RU2464333C1 - Titanium plate - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: titanium plate contains (wt %) iron of more than 0.10% and less than 0.60%, oxygen of more than 0.005% and less than 0.10%, carbon of less than 0.015%, nitrogen of less than 0.015%, hydrogen of less than 0.015%; all the rest is represented with titanium and inevitable impurities; plate has two-phase structure formed of α-phase and β-phase; at that, β-phase is formed so that it has mean diameter of grains of 3 mcm or less, which is equivalent to circular one.

EFFECT: plate has high strength and good processibillity.

2 dwg, 1 tbl, 22 ex

Description

FIELD OF THE INVENTION

The present invention relates to a titanium plate, and more particularly, to a titanium plate with excellent machinability.

BACKGROUND

Titanium materials, such as titanium alloys and pure titanium, have traditionally been widely used in sports and leisure equipment, medical equipment, various parts for industrial plants, equipment related to aviation and space technology, and the like, since titanium materials in They are generally light and high strength compared to iron-based materials such as iron and its alloys.

In addition, since titanium materials also have excellent resistance to corrosion and the like, they are used, for example, for plate materials in plate heat exchangers, silencer parts in motorcycles and the like.

To produce such products, a plate formed from a titanium material (titanium plate) is subjected, for example, to various treatments including plastic deformation, such as bending and drawing.

Therefore, it is necessary that the titanium plate has excellent machinability in a manufacturing process, such as a hood, to be suitable for such a variety of applications.

However, recently, due to requirements in terms of reducing the thickness of the titanium plate to reduce the cost of the material and the like, the need for increasing strength has been constantly increasing.

That is, more and more, satisfactory formability and strength, which are characteristics in a compromise ratio, were simultaneously needed.

Sponge titanium used as a raw material for a titanium plate and the like is obtained by the Kroll method, and, for example, pure titanium is obtained by a method in which sponge titanium formed in the Kroll process is melted or the like to produce an ingot.

Pure titanium is classified according to the content of elements other than titanium, such as iron and oxygen, in the Japanese Industrial Standard (JIS), which describes JIS-class 1, JIS-class 2, JIS-class 3, JIS-class 4 and the like .

Regarding the characteristics of the respective materials, JIS-Class 1 titanium, in which the iron and the like are low, has the lowest strength and excellent formability.

JIS-Class 2 titanium is known to have higher strength than JIS-Class 1 titanium, and JIS-Class 3 titanium has higher strength than JIS-Class 2 titanium.

JIS class 2 titanium, on the other hand, has worse moldability than JIS class 1 titanium, and JIS class 3 titanium has worse moldability than JIS class 2 titanium, and it is difficult to obtain a well formed product by exposing the JIS class 2 titanium plate or 3 hoods or the like.

With respect to the foregoing purpose, Patent Documents 1 to 3 below describe that formability is improved by adjusting components other than titanium, such as iron, to titanium material to a range below a predetermined level.

However, sufficient strength of the titanium materials described in these Patent Documents cannot be expected.

In addition, since the reduction reaction in the Kroll process, as described above, is usually carried out intermittently (in batch mode) in a reservoir made of carbon steel or an iron alloy, the resulting sponge titanium contains more iron in the region close to the wall of the reservoir than in the region close to the central part of the tank.

Because of this, if the iron content is limited, for example, to a range from 0.035% to 0.100%, as described in Patent Document 3, it is necessary to use titanium from the central part of the tank, which limits the use of the material and creates a problem of increasing cost.

It should be noted that in the following Patent Documents 4 and 5 allow a higher iron content than the inventions described in Patent Documents 1-3, but it cannot be said that the materials in Patent Documents 4 and 5 have sufficient formability.

PROTOTYPE DOCUMENT

PATENT DOCUMENT

Patent Document 1: Japanese Patent Application Laid-Open No. Sho-63-60247

Patent Document 2: Japanese Patent Application Laid-Open No. Hei-9-3573

Patent Document 3: Japanese Patent Application Laid-Open No. 2006-316323

Patent Document 4: Japanese Patent Application Laid-Open No. 2008-127633

Patent Document 5: Japanese Patent Application Laid-Open No. 2002-180166

SUMMARY OF THE INVENTION

PROBLEMS SOLVED BY THE INVENTION

An object of the present invention is to provide a titanium plate having high strength and excellent machinability.

MEANS FOR SOLVING PROBLEMS

As a result of comprehensive and in-depth studies to achieve the above objective, the authors of the present invention have found that a titanium plate having high strength and excellent machinability can be obtained by forming the titanium plate such that it can have a predetermined iron and oxygen content, and crystalline grains can be in a predetermined state, and the present invention was made as a result of such a discovered fact.

More specifically, the present invention related to a titanium plate for achieving the above purpose is characterized in that the titanium plate has, by weight, an iron content of more than 0.10% and less than 0.60%, an oxygen content of more than 0.005% and less than 0, 10%, carbon content less than 0.015%, nitrogen content less than 0.015%, hydrogen content less than 0.015%, with the rest being titanium and unavoidable impurities, in which a two-phase structure is formed from the α phase and β phase, and the β phase is formed to have an equivalent circular average diameter grains 3 m or less.

Advantages of the Invention

A titanium plate having high strength and excellent machinability can be provided by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a micrograph showing the microstructure of a titanium plate from Example 7.

Figure 2 is a graph showing the relationship between the equivalent circular average grain diameter of the β-phase grains and the Ericksen number.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Next, a preferred embodiment of the present invention will be described.

The titanium plate in the present embodiment is formed from titanium material containing the following components, wherein a two-phase structure is formed from the α-phase and β-phase, and the β-phase is formed so as to have an average circular grain diameter of 3 μm or less equivalent to the circular.

The titanium material has, by weight, an iron (Fe) content of more than 0.10% and less than 0.60%, an oxygen (O) content of more than 0.005% and less than 0.10%, a carbon (C) content of less than 0.015%, a nitrogen content (N) less than 0.015%, a hydrogen content of less than 0.015%, and the remainder is titanium (Ti) and inevitable impurities.

As described above, iron (Fe) is contained in the titanium material in an amount, by weight, of more than 0.10% and less than 0.60%.

Fe is a β-stabilizing element, and although part of Fe forms a solid solution, most of Fe forms a β-phase.

In addition, it is known that Fe is present as a TiFe compound as a result of heat treatment or the like, which inhibits the growth of crystalline grains.

Therefore, it was traditionally believed that when the Fe content in the titanium material increases, the size of the crystal grains in the α phase formed in the titanium plate is reduced, which can increase the strength of the titanium material and the workability during polishing, but the index showing plasticity (formability) decreases such as the Ericksen number.

However, as described in detail below, even if the Fe content in the titanium plate increases, a decrease in ductility can be suppressed, and an increase in strength can be achieved by adjusting the O content to a predetermined value, and adjusting the size of the β phase to a predetermined value.

The Fe content in the titanium material forming the titanium plate according to the present embodiment is more than 0.10% and less than 0.60% by weight, because if the Fe content is 0.10% or less, it may not be possible to impart sufficient strength to the obtained titanium plate.

On the other hand, if the content is 0.60% or more, a decrease in ductility can occur even if the O content in the titanium material is set to a predetermined level, which can lead to a decrease in the formability of the titanium plate.

It should be noted that during the Kroll process, titanium material having an iron content of 0.60% or more is mainly formed only in a small area near the reservoir.

Therefore, in the present embodiment, the majority of sponge titanium obtained by the Kroll method can be used as raw material, since in the titanium plate according to the present embodiment, the upper limit of the iron content as its component is set at 0.60% by weight.

That is, it can be said that the titanium plate according to the present embodiment is suitable as a consumable used to obtain a molded product, so that the raw material can be purchased without difficulty.

Oxygen (O) is contained in the titanium material in an amount by weight of more than 0.005% and less than 0.10%.

The O content in the titanium material forming the titanium plate according to the present embodiment is more than 0.005% and less than 0.10% by mass, because if the O content is 0.10% or more, the strength of the titanium plate can be excessively increased, and As a result, good formability may not be achieved even if the β phase is corrected.

In addition, it is important that each of carbon (C), nitrogen (N) and hydrogen (H) is contained in an amount corresponding to JIS class 2 or less, in order to ensure good workability in production.

More specifically, it is important that the levels of each of C, N and H were less than 0.015% of the mass.

In addition, it is preferable that the content of C is 0.01% or less, the content of N is 0.01% or less, and the content of H is 0.01% or less.

Although it is not necessary to establish a lower limit for the above levels of C, N, and H from the point of view of machinability of a titanium plate, the cost of manufacturing a titanium plate can increase significantly if one intends to reduce the content to the utmost.

From the standpoint of preventing such an increase in value, the content of C is preferably 0.0005% or more, the content of N is preferably 0.0005% or more, and the content of H is preferably 0.0005% or more.

A titanium plate, which requires good machinability in manufacturing, traditionally mainly involves only the α phase, since such a titanium plate is made of a titanium material having a low iron content corresponding to JIS class 1 or JIS class 2.

Since the larger the α-grain size, the better the workability, it is important that the titanium plate according to the present embodiment has a two-phase structure of α + β, in which the β-phase has an equivalent circular average grain diameter of 3 μm or less.

An index that shows workability, such as the Ericksen number, can be improved by forming the titanium plate so that it has such a structure.

If the equivalent circular average β-phase grain diameter exceeds 3 μm, workability may be deteriorated with a decrease in Ericksen number, for example, to a level of less than 10 mm.

This is due to the likelihood of cracks at the interface between the coarser β-phase and α-phase due to stress concentration, which affects the machinability of the titanium plate.

Although the lower limit of the equivalent circular average average grain diameter of the β phase is not specifically indicated, it is preferably 0.05 μm or more, since the production cost will increase significantly upon receipt of a titanium plate having an equivalent circular average average grain diameter of less than 0.05 μm .

It should be noted that the equivalent circular circular average grain diameter of the β-phase can be determined by the method described in the "Examples" section below.

It should be noted that these discovered facts were found by the authors of this application by the following methods.

That is, cold-rolled plates, each of which had a thickness of 0.5 mm, were obtained experimentally in a small-sized vacuum electric arc melting furnace using numerous types of titanium materials, each of which had a different iron content, at the same time with changing firing conditions . Then, the obtained cold-rolled plates (titanium plates) were evaluated by formability using the Ericksen test (details will be described in the Examples section below).

Then it was found that the grain size of the β-phase increases, for example, with an increase in the duration of annealing, and that the stronger the grain size of the β-phase increases, the smaller the Ericksen number becomes.

A crack was discovered at the interface between the large β-grain and the α-phase in a detailed study of the structure and surface of the fracture. Then, the annealing conditions were changed to reduce the grain size of the β-phase, and it was found that with a decrease in the grain size of the β-phase, the Ericksen number increased, showing an improvement in formability.

In particular, it was found that the circular equivalent average β-phase grain diameter of 3 μm is considered as a limit value and that when the circular equivalent average β-phase grain diameter is 3 μm or less, a high strength titanium plate with excellent machinability.

As shown in the description of the process of detecting this fact, the grain size of the β-phase can be adjusted due to the iron content in the titanium material, the temperature of the final annealing and the duration of the final annealing during the production of the titanium plate, and the like.

Next, these conditions will be described in a method for producing a titanium plate.

When considering now the conditions of the temperature of the final annealing and the duration of the final annealing during the production of the titanium plate, the size of the crystal grains can be reduced by suppressing the growth of β grains by lowering the temperature of the final annealing.

In addition, the size of the crystal grains can be reduced by suppressing the growth of crystal grains by shortening the duration of the final annealing.

More specifically, if the temperature of the final annealing is less than 550 ° C, the structure formed after cold rolling cannot recrystallize, impairing the formability.

On the other hand, if the temperature exceeds 800 ° C, the diffusion rate of iron into titanium may increase, making crystalline grains larger in the β phase.

Accordingly, the temperature of the final annealing is preferably any temperature in the range of 550 ° C. or more and 800 ° C. or less.

In addition, the duration of the final annealing is determined by the above temperature of the final annealing, the thickness of the titanium plate, the capacity of the annealing furnace, and the like.

More specifically, when the temperature of the final annealing is 650 ° C or more, and 800 ° C or less, the duration of the final annealing is preferably longer than 0 minutes and 15 minutes or less.

It should be noted that since the structure recrystallizes during heating, even when the final annealing is completed immediately after the temperature of the titanium plate has reached the above final annealing temperature, the risk of moldability reduction is low if the final annealing time exceeds at least 0 minutes.

On the other hand, the value of the upper limit of the duration of the final annealing is determined at the level of 15 minutes at the aforementioned temperature of the final annealing, because if the final annealing is carried out for more than 15 minutes, the crystalline grains of the β-phase can become larger, reducing the workability of the titanium plate.

It should be noted that when the temperature of the final annealing is 550 ° C or more, and less than 650 ° C, the final annealing is preferably performed so that the following expression (1) can be satisfied, in which t (minutes) represents the duration of the annealing, and T ( ° C) represents the annealing temperature.

Expression 1

t≥32.5-0.05 × T (1)

(in which 550≤T <650)

Recrystallization requires a certain amount of time, since recrystallization in such a temperature range proceeds only at a low rate.

Thus, an improvement in formability by recrystallization can be achieved by selecting conditions that satisfy the above expression (1).

However, if long-term annealing is carried out in the case where the temperature of the final annealing is more than 630 ° C and less than 650 ° C, the β-phase crystalline grains can become larger, reducing the workability of the titanium plate.

Therefore, it is preferable to perform the final annealing in such a way that the following expression (2) is satisfied in this temperature range.

Expression 2

t <9277.5-14.25 × T (2)

(in which 630 <T <650)

In addition, the annealing time is preferably 300 minutes or less in the case where the temperature of the final annealing varies in the temperature range between 550 ° C. or more and 630 ° C. or less.

By choosing such conditions, it is possible to suppress the enlargement of the β phase in the structure to be formed in the titanium plate, and to give the titanium plate good machinability.

It should be noted that if final annealing with a duration exceeding 300 minutes is carried out in this temperature range, the β-phase crystalline grains can become larger, reducing the workability of the titanium plate.

Using the production conditions illustrated above, the grain size of the β phase in the titanium plate can be adjusted to a predetermined level or less, thereby obtaining a titanium plate with excellent strength and machinability.

It should be noted that, although not described in detail here, the known characteristics of traditional titanium plates and methods for producing titanium plates can be applied to the titanium plate according to the present embodiment within a range that does not significantly affect the effect of the present invention.

Examples

The present invention will now be described in more detail with reference to Examples, but the present invention is not limited to such.

Examples 1-22, Comparative Examples 1-3

Preparation of test samples

An ingot (with a diameter of 140 mm) was obtained using small-scale vacuum arc melting, and the ingot was heated to a temperature of 1150 ° C and then forged to obtain a plate having a thickness of 50 mm.

The plate was hot rolled at a temperature of 850 ° C. to a thickness of 5 mm, and then annealed at a temperature of 750 ° C., and the scale on the surface of the annealed plate was cut to obtain a plate material having a thickness of 4 mm.

The plate material was further cold rolled to obtain a plate sample (titanium plate) having a thickness of 0.5 mm.

A titanium plate having a thickness of 0.5 mm was subjected to final annealing in a vacuum atmosphere to obtain a test sample for evaluation.

Upon final annealing, the size of the crystal grains of the test sample was adjusted by adjusting the temperature (550 ° C or more and 800 ° C or less) and time (300 minutes or less).

Component measurement

The amounts of iron and oxygen contained in the titanium plate were measured using a plate material having a thickness of 4 mm, from which the surface scale was cut.

The iron content was measured according to JIS H1614, and the oxygen content was measured according to JIS H1620.

Tensile Strength Measurement

Further, the tensile strength of the test sample (titanium plate) in which the crystal grain size was adjusted as described above was measured according to JIS Z 2241.

Workability Assessment

Further, in order to evaluate the workability of the titanium plate, the Ericksen number was measured according to JIS Z2247 for a test sample (titanium plate) in which the crystal grain size was adjusted as described above.

Structure study

The state of the microstructure of the titanium plate, which was observed in the micrograph, is shown in Figure 1 (microstructure of Example 7).

Since the β-phase appears black and the α-phase appears white in this photograph of the structure, the photograph was subjected to binary conversion using an image analysis program to determine the average area of the β-phase, and the diameter of the circle having the same area as this average area to determine the equivalent circular average grain diameter.

The results of the foregoing are shown in Table 1.

In Table 1, the iron content and oxygen content in Examples 1-4 are the same as the values in Comparative Example 1, but the circular equivalent average diameter of the β-phase grains was adjusted due to the difference in annealing conditions, and the smaller the average circular diameter of the β-equivalent grains phase, the higher the Ericksen number.

In addition, the same trend was observed in other Examples and Comparative Examples, and the fact that the present invention can create a titanium plate having high strength and excellent machinability is also clear from Figure 2, showing the relationship between the equivalent circular average grain diameter of the β-phase and Ericksen number in Table 1.

Claims (1)

A titanium plate having, by weight, an iron content of more than 0.10% and less than 0.60%, an oxygen content of more than 0.005% and less than 0.10%, a carbon content of less than 0.015%, a nitrogen content of less than 0.015%, a hydrogen content of less than 0.015 %, with the rest being titanium and unavoidable impurities, in which a two-phase structure is formed from the α-phase and β-phase, the β-phase being formed so that it has an equivalent circular average grain diameter of 3 μm or less.

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