 3 without ferrochrome added exhibit the tensile strength in a range of 786 to 1064 MPa and the yield strength in a range of 712 to 855 MPa. On the other hand, it may be seen that, in the case of the titanium alloy specimens prepared by adding ferrochrome in an amount equal to or smaller than 3.0% by weight to the titanium-molybdenum alloys, the tensile strength increased to a maximum of 1510 MPa and the yield strength increased to a maximum of 1420 MPa. In other words, in the case of the titanium alloy prepared with the addition of ferrochrome, the increase in the strength may be seen, compared to the titanium alloy without ferrochrome.
In particular, referring to Table 6, it may be seen that Present Examples 2 to 4 have the tensile strength in a range of 1109 to 1510 MPa and the good elongation.
Table 7 shows elongation measurement results and crack occurrence observation results of the specimens according to Comparative Examples 4 to 6 and specimens according to Present Examples 1 to 12.
Referring to
Additionally, referring to Table 7, it may be seen that the cracks occurred in the titanium alloy specimens according to Comparative Examples 4 and 6, but no cracks occurred in the titanium alloy specimens according to Present Examples 1 to 12.
As described above, the present disclosure has been described with reference to illustrative drawings, but the present disclosure is not limited by the embodiment disclosed herein and the drawings, and it is obvious that various modifications may be made by those skilled in the art within the scope of the technical idea of the present disclosure. In addition, although the effects of the composition of the present disclosure are not explicitly described and illustrated in the above description of the embodiment of the present disclosure, it is natural that the predictable effects of the corresponding composition should also be recognized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0191856 | Dec 2021 | KR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/019715 | 12/6/2022 | WO |
