WO2020085586A1 - Titanium alloy with high strength and high ductility comprising elements with melting points of 1,900℃ or lower - Google Patents

Abstract

The present invention relates to a titanium alloy with high strength and high ductility comprising low melting point elements having melting points of 1,900℃ or lower. The titanium alloy according to the present invention comprises Al, Fe, Mn, and O, and the remainder being Ti and inevitable impurities, in which a valence electron ratio (e/a) is from 3.967 to 4.040, a Bo value is from 2.721 to 2.752, and an Md value is from 2.330 to 2.397.

Description

High-strength, highly ductile titanium alloy composed of elements with melting points below 1,900 ℃

The present invention does not include V, Cr, Nb, Mo, Hf, Ta, W, etc., whose melting point exceeds 1,900 ° C, which is mainly used for strengthening the titanium alloy, and elements such as Al, Mn, Fe, etc., whose melting point is 1,900 ° C or less. It relates to a high-strength, highly flexible titanium alloy that is easily added and dissolved.

In addition, the present invention relates to a titanium alloy having a high strength and high ductility properties while being composed of a low melting point element having a melting point of 1,900 ° C or lower.

In addition, the present invention relates to a titanium alloy composed of a low melting point element having a melting point of 1,900 ° C or less, which simultaneously has a tensile strength of 1,300 MPa or more and an elongation of 10% or more.

Titanium alloys have properties such as high corrosion resistance, high specific strength, and biocompatibility, and are widely applied in various fields such as aerospace, power generation, chemical, transportation equipment, electronics, leisure, and eyeglass frames.

Recently, as the industry is advanced, the demand for high-strength titanium alloys is increasing because parts are exposed to extreme environments or miniaturized.

The maximum tensile strength of the commonly used Ti-6Al-4V alloy is about 1,200 MPa. In order to manufacture titanium alloy having a tensile strength of 1,300 MPa or more, five methods are mainly used: ultra-fine crystallization, work hardening, precipitation hardening, dispersion hardening, and solid solution hardening.

For the ultra-fine crystallization, since a severe strain that cannot be obtained with a general facility must be added to the titanium alloy, special facilities are required, and there are limitations on the shape and size of the titanium material that can be obtained when using special facilities.

The work hardening, precipitation hardening to precipitate omega, etc., and dispersion hardening to disperse carbides are effective for high strength, but lead to a significant reduction in elongation and an increase in process cost.

In the final solid solution strengthening, the alpha-phase stabilizing elements of titanium are Al, O, N or beta-phase stabilizing elements V, Cr, Nb, Mo, Hf, Ta, and W. The alpha phase stabilizing element is effective in increasing the strength, but causes a severe decrease in elongation, and the beta phase stabilizing element improves strength while relatively decreasing the elongation. Therefore, an alpha phase stabilizing element and a beta phase stabilizing element are simultaneously added to the high-strength high ductility to control the balance of strength and ductility.

However, when beta-phase stabilizing elements such as V, Cr, Nb, Mo, Hf, Ta, and W are used, the elements themselves are expensive, and the specific gravity and melting point are high, so that uniform dissolution is difficult, and dissolution costs increase.

In order to overcome these technical limitations, attempts have been made to develop low-cost, high-strength titanium by adding trace amounts of low-melting, low-cost elements Al, Fe, and Si.

In this regard, Non-Patent Document 1 discloses a low-cost titanium alloy in which Al: 2.0-7.0% and Fe: 0.5-5.0% are added in a weight ratio.

However, the room temperature tensile strength of the titanium alloy disclosed in Non-Patent Document 1 is at a level similar to the Ti-6Al-4V alloy commonly used at a maximum of 1,100 MPa.

In addition, Patent Document 1 discloses a low-cost high-strength titanium alloy in which Fe: 3.5-4.5%, Si: 0.3-1.0%, and Al: 1.5-6.5% are added in a weight ratio.

However, the titanium alloy disclosed in Patent Document 1 has a problem that the tensile strength at room temperature is 975 to 1,241 MPa and 1,300 MPa or less, and when the tensile strength is 1,241 MPa, the elongation is rapidly decreased to 6.3%.

In addition, in order to obtain a strength of 1,000 MPa or more in Non-Patent Document 1 and Patent Document 1, the Fe content should be included at least 4%, and when Fe is included as much as 4%, TiFe is likely to precipitate in the environment of use. When TiFe is precipitated in the use environment, the ductility decreases sharply, and reliability of parts may deteriorate when used for a long time.

On the other hand, a non-patent document 2, which is a more recent study, discloses a Ti-5% Al-2% Fe-3% Mo alloy (weight ratio) having a tensile strength of 1,300 MPa or more and an elongation of 10% or more.

However, the titanium alloy disclosed in Non-Patent Document 2 has a melting point of 2,600 ° C or higher and contains expensive element Mo, so that dissolution is difficult and manufacturing cost increases.

As can be seen from Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2, when a low-melting point element is added, it is difficult to increase the strength, and when it becomes high-strength, a high-melting point element is added, so it is composed of a low-melting point element of 1,900 ° C or less. It is very difficult to develop a titanium alloy having a tensile strength of 1,300 MPa or more and an elongation of 10% or more.

<Prior Art Document>

[Patent Document]

(Patent Document 1) Korean Patent Publication No. 10-2002-0005072

[Non-patent literature]

(Non-Patent Document 1) Hideki Fujii et al., Development of High-Performance Ti-Al-Fe Alloy Series, Titanium `95: Science and Technology, 2539 ~ 2546.

(Non-Patent Document 2) Tomonori Kunieda et al., Effect of Heat Treatment Conditions on Mechanical Properties in High Strength Titanium Alloy Super-TIX ^TM 523AFM, Nippon Steel & Sumitomo Metal Technical Report No. 106 July (2014), 47-52.

An object of the present invention is to provide a titanium alloy excellent in strength and ductility without adding expensive, high specific gravity, and high melting point elements.

In particular, the present invention is to provide a titanium alloy excellent in strength and ductility by adding low melting point elements Al, Fe, and Mn to Ti, and O, which has a higher solid solution limit and is easier to control than C and N, is added. The purpose.

In order to achieve the above object, the titanium alloy according to the present invention contains Al, Fe, Mn and O as alloying elements, and contains the remaining Ti and unavoidable impurities, and the valence electron ratio defined by the following formula (e / a) Is 3.967 ~ 4.040, Bo value defined by the following Equation 2 is 2.721 ~ 2.752, and Md value defined by the following Equation 3 is 2.330 ~ 2.397.

[Equation 1]

Valence electron ratio (e / a) = (Ti (atomic%) × 4 + Al (atomic%) × 3 + Fe (atomic%) × 8 + Mn (atomic%) × 7) ÷ 100

[Equation 2]

Bo value = (Ti (atomic%) × 2.790 + Al (atomic%) × 2.426 + Fe (atomic%) × 2.651 + Mn (atomic%) × 2.723) ÷ 100

[Equation 3]

Md value = (Ti (atomic%) × 2.447 + Al (atomic%) × 2.200 + Fe (atomic%) × 0.969 + Mn (atomic%) × 1.194) ÷ 100

At this time, it is preferable that the titanium alloy includes C: 0.05% by mass or less and N: 0.03% by mass or less. When C exceeds 0.05% by mass or N exceeds 0.03% by mass, carbides and nitrides may precipitate, thereby deteriorating mechanical strength properties.

Further, it is more preferable that the valence electron ratio (e / a) is 3.988 to 4.040, the Bo value is 2.728 to 2.751, and the Md value is 2.346 to 2.387.

In addition, the titanium alloy may be composed of only elements having a melting point of 1,900 ° C or less.

Preferably, the titanium alloy is Al: 3.5 to 6.5 mass%, Fe: 0.5 to 3.5 mass%, Mn: 0.5 to 3.5 mass%, O: 0.07 to 0.4 mass%, C: 0.05 mass% or less and N: It may contain 0.03% by mass or less. More preferably, the titanium alloy is Al: 3.5 to 6.5 mass%, Fe: 1.5 to 2.5 mass%, Mn: 1.5 to 2.5 mass%, O: 0.13 to 0.2 mass%, C: 0.02 mass% or less and N: 0.02% by mass or less.

 In addition, the titanium alloy may have a tensile strength of 1,300 MPa or more and an elongation of 10% or more. Furthermore, the titanium alloy may have a product of tensile strength and elongation of 16,000 MPa ·% or more.

The titanium alloy according to the present invention is advantageous in mass production because it is inexpensive and contains only alloy elements having a melting point of 1900 ° C. or less, and does not require high energy upon dissolution, and also does not require segregation and re-dissolution due to non-uniform dissolution.

In addition, in the case of the titanium alloy according to the present invention, by controlling the amount of alloying elements added, there is an effect of simultaneously securing high strength and excellent elongation. In particular, in the case of the present invention, while reducing the Fe content to 4% by mass or less, Mn may be added to prevent or delay the precipitation of TiFe.

Accordingly, the titanium alloy according to the present invention can be applied to various fields such as aerospace, aerospace, power generation, chemical, transportation equipment, electronics, leisure, eyeglass frame industry through high strength and excellent elongation.

1 is a comparison of the tensile strength × elongation value for the change in valence electron ratio (e / a) in a titanium alloy composed of elements having a melting point of 1,900 ° C. or less.

 Figure 2 is a comparison of the tensile strength × elongation value for the Bo value change in a titanium alloy composed of elements having a melting point of 1,900 ° C or less.

 3 is a comparison of the tensile strength x elongation value for the change in Md value in a titanium alloy composed of elements having a melting point of 1,900 ° C or less.

Hereinafter, a titanium alloy (hereinafter referred to as “titanium alloy”) having high strength and high ductility properties while being composed of a low melting point element having a melting point of 1,900 ° C. or less according to the present invention will be described with reference to the accompanying drawings.

Prior to this, the terms or words used in this specification and claims should not be interpreted in a conventional and lexical sense, and the inventor can appropriately define the concept of terms in order to best describe the invention of the asset. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

Therefore, the configuration shown in the embodiments and drawings described in this specification is only a preferred embodiment of the present invention, and does not represent all of the technical spirit of the present invention, and various equivalents can be substituted at the time of application. It should be understood that there may be water and variations.

As described above, when developing beta-phase stabilizing elements such as V, Cr, Nb, Mo, Hf, Ta, and W in order to develop a high-strength, highly ductile titanium alloy, the element itself is expensive and has a high specific gravity and melting point, resulting in uniform dissolution. Not only is it difficult, but the cost of melting increases.

The present inventors tried to develop a high-strength high-ductility high-titanium titanium alloy, which is composed of elements having a melting point of 1,900 ° C. or less, which is easy to dissolve and can reduce manufacturing cost. As a result, the valence electron ratio (e / a), Bo value, and Md value of the titanium alloy When it was kept in a predetermined range at the same time, it turned out that the above-described characteristics can be simultaneously realized, and the present invention has been reached.

In the present invention, the valence electron ratio (e / a), the Bo value, and the Md value are defined by the following Equations 1 to 3. For the definitions of equations 2 and 3 for Bo and Md values, see M. Morinaga et al., Theoretical design of titanium alloys, in: sixth world conference on titanium (1988) 1601-1606. -Xα cluster method).

[Equation 1]

Valence electron ratio (e / a) = (Ti (atomic%) × 4 + Al (atomic%) × 3 + Fe (atomic%) × 8 + Mn (atomic%) × 7) ÷ 100

[Equation 2]

Bo value = (Ti (atomic%) × 2.790 + Al (atomic%) × 2.426 + Fe (atomic%) × 2.651 + Mn (atomic%) × 2.723) ÷ 100

[Equation 3]

Md value = (Ti (atomic%) × 2.447 + Al (atomic%) × 2.200 + Fe (atomic%) × 0.969 + Mn (atomic%) × 1.194) ÷ 100

The titanium alloy according to the present invention includes Al, Fe, Mn and O as alloying elements, and is composed of the remaining Ti and unavoidable impurities. Preferably, the titanium alloy according to the present invention does not contain expensive, high specific gravity elements having a melting point exceeding 1,900 ° C.

When the valence electron ratio (e / a) is less than 3.967 or exceeds 4.040, tensile strength of 1,300 MPa or more and elongation of 10% or more cannot be simultaneously implemented, so 3.967 to 4.040 are preferred, and valence electron ratio (e / a) It is more preferable to make 3.988 to 4.040.

When the Bo value is less than 2.721 or more than 2.752, since tensile strength of 1,300 MPa or more and elongation of 10% or more cannot be simultaneously implemented, 2.721 to 2.752 are preferred, and more preferably 2.728 to 2.751.

When the Md value is less than 2.330 or exceeds 2.397, since tensile strength of 1,300 MPa or more and elongation of 10% or more cannot be simultaneously implemented, 2.330 to 2.397 is preferred, and more preferably 2.346 to 2.387.

The titanium alloy according to the present invention is Al: 3.5 to 6.5 mass%, Fe: 0.5 to 3.5 mass%, Mn: 0.5 to 3.5 mass to maintain the valence electron ratio (e / a), Bo value and Md value in the above range %, O: It is preferable to contain 0.07 to 0.4 mass%. When the Al content is less than 3.5% by mass, the beta phase is too stabilized, and when the Al content exceeds 6.5% by mass, the alpha phase is excessively stabilized, and elongation may be insufficient, respectively. In addition, when the Fe content is less than 0.5% by mass, the solid solution strengthening effect is low, and thus the tensile strength may be insufficient. When the Fe content exceeds 3.5% by mass, the solid solution strengthening effect may be too large and the elongation may be insufficient. In addition, when the amount of Mn added is less than 0.5% by mass, the solid solution strengthening effect is insufficient, and when the Mn content exceeds 3.5% by mass, the beta phase may be excessively stabilized. In addition, when the O content is less than 0.07 mass%, the solid solution strengthening effect is low, and thus the tensile strength may be insufficient. When the O content is more than 0.4 mass%, the solid solution strengthening effect may be too large and the elongation may be insufficient.

On the other hand, the titanium alloy according to the present invention may include C: 0.05% by mass or less and N: 0.03% by mass or less, when the content of C exceeds 0.05% by mass or the content of N exceeds 0.03% by mass, carbide or nitride Mechanical properties, in particular, elongation may be greatly reduced by the precipitation of. When the contents of Al, Fe, Mn, and O are out of the above-mentioned range, it is difficult to satisfy all the valence electron ratios (e / a), Bo values, and Md values according to Equations 1 to 3 above.

More preferred composition of the titanium alloy according to the present invention is Al: 3.5 ~ 6.5 mass%, Fe: 1.5 ~ 2.5 mass%, Mn: 1.5 ~ 2.5 mass%, O: 0.13 ~ 0.2 mass%, C: 0.02 mass% or less and N: 0.02 mass% or less can be suggested.

On the other hand, the titanium alloy according to the present invention may contain impurities that are inevitably included in the raw material or the manufacturing process, and these impurities are 1 mass% or less, preferably 0.1 mass% or less, and more preferably 0.01 mass% or less. To manage.

The titanium alloy according to the present invention is produced by first manufacturing and casting an alloy molten metal, and then making a billet. After the first hot working at about 1050 to 1200 ° C in the beta single phase region, cooling to room temperature, and in the alpha + beta two phase region about 800 to After the second hot working at 980 ° C, water cooling is performed, and finally, after annealing heat treatment at about 900 to 970 ° C, water cooling may be performed.

After the annealing heat treatment and water cooling, additional heat treatment may be performed at 450 to 580 ° C for 2 to 10 hours. Further heat treatment may improve long-term high temperature creep and fatigue properties.

Example

Hereinafter, the configuration and operation of the present invention through a preferred embodiment of the present invention will be described in more detail. However, this is provided as a preferred example of the present invention and cannot be interpreted as limiting the present invention by any means.

The contents not described here will be sufficiently technically inferred by those skilled in the art, and thus the description thereof will be omitted.

1. Preparation of titanium alloy

The titanium alloys according to Examples 1 to 12 and Comparative Examples 1 to 10 of the present invention are prepared by manufacturing and casting a titanium alloy molten metal to have a composition as shown in Table 1 below, and then cooled to room temperature after primary hot working at 1075 ° C. Then, after 2nd hot working at 880 ° C, water cooling was performed, and finally, after annealing heat treatment at 900 ° C, water cooling was performed.

[Table 1]

As shown in Table 1, the titanium alloys according to Examples 1 to 12 of the present invention satisfy all valence electron ratios (e / a) of 3.967 to 4.040, Bo values of 2.721 to 2.752, and Md values of 2.330 to 2.397.

On the other hand, the titanium alloys according to Comparative Examples 1 to 8 do not satisfy one or more of valence electron ratio (e / a) 3.967 to 4.040, Bo values 2.721 to 2.752, and Md values 2.330 to 2.397.

In addition, the titanium alloys according to Comparative Examples 9 and 10 satisfy the valence electron ratio (e / a) of 3.967 to 4.040, Bo values of 2.721 to 2.752, and Md values of 2.330 to 2.397, but the content of C is 0.05 mass%. This is the case when it exceeds or the content of N exceeds 0.03% by mass.

2. Mechanical property evaluation

The results of evaluating the mechanical properties of the titanium alloys prepared according to Examples 1 to 12 and Comparative Examples 1 to 10 are shown in Table 2 below. In Table 2, when the product of tensile strength and elongation is 10,000 or more, it is rounded off at the 10th place, and when the product of tensile strength and elongation is less than 10,000, it is rounded up to the 1st place.

[Table 2]

As shown in Table 2, the titanium alloys according to Examples 1 to 12 of the present invention all exhibit tensile strength of 1,300 MPa or more and elongation of 10% or more simultaneously, and the product of tensile strength and elongation is 16,000 MPa ·% or more. That is, in the case of the titanium alloys according to Examples 1 to 12, it is possible to exhibit high strength and high ductility properties even though only elements having a melting point of 1,900 ° C. or less are added.

 On the other hand, looking at the results of Comparative Examples 1 and 2 and Examples 1 to 3, it can be seen that the effect of the Mn content on tensile properties. If Mn is not added in the similar Al, Fe, and O contents as in Comparative Example 1, the solid solution strengthening effect is low, and the tensile strength is significantly lower than in Examples 1 to 3. In addition, as in Comparative Example 2, when Mn was included in 4% or more, the beta phase was too stabilized to achieve tensile strength and elongation as in Examples 1 to 3.

On the other hand, looking at the results of Comparative Examples 3 to 4 and Examples 4 to 6, it can be seen that the effect of Al content on the tensile properties. When only 3% of Al is added, as in Comparative Example 3 at similar Fe, Mn, and O contents, the beta phase is too stabilized and the elongation is remarkably lower compared to Examples 4 to 6. In addition, as in Comparative Example 4, when the Al content was 7% or more, the alpha phase was too stabilized to achieve the same elongation as Examples 4 to 6.

 On the other hand, looking at the results of Comparative Examples 5 to 6 and Examples 5 and 7, it can be seen that the effect of the O content on the tensile properties. As in Comparative Example 5, when only 0.05% of O was added at similar Al, Fe, and Mn contents, the solid solution strengthening effect was low, and the tensile strength was significantly lower than in Example 5 or Example 7. In addition, as in Comparative Example 6, when O was included at 0.5% or more, the solution strengthening effect was too large to implement the elongation as in Example 5 or Example 7.

 On the other hand, looking at the results of Examples 6 and 8 and 9 of Comparative Examples 7 to 8, it can be seen that the Fe content has an effect on tensile properties. If Fe is not added in the similar Al, Mn, and O contents as in Comparative Example 7, the solid solution strengthening effect is low, and the tensile strength is significantly lower than in Examples 6 and 8 to 9. In addition, when Fe is included in 4% or more, as in Comparative Example 8, the solution strengthening effect is too large to implement the elongation as in Example 6 and Examples 8 to 9.

On the other hand, when comparing the results of Examples 10 to 11 and Comparative Example 9, it can be seen that when N is added in excess of 0.03% by mass, the elongation decreases rapidly due to nitride precipitation. Further, when comparing the results of Examples 10 to 12 and Comparative Example 10, it can be seen that when C is added in excess of 0.05% by mass, the elongation decreases rapidly due to carbide precipitation.

1 to 3 are diagrams showing the results of Tables 1 and 2 above.

As can be seen in Figure 1, the valence electron ratio (e / a) of the titanium alloys according to Examples 1 to 12 is located between 3.967 and 4.040, and the valence electron ratio according to the embodiment of the present invention (e / Examples 1 to 12 having a) have a higher tensile strength x elongation value than the comparative examples.

 2, the Bo values of the titanium alloys according to Examples 1 to 12 are located between 2.721 and 2.752, and Examples 1 to 12 having Bo values according to the embodiments of the present invention are not It has a higher tensile strength x elongation value than the comparative examples.

 3, the Md value of the titanium alloys according to Examples 1 to 12 is located between 2.330 and 2.397, and Examples 1 to 12 having Md values according to the embodiments of the present invention are not It has a higher tensile strength x elongation value than the comparative examples.

 As can be seen from the above, the titanium alloys of Examples 1 to 12 of the present invention satisfying all the above three conditions are composed only of elements having a melting point of 1,900 ° C or less, and are easy to mass-produce while simultaneously achieving high strength and high elongation characteristics. However, the alloy which is not, does not implement at least one of high strength and high elongation.

Although the present invention has been described with reference to examples, it is only exemplary, and those skilled in the art to which the art pertains will appreciate that various modifications and other equivalent examples are possible. Therefore, the true technical protection scope of the present invention should be defined by the claims.

Claims (7)

1. As a titanium alloy,

   Al, Fe, Mn and O, and the remaining Ti and inevitable impurities,

   The valence electron ratio (e / a) defined by Equation 1 below is 3.967 to 4.040, the Bo value defined by Equation 2 below is 2.721 to 2.752, and the Md value defined by Equation 3 below is 2.330 to 2.397,

   The titanium alloy is characterized in that C: 0.05% by mass or less and N: 0.03% by mass or less, characterized in that, titanium alloy.

   [Equation 1]

   Valence electron ratio (e / a) = (Ti (atomic%) × 4 + Al (atomic%) × 3 + Fe (atomic%) × 8 + Mn (atomic%) × 7) ÷ 100

   [Equation 2]

   Bo value = (Ti (atomic%) × 2.790 + Al (atomic%) × 2.426 + Fe (atomic%) × 2.651 + Mn (atomic%) × 2.723) ÷ 100

   [Equation 3]

   Md value = (Ti (atomic%) × 2.447 + Al (atomic%) × 2.200 + Fe (atomic%) × 0.969 + Mn (atomic%) × 1.194) ÷ 100
2. According to claim 1,

   Titanium alloy, characterized in that the valence electron ratio (e / a) is 3.988 to 4.040, Bo value is 2.728 to 2.751, and Md value is 2.346 to 2.387.
3. According to claim 1,

   The titanium alloy is a titanium alloy, characterized in that it contains only elements having a melting point of 1,900 ° C or less.
4. According to claim 1,

   The titanium alloy, Al: 3.5 to 6.5% by mass, Fe: 0.5 to 3.5% by mass, Mn: 0.5 to 3.5% by mass, O: 0.07 to 0.4% by mass, characterized in that the titanium alloy.
5. According to claim 4,

   The titanium alloy is Al: 3.5 to 6.5 mass%, Fe: 1.5 to 2.5 mass%, Mn: 1.5 to 2.5 mass%, O: 0.13 to 0.2 mass%, C: 0.02 mass% or less and N: 0.02 mass% or less Titanium alloy, characterized in that it comprises a.
6. According to claim 1,

   The titanium alloy is characterized in that it has a tensile strength of 1,300MPa or more and an elongation of 10% or more.
7. The method of claim 6,

   The titanium alloy is a titanium alloy, characterized in that the product of tensile strength and elongation is 16,000 MPa ·% or more.

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