KR20140004793A - Pure titanium sheet having excellent balance between press formability and strength and excellent corrosion resistance, and process for manufacturing same - Google Patents

Abstract

The pure titanium plate of the present invention contains Fe: 0.02 to 0.10%, O: 0.04 to 0.20%, and the remainder is made of titanium and inevitable impurities, and the content of Fe and O is represented by the following formula (1) The area ratio of the region where the Schmidt factor of the {11-22} <11-23> twin system based on the rolling direction of the 1/4 position of the sheet thickness is 0.45 or more is 43% or more, and the volume of β phase The rate is 0.3% or less.
[Equation (1)]
[O content (mass%)] + 0.12 x [Fe content (mass%)] ≥0.050

Description

Pure titanium plate excellent in balance of press formability and strength and corrosion resistance, and a manufacturing method thereof {PURE TITANIUM SHEET HAVING EXCELLENT BALANCE BETWEEN PRESS FORMABILITY AND STRENGTH AND EXCELLENT CORROSION RESISTANCE, AND PROCESS FOR MANUFACTURING SAME}

The present invention relates to a pure titanium plate having excellent balance of press formability and strength at room temperature and corrosion resistance, and a method for producing the same, and in particular, having a strength (tensile strength) of 343 MPa or more even at room temperature, and excellent press formability. The pure titanium plate which has gap corrosion resistance, and its manufacturing method are related. Moreover, this invention relates to the method of manufacturing a heat exchange member of a plate type heat exchanger by press molding such a pure titanium plate.

Titanium has excellent corrosion resistance, press formability, specific strength, light weight, and the like, for example, aircraft parts, chemical plant members, coastal structural materials (particularly, manganese structural materials in which corrosion is promoted by seawater contact), and automobiles. It is widely used in a wide range of fields and uses, such as construction materials.

In recent years, environmental load reduction and energy saving are demanded in various fields, and in order to meet the demand for further light weight and thinning of titanium, which is considered to be light and strong, high strength is desired. It is also used in body parts such as mobile phones, mobile personal computers, cameras, eyeglass frames, plate heat exchangers, separators in fuel cells, exterior parts of home appliances, and transport target devices, and the like, and further improving moldability. It is becoming.

The pure titanium plate used for these is prescribed | regulated by the specification of JISH4600, and there exist grades, such as JIS 1 type, 2 type, 3 type, etc. by impurities amount, intensity | strength, etc., such as Fe and O. As the grade increases, the minimum strength is increased, and their use is classified according to the use.

When the concentration of Fe and O is low as in the case of JIS 1 type, since the strength is low but the ductility is high, conventional JIS type 1 pure titanium plate was used for the member which requires high formability.

For example, a plate type heat exchanger (PHE) may be used as one of the most commonly used pure titanium plates. However, the pure titanium plate applied to the present application is generally used in view of improving the heat exchange rate. In order to enlarge the heat exchange effective area, press molding (anisotropic bulging molding) is performed in a cold to complex corrugated board shape, and the material is exposed to an extremely harsh press environment. As the pure titanium sheet used for such harsh press forming conditions, soft JIS one kind of pure titanium that is most easily formed on the standard is used.

However, the heat exchange rate improvement of the heat exchanger is not limited to the shape of the heat exchanger itself as described above, and is also achieved by, for example, an increase in the flow rate of the fruit (or the refrigerant), and these require high pressure resistance. Pure titanium sheet is required to have higher strength and excellent moldability.

As pure titanium plates with high strength, two or three kinds of JIS having high Fe and O concentrations are used. However, the higher the Fe and O concentration, the higher the strength, but the moldability deteriorates, and in the prior art, it is impossible to achieve both high strength and high formability. In addition, depending on the production history, gap corrosion of a titanium product may be a problem in a high temperature and high humidity environment where the use environment tends to corrode.

As means for improving the press formability of the pure titanium plate, for example, controlling the structure of titanium (Patent Document 1) or alloying titanium has been proposed (Patent Document 2). However, titanium aimed at such a technique is for the purpose of improving the formability of the pure titanium plate which has the strength (yield strength) level equivalent to JIS class 1, but when the strength level is raised, the formability does not show improvement.

As a means of improving the press formability of a pure titanium plate having a high strength level, a technique of adjusting the content of Fe and O and controlling the grain size of titanium is proposed (Patent Document 3). However, it is difficult to achieve balance between press formability and strength only by controlling the Fe, O content or the grain size of titanium.

In addition, as mentioned above, in recent years, the field of application of pure titanium plates has reached a wide range. However, when used in a corrosive environment, an improvement in gap corrosion resistance has been required.

As a titanium plate which improved gap corrosion resistance, in patent document 4, it is disclosed that a platinum group element adheres to the pure titanium plate surface. However, since the platinum group element is expensive, there is a problem that the manufacturing cost is high, and it is difficult to use it universally.

In addition, Patent Literature 5 discloses a titanium alloy sheet containing Cu, Ni, and Mo as a technique for improving the balance between strength and press formability. However, the addition of alloying components lowers the productivity, making it unsuitable for industrial scale production. Moreover, there is no specific disclosure about corrosion resistance.

Thus, pure titanium sheet which is excellent in the balance of press formability and intensity | strength under room temperature, and also has excellent gap corrosion resistance is not provided yet.

Japanese Patent Publication No. 2004-285457 Japanese Patent Publication No. 2002-317234 Japanese Patent Publication No. 2009-228092 Japanese Patent Publication No. 49-31610 Japanese Patent Laid-Open No. 2010-236067

This invention is made | formed in view of the said conventional problem, The objective is to provide the pure titanium plate which has the characteristic of excellent balance of press formability and strength, and corrosion resistance (gap corrosion resistance), and its manufacturing method. Specifically, a pure titanium plate having a tensile strength of 343 MPa or more at room temperature, excellent in press formability (ductility of anisotropic bulging molding and isotropic bulging molding), and excellent in corrosion resistance to gaps, and The manufacturing method is provided.

The present invention that can solve the above problems contains Fe: 0.02 to 0.10% (the meaning of "mass%", the same as for the chemical components below), O: 0.04 to 0.20%, the remainder is titanium and inevitable impurities A Schmidt of a {11-22} <11-23> twin system in which the Fe and O content satisfies the following formula (1) and the rolling direction at the 1/4 position of the sheet thickness is the axis; It is a pure titanium plate excellent in the balance of press formability and strength and corrosion resistance which have the point that the area ratio of the area | region whose factor is 0.45 or more is 43% or more, and the volume ratio of (beta) phase is 0.3% or less.

[Formula (1)

[O content (mass%)] + 0.12 x [Fe content (mass%)] ≥0.050

As a method for producing a pure titanium plate excellent in balance of press formability and strength and corrosion resistance, a process of hot rolling, intermediate annealing, cold rolling, and final annealing is performed, and after the intermediate annealing, descaling of the surface of the pure titanium plate is performed. It is recommended to perform cold annealing after the reduction ratio is 70% or more, and then perform final annealing on the condition that H defined by the following formula (2) becomes a positive value.

[Expression (2)]

[only,

T: heating temperature at final annealing (° C), t: annealing time (seconds)

X ₀ : Fe concentration (mass%) in a pure titanium plate

A = 891, B = 0.428, n = 0.135]

The pure titanium sheet undergoes hot rolling, cold rolling, and final annealing, and after the hot rolling, deintercalation of the surface of the pure titanium sheet without intermediate annealing, followed by cold rolling having a reduction ratio of 20% or more. It can also be obtained by the manufacturing method which has a summary in performing final annealing on condition that H defined by following formula (2) becomes a positive value after that.

[Expression (2)]

[only,

T: heating temperature at final annealing (° C), t: annealing time (seconds)

X ₀ : Fe concentration (mass%) in a pure titanium plate

A = 891, B = 0.428, n = 0.135]

According to the present invention, the chemical component composition is strictly defined after considering the balance of each element, and the Schmidt factor and β phase of a specific twin system of crystal grains of pure titanium plates are specified at a specific ratio, so that the tensile strength is high even at room temperature. In addition, a pure titanium sheet excellent in press formability and gap corrosion resistance can be obtained. Such a pure titanium plate is capable of exhibiting a good molding processability when a high strength at room temperature is required in a wide range of fields as described above, and further excellent in corrosion resistance.

In addition, according to the present invention, the pure titanium plate can be manufactured at low cost.

1 is a perspective view of a titanium plate used in a plate heat exchanger (PHE).
FIG. 2A is a plan view of a press-molding die for explaining a method of evaluating press formability, and FIG. 2B is a schematic cross sectional view between FF in FIG. 2A.

The press formability of the pure titanium sheet is known to be excellent in press formability as the twin strain is more likely to occur, in addition to the sliding deformation, and the twin strain also contributes greatly to the deformation of the material. It is known that pure titanium tends to generate twin strain more softly and has better press formability. However, when the strength level is high, twin titanium strain hardly occurs and press formability is known to be low.

MEANS TO SOLVE THE PROBLEM The present inventors examined metal structure from various angles, in order to improve press formability, maintaining a high strength level (343 Mpa or more of tensile strength), and to provide the pure titanium plate excellent also in gap corrosion resistance, I gained the following knowledge.

That is, when cold rolling in one direction, strength anisotropy is generated in the pure titanium plate, and the strength in the high ductility rolling direction is lower than the low ductility width direction. Proceed. Therefore, in order to improve the press formability, the structure control for urging the activation of twin deformation that contributes to deformation in the rolling direction, which is the main deformation direction, is effective, and twin deformation is performed even when the tensile strength level is 343 MPa or more. It is important to form a crystal orientation that is easy to generate.

Therefore, in the present invention, as a result of examining the Schmitt factor affecting the ease of twin strain generation, the twin strain deformation when a tensile load is applied in the rolling direction of the 1/4 x plate thickness of the pure titanium plate When the value of the Schmitt factor and its distribution ratio (area rate) are in a specific range, it was found that press formability can be improved while maintaining a high strength level, and the present invention has been reached.

Specifically, the crystal grains of the principal phase of the pure titanium plate have a hexagonal crystal structure, and the twin system mainly active during bulging is {11-22} <11-23>. Therefore, in order to improve the moldability mainly in the case of deformation in the rolling direction, it is effective to activate the activity of the {11-22} <11-23> twin system when a load is generated in the rolling direction. For that purpose, it is effective to increase the Schmitt factor of the {11-22} <11-23> twin system.

As a result of repeated studies by the present inventors, the value of the Schmidt factor of the twin system mentioned above must be at least 0.45 or more in order to facilitate the operation of twin deformation.

First of all, if the proportion of the grains having a Schmitt factor more than this specific value is too small, even if the activity of twin deformation can easily occur, it does not contribute significantly to the improvement of the overall material, that is, press formability. Therefore, the area ratio of the area | region where the said Schmitt factor is 0.45 or more, 43% or more of the whole, Preferably 45% or more is required. If 43% or more exists in area ratio, the pure titanium plate which has remarkably excellent press formability is obtained, maintaining the intensity level of 343 Mpa or more. The upper limit of this area ratio is not specifically limited.

Moreover, in the mirror index which shows a crystal plane, when the index becomes negative, the notation which sticks a bar over a number is common. However, when the exponent becomes negative, in the present specification, it is expressed as a negative number for convenience. Therefore, -2 in the above {11-22} indicates that the index is negative.

Thus, in the present invention, the Schmitt factor is employed as an index for improving press formability. In general, the magnitude of the critical decomposition shear stress (τ) required to move dislocations along a particular crystal plane varies with the crystal plane and the crystal axial direction, and [τ = σcosφcosλ] where σ is the tensile stress in the tensile axis direction, ? is known by the angle formed by the sliding surface normal and the tensile axis, and λ represents the angle formed by the sliding direction and the tensile axis.

[Cosφcosλ] in the above formula is called a Schmitt factor, and represents the ratio of the force used to move the dislocation among the external forces applied to the tensile axis. When an external force is applied to the titanium plate, the sliding system / twin system having a high Schmitt factor value acts at a smaller external force, and as a result, the metal plate tends to plastically deform. The pure titanium sheet which satisfies the requirements of the Schmitt factor is promoted by twin deformation when a tensile load is applied in the rolling direction, and greatly improves press formability (particularly anisotropic bulging formability) in which the main deformation direction is the rolling direction. .

In addition, it is known that pure titanium plates are generally higher in strength as the impurity element content is higher, and twin deformation is less likely to occur, and therefore press formability is poor. However, in the present invention, as described later, the chemical composition is strictly defined, and the Schmitt factor is controlled so that twin deformation is likely to occur, so that twin deformation can be activated even if the impurity element content is high and the tensile strength is high. As a result, press formability is improved.

In addition, the present inventors have found that it is important to suppress the precipitation of the β-phase in order to increase the gap corrosion resistance even under such an environment, because the gap corrosion tends to occur under particularly high temperature and high humidity environments. That is, the titanium of the present invention is preferably a metal structure mainly composed of the α phase (hexagonal crystal). Since the gap corrosion resistance deteriorates when the volume ratio of the β phase (body centered cubic crystal) increases, the upper limit of the volume ratio of the β phase is 0.3% or less, preferably 0.2% or less, and more preferably 0%.

In addition, in the pure titanium sheet of the present invention, it is important to appropriately adjust Fe and O which are elements that affect press formability and tensile strength. The reason for range setting of each of these components in the pure titanium plate of this invention is as follows.

Fe: 0.02 to 0.10%

Fe is an element which contributes to the strength improvement of a pure titanium plate, and in order to exhibit such an effect, content of Fe is 0.02% or more, Preferably it is 0.03% or more. However, if the Fe content is too large, the β phase generated will be increased even if the annealing conditions are optimized, and the gap corrosion resistance will deteriorate. Therefore, Fe content is 0.10% or less, Preferably it is 0.08% or less, More preferably, you may be 0.07% or less.

O: 0.04 to 0.20%

O is an effective element in securing the strength of the pure titanium plate, and in order to exert such an effect, the content of O is 0.04% or more, preferably 0.045% or more, more preferably 0.050% or more, even more preferably 0.07 It is% or more. However, when there is too much O content, intensity | strength will become high too much and press formability may fall rather, or it may fracture at the time of edge cracking or cold rolling. Therefore, O content is 0.20% or less, Preferably it is 0.18% or less, More preferably, you may be 0.15% or less.

In the present invention, the relationship between the content of Fe and O is defined from the viewpoint of suppressing the precipitation of β-phase and improving the intergranular corrosion resistance while improving the balance between strength and press formability by adding Fe and O. It is important. Specifically, it is necessary to adjust content of Fe and O within the said range so that it may become [O content (mass%)] + 0.12 * [Fe content (mass%)] ≥0.050 [formula (1)]. When content of Fe and O derived from said formula (1) is less than 0.050, there exists a possibility that intensity | strength may run short. In order to further increase the effect of adding Fe and O, the value of the formula (1) is preferably adjusted to 0.055 or more, more preferably 0.060 or more, even more preferably 0.080 or more.

In the pure titanium plate of the present invention, in addition to the above components, the remainder comprises titanium and unavoidable impurities. "Inevitable impurities" include impurity elements (typically N, C, H, Si, Cr, Ni, etc.) that are inevitably included in sponge titanium of a raw material, or elements that may be introduced into a product in a manufacturing process ( For example H).

Of these unavoidable impurities, for example, N is also an element contributing to the strength improvement of the pure titanium plate. However, the N content is preferably 0.02% or less, more preferably from the point that the cold content is impaired when the content increases. Preferably it is 0.01% or less. On the other hand, although N content may be 0%, since excessive reduction causes rather a cost increase, Preferably it is 0.001% or more, More preferably, it is 0.002% or more.

Although C is an element contributing to the strength improvement, the C content is preferably less than 0.015%, more preferably 0.012% or less, in view of the fact that the cold content is impaired when the content increases. On the other hand, the lower limit of the C content is not particularly limited, and may be 0%, but excessive reduction leads to an increase in cost, so it is preferably 0.002% or more, and more preferably 0.003% or more.

The pure titanium plate of this invention has a tensile strength of 343 Mpa or more at room temperature (25 degreeC). As described above, pure titanium plates are used in various fields, and high strength is required even at room temperature. The tensile strength of the pure titanium plate of the present invention is preferably 370 MPa or more. Above all, if the tensile strength is too high, the ductility decreases and the press formability deteriorates, so it is preferably 600 MPa or less.

As described above, the strength and ductility of the pure titanium plate are opposite properties. The present invention is a pure titanium plate capable of satisfying both of these properties, and has a tensile strength of 343 MPa or more and excellent press formability, and excellent intergranular corrosion resistance. It is to provide a pure titanium plate having a.

Next, manufacturing conditions are demonstrated using the said pure titanium plate as an example. For example, in the case of a pure titanium plate, it is generally manufactured by the following process. Since the physical properties of titanium differ depending on the chemical composition of the titanium material to be used and the setting conditions of each process, it is necessary to select conditions comprehensively as a series of manufacturing processes, and to set the conditions strictly for each process. It is not necessarily appropriate.

Pure titanium plates generally obtain a titanium ingot adjusted to a specific component composition by casting. Thereafter, [I. Ingot forging, rolling] → [II. Hot rolling] → [III. Intermediate annealing] → [IV. Cold rolling] → [V. Final annealing]. Between each process, you may perform a descaling process by performing a blast, an acid washing process, etc. as needed.

[I. Ingot forging, rolling] is a step carried out as needed, and is carried out to break up the coarse cast structure, for example, cracking at about 800 to 1100 ° C from productivity (easiness of processing) or the like, and forging or rolling. This can be started.

[II. Hot rolling] may be hot rolling so as to have a desired plate thickness after maintaining at about 700 to 950 ° C, for example.

[III. Intermediate annealing] is a step performed as necessary, and for example, air-cooling may be performed after cracking at about 700 to 850 ° C.

In the case of performing the intermediate annealing, after the intermediate annealing, the descaling process is performed, followed by [IV. Cold rolling]. Done before final annealing [IV. Cold rolling] is a reduction ratio of 70% or more, preferably 80% or more. By performing cold rolling at a reduction ratio of 70% or more, subsequent [V. Final annealing], while maintaining the tensile strength of the pure titanium plate at 343 MPa or more, excellent characteristics of press formability are obtained.

That is, in the production of the pure titanium plate of the present invention, after the intermediate annealing [IV. Cold rolling], when the reduction ratio is 70% or more, the Schmidt factor of the {11-22} <11-23> twin system can make the area ratio of 0.45 or more crystal grains 43% or more. This is because [IV. Cold rolling] is set to 70% or more, and then [V. Final annealing], the desired crystal orientation can be obtained, so that good press formability can be obtained and the tensile strength can also be maintained at 343 MPa or more.

In addition, as the reduction ratio increases, press formability is improved. However, if the reduction ratio is too high, edge cracking occurs at the end of the pure titanium plate, or the pure titanium plate breaks during cold rolling, thereby inhibiting productivity. Silver is preferably at most 95%, more preferably at most 90%.

On the other hand, [III. Intermediate annealing] is not performed. Hot rolling], followed by the descaling treatment. Cold rolling]. And in this case, [IV. Cold rolling] is 20% or more, preferably 25% or more. Even when the intermediate annealing is omitted, the tensile strength of the pure titanium sheet can be increased to 343 MPa or more by appropriately cold rolling and final annealing, and also has excellent press formability. In the case of cold rolling without performing intermediate annealing, the reason why the above excellent characteristics are obtained even if the reduction ratio is low is that the strained structure formed on the raw material at the time of hot rolling remains in the material without being offset by the intermediate annealing. Since the excellent press formability can be obtained even at a low reduction ratio without performing intermediate annealing, for example, when the thickness of the pure titanium sheet is thick and a high reduction ratio cannot be taken, for example, the sheet of pure titanium sheet is hot rolled. The same applies when the thickness is sufficiently thin. In addition, the reduction ratio is preferably 95% or less, and more preferably 90% or less.

[V. Final annealing] may be annealed under the conditions of heating temperature and annealing time so that the following formula (2) becomes a positive value, and then air-cooled to room temperature, and by setting it as such conditions, precipitation of β-phase which affects the gap corrosion resistance Can be suppressed. The pure titanium plate of the present invention contains a small amount of Fe as described above, but the heating temperature and the holding time at which the β phase precipitates are determined by the Fe content, so that the following formula (2) becomes a positive value: The final annealing is performed. Equation (2) is that,

[Expression (2)]

However, in formula, T: heating temperature at the time of final annealing (degreeC), t: annealing time (seconds), X ₀ : Fe concentration (mass%) in a pure titanium plate, A = 891, B = 0.428, n = 0.135 to be.

In addition, Formula (2) is obtained based on the following experiment. That is, as mentioned above, the precipitation rate of the β phase depends on the Fe concentration in the pure titanium plate and the holding temperature during the heat treatment, and the higher the Fe concentration, the faster the temperature. Therefore, the relational expression (Equation 2) which is the basis of the precipitation rate is calculated | required using the precipitation rate formula computed based on atom diffusion and concentration distribution, and each coefficient A and B in Formula (2) is based on experimental data. Decided.

In formula, T is the heating (annealing) temperature (degreeC) at the time of final annealing, and it is preferable that it is 550 degreeC <= T (degreeC) <= 890 degreeC. When the annealing temperature T is less than 550 degreeC, recrystallization does not occur and ductility may deteriorate remarkably. The minimum temperature required for recrystallization changes with the holding time, and for example, the shorter the holding time, the higher the temperature is required. Heating temperature T becomes like this. Preferably it is 600 degreeC or more, More preferably, it is 700 degreeC or more. In addition, when annealing is performed by heating above the β transformation point, since it becomes a needle-like structure after cooling, and press formability is impaired, it is preferable to perform final annealing below β transformation temperature. Heating temperature T becomes like this. Preferably it is 870 degrees C or less, More preferably, it is 850 degrees C or less.

In addition, general conditions can be employ | adopted for the conditions of other conditions in cold rolling and final annealing, and the other process.

In addition, in the formula, t is an annealing time (second), which is a holding time at the heating temperature T (° C.), and is maintained within the range of the heating temperature T (° C.) ± 5 ° C. if it is within the range of the temperature range. It means you have to. If the annealing time t is too short, it is difficult to control the annealing process, and the productivity worsens even if the annealing time t is too long. Therefore, the annealing time t (seconds) is preferably in the range of 10 seconds? T (seconds)? 120,000 (seconds).

The thickness of the pure titanium sheet of the present invention may be set in consideration of required strength and the like, and is not particularly limited.

Since the pure titanium sheet according to the present invention has high strength and excellent ductility, and also has excellent interfacial corrosion resistance under a high temperature and high humidity environment, the structural material of aircraft parts, chemical plant members, and coastal portions (particularly, seawater) (Structural elements in which corrosion is promoted by corrosion), automobiles, building materials, cellular phones, mobile personal computers, cameras, body parts, eyeglass frames, plate heat exchangers, fuel cell separators, exterior products for home appliances, and transportation It can be widely applied to applications requiring high formability and mechanical strength in a wide range of fields such as machine target members. In particular, it is suitable for the heat exchange member of a plate type heat exchanger.

<Examples>

Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited by the following Example of course, It is a matter of course that it changes and implements suitably in the range suitable for the meaning mentioned above and later. It is possible that they all fall within the technical scope of the present invention.

The ingot containing Fe and O shown in the "component" in Table 1, and the raw material of remainder titanium and an unavoidable impurity were obtained by casting by CCIM (cold crucible induction dissolution method). The ingot was subjected to a flake rolling of a block shape having a width of 130 mm and a thickness of 45 mm, further heated to 750 ° C. to hot rolling to obtain a hot rolled sheet having a thickness of about 4 mm (Nos. 3 to 16). In addition, some test materials faced the thickness of the hot rolled sheet in consideration of the final sheet thickness (0.5 mm) and the cold rolling rate shown in Table 1, and appropriately adjusted the sheet thickness. Some of the hot rolled sheets shown in Table 1 were subjected to intermediate annealing at 700 ° C. for 5 minutes, then immersed in a salt bath furnace, and then acid washed and descaled. The other part was descaled without intermediate annealing. After the descaling treatment, the sheet thickness was adjusted by roughing and acid washing, cold rolling was performed at the "rolling reduction rate" shown in Table 1, and final annealing was then performed under "final annealing conditions" shown in Table 1. In addition, some test materials set the reduction ratio other than 85%. After the final annealing, it was immersed in a hydrofluoric acid solution and descaled, and the pure titanium plate of 0.5 mm of plate | board thickness used as a test material was obtained. H value of each pure titanium plate was computed based on said Formula (2), and it described in the "Value H of Formula (2)" column of Table 1.

The following evaluation was performed about each obtained pure titanium plate.

(Measurement method of Schmitt factor)

The field emission scanning electron microscope (FESEM) (JSM5410, manufactured by Nippon Denshi Co., Ltd.) was equipped with a backscattered diffraction pattern (EBSP) system in which the order of arbitrary points was determined. The texture of the titanium plate surface was evaluated.

Specifically, the surface of the pure titanium sheet is polished to 1/4 of the thickness of the plate, and then set in the SEM barrel, and the EBSP projected on the screen by irradiating an electron beam is taken with a high-sensitivity camera and introduced into the computer as an image. Then, this image was analyzed to determine the crystal orientation. At this time, the Schmitt factor of the {11-22} <11-23> twin system when the tensile load direction was matched with the rolling direction was evaluated for each measurement point, and the data of the orientation mapping were collected. In addition, this measurement visual field range was 1 mm x 1 mm, and the measurement pitch was 1 micrometer. In this case, it is assumed that the azimuth difference between the measurement points adjacent to each other is within ± 15 ° and belongs to the same crystal plane.

({11-22} <11-23> Area ratio of crystal grains (α phase) having Schmidt factor of 0.45 or more in twin system

After the measurement of the Schmidt factor, the sum of the measured points of Schmidt factor 0.45 or more divided by the number of all the measured points and multiplied by 100 to obtain the area ratio of the grains having a Schmitt factor of 0.45 or more, and the "assembly structure (%)" in Table 1 It is described in.

(volume ratio on β)

The surface of the rolled surface of the pure titanium plate was mechanically polished to a quarter position of the plate thickness, and after finishing the mirror surface by buff polishing and chemical polishing, the reflection electron image (BSE) observation was performed. An arbitrary area of 270 μm × 230 μm was observed at a magnification of 10,000 times for each sample, and the average of the volume fractions of the β phase was determined and described in the “β phase volume percentage (%)” column of Table 1. In the present Example, it was set as the pass rate if the volume ratio of (beta) phase is 0.3% or less.

Tensile strength evaluation

No. 13 test piece (direction in which the rolling direction coincides with the load axis (L direction)) specified in JISZ2201 was sampled from the pure titanium plate, the tensile test was performed based on JISH4600 at room temperature, and the tensile strength was measured. The result was written in the "tensile strength" column of Table 1. The case where the tensile strength is 343 Mpa or more was evaluated as pass.

Press formability (score)

2 (a) and 2 (b) are explanatory diagrams for evaluating the press formability (anisotropic bulging formability). Press mold which simulates the heat exchange part of a plate type heat exchanger using the pure titanium plate produced as the said test material [size: 160 mm x 160 mm (evaluation part: 100 mm x 100 mm), pitch: 10 mm, maximum height : 4mm, radius of curvature R: Herringbone type having six types of ridges of 0.4, 0.6, 0.8, 1.0, 1.4, and 1.8mm; a die having a different radius of curvature R of the mountain by the ridge] The press formability of the titanium plate was evaluated by a hydraulic press. Press conditions apply press oil (kinematic viscosity 34mm <2> / s (temperature 40 degreeC)) to both surfaces of the metal mold | die which is a test piece, and apply | coil on the lower side metal mold | die so that the rolling direction of each test material may correspond with the up-down direction of FIG. After arranging and restraining a flange part with a pressure plate, it carried out on condition of a press speed of 1 mm / sec and a press-in depth of 3.4 mm.

As shown in Fig. 2 (Fig. 2 (a) is a plan view and Fig. 2 (b) is a sectional view), the intersection point between the ridge portion and the broken line (five points on the mountain side and one on the valley side) is shown in FIG. 36 places.

About A line (mountain side), C line (mountain side), C 'line (valley side) and E line (mountain side) which are the origins of a crack, when it is visually judged and there is no crack (health), it is two points, a necking ( If a part tends to become thinner and narrowed, one point, if a necking occurs, one point, and if a crack occurs, it is set to 0 points, and there is no crack for B line (mountain side) and D line (mountain side). 2 points, 0.5 point if necking occurred, and 0 point if cracking occurred.

The score of moldability was computed by following formula (3), and it was set as the index of the press moldability evaluation in this invention. Specifically, the state of cracking was digitized by multiplying each score by the inverse of the radius of curvature R, and the sum was calculated. This total value is normalized to 100 when no cracking or necking is confirmed, and then the functions F (T, μ, t) depending on the temperature (T), the lubricating oil viscosity (μ), and the test plate thickness (t), and The functions G (α, p) depending on the angle α of the ridgeline and the pitch p of the mold were multiplied and calculated as a moldability score. In addition, in the present Example, since temperature T, the lubricating oil viscosity (μ), the test piece plate thickness (t), the angle (alpha) of the ridgeline of the metal mold | die, and pitch (p) were made constant, FxG was made into 1 conveniently. The score was computed and described in the "forming score" column of Table 1.

[Expression (3)]

Formability score = (F × G) × [ΣE (ij) / R (j)] / [(ΣA, C, C ′, E2 / R (j)) + (ΣB, D1 / R (j))] × 100)

Wherein,

Regarding A, C, C ', and E, E (ij) = 1.0 × (no crack: 2, narrow portion: 1, crack: 0),

About B and D, it computed as E (ij) = 0.5x (no crack: 2, a narrow part: 1, and a crack: 0).

The moldability score evaluated 70 or more points as being excellent in moldability.

(Gap corrosion test)

A 30 mm x 50 mm test piece was cut out from the produced pure titanium plate, a hole of φ 7 mm was drilled in the center, and a Teflon (registered trademark) multiclevis (ASTM G1671) was installed on both sides. It was set as the test piece for corrosion evaluation. Although this multiclevis forms 12 gap parts, in this test, since multiclevis was provided in both surfaces of a test piece, the gap parts total 24 places. This test piece was immersed in boiling 10% NaCl aqueous solution for 360 hours, after which the presence or absence of gap corrosion was visually confirmed and the number of generation points of gap corrosion was measured. When the number of occurrence points of gap corrosion was five or less, the gap corrosion resistance was evaluated as good. The result was described in the "Corrosion-resistant corrosion rate" column of Table 1.

(Comprehensive evaluation)

As the mechanical properties at room temperature, the cases where the tensile strength at room temperature is 343 MPa or more, the press formability score is 70 or more, and the number of gap corrosion occurrences are 5 or less are set as pass, respectively. It was evaluated that the balance of the properties was excellent and the gap corrosion resistance was also excellent. The results are shown in Table 1.

From Table 1, it can be considered as follows. That is, No. 2 to 6, 9, 10 and 12 to 16 are pure titanium plates satisfying the requirements specified in the present invention, and it is understood that not only the balance of strength and press formability at room temperature is excellent, but also the gap corrosion resistance is excellent. .

On the other hand, Since 1, 7, 8, and 11 do not satisfy the requirements specified in the present invention, there is a problem that the strength at room temperature cannot be secured, or the press formability and gap corrosion resistance at room temperature are inferior.

No. 1 and No. 2. 11 is an example of the low rolling reduction in cold rolling before final annealing. In this example, since the area ratio ("assembly structure (%)") of the crystal grain whose Schmidt factor has a value of 0.45 or more was less than 43%, press formability was bad.

No. 7 is an example in which the amount of O contained in a pure titanium plate is small, the value of Formula (1) is less than the prescription | regulation of this invention, and tensile strength was less than 343 Mpa.

No. 8 is an example (the value of "H" is negative in a table | surface) whose value of Formula (2) is less than the prescription | regulation of this invention. In this example, since the area ratio ("assembly structure (%)") of the crystal grain whose Schmitt factor has a value of 0.45 or more was less than 43%, the volume ratio of the β-phase exceeded the specification, The gap corrosion was bad.

Although the present invention has been described in detail with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

This application is based on the Japanese patent application (Japanese Patent Application No. 2011-120766) which applied on May 30, 2011, and the Japanese patent application (Japanese Patent Application No. 2012-074836) applied on March 28, 2012. The contents of which are incorporated herein by reference.

The pure titanium plate of the present invention is suitable for aircraft parts, chemical plant members, structural materials in coastal areas (particularly all-man structural materials in which corrosion is promoted by seawater contact), automobiles, building materials, mobile phones, mobile personal computers, cameras, and other bodies. It is useful for a frame, a plate heat exchanger, a fuel cell separator, a home appliance, an object for transportation equipment, and the like.

Claims (6)

Fe: 0.02 to 0.10% (the meaning of "mass%", the same as for the chemical component below),
O: contains 0.04 to 0.20%,
The balance is made up of titanium and inevitable impurities,
The content of Fe and O meets the following formula (1),
The area ratio of the area | region where the Schmidt factor of the {11-22} <11-23> twin system based on the rolling direction of the sheet thickness quarter position is 0.45 or more is 43% or more,
Furthermore, the volume ratio of (beta) phase is 0.3% or less, The pure titanium plate excellent in the balance of press formability and strength, and corrosion resistance.
[Equation (1)]
[O content (mass%)] + 0.12 x [Fe content (mass%)] ≥0.050 As a manufacturing method of the pure titanium plate excellent in the balance of press formability and strength of Claim 1, and corrosion resistance,
Through the process of hot rolling, intermediate annealing, cold rolling, final annealing,
After the said intermediate annealing, after performing the descaling process of the surface of a pure titanium plate, cold rolling whose rolling reduction is 70% or more is performed, and final annealing is performed on condition that H defined by following formula (2) becomes a positive value after that. The manufacturing method characterized by the above-mentioned.
[Equation (2)]

[only,
T: heating temperature at final annealing (° C), t: annealing time (seconds)
X ₀ : Fe concentration (mass%) in a pure titanium plate
A = 891, B = 0.428, n = 0.135] As a manufacturing method of the pure titanium plate excellent in the balance of press formability and strength of Claim 1, and corrosion resistance,
Through the process of hot rolling, cold rolling, final annealing,
After the hot rolling, after descaling the pure titanium plate surface without performing intermediate annealing, cold rolling with a reduction ratio of 20% or more is performed, and then the condition H defined by the following formula (2) becomes a positive value The final annealing is carried out by the method of manufacturing.
[Equation (2)]

[only,
T: heating temperature at final annealing (° C), t: annealing time (seconds)
X ₀ : Fe concentration (mass%) in a pure titanium plate
A = 891, B = 0.428, n = 0.135] A method for producing a heat exchange member of a plate heat exchanger, comprising the step of press molding the pure titanium plate according to claim 1. The process of manufacturing a pure titanium plate by the manufacturing method of the pure titanium plate of Claim 2,
And a press step of press-molding the manufactured pure titanium plate. The process of manufacturing a pure titanium plate by the manufacturing method of the pure titanium plate of Claim 3,
And a press step of press-molding the manufactured pure titanium plate.

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