JP2013095964A - Titanium plate, method for producing titanium plate and method for manufacturing heat-exchanging plate for plate-type heat-exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium plate which displays excellent formability without lowering the strength, a method for producing the titanium plate, and a method for manufacturing a heat-exchanging plate for plate-type heat-exchanger.SOLUTION: In the titanium plate composed of the pure-titanium for industry, containing crystal grain structure of α-phase (HCP-structure), the titanium plate is characterized in that coarse crystal grains having 4 times or more of the average grain diameter of the crystal grain, are contained in the proportion of ≥0.5 pieces to the 100 pieces of the crystal grains.

Description

  The present invention relates to a titanium plate applied to a heat exchange plate of a plate heat exchanger, a method of manufacturing the titanium plate, and a method of manufacturing a heat exchange plate of the plate heat exchanger.

Titanium plates have excellent corrosion resistance, so they are used for heat exchangers such as chemical, electric power, and food manufacturing plants, consumer products such as camera bodies and kitchen equipment, transportation equipment for motorcycles and automobiles, and home appliances. It is widely used even for things such as exterior materials.
Among them, in order to increase the heat exchange efficiency, the plate type heat exchanger needs to be processed into a wave pattern by press forming a titanium plate to increase the surface area. Therefore, when a titanium plate is applied to a plate heat exchanger, excellent formability is required for the titanium plate.

  In addition, when applying a titanium plate to a plate heat exchanger, in addition to the above-described formability, in order to realize the durability improvement and weight reduction required as a plate heat exchanger, A certain level of strength is also required.

Here, the titanium plate (industrial pure titanium) is stipulated in the standard of JIS H4600, and is classified into JIS class 1, class 2, class 3, etc. according to the content, strength, etc. of Fe, O, etc. .
As this grade increases, the content of Fe, O, etc. increases, and the strength increases. Therefore, when a titanium plate is used for an application that requires high strength, those of a large grade are used.
On the other hand, titanium plates with low grades, such as JIS Class 1 titanium plates, have a low content of Fe, O, etc. and have high ductility (improving formability), so titanium is used for applications that require excellent formability. When using a board, the thing of JIS1 type is used.

  However, when the content of Fe, O, etc. was increased and the strength of the titanium plate was improved, the moldability decreased, the content of Fe, O, etc. was decreased, and the formability of the titanium plate was improved. In such a case, the strength decreases.

  Moreover, as a method for improving the strength of the titanium plate, there is a method of refining the crystal grain of the titanium plate, but the formability of the titanium plate is lowered with the refinement of the crystal grain.

  As described above, when a titanium plate is applied to a plate heat exchanger, the titanium plate is required to have a certain level of strength (JIS 2 or 3 types of strength) and excellent formability. Nevertheless, it has been very difficult to improve moldability while avoiding strength reduction.

In addition, regarding the titanium plate, the following various technologies that focus on improving the strength and formability are disclosed.
For example, Patent Document 1 discloses a titanium plate manufacturing method that specifies the content of Fe, Ni, and Cr, regulates the average crystal grain size to 20 to 80 μm, and specifies the conditions for pickling treatment. Yes.
Patent Document 2 discloses a titanium plate that specifies that Fe contains more than O and that has an average crystal grain size of 10 μm or less.

Patent Document 3 discloses a titanium plate in which the chemical composition is specified and the average crystal grain size of the β phase is specified to be 3 μm or less.
Patent Document 4 discloses a titanium plate that regulates the content of Fe and O and specifies the deviation angle of crystal grains.

Japanese Patent Laid-Open No. 10-30160 JP 2009-228092 A JP 2010-209462 A JP 2011-26649 A

However, since the techniques according to Patent Documents 1 to 3 are almost the same as the conventional manufacturing process, the obtained titanium plate is composed of a crystal grain structure having a normal uniform particle size distribution. I can judge. As a result, with the techniques according to Patent Documents 1 to 3, sufficient moldability cannot be obtained.
In the technique according to Patent Document 4, the upper limit values of the Fe and O contents are regulated low, and sufficient strength cannot be obtained. Further, if Fe and O are contained in excess of the regulated upper limit value, ear cracks occur during cold rolling, and the yield decreases, which is not preferable in terms of productivity.

  The present invention has been made in view of the above problems, and the problem is that a titanium plate, a titanium plate manufacturing method, and a plate-type heat exchanger exhibit excellent formability without lowering strength. It is in providing the manufacturing method of a heat exchange plate.

In order to solve the above-mentioned problems, the inventors of the present invention have made the following studies on the relationship between the crystal grain structure and formability of a titanium plate.
The industrial pure titanium that constitutes the titanium plate of the present invention is, for example, titanium specified in the standard of JIS H4600, and is mainly composed of an α phase crystal grain structure composed of a hexagonal crystal structure (HCP structure). Metal material.
Here, in order to form the metal material appropriately, it is necessary to plastically deform, and for that purpose, it is necessary to cause slip deformation due to dislocation or twin deformation. As a slip system that operates in the α phase grain structure, {0001} <11-20> bottom surface slide, conical surface slip, in addition to {10-10} <11-20> column surface slip, which is most likely to be active. There exists {11-22} <11-23> twins as twin deformation.

However, compared with steel materials with BCC structure and aluminum with FCC structure, industrial pure titanium is said to have fewer sliding systems and multiple sliding systems are difficult to operate. It is considered difficult to improve the formability of a titanium plate made of industrial pure titanium.
Therefore, the inventors of the present invention considered that it is important to eliminate the incentive, that is, to activate a plurality of slip systems and twin systems in order to improve the formability of the titanium plate. Then, the present inventors have found that a plurality of slip systems and twin systems can be activated by setting the α phase crystal grain structure of the titanium plate to a mixed structure of fine crystal grains and coarse crystal grains, thereby completing the present invention. It came to.

  That is, the titanium plate according to the present invention is a titanium plate made of industrial pure titanium containing an α phase (HCP structure) crystal grain structure, and has a grain size that is at least four times the average grain size of the crystal grains. The crystal grains are included in a ratio of 0.5 or more out of 100 crystal grains.

As described above, the titanium plate according to the present invention includes coarse crystal grains at a predetermined ratio, and therefore, when forming, the fine crystal grains (other than the coarse crystal grains) existing around the coarse crystal grains are formed. Stress is applied in various directions. As a result, not only the primary slip system but also multiple slip systems and twin crystal systems (hereinafter referred to as secondary slip systems as appropriate) are likely to be active in the coarse crystal grains, resulting in uniform plastic deformation as a whole. Become. Therefore, the titanium plate according to the present invention can exhibit excellent formability.
Further, in the conventional technique such as Patent Document 4 described above, a method of reducing the content of impurity elements (particularly oxygen) is used in order to improve the formability of the titanium plate. While the moldability of is improved, the strength is reduced. On the other hand, according to the present invention, since it is not necessary to reduce the content of the impurity element, the formability can be improved without causing a decrease in the strength of the titanium plate.

In the titanium plate according to the present invention, the area ratio of the coarse crystal grains is preferably 90% or less.
As described above, the titanium plate according to the present invention has an area ratio of coarse crystal grains of a predetermined value or less, so that the secondary slip system in the coarse crystal grains can be more appropriately activated to ensure the effect of improving the formability. Can be.

Moreover, it is preferable that the titanium plate which concerns on this invention contains Fe: 0.040-0.300 mass%, O: 0.05-0.25 mass%, and remainder consists of titanium and an unavoidable impurity.
In the titanium plate according to the present invention, the ratio of the Fe content to the O content (Fe content / O content) is preferably 1.1 or less.
As described above, the content of Fe and O in the titanium plate according to the present invention is a predetermined amount, so that the effect of improving the formability can be further ensured while avoiding the decrease in strength. .

In addition, the titanium plate according to the present invention is preferably used as a heat exchange plate of a plate heat exchanger by forming the titanium plate.
Thus, since the titanium plate according to the present invention exhibits excellent formability without lowering the strength, it can be appropriately used as a heat exchange plate of a plate heat exchanger.

  Moreover, the manufacturing method of the titanium plate which concerns on this invention is a titanium plate which manufactures a titanium plate by giving at least cold rolling and annealing about the industrial pure titanium containing the crystal grain structure of alpha phase (HCP structure). A light rolling process in which after the annealing, the titanium plate is subjected to a light rolling at a rolling reduction of 0.5 to 7.0%, and after the light rolling process, the titanium plate And an annealing step in which annealing is performed at a holding temperature of 600 to 880 ° C.

  Thus, the titanium plate manufacturing method according to the present invention removes pinning (suppression of crystal grain growth) due to the β phase existing in the crystal grain boundary of the α phase by performing light rolling on the titanium plate. be able to. And the crystal grain of the alpha phase from which pinning was removed can be made into a coarse crystal grain by annealing after light rolling. As a result, the titanium plate produced by the method for producing a titanium plate according to the present invention can exhibit excellent formability without a decrease in strength.

Moreover, the manufacturing method of the heat exchange plate of the plate type heat exchanger which concerns on this invention is characterized by performing a shaping | molding process to the said titanium plate.
As described above, the method for producing a heat exchange plate of a plate heat exchanger according to the present invention is produced by subjecting a predetermined titanium plate to a molding process, and therefore exhibits excellent formability without a decrease in strength. The heat exchange plate can be manufactured.

Since the titanium plate according to the present invention contains coarse crystal grains at a predetermined ratio, it can exhibit excellent formability without a decrease in strength.
Moreover, since the manufacturing method of the titanium plate which concerns on this invention performs light rolling and annealing to a titanium plate, the titanium plate which exhibits the outstanding moldability can be manufactured, without intensity | strength falling.
In addition, the method for producing a heat exchange plate of a plate heat exchanger according to the present invention is produced by subjecting a predetermined titanium plate to a molding process. Therefore, heat that exhibits excellent formability without lowering the strength. An exchange plate can be manufactured.

It is the result of having observed about the titanium plate which concerns on embodiment of this invention by a back-scattered electron diffraction image (EBSP) using the field emission scanning microscope (FESEM). The molding die used in order to evaluate moldability in the Example of this invention is shown, (a) is a top view, (b) is sectional drawing of the dashed-dotted line of (a). It is a flowchart which shows the manufacturing process of the heat exchanger plate of the titanium plate which concerns on embodiment of this invention, and a plate type heat exchanger.

  Hereinafter, the form for implementing the titanium plate which concerns on this invention, the manufacturing method of a titanium plate, and the manufacturing method of the heat exchange plate of a plate-type heat exchanger is demonstrated in detail.

[Titanium plate]
The titanium plate according to the present invention is a titanium plate made of industrial pure titanium containing an α-phase (HCP structure) crystal grain structure, and coarse crystal grains having a grain size of 4 times or more of the average grain size of the crystal grains. , And contained at a ratio of 0.5 or more in 100 crystal grains.
Moreover, the titanium plate according to the present invention has preferable conditions regarding the area ratio of coarse crystal grains, the content of Fe and O, the ratio of the content of Fe to the content of O, and the application.

First, after explaining the relationship between the α phase crystal grain structure and formability of the titanium plate according to the present invention, each specific matter will be explained.
(Relation between α phase crystal grain structure and formability)
The α phase crystal grain structure of the titanium plate according to the present invention is a mixed structure of coarse crystal grains and fine crystal grains (crystal grains other than coarse crystal grains) as shown in FIG.
First, the initial stage of forming the titanium plate will be described. Plastic deformation starts from a coarse crystal grain region having a large crystal grain size and a low strength (YS). Here, in coarse crystal grains, it is assumed that the column face slip acts as a primary slip system (main slip system), but each fine crystal grain around the coarse crystal grains has a different crystal orientation from the coarse crystal grains. Considering the sample coordinate system, the slip system acts in a direction different from the primary slip system in the fine crystal grains. Accordingly, a plurality of directions of stress are applied to coarse crystal grains from a plurality of adjacent fine crystal grains to each micro region along the grain boundary. As a result, in coarse crystal grains, multiple slip systems and twin systems (secondary slip systems) are likely to be active, and uniform plastic deformation occurs throughout the titanium plate, which improves the formability of the titanium plate. It is done.

  Even after the formation of the titanium plate and the fine crystal grain region starts to deform, fine crystal grains with different crystal orientations exist around the coarse crystal grain region. On the other hand, it is considered that stress in a plurality of directions is applied to each micro region along the grain boundary from a plurality of adjacent fine crystal grains to induce the activity of the secondary slip system.

  Regardless of the initial and late stages of forming the titanium plate, the stress level borne by the fine crystal grain region is higher than that of the coarse crystal grain region, and compared with a titanium plate composed of coarse crystal grains of uniform size. Thus, the titanium plate according to the present invention is considered to have a high effect of inducing a secondary slip system.

  In addition, when the α phase crystal grain structure of the titanium plate is composed only of coarse crystal grains without containing fine crystal grains, the crystal orientations of adjacent coarse crystal grains must be the same (highly oriented). Therefore, a slip system in almost one direction will be active. Therefore, with respect to the coarse crystal grains, stress in only a specific direction is applied to each micro region along the grain boundary from adjacent coarse crystal grains. As a result, it is considered that the secondary sliding system is hardly activated and the moldability is not improved.

(Coarse crystal grains)
Coarse crystal grains are crystal grains having a grain size that is at least four times the average grain size of the crystal grains present in the titanium plate. The reason specified in this way is that the surface area of a crystal grain having a particle size of less than 4 times is not sufficiently large, and the number of crystal grains adjacent to the crystal grain is reduced, so that the effect of activating the secondary slip system is effective. It is because it is not obtained so much.
The particle size is a circle equivalent diameter.

(Ratio of coarse crystal grains)
When the coarse crystal grain of the titanium plate is less than 0.5 out of 100 crystal grains, even if the secondary slip system in the coarse crystal grain is activated, there are few coarse crystal grains. The effect of improving the property cannot be sufficiently obtained.
Therefore, the coarse crystal grain of the titanium plate is 0.5 or more out of 100 crystal grains.

The upper limit of the proportion of coarse crystal grains in the titanium plate can be defined by the area ratio described later. However, it is difficult to activate the secondary slip system by reducing the proportion of fine grains. In order to prevent this, the proportion of coarse crystal grains is preferably 15 or less per 100 crystal grains.
In addition, what is necessary is just to perform by the method described in an Example about the calculation method of the abundance ratio of the coarse crystal grain of a titanium plate, for example.

(Area ratio of coarse crystal grains)
If the area ratio of the coarse crystal grains exceeds 90%, the number of fine crystal grains present around the coarse crystal grains decreases, and the secondary slip system in the coarse crystal grains is difficult to activate.
Therefore, the area ratio of coarse crystal grains is 90% or less.
And in order to ensure the activation of the secondary slip system in the coarse crystal grains, the area ratio of the coarse crystal grains is preferably 80% or less, and more preferably 70% or less.

The lower limit of the area ratio of the coarse crystal grains of the titanium plate can be defined by the abundance ratio of the coarse crystal grains described above, but the effect of improving the formability of the titanium plate is small due to the small number of coarse crystal grains. In order to prevent this, the area ratio is preferably 20% or more.
In addition, what is necessary is just to perform by the method described in an Example about the calculation method of the area ratio of the coarse crystal grain of a titanium plate, for example.

(Component composition)
The titanium plate contains a small amount of C, H, O, N, Fe, Si, Cr, Ni, etc. as unavoidable impurities, but in the present invention, the content is relatively large, and the effect of the invention is affected. The preferable range of the Fe and O contents that affect the above is defined.

(Component composition Fe: 0.040-0.300 mass%)
When the Fe content is less than 0.040% by mass, a desired mixed grain structure (mixed structure of fine crystal grains and coarse crystal grains) cannot be obtained. On the other hand, if the Fe content exceeds 0.300% by mass, the segregation of the ingot increases and the productivity deteriorates. In addition, the effect of suppressing the growth of crystal grains by the β phase becomes too strong, and even when light rolling and annealing described later are performed, coarse crystal grains are hardly generated.
Therefore, the content of Fe is preferably 0.040 to 0.300 mass%.

(Component composition O: 0.05-0.25 mass%)
If the O content is less than 0.05% by mass, the strength is lowered. On the other hand, if the content of O exceeds 0.25% by mass, the titanium plate becomes too brittle, and cracks during cold rolling tend to occur, resulting in a decrease in productivity.
Therefore, the content of O is preferably 0.05 to 0.25% by mass.

(Ratio of Fe content to O content)
When the ratio of the Fe content to the O content (Fe content / O content) exceeds 1.1, the Fe content is too high and the desired mixed grain structure (fine crystal grains and coarse grains) A mixed structure with crystal grains) cannot be obtained.
Therefore, the ratio of the Fe content to the O content is preferably 1.1 or less. More preferably, it is 1.0 or less.

[Heat exchange plate of plate heat exchanger]
A plate-type heat exchanger is a method of laminating plates made of metal plates with unevenness, forming a plate-like pipe line with a sealing gasket between each plate, and then adding fluid to the laminated plate-like line. This is a heat exchanger that allows heat to flow between them.
And the heat exchange plate of the plate type heat exchanger which concerns on this invention is a heat exchange plate which shape | molded the titanium plate so that it could apply to an above described plate type heat exchanger.

Next, the manufacturing method of the heat exchanger plate of the titanium plate and plate type heat exchanger which concerns on this invention is demonstrated.
[Production method of titanium plate]
First, as in the case of manufacturing a conventional titanium plate, as shown in FIG. 3, an ingot (industrial pure titanium) is subjected to ingot rolling S1, and then hot rolling S2, intermediate rolling S3, cold rolling S4, Annealing S5 is performed.
Here, the detailed conditions of the partial rolling S1 to the annealing S5 are not particularly limited, and may be performed by a conventional method.

For example, for cold rolling S4, an appropriate reduction ratio and annealing conditions are selected according to the cold rolling properties of the material (ease of occurrence of ear cracks, deformation load, etc.), and cold rolling and annealing are performed. You can do it repeatedly. Moreover, the rolling reduction of the cold rolling performed just before annealing S5 should just secure the processing amount sufficient for a raw material to recrystallize by annealing S5, for example, the rolling reduction of 50% or more. And among annealing S5, about finish annealing, what is necessary is just to carry out in the two-phase area | region of (alpha) phase and (beta) phase.
In addition, when the scale has adhered to the titanium plate surface after annealing S5, the process of removing a scale, for example, a salt heat treatment process, a pickling process process, etc. may be performed.

Next, the state of the crystal grain structure of the titanium plate when the cold rolling S4 and the annealing S5 are performed will be described.
For example, when cold rolling S4 with a reduction rate of about 50% is applied to a titanium plate, and then annealing S5 is performed at a recrystallization temperature or higher, a recrystallized structure is formed in the titanium plate (nucleation / growth type recrystallization). Crystal structure).
Here, it is known that the more Fe (β-stabilizing element in a broad sense) contained in the titanium plate, the smaller the grain size of the crystal grains after annealing S5. This is presumably because Fe forms a β phase (BCC structure) and suppresses (pins) growth of α phase crystal grains during annealing S5. Specifically, in the case of annealing at 850 ° C. for several minutes, when the titanium plate contains 0.04% by mass of Fe, the grain size of the crystal grains is about 50 μm and contains 0.06% by mass of Fe. For those, the grain size of the crystal grains is about 15 μm.
In addition, the grain size of the obtained crystal grain depends on the annealing S5 condition and the like, and the longer the annealing S5 time, the larger the grain size of the crystal grain.
In addition, at the time of completion | finish of annealing S5, adjusting the conditions of partial rolling S1-annealing S5 (especially cold rolling S4 and annealing S5) so that the average particle diameter of a crystal grain may be several to several dozen micrometer. Is preferred.

(Light rolling and annealing)
The titanium plate manufacturing method according to the present invention is characterized in that after the annealing S5, the light reduction rolling S6 and the annealing S7 are performed.
First, the mechanism by which a mixed grain structure (mixed structure of fine crystal grains and coarse crystal grains) is formed by light rolling under S6 and annealing S7 will be described.
As described above, in the titanium plate at the end of the annealing S5, the β phase is precipitated at the α phase grain boundaries, and the growth of crystal grains is suppressed by the β phase. Thereafter, when the light reduction rolling S6 is performed on the titanium plate at a sufficiently small reduction rate so that recrystallization does not occur, strain is applied to a plurality of regions that are easily deformed in the titanium plate. Specifically, the strain is applied mainly to a plurality of regions in the vicinity of the grain boundary of the α phase and the vicinity of the precipitate of the β phase, which are places where non-uniform deformation is likely to occur. As a result, a part of pinning by the β phase existing at the crystal grain boundary of the α phase is released.
Thereafter, annealing S7 is applied to the titanium plate, so that some α-phase crystal grains that are not pinned grow greatly. Further, (or) strain energy is accumulated around the precipitate of the β phase, and a part of the β phase is re-dissolved by annealing S7, so that the α-phase crystal grains adjacent to the re-dissolved β phase are formed. Grows greatly.
It is considered that a mixed grain structure (mixed structure of fine crystal grains and coarse crystal grains) is formed on the titanium plate by performing the light reduction rolling S6 and the annealing S7 by the mechanism as described above.

(Conditions for light rolling)
As for the light reduction rolling S6, if the reduction ratio is less than 0.5%, sufficient strain cannot be applied to the titanium plate, so that the existence ratio of coarse crystal grains does not exceed a certain level. On the other hand, when the rolling reduction exceeds 7.0%, most of the pinning due to the β phase is released, so that most crystal grains grow greatly in the subsequent annealing S7, and the grain size distribution becomes uniform. End up. As a result, the effect of improving moldability cannot be obtained much.
Therefore, the rolling reduction of the light rolling S6 is preferably 0.5 to 7.0%.

(Annealing conditions)
Regarding the annealing S7, if the holding temperature is less than 600 ° C., the α-phase crystal grains are not sufficiently coarsened, and the existence ratio of the coarse crystal grains does not exceed a certain level. In addition, coarse crystal grains do not grow to a predetermined size or more. On the other hand, when the holding temperature exceeds 880 ° C., the existence ratio of the coarse crystal grains is increased too much, and as a result, the existence ratio of the fine crystal grains is reduced, so that the secondary slip system in the coarse crystal grains is hardly activated.
Therefore, it is preferable that the holding temperature of annealing S7 is 600-880 degreeC.
In addition, about the time of annealing S7, although the suitable range changes with light reduction ratios, for example, when performing light reduction of 2% reduction ratio and annealing at 600 degreeC, it may be about 2 hours at 800 degreeC, and it may be about 4 minutes. preferable. Further, the method of annealing S7 is not particularly limited, and the atmosphere may be any of air, vacuum, and reducing gas atmosphere, and the method may be either a batch furnace or a continuous furnace.

[Method for producing heat exchange plate of plate heat exchanger]
In addition, the heat exchange plate of a plate-type heat exchanger can be manufactured by performing shaping | molding process S8 to a titanium plate using a well-known method, for example, a shaping die, after annealing S7.

  Next, the titanium plate will be specifically described by comparing an example satisfying the requirements of the present invention with a comparative example not satisfying the requirements of the present invention.

[Production of test materials]
For a pure titanium hot-rolled sheet (thickness 3.5 mm) having the composition shown in Table 1 (JIS H4600), a normal a. Cold rolling, b. Intermediate annealing, c. Cold rolling, d. Finish annealing, e. By performing the pickling process, a cold-rolled material as a test material was obtained.
In addition, d. So that the α phase recrystallizes and the β phase precipitates on the cold-rolled material to be tested. Finish annealing was performed in the two-phase region of the α phase and the β phase, and in an air atmosphere. In addition, c. So that the plate thickness becomes 0.5 mm after light rolling under rolling, annealing and pickling treatment described later. The rolling reduction of cold rolling was adjusted.

[Production of test materials]
The test material was subjected to light rolling at the rolling reduction shown in Table 1, annealed at the holding temperature and holding time shown in Table 1, and then pickled to give a test material having a thickness of 0.5 mm. Got.
The annealing atmosphere was performed in air or vacuum. Annealing in a vacuum atmosphere was performed under conditions of a temperature rising time of 36 h and a degree of vacuum of 4 × 10 ⁻⁵ torr.

[Measurement of α phase crystal grains]
Regarding the longitudinal section of the test material, a region of 1 mm in the rolling direction and 0.45 mm in the thickness direction is subjected to structure observation by a back-scattered electron diffraction image (EBSP) using a field emission scanning microscope (FESEM), and α phase The crystal grain size, the presence ratio of coarse crystal grains in 100 crystal grains, and the area ratio of coarse crystal grains were measured. Note that when the number of crystal grains included in the region was less than 200, measurement was performed by increasing the measurement region until the number of crystal grains reached 200 or more.
Specifically, a boundary having an orientation difference of 15 ° or more was recognized as a crystal grain boundary, and the equivalent circle diameter and average equivalent circle diameter of each crystal grain were calculated. Thereafter, the presence ratio of coarse crystal grains in 100 crystal grains (= number of coarse crystal grains present in measurement region / number of all crystal grains present in measurement region × 100), and area ratio of coarse crystal grains ( = Area of coarse crystal grains present in measurement region / area of measurement region × 100). At that time, since a crystal grain having an equivalent circle diameter of less than 4 μm may cause noise, the calculation was performed on a crystal grain of 4 μm or more.

[Evaluation of strength]
A No. 13 test piece defined in JISZ2201 was taken from the test material in a direction in which the rolling direction of the test material coincides with the load axis, and a tensile test was performed at room temperature based on JIS 4600. 0.2% proof stress (YS) Was measured.
In addition, the case where 0.2% yield strength (YS) was 250 Mpa or more was judged to be a pass.

[Evaluation of formability]
The moldability was evaluated by performing press molding using a molding die simulating the heat exchange part (plate) of the plate heat exchanger for each test material, and the moldability was evaluated.
As shown in FIG. 2 (a), the shape of the molding die is such that the molding part is 100 mm × 100 mm, the pitch is 10 mm, the maximum height is 4 mm, and there are six twill lines, each twill line being at the apex, It has six types of R shapes of R = 0.8, 1.6, 1.2, 1.0, 2.0, and 0.6 in order from the top to the bottom of FIG.
Using this molding die, press molding was performed by an 80-ton press. In press molding, both surfaces of each test material are sandwiched between polyethylene sheets having a thickness of 0.03 mm for lubrication, and then the lower gold is so aligned that the rolling direction of each test material coincides with the vertical direction in FIG. After placing on the mold and restraining the flange portion with a plate press, the mold was pushed in under the condition of a press speed of 1 mm / sec. The maximum indentation depth (Y: unit mm) at which the indentation and cracking did not occur at intervals of 0.1 mm were obtained by experiments.
In addition, it was set as the pass when YS (unit is MPa) in the L direction (rolling direction) and the formability index (F) defined by the following formula (1) is a positive value.
F = Y− (A−B × X) (1)
A = 4.5, B = 0.006, X = Numerical value obtained by making YS in the L direction dimensionless Y = Numerical value obtained by making the maximum indentation depth dimensionless

[Examination of results]
Test materials 2 to 6, 8, and 11 are titanium plates that satisfy the requirements defined in the present invention, and it can be determined that both strength and formability are acceptable, and the balance between strength and formability is excellent.

On the other hand, since the test materials 1, 7, 9, and 10 do not satisfy the requirements defined in the present invention, at least one of strength and formability does not satisfy the acceptance standard, and the balance between strength and press formability is poor. I understand that.
Since the test materials 1 and 10 were subjected to final annealing without being subjected to light rolling, the crystal grains showed a uniform grain size distribution, and there were no coarse crystal grains. As a result, although it had excellent strength, the moldability was not excellent.
Test material 7 is an example in which the rolling reduction in light rolling is too high. Although relatively large crystal grains were formed, the grain size distribution of the crystal grains became uniform and there were no coarse crystal grains, so the moldability was not excellent.
Since the test material 9 had a low Fe content and the β phase was not sufficiently precipitated, normal grain growth occurred after the light rolling and annealing process. As a result, the crystal grains showed a uniform particle size distribution, and neither strength nor moldability was excellent.

Claims (7)

It is a titanium plate made of industrial pure titanium containing an α phase (HCP structure) crystal grain structure,
A titanium plate, wherein coarse crystal grains having a grain size of 4 times or more of an average grain size of the crystal grains are contained in a ratio of 0.5 or more out of 100 crystal grains.   The titanium plate according to claim 1, wherein the area ratio of the coarse crystal grains is 90% or less.   3. Fe: 0.040-0.300 mass%, O: 0.05-0.25 mass%, The remainder consists of titanium and inevitable impurities, The claim 1 or 2 characterized by the above-mentioned. Titanium plate.   The titanium plate according to claim 3, wherein a ratio of the Fe content to the O content (Fe content / O content) is 1.1 or less.   The titanium plate according to any one of claims 1 to 4, wherein the titanium plate is molded and used as a heat exchange plate of a plate heat exchanger. For industrial pure titanium containing a crystal grain structure of α phase (HCP structure), at least cold rolling, and a titanium plate manufacturing method for manufacturing a titanium plate by annealing,
After the annealing, a light reduction rolling step of performing light reduction rolling on the titanium plate at a reduction rate of 0.5 to 7.0%,
After the light rolling process, an annealing process for annealing the titanium plate at a holding temperature of 600 to 880 ° C .;
The manufacturing method of the titanium plate characterized by the above-mentioned.   The manufacturing method of the heat exchange plate of the plate type heat exchanger characterized by performing a shaping | molding process to the titanium plate as described in any one of Claims 1 thru | or 4.

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