TWI415796B - Titanium plate - Google Patents

Abstract

An object of the present invention is to provide a titanium plate having high strength and excellent workability. In order to achieve the above object, there is provided a titanium plate having, by mass, 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 balance being titanium and unavoidable impurities, wherein a two-phase structure of an ±-phase and a ²-phase is formed, and the ²-phase is formed so as to have a circle-equivalent average grain size of 3 µm or less.

Description

Titanium plate

The present invention relates to a titanium plate, and more particularly to a titanium plate excellent in workability.

Titanium alloys such as titanium alloys and pure titanium are generally lighter and stronger than iron-based materials such as iron and alloys. Therefore, they are widely used in sportswear, medical equipment, various device components, and aerospace related machines. .

Further, since the titanium material has excellent corrosion resistance and the like, it can be used, for example, as a plate material for a plate heat exchanger, a muffler for an automatic two-wheeled vehicle, or the like.

In the production of such a product, for example, a plate (titanium plate) made of a titanium material is subjected to various processes such as bending work, twisting, and the like, which are accompanied by plastic deformation.

Therefore, it is required to supply the titanium plate for various uses to have excellent workability in forming processing such as twisting.

However, the recent demand for material cost reduction, etc., and the result of thinning the titanium sheet will require an increase in strength.

That is, it is required to be able to simultaneously satisfy the characteristics of the coordination relationship between formability and strength.

The sponge titanium used for the raw material of the titanium plate or the like is produced by a chlorine method, and is produced, for example, by pure titanium, by subjecting the titanium sponge obtained by the chlorine method to arc melting or the like to obtain an ingot.

In the Japanese Industrial Standards (JIS), pure titanium is classified into iron and oxygen contents other than titanium, and JIS is classified into JIS, JIS, JIS, JIS, and JIS according to JIS regulations.

Among these material characteristics, JIS1 having a small content of iron and the like has the lowest strength and excellent formability.

This shows that the JIS 2 species and the JIS species have higher intensities.

In addition, since JIS has two types of JIS and JIS, the moldability is lowered. Therefore, when a titanium plate is subjected to twisting or the like, it is difficult to obtain a good molded product.

On the other hand, in the following Patent Documents 1 to 3, it has been described that the moldability can be improved when the content of components other than titanium such as iron in the titanium material is controlled within a certain range or less.

However, the materials described in these patent documents cannot obtain sufficient strength.

Further, the reduction reaction in the chlorine method is generally carried out in a discontinuous (batchwise) manner in a carbon steel or iron alloy container, and therefore, in the obtained sponge titanium, the amount of iron contained in the titanium sponge near the container side is close to The sponge has more titanium in the center of the container.

Therefore, when the iron content is, for example, 0.035% to 0.100% as in the case of Patent Document 3, only the titanium in the center portion of the container can be used. Therefore, the use of the material is restricted and the cost is increased.

Further, in the following Patent Documents 4 and 5, compared with Patent Documents 1 to 3, although it is allowed to contain a large amount of iron, it is not necessarily a sufficient formability.

[Prior patent documents] [Patent Literature]

Patent Document 1: Japanese Patent Publication No. 63-60247

Patent Document 2: Japanese Patent Publication No. 9-3573

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

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

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

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

In order to solve the above problems, the inventors of the present invention have found that a titanium plate having a high iron content and a high crystal content can be formed by forming a titanium plate having a constant iron and oxygen content and a constant crystal grain, and the present invention can be completed.

That is, the titanium plate for solving the above problems is characterized in that the iron content in the mass is more than 0.10%, less than 0.60%, the oxygen content is 0.005%, less than 0.10%, the carbon content is less than 0.015%, and the nitrogen content is The amount of hydrogen is less than 0.015%, the hydrogen content is less than 0.015%, and the residue is formed by titanium and unavoidable impurities, and the two-phase structure of the α phase and the β phase is formed, and the circle of the above-mentioned β phase is formed to have a mean average particle diameter of 3 μm. the following.

The present invention can provide a titanium plate having high strength and excellent workability.

(Formation of the invention)

Preferred embodiments of the present invention will now be described.

The titanium plate of the present embodiment is formed of a titanium material containing the following components, and forms a two-phase structure of an α phase and a β phase, and the formed β phase has a circle-equivalent average particle diameter of 3 μm or less.

The titanium material has a mass (iron) content of more than 0.10%, less than 0.60%, an oxygen (O) content of less than 0.005%, less than 0.10%, a carbon (C) content of less than 0.015%, and nitrogen (N). The content is less than 0.015%, the hydrogen (H) content is less than 0.015%, and the residue is formed of titanium (Ti) and unavoidable impurities.

As described above, the content of the iron (Fe) contained in the titanium material is less than 0.10% in mass less than 0.60%.

Iron (Fe) is a β-stabilizing element, and a part of the solid solution is likely to form a β phase.

Further, it is known that iron is present as TiFe by heat treatment or the like, which hinders the growth of crystal grains.

Therefore, it is inferred that when the iron content in the prior titanium material is large, the crystal grain size of the α phase formed in the titanium plate is reduced, and the Erickson value of the material which can improve the strength of the titanium material and the workability of the polishing process is lowered ( Erichsen value) and the like indicate the index of ductility (formability).

However, even if the iron content in the titanium plate is increased, and the β phase is adjusted to a constant value by setting the oxygen content to a constant value, it is possible to suppress the decrease in ductility and increase the strength.

In the present embodiment, the iron content of the titanium material forming the titanium plate is such that the mass exceeds 0.10% and does not reach 0.60%. When the iron content is 0.10% or less, sufficient strength cannot be imparted to the formed titanium plate.

When the content is 0.60% or more, even if the oxygen content in the titanium material is constant, the ductility is lowered, and the moldability of the titanium plate is lowered.

Further, in the general chlorine method, a titanium material having an iron content of 0.60% or more is formed only in a field close to a container.

Since the upper limit of the content of the iron component of the titanium plate in the present embodiment is 0.60% by mass, the sponge titanium obtained by the chlorine method can be used almost as a raw material.

That is, since the titanium plate of the present embodiment is easily obtained from a raw material, it is applied to a consumable used in molding a molded article.

The content of the oxygen (O) contained in the titanium material is less than 0.005% in mass less than 0.10%.

In the present embodiment, the oxygen content of the titanium material forming the titanium plate is such that the mass exceeds 0.005% and is less than 0.10%. When the oxygen content is 0.10% or more, the strength of the titanium plate is excessively increased, so that even the β phase is adjusted. It is feared that a product having good formability cannot be formed.

Moreover, in order to ensure good workability at the time of molding processing, the carbon (C), nitrogen (N), and hydrogen (H) content is equivalent to two or more types of JIS.

More specifically, the contents of carbon, nitrogen, and hydrogen are each less than 0.015% in mass.

Further, the carbon content is 0.01% or less, the nitrogen content is 0.01% or less, and the hydrogen content is preferably 0.01% or less.

From the viewpoint of the processability of the titanium plate, the above-mentioned lower limits of the carbon, nitrogen, and hydrogen contents are not set, but when the content is extremely lowered, the manufacturing cost of the titanium plate is greatly increased.

Therefore, from the viewpoint of suppressing such cost increase, the carbon content is 0.0005% or more, the nitrogen content is 0.0005% or more, and the hydrogen content is 0.0005% or more.

Titanium sheets are used when it is required to have good workability in forming processing, and it is equivalent to a titanium material having a small iron content of JIS type 1 and JIS type 2, and is generally α single phase.

The larger the size of the α-particle size, the more excellent the moldability. Therefore, in the present embodiment, the titanium plate has a two-phase structure of α + β phase, and the round-equivalent average particle diameter of the β phase is 3 μm or less.

When the formed titanium plate has such a structure, an index indicating workability such as an Eriksson value can be improved.

When the average phase particle diameter of the β phase is more than 3 μm, the Erikson value may be lowered, for example, less than 10 mm, and the workability may be lowered.

This is because the boundary between the coarsened β phase and the α phase tends to be cracked due to stress concentration, so that the workability of the titanium plate is lowered.

The lower limit of the β-phase equivalent average particle diameter is not particularly limited, but when it is less than 0.05 μm, the production cost is greatly increased in order to obtain a titanium plate, and therefore it is preferably 0.05 μm or more.

The equivalent average particle diameter of the β phase is determined by the method described in the "Example" of the latter stage.

These findings were discovered by the present inventors by the following methods.

That is, in a small vacuum arc melting furnace, a plurality of kinds of titanium materials having different iron contents are used, and a cold-rolled plate having a thickness of 0.5 mm is tested while changing the annealing conditions, and the obtained cold-rolled plate is evaluated by an Erikson test ( Formability of titanium plate) (details are described in "Examples" described later).

It has also been found that, for example, elongated annealing time increases the particle size of the beta phase, and increasing the particle size of the beta phase reduces the Eriksson value.

In addition, when the structure and the cross-section were investigated in detail, it was found that the interface between the coarse β-particle and the α-phase was cracked. Therefore, it was judged that changing the annealing condition and reducing the particle size of the β-phase can increase the Erikson value and improve the formability.

In particular, when the circle-equivalent average particle diameter of the β phase is limited to 3 μm, a high-strength titanium plate excellent in workability can be obtained below this value.

As described in the course of obtaining this insight, the particle size of the β phase can be adjusted by the iron content in the titanium material, the annealing temperature at the time of manufacturing the titanium plate, and the annealing processing time.

These conditions in the method of manufacturing a titanium plate will be explained below.

In each of the conditions of the annealing temperature and the annealing time in the production of the titanium plate, lowering the annealing temperature suppresses the growth of the β particles and reduces the crystal grain size.

Further, shortening the annealing processing time can suppress the growth of crystal grains and reduce the crystal grain size.

More specifically, when the annealing temperature is less than 550 ° C, the processed structure after the cold rolling can be prevented from being crystallized, so that the moldability is lowered.

Further, at a temperature exceeding 800 ° C, the diffusion of iron in the titanium is accelerated, and the crystal grains of the β phase are coarsened.

Therefore, the annealing temperature is preferably any temperature in the range of 550 ° C to 800 ° C.

Further, the annealing processing time can be determined by the annealing processing temperature, the thickness of the titanium plate, the capacity of the annealing furnace, and the like.

That is, when the annealing temperature is 650 ° C or more and 800 ° C or less, the annealing processing time is preferably more than 0 minutes but not more than 15 minutes.

Since the temperature of the titanium sheet reaches the annealing temperature and the annealing process is completed, the structure is recrystallized by heating. Therefore, even if the annealing time is less than 0 minutes, the possibility of further lowering the moldability is low.

Further, the reason why the annealing processing time has an upper limit of the annealing processing time of 15 minutes is that when the annealing process is performed for more than 15 minutes, the crystal grains of the β phase are coarsened, and the workability of the titanium plate is lowered.

When the annealing temperature is 550 ° C or higher and less than 650 ° C, it is preferably carried out, and the annealing time is t (minutes), and when the annealing temperature is T (° C.), the annealing process according to the following formula (1) is satisfied.

[Number 1]

T≧32.5-0.05×T.........(1)

(but 550≦t<650)

The rate of recrystallization in this temperature range is slow, so a certain degree of recrystallization time is required.

Therefore, the moldability can be improved by recrystallization by selecting the conditions corresponding to the above formula (1).

However, when the annealing temperature exceeds 630 ° C and does not reach 650 ° C, annealing for a long period of time causes the crystal grains of the β phase to coarsen and the workability of the titanium plate is lowered.

Therefore, it is preferred to carry out annealing processing in accordance with the following formula (2) in the temperature range.

[Number 2]

t<9277.5-14.25×T .........(2)

(but 630<T<650)

Further, when the annealing temperature is in the range of 550 ° C to 630 ° C, the annealing time is preferably 300 minutes or shorter.

The selection of such conditions suppresses the coarsening of the β phase formed in the structure of the titanium plate, and imparts good workability to the titanium plate.

Further, when the annealing processing time is set to more than 300 minutes in this temperature range, the crystal grains of the β phase are coarsened, and the workability of the titanium plate is lowered.

By using the above-described production conditions, the particle size of the β phase in the titanium plate can be adjusted to a certain value or less to obtain a titanium plate having excellent strength and workability.

Further, although not detailed in the foregoing, the titanium plate of the present embodiment can be used in the conventional titanium plate and titanium plate manufacturing method, without significantly impairing the effects of the present invention.

Example

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited thereto.

(Examples 1 to 22, Comparative Examples 1 to 3) (making a test piece)

After the ingot (Φ 140 mm) was produced by a small vacuum arc dissolution, the ingot was heated to 150 ° C, and then forged to a thickness of 50 mm.

The thick block was thermally extended to a thickness of 5 mm at 850 ° C, and then annealed at 750 ° C to remove the scale on the surface to prepare a plate having a thickness of 4 mm.

Further, the plate was cold-rolled to prepare a plate-shaped sample (titanium plate) having a thickness of 0.5 mm.

The titanium sheet having a thickness of 0.5 mm was subjected to annealing treatment in a vacuum environment to prepare a test piece for evaluation.

In the annealing process, the crystal grain size of the test piece is adjusted by adjusting the temperature (550 ° C or more and 800 ° C or less) and the time (300 minutes or less).

(determining ingredients)

The amount of iron and the amount of oxygen contained in the titanium plate were measured using a plate having a thickness of 4 mm from which the surface area scale was removed.

The iron content was measured in accordance with JIS H1614, and the oxygen content was measured in accordance with JIS H1620.

(measuring tensile strength)

Further, the tensile strength of the test piece (titanium plate) in which the crystal grain size was adjusted as described above was measured in accordance with JIS Z2241.

(evaluation of processability)

Further, the workability of the titanium plate was evaluated by measuring the Eriksson value of the test piece (titanium plate) in which the crystal grain size was adjusted as described above in accordance with JIS Z2247.

(investigation organization)

The appearance of the microstructure of the titanium plate was observed using a microscope photograph as shown in Fig. 1 (microstructure of Example 7).

In the photograph of the tissue, the β phase is in black and the α phase is in white. Therefore, after the photo is binarized using the image analysis program and the average area of the β phase is obtained, the circle having the same area as the average area is calculated. The diameter is used as a circle with a fairly average particle size.

The above results are shown in Table 1.

The iron content and the oxygen content of Examples 1 to 4 and Comparative Example 1 in Table 1 are the same, but the equivalent average particle diameter of the β phase can be adjusted by different annealing conditions, and the circle of the β phase is equivalent to the average particle diameter. The greater the value of Erikson in hours.

Further, other examples and comparative examples have the same tendency, and it is understood from Fig. 2 showing the relationship between the circle-equivalent average particle diameter of the β phase in Table 1 and the Eriksson value, and the present invention can provide high strength and workability. Excellent titanium plate.

Fig. 1 is a photomicrograph showing the microstructure of a titanium plate of Example 7.

Fig. 2 is a graph showing the relationship between the equivalent average particle diameter of the β phase and the ERICHSEN value.

Claims (1)

A titanium plate characterized in that, under the mass, the iron content is more than 0.10%, less than 0.60%, the oxygen content is more than 0.005%, less than 0.10%, the carbon content is less than 0.015%, and the nitrogen content is less than 0.015%, hydrogen. The content is less than 0.015%, and the residue is formed of titanium and an unavoidable impurity, and forms a two-phase structure of the α phase and the β phase, and the circle of the β phase formed has a uniform average particle diameter of 3 μm or less.