KR20150119301A - Titanium sheet - Google Patents

Abstract

A titanium plate having strength and moldability and a plate-type heat exchanger plate using the same are provided. and the balance of titanium and inevitable impurities, wherein the balance of Fe and Fe is 0.020 to 0.150 mass%, O is 0.020 to 0.150 mass%, and C is 0.002 to 0.100 mass% Wherein the sum of the content of C (mass%) is 0.80 times or more of the content of O (mass%) and the concentration of C in the crystal grain boundaries is 1.0 mass% or more.

Description

Titanium plate {TITANIUM SHEET}

The present invention relates to a titanium plate having both high strength and high strength.

Generally, titanium materials are excellent in non-strength and corrosion resistance. Taking advantage of these characteristics, titanium materials are widely used in various fields such as exterior materials for optical devices such as camera bodies, exterior materials such as home appliances, materials for jewelry such as glasses and watches, members of public goods such as kitchen appliances, , Electric power, food manufacturing, and so on.

In recent years, a plate of a heat exchanger, particularly a plate heat exchanger, has been required to increase the surface area by processing into a ripple shape by press molding in order to increase the heat exchange efficiency required as a required property. Therefore, the titanium plate used for the plate of the heat exchanger, especially plate type heat exchanger, is required to have excellent moldability in order to form a deeper ripple shape.

Titanium plates commonly used for these materials are specified in JIS H4600 (issued on July 1, 1964) of the JIS standard. The titanium plate specified here is classified again into one, two, or three kinds of grades depending on the amount of impurities such as Fe and O, strength, etc., and as the grade increases, the lowest strength of the titanium plate becomes high . Also, the titanium plate is classified according to the grade of JIS standard, and is used according to the use.

Titanium plates with low concentrations of Fe and O, such as JIS 1, have low ductility but high ductility. For this reason, a pure titanium plate of JIS 1 type has been used for a member which requires high formability in the past.

In recent fields of heat exchangers, there is an increasing demand for higher strength and lighter weight in addition to improvement in heat exchange efficiency. In order to comply with these demands, it is necessary to apply a titanium plate of JIS Class 2, Class 3 or the like having a higher strength to a heat exchanger. However, titanium plates having these strengths are poor in moldability. As a result, these high-strength titanium plates are required to have improved formability in a further layer.

However, the pure titanium industrial grade specified by the JIS standard is a metal material composed mainly of an? -Phase crystal structure composed of a hexagonal crystal (HCP) structure.

In general, in order to form a metal material such as titanium, it is known that plastic deformation by slip deformation and twin deformation due to dislocation movement is required.

The slip system that is readily active on the α-phase of titanium has a pole face slip {10-10} <11-20>, besides, a bottom slip {0001} <11-20> and a pyramid slip. Further, in the deformation during press forming, twinning of {11-22} <11-23> may be active. However, in comparison with aluminum having a BCC structure or aluminum having an FCC structure, titanium has a small number of active slip systems, and a plurality of slip systems are hard to act easily. As a result, it is known that plastic deformation of titanium is difficult.

On the other hand, as means for improving the strength of the titanium material, two means for improving the strength by increasing the concentration of the impurity element such as O and Fe of the titanium material or improving the strength by refining the crystal grain of the titanium material are known.

However, there has been a problem that the moldability of the titanium material is largely lowered by increasing the strength of the titanium material by these conventional methods.

On the basis of the characteristics of titanium, a technique for improving the moldability of a titanium material as described below is disclosed.

Patent Document 1 discloses a pure titanium material having a Fe content, a Ni content and a Cr content satisfying a predetermined relationship, a content of O (oxygen) of 900 ppm or less, and a balance of Ti and inevitable impurities, Rolled and then subjected to an annealing treatment at a temperature of 600 to 850 占 폚 to obtain an average grain size of the pure titanium plate of 20 to 80 占 퐉 and thereafter subjected to pickling treatment in a dilute hydrofluoric acid aqueous solution satisfying a predetermined relational expression And the like. The present invention also provides a method for producing a pure titanium plate.

In Patent Document 2, it is characterized in that the amount of H, O, N and Fe is specified in one or two kinds of JIS H 4600, C contains 50 to 800 ppm, and the balance is composed of titanium and inevitable impurities A titanium plate excellent in ductility has been proposed.

Japanese Patent No. 3228134 Japanese Patent Application Laid-Open No. 2002-317234

However, in the titanium plates proposed in Patent Documents 1 and 2, if the concentration of the impurity element such as O and Fe is made high, or if the strength is made higher by making the crystal grains finer, the ductility of the titanium plate becomes lower and the formability of the titanium plate becomes lower There is a problem that it is greatly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a titanium plate having strength and moldability.

That is, it has been found that the ductility of the titanium plate is further improved by precisely and finely controlling the amounts of addition of Fe, O, and C with respect to the improvement in ductility of the titanium plate, which has been limited by the conventional combination of C and Al. It has also been found that the distribution of C to the crystal grain boundaries affects the ductility improving effect. Further, it has been found that the ductility of the titanium plate is further improved by precisely and finely controlling the degree of C concentration in the crystal grain boundaries.

The greater the C content of the titanium plate, the greater the strength of the titanium plate. However, the ductility of the titanium plate can obtain the effect of the C content in the optimum range with the C content of the titanium plate. Further, as a result of precise and fine examination, it was found that the optimum range depends on the amount of Fe and O added. In particular, O has a great effect of increasing the strength of the titanium plate, but also deteriorates the ductility of the titanium plate. Therefore, in order to more effectively express the effect of the C content, it is preferable that the amount of O added is small. On the other hand, with regard to Fe, it has been found that the addition of a large amount is effective in improving the balance between the strength and the moldability of the titanium plate when containing C.

Further, it has been found that the balance of strength and ductility is increased in the presence of C in the crystal grain structure of the titanium plate as the degree of thickening to the grain boundaries is increased and the same amount is added.

Based on the above finding, the inventors of the present invention have made intensive studies, and as a result, have found that the balance between strength and moldability of the titanium plate is improved by controlling the contents of Fe, O, and C and the ratio between them, , The moldability of the titanium plate is further improved, and the present invention has been accomplished.

The titanium plate according to the present invention is a titanium plate having a crystal grain structure of an alpha phase and contains 0.020 to 0.150 mass% of Fe, 0.020 to 0.150 mass% of O, 0.002 to 0.100 mass% of C, (% By mass) of the content of O (mass%), and the concentration of C in the crystal grain boundaries is 1.0% by mass or more .

According to such a configuration, the balance between the strength and the formability of the titanium plate is improved by controlling the content of Fe, O, and C and the ratio of each other to activate a plurality of slip systems / twin systems. Further, when the concentration of C in the crystal grain boundaries is set to 1.0% by mass or more, the formability of the titanium plate is further improved.

The titanium plate of the present invention preferably has an average crystal grain size of 5 to 80 占 퐉.

According to such a constitution, the titanium plate is more likely to undergo slip deformation and twin deformation of the potential while securing the strength of the titanium plate at the time of molding. As a result, the moldability of the titanium plate is further improved.

Further, the titanium plate of the present invention can be used in a plate type heat exchanger.

By using the titanium plate of the present invention, a plate type heat exchanger having high strength and high formability can be obtained.

The titanium plate according to the present invention has both strength and formability by defining a predetermined composition and a concentration of C in the crystal grain boundaries.

Fig. 1 (a) is a plan view of a molding die used for evaluating moldability of a titanium plate according to the present invention. Fig. (b) is a sectional view of the forming die on the line E-E.

Next, the composition of the titanium plate of the present invention will be described in detail.

[Furtherance]

The titanium plate according to the present invention has a crystal grain structure of an? Phase (HCP structure) and contains 0.020 to 0.150 mass% of Fe, 0.020 to 0.150 mass% of O, 0.002 to 0.100 mass% of C, And the inevitable impurities, and the sum of Fe and C (mass%) is 0.80 times or more of the O content (mass%). In the titanium plate of the present invention, the concentration of C in the crystal grain boundaries is 1.0% by mass or more.

(Fe: 0.020 to 0.150 mass%)

Fe is an important element for improving the strength and moldability of a titanium plate.

If the Fe content is less than 0.020 mass%, the strength of the titanium plate is insufficient. As a result, the amount of deformation to be introduced in order to increase the strength of the titanium plate is increased, and consequently the formability of the titanium plate is deteriorated. Therefore, the content of Fe is 0.020 mass% or more.

On the other hand, if the content of Fe exceeds 0.150 mass%, the segregation of Fe in the ingot becomes large and the productivity becomes poor. Further, as the amount of precipitation of the? Phase is increased, the crystal grains of Ti are made finer. As a result, the moldability of the titanium plate is lowered.

Therefore, the content of Fe is set to 0.150 mass% or less.

The content of Fe is preferably 0.100 mass% or less.

The content of Fe is more preferably 0.080 mass% or less.

(O: 0.020 to 0.150 mass%)

O is an element that increases the strength of a titanium plate while deteriorating moldability.

If the content of O is less than 0.020 mass%, the strength of the titanium plate is lowered. As a result, the amount of deformation to be introduced in order to increase the strength of the titanium plate is increased, and consequently the formability of the titanium plate is deteriorated. Therefore, the content of O is 0.020 mass% or more.

On the other hand, if the content of O exceeds 0.150 mass%, the titanium plate becomes brittle and the formability is deteriorated. Further, the titanium plate is easily broken at the time of cold rolling, and the productivity of the titanium plate is lowered.

Therefore, the content of O is set to 0.150 mass% or less.

The content of O is preferably 0.125 mass% or less.

The content of O is more preferably 0.100 mass% or less.

(C: 0.002 to 0.100% by mass)

C is an element that improves the strength and moldability of a titanium plate.

If the content of C is less than 0.002 mass%, it becomes difficult to set the concentration of C in the crystal grain boundaries to a predetermined concentration, and the effect of improving the balance between strength and moldability of the titanium plate can not be obtained. Further, the strength of the titanium plate is lowered. Therefore, the content of C is 0.002 mass% or more.

On the other hand, if the content of C exceeds 0.100 mass%, the strength of the titanium plate is increased more than necessary and the formability of the titanium plate is deteriorated.

Therefore, the content of C is 0.100 mass% or less.

The content of C is preferably 0.090 mass% or less.

The content of C is more preferably 0.080 mass% or less.

(The remainder)

Inevitable impurities in the titanium plate according to the present invention refer to impurity elements inevitably contained in a pure titanium industrial plate. Typically, the impurity element includes nitrogen, hydrogen, chromium, nickel, and the like. In addition, elements that are likely to be introduced into the product in the manufacturing process, such as hydrogen, are also included in the inevitable impurities. When the impurity content is large, it is difficult for the titanium plate to have both strength and formability. For this reason, it is preferable that the titanium plate is suitably reduced inevitable impurities. In addition, by using an alloy material having a small amount of impurities, inevitable impurities of the titanium plate can be reduced.

(Composition index R: 0.80 or more)

The balance between the strength and the formability of the titanium plate is improved by controlling not only the content of Fe, O, and C but also the degree of correlation with each other.

The sum of the contents of Fe and C (mass%) is 0.80 times or more of the content (mass%) of O.

The content of Fe, O and C is preferably not less than 0.80 in the composition index R represented by the following formula (1) when the content (mass%) in the titanium plate is represented by [Fe], [C] .

For the control of the composition index R, for example, iron is used as Fe, O is used as titanium oxide, and C is used as a raw material of titanium scrap, for example, TiC , And controlling the contents of Fe, O, and C in the titanium plate.

As described above, the strength of the titanium plate increases as the content of C increases. On the other hand, the ductility of the titanium plate is obtained in an optimum range in which the content of C is present. The range in which the content of C is optimum depends on the contents of Fe and O. In particular, O has a great effect of increasing the strength of the titanium plate. On the other hand, O also deteriorates the ductility of the titanium plate. Therefore, in order to more effectively express the effect of the C content, the smaller the O content is, the better. Further, in order to more effectively improve the balance between strength and formability of the titanium plate by C, the Fe content is more effective.

Therefore, the lower limit value of the composition index R is 0.80 or more.

When the value of the composition index R is 0.80 or more, a plurality of slip systems / twin systems can be activated, and the balance between strength and formability of the titanium plate is improved.

The value of the composition index R is preferably 0.85 or more.

It is more preferable that the value of the composition index R is 0.90 or more.

If the value of the composition index R is less than 0.80, a plurality of slip systems / twin systems can not be activated and the formability of the titanium plate is lowered.

The upper limit value of the composition index R is preferably 12.5 or less in the above content range of Fe, O, and C.

When the value of the composition index R exceeds 12.5, the content of any one of Fe, O, and C deviates from the above preferable range. Therefore, when the value of the composition index R is 12.5 or less and the balance between the strength and the formability of the titanium plate .

It is more preferable that the value of the composition index R is 10.0 or less.

It is more preferable that the value of the composition index R is 6.0 or less.

These detailed mechanisms are unclear, but are estimated as follows. In the titanium plate, O and Fe are employed in the Ti matrix. O is an interstitial element, and Fe is a substitutional element, and even in the same employment state, the existence form is different. Further, in the titanium plate, since the solubility limit of Fe is smaller than 0, the? Phase is precipitated at an Fe content of some degree or more (about 0.05 mass% or more). Therefore, in the titanium plate, the influence on C is presumed to be different between O and Fe.

Therefore, by satisfying the formula (1) in the content of Fe, O, and C in the titanium plate, the balance between the strength and the moldability of the titanium plate is improved.

(Concentration of C in crystal grain boundaries: 1.0% by mass or more)

The concentration state of C in the crystal grain boundaries (the state of concentration of C in grain boundaries) affects the ductility improving effect of the titanium plate. Therefore, the ductility of the titanium plate is improved by precisely and finely controlling the concentration of C in the crystal grain boundaries (concentration in C grain boundaries). Further, by precisely and finely controlling the concentration of C in the crystal grain boundaries, the balance between the strength and the formability of the titanium plate is improved, as compared with the case of the other strength increasing (O increasing, grain refinement, and preliminary deformation).

When the concentration of C in the crystal grain boundaries is less than 1.0% by mass, the effect of improving the balance between the strength and the formability of the titanium plate can not be obtained even if the titanium plate contains a predetermined amount of C as a whole.

Therefore, the concentration of C in the crystal grain boundaries is set to 1.0 mass% or more.

The concentration of C in the crystal grain boundaries is preferably 2.0 mass% or more.

The concentration of C in the crystal grain boundaries is more preferably 5.0 mass% or more.

The concentration of C in the crystal grain boundaries is controlled by a later manufacturing method. More specifically, the annealing is performed by controlling the cold rolling rate in the cold rolling step before the final annealing. It is also performed by controlling the annealing temperature and the annealing time in the final annealing step.

If the cold rolling rate in the cold rolling step before the final annealing is lowered, C is likely to actively concentrate (distribute) in the crystal grain boundaries. If the annealing temperature in the final annealing step is high, C is positively concentrated in the crystal grain boundaries. If the annealing time in the final annealing process is long, C is positively concentrated in the crystal grain boundaries.

Since C is an interstitial element in the crystal grain structure of the titanium plate, it exists in a solid state in the content range of the present invention. C, the balance between the strength and the formability of the titanium plate is improved even if the degree of concentration (distribution concentration) of the titanium in the grain boundary is high, even if the content is the same throughout the titanium plate.

This mechanism is unclear, but is estimated as follows. In the titanium plate, deformation concentration occurs at the Ti crystal grain boundaries due to the twinning or deformed structure formed by the progress of the plastic deformation, leading to fracture. Further, in the titanium plate, when C is segregated in the crystal grain boundaries, the strength of the Ti crystal grain boundaries is increased, and concentration of strain on specific grain boundaries hardly occurs. As a result, it is presumed that the balance between the strength and the moldability of the titanium plate is improved.

(Average crystal grain size: 5 to 80 占 퐉)

The average crystal grain size affects the formability of the titanium plate, but the effect of the present invention is exerted when the titanium plate according to the present invention has a range of the average average crystal grain size (2 to 150 mu m).

When the average crystal grain size is less than 5 탆, twin crystal distortion hardly occurs upon introduction of strain into the titanium plate. On the other hand, when the average crystal grain size exceeds 80 탆, In any case, the moldability of the titanium plate is slightly lowered. Therefore, the average crystal grain size is preferably 5 to 80 mu m. If the average crystal grain size is in the range of 5 to 80 탆, the formability index F is higher as described later, because the formability is better than outside the range.

The average crystal grain size is more preferably 10 to 60 mu m.

The control of the average crystal grain size is carried out by a later manufacturing method. Specifically, the annealing temperature is controlled by controlling the cold rolling rate before the final annealing process, the annealing temperature in the final annealing process, and the annealing time.

When the cold rolling rate before the final annealing process is lowered, the average crystal grain size becomes larger. In addition, when the annealing temperature in the final annealing step is high, the average crystal grain size becomes large.

However, if the annealing temperature is excessively high and becomes too close to the? Transformation temperature T ?, the growth of the crystal grains is inhibited by the newly formed? -Phase. Further, when the annealing time in the final annealing step is long, the average crystal grain size becomes large.

The average crystal grain size can be measured by, for example, orienting the observed structure of a scanning electron microscope (SEM) using an Electron Back Scattered Diffraction Pattern (EBSD). The EBSD irradiates a sample with an electron beam and specifies the crystal orientation by using the reflected electron Kikuchi ray diffraction generated at that time.

In the SEM / EBSD measurement data, the average crystal grain size is defined as a grain boundary with a bearing difference of 5 degrees or more defined as a grain boundary, and the diameter when the area of each crystal grain surrounded by the crystal grain boundaries is approximated to a circle is referred to as a circle equivalent Diameter. The mean value of the circle equivalent diameters was calculated for 100 or more crystal grains used in the calculation and the average value of the diameters of the average circle equivalent diameters calculated by performing similar measurements at a plurality of points (5 or more) define.

[Plate Heat Exchanger Plate]

The plate for a plate heat exchanger according to the present invention is obtained by processing the titanium plate of the present invention into a predetermined shape such as a deep ripple shape by a known method such as a pressing process.

The titanium plate according to the present invention combines strength and formability by the chemical composition and the distribution state of C to crystal grain boundaries. Thus, even if the plate for heat exchanger is processed to form a deep ripple shape at the time of processing, the titanium plate of the present invention does not cause cracking and is excellent in moldability. Further, since the plate heat exchanger plate according to the present invention has strength, it can withstand a severe use environment of a long-term heat exchanger.

[Production method of titanium plate]

Next, a method for producing a titanium plate according to the present invention will be described.

The titanium plate of the present invention can be manufactured by a conventional method such as a dissolving process, a redissolving process, a casting process, a hot forging process, a hot rolling process, an intermediate annealing process, a cold rolling process, Final annealing process].

The method of controlling the concentration of C (graininess of C) in the crystal grain boundaries in the production process of the titanium plate according to the present invention is as follows.

(Dissolution step)

In the melting process, O, Fe, and C are added to the molten metal.

C is uniformly dispersed in a titanium plate, it is preferable to add C to the molten metal in the form of Ti carbide (TiC) instead of C alone. As a result, the dissolution by the VAR method, which is a conventional mass production method, facilitates the incorporation of C.

(Cold rolling process)

In the cold rolling step, the appropriate rolling reduction and annealing conditions are selected in accordance with the cold rolling property of the material (easiness of edge cracking, deformation load, etc.), and cold rolling and annealing are repeated. The reduction rate of the cold rolling performed immediately before the final annealing step ensures a sufficient amount of processing, for example, a reduction rate of 30% or more, for the material to be recrystallized in the final annealing step.

The cold rolling rate in the cold rolling step prior to final annealing is preferably 85% or less. By this condition, the development of the recrystallized texture after the final annealing is suppressed, the ratio of the small-diameter grain boundaries in which C is difficult to be concentrated is reduced, and the ratio of large-diameter grain boundaries in which C is likely to be concentrated is increased.

The cold rolling rate is preferably as low as possible, more preferably 70% or less.

The cold rolling rate is more preferably 60% or less.

(Final annealing process)

In the final annealing step, by accelerating the diffusion of C during annealing, C is positively concentrated in the crystal grain boundaries. The final annealing conditions are preferably high temperature and long time.

Hereinafter, the case of the continuous annealing furnace and the case of the batch annealing furnace (vacuum furnace) will be described.

(By continuous annealing)

The annealing temperature of the final annealing by the continuous annealing furnace is preferably 600 to 890 캜.

When the annealing temperature is less than 600 ° C, the concentration of C in the crystal grain boundaries does not sufficiently take place, so that the concentration of C in the crystal grain boundaries does not exceed 1.0% by mass. If the annealing temperature exceeds 890 占 폚, the grain growth is conspicuous following the recrystallization occurring during the annealing, and the degree of integration of the specific orientation is increased. As a result, the ratio of the small-diameter grain boundaries, in which C is difficult to be thickened, is increased, and the concentration of C in the crystal grain boundaries is rather unlikely to occur, and the concentration of C in the crystal grain boundaries is difficult to be 1.0 mass% or more.

The annealing temperature of the final annealing by the continuous annealing furnace is more preferably 700 to 890 캜.

In the final annealing by the continuous annealing furnace, the holding is not essential (it may be 0 minute), but it is preferable to set the holding time to 10 minutes or less.

If the holding time exceeds 10 minutes, the grain growth is remarkably generated continuously after the recrystallization occurring during the annealing, and the degree of integration of the specific orientation is increased. As a result, the ratio of the small-diameter grain boundaries, in which C is difficult to be thickened, is increased, and the concentration of C in the crystal grain boundaries is rather unlikely to occur, and the concentration of C in the crystal grain boundaries is difficult to be 1.0 mass% or more.

The holding time of the final annealing by the continuous annealing furnace is more preferably from 1 minute to 10 minutes.

[Batch annealing furnace (vacuum furnace)]

The annealing temperature of the final annealing by the batch annealing furnace (vacuum furnace) is preferably 550 to 700 占 폚.

When the annealing temperature is less than 550 캜, the concentration of C in the crystal grain boundaries does not sufficiently occur, and therefore the concentration of C in the crystal grain boundaries does not exceed 1.0% by mass. If the annealing temperature exceeds 700 캜, the grain growth occurs consecutively after the recrystallization occurring during the annealing, and the degree of integration of the specific orientation is increased. As a result, the ratio of the small-diameter grain boundaries, in which C is difficult to be thickened, is increased, and the concentration of C in the crystal grain boundaries is rather unlikely to occur, and the concentration of C in the crystal grain boundaries is difficult to be 1.0 mass% or more.

The annealing temperature of the final annealing by the batch annealing furnace (vacuum furnace) is more preferably 600 to 700 占 폚.

The holding time of the final annealing by the batch annealing furnace (vacuum furnace) is preferably 30 minutes to 4 hours.

If the holding time is less than 30 minutes, the concentration of C in the crystal grain boundaries does not sufficiently take place, so that the concentration of C in the crystal grain boundaries does not become 1.0% by mass or more. If the holding time exceeds 4 hours, grain growth is remarkably caused continuously after recrystallization occurring during annealing, and the degree of integration of a specific orientation is increased. As a result, the ratio of the small-diameter grain boundaries, in which C is difficult to be thickened, is increased, and the concentration of C in the crystal grain boundaries is rather unlikely to occur, and the concentration of C in the crystal grain boundaries is difficult to be 1.0 mass% or more.

The holding time of the final annealing by the batch annealing furnace (vacuum furnace) is more preferably 1 to 4 hours.

Further, when scale is attached to the surface of the titanium plate after annealing, it is preferable to perform a scale removal process, for example, a salt heat treatment, a pickling treatment, and the like.

Example

Hereinafter, examples in which the effects of the present invention are confirmed will be specifically described in comparison with comparative examples which do not satisfy the requirements of the present invention.

The present invention is of course not limited by the following examples, and it is of course possible to carry out the present invention by appropriately changing the scope of the present invention, and they are all included in the technical scope of the present invention.

(Test material)

A pure titanium ingot (JIS H 4600) of Fe, O composition shown in Table 1 was dissolved by a VAR method using a consumable electrode, and a raw material of C was added to the molten metal in the form of Ti carbide (TiC) (Composition index R is 0.80 or more) of 0.80 times or more of the content (mass%) of O and the content (mass%) of Fe and C as shown in Fig. A titanium material (titanium ingot) having a phase grain structure was obtained.

Next, the titanium material was hot-forged at 1000 캜 for 30 minutes, and then hot-rolled at 800 캜 to obtain a hot-rolled sheet having a thickness of 4.0 mm. After the scale of the surface of the hot rolled plate was removed, cold rolling and intermediate annealing (750 占 폚 for 5 minutes in a continuous annealing furnace) were carried out. Further, it was immersed in a salt furnace, then pickled and subjected to descaling treatment. In addition, cold rolling and final annealing under the conditions shown in Table 1 were carried out to obtain test materials (Test Material Nos. 1 to 27) having a sheet thickness of 0.5 mm. The final annealing was performed by continuous annealing, or in a batch annealing furnace (vacuum furnace). Thus, the concentration of C in the crystal grain boundaries was set to 1.0 mass% or more.

When the final annealing was performed by continuous annealing, the resultant was immersed in a salt furnace after the final annealing, then pickled and subjected to a descaling treatment to adjust the cold rolling ratio before and after the intermediate annealing so that the plate thickness became 0.5 mm.

(Evaluation of C concentration in crystal grain boundaries)

The concentration of C in the crystal grain boundaries was evaluated by a field emission transmission electron microscope (FE-TEM) and an energy dispersive X-ray spectrometer (EDX) . Using a JEM-2010F (FE-TEM) manufactured by Nihon Denshi Co., Ltd., equipped with a Noran Vantage (EDX), the grain boundaries of the test material were inclined so as to be perpendicular to the observation direction, The beam diameter of the electron beam was narrowed to about 1 nm, and point analysis was performed on the crystal grain boundaries to measure the EDX spectrum.

Further, the irradiation time of the electron beam for the EDX spectrum measurement was 30 seconds. From the spectrum, the C concentration in grain boundaries was analyzed. At each field of view, 10 concentrations of the C concentration in the crystal grain boundaries were analyzed and the average value thereof was calculated. In addition, the above measurement was carried out at 5 fields of view for each test material, and the average value thereof was calculated to be the concentration of C at the crystal grain boundaries.

(Measurement of average crystal grain size of? -phase particles)

The test specimens were to be observed in a region of 0.5 mm in the rolling direction and 0.5 mm in the plate width direction on the rolled surface in each of the surface layer portion in the plate thickness direction, the 1/4 t portion in the plate thickness direction, And tissue observation was performed by EBSD (Electron Back Scattered Diffraction Pattern, manufactured by Oxford Instruments, Nordlys II).

In the observation of the structure, the boundary of the azimuth angle of 5 ° or more was recognized as grain boundaries. Based on the recognized grain boundaries, the circle equivalent diameter of each crystal grain was calculated. The average circle equivalent diameter was calculated based on the calculated 100 crystal grains. This measurement was carried out at arbitrary five places for each of the above-mentioned parts. Further, an average value of the average circle equivalent diameters at arbitrary five points was calculated, and the average crystal grain size was calculated.

(Evaluation of tensile strength)

The test piece No. 13 specified in JIS Z 2241 (enacted on July 22, 1952) was taken in the direction in which the rolling direction of the test material coincided with the load axis. Next, a tensile test was carried out at room temperature on the basis of JIS H 4600, and a 0.2% proof stress (YS) was measured.

Test specimens with a 0.2% proof stress (YS) of 200 MPa or more were passed.

(Evaluation of formability)

Moldability was evaluated by press molding simulating a plate (heat exchanging portion) of a plate heat exchanger.

As shown in Fig. 1, the mold used had a ridge portion of 100 mm x 100 mm, a pitch of 17 mm and a maximum height of 6.5 mm, and each ridge portion had an R shape of R = 2.5 at the apex have. Each of the ridgelines has a bent portion bent in one direction at a middle portion thereof and is linear from the bent portion to both ends so that the ridge portion is formed obliquely to the rim of the molded portion from the intermediate bent portion to both ends thereof, have. The press machine was an 80-ton press machine (Amino-manufactured universal plastic working machine).

The press molding was carried out in the following order. First, rust preventive oil (R303P) was applied to both sides of each test piece. Next, the test material was placed on the lower mold so that the rolling direction of the test materials coincided with the vertical direction in Fig. 1 (a), and the flange portion was restrained by the blank holder. Then, the mold was pressed under the condition of a press speed of 1 mm / sec.

The mold was press-fitted into each test material at intervals of 0.1 mm to obtain the maximum indentation depth X at which no cracks occurred in the test materials.

The moldability was determined to be acceptable when the moldability index F defined by the following formula (2) was a positive value. The evaluation results are shown in Table 1.

X: Indentation depth

YS: 0.2% proof

(Example)

Test item numbers 1 to 16 were titanium plates which satisfied all of the requirements (composition, composition index R, and grain boundary C concentration) specified in the present invention, and were excellent in balance between strength and press formability.

(Comparative Example)

Since Test Nos. 17 to 27 do not satisfy the requirements specified in the present invention, the balance of strength and press formability was inadequate, especially since the requirements for the concentration of C in grain boundaries were not satisfied.

As test results Nos. 17 to 20, the concentration of C in the crystal grain boundaries was low and the concentration of C in the crystal grain boundaries deviated from the specified range. As a result, the balance between the strength and the formability of the titanium plate was inferior. In addition to this, Test Reas Nos. 18 to 20 had the following characteristics.

In test piece No. 18, the content of C component specified in the present invention exceeded the range of the present invention, so that the strength was increased more than necessary.

In test piece No. 19, since the content of the Fe component specified in the present invention exceeded the range of the present invention, the amount of precipitated β phase was increased, so that the grain size of Ti became finer.

Test item No. 20 had an increased strength and became weaker than necessary because the content of O component specified in the present invention exceeded the range of the present invention.

The test piece No. 21 was found to have a high strength but was fragile because the composition index R did not fall within the scope of the present invention and the concentration of C in the crystal grain boundaries was low and the concentration of C in the grain boundaries did not fall within the specified range Moldability was reduced.

Since the final cold rolling reduction rate was high, the concentration of C in the crystal grain boundaries was low and the concentration of C in the crystal grain boundaries did not fall within the specified range.

The test piece No. 23 had a low annealing temperature at the final annealing, a low concentration of C in the crystal grain boundaries, and a low C concentration in the crystal grain boundaries, resulting in poor formability.

Test item No. 24 had a low annealing temperature for final annealing, a low concentration of C in grain boundaries, and a low C concentration in the crystal grain boundaries, resulting in insufficient strength and poor formability.

The test piece No. 25 had a short annealing time, so that the annealing became insufficient, and the concentration of C in the crystal grain boundaries was low, so that the concentration of C in the crystal grain boundaries did not fall within the specified range.

Test item No. 26 had a long annealing time, and the concentration of C in the crystal grain boundaries was so low that the concentration of C in the crystal grain boundaries did not fall within the specified range, resulting in poor formability.

Test item No. 27 had excessive annealing time because of the long final annealing time, and the concentration of C in the crystal grain boundaries was so low that the concentration of C in the crystal grain boundaries did not fall within the specified range, resulting in poor formability.

Although the present invention has been described in detail with reference to the embodiments and the examples showing the production method of the titanium plate and the titanium plate according to the present invention, Should be interpreted on the basis of. It goes without saying that the contents of the present invention can be modified or changed based on the above description.

1: Mold

Claims (3)

a titanium plate having an? -phase crystal grain structure,
Fe: 0.020 to 0.150 mass%
O: 0.020 to 0.150 mass%
C: 0.002 to 0.100% by mass,
The balance being composed of titanium and inevitable impurities,
Wherein the sum of the contents of Fe and C (mass%) is 0.80 times or more of the content (mass%) of O,
And the concentration of C in the crystal grain boundaries is 1.0% by mass or more. The method according to claim 1,
Wherein the average crystal grain size is 5 to 80 占 퐉. 3. The method according to claim 1 or 2,
A titanium plate, characterized in that it is used in a plate-type heat exchanger.

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