JP2011025269A - Press forming method for titanium sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a press forming method for a titanium sheet which has excellent press formability without generating cracks at the apexes of V-shaped press patterns upon press forming. <P>SOLUTION: In the press forming method for a titanium sheet, a titanium sheet comprising, by mass, ≤0.15% (not including 0%) Fe and ≤0.15% (not including 0%) O is press-formed so as to form V-shaped press patterns at the titanium sheet, provided that the direction in which the integration degree of the C axis of the α phase (hexagonal crystal) is high in the titanium sheet is defined as an A direction, and the orthogonal direction thereof is defined as a B direction, with the apexes direction of the V-shaped press patterns as the A direction, the press patterns are formed on the titanium sheet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a titanium plate press-forming method for forming a V-shaped press pattern (unevenness) on a titanium plate used as a component of a plate heat exchanger or the like.

  Titanium has been widely used mainly in the aircraft industry because it has various processing characteristics such as weldability, superplasticity, and diffusion bondability in addition to light weight, high strength, and high corrosion resistance. In order to make further use of these properties, titanium has recently been used as a constituent material for heat exchangers and chemical plant members, and is particularly resistant to seawater. For this reason, it is often used in seawater heat exchangers.

  In particular, a plate material of pure titanium, that is, a titanium plate, is widely adopted as a constituent material of the plate heat exchanger. However, since it is necessary to improve the heat transfer efficiency, as shown in FIG. A V-shaped press pattern 2 (FIG. 2 is a schematic diagram for explanation, see FIG. 3 for a detailed press pattern) was formed by press molding.

  The V-shaped press pattern 2 is formed by press-molding the titanium plate 1 that has been rolled and annealed with a die (not shown) in which a V-shaped press pattern is formed. In the press forming, the titanium plate 1 was placed and pressed so that the rolling direction X of the titanium plate 1 during rolling and the apex 3 direction of the V-shaped press pattern 2 coincided with each other.

  The reason for this is that the width of the titanium plate 1 is affected by the length of the rolling roll in the rolling process, so that there is a limit to the production of the wide titanium plate 1, and a large molded product is produced (press molding). ), The titanium plate 1 had to be placed so that the rolling direction X of the titanium plate 1 and the direction of the apex 3 of the V-shaped press pattern 2 coincided with each other. In addition, the titanium plate 1 made of pure titanium is such that the rolling direction X is more ductile than the rolling vertical direction, and the rolling direction X is in a direction that coincides with the apex direction of the V-shaped press pattern 2. This is because it is thought that cracking can be suppressed by placing the plate and press-molding.

  Specifically, there is no prior art document showing the plate placement direction of the titanium plate when forming a V-shaped press pattern on a titanium plate used as a component for a conventional plate heat exchanger. However, Patent Document 1 previously filed by the applicant of the present application describes that in a plate heat exchanger, the surface of a titanium plate is formed into a concavo-convex shape by press molding in order to improve heat transfer. The press forming is performed by placing a titanium plate so that the rolling direction coincides with the apex direction of the V-shaped press pattern.

  Thus, when producing the component material of a plate-type heat exchanger, the titanium plate is placed and pressed so that the rolling direction X coincides with the apex direction of the V-shaped press pattern. Although it was molded, when the titanium plate was press-molded, a crack sometimes occurred at the apex of the V-shaped press pattern.

JP 2006-291362 A

  The present invention has been made in view of the above-described conventional circumstances, and provides a press forming method of a titanium plate that is excellent in press formability without causing cracks at the apex of a V-shaped press pattern during press forming. It is an object to do.

  The invention according to claim 1 is a method of press-molding a titanium plate containing, by mass%, Fe of 0.15% or less (excluding 0%) and O of 0.15% or less (excluding 0%). A titanium plate press forming method for forming a V-shaped press pattern on the titanium plate, wherein the direction in which the α-phase (hexagonal) C axis of the titanium plate is highly integrated is the A direction, and the orthogonal direction thereof. Is a titanium plate press-forming method, wherein the press pattern is formed on the titanium plate with the apex direction of the V-shaped press pattern as the A direction.

  The invention according to claim 2 is the press forming method of the titanium plate according to claim 1, wherein the total elongation in the A direction of the titanium plate is 20% or more.

  The invention according to claim 3 is the press forming method of the titanium plate according to claim 1 or 2, wherein the average crystal grain size of the α phase of the titanium plate is 10 to 200 µm.

  According to the present invention, no crack is generated at the apex of the V-shaped press pattern during press forming, and a titanium plate having excellent press formability can be obtained by press forming.

It is a plane schematic diagram of the titanium plate which shows the press molding method of one embodiment of the present invention. It is the plane schematic diagram of the titanium plate which shows the conventional press molding method. The press molding die used in order to evaluate press formability in an example is shown, (a) is a top view and (b) is an FF line sectional view of (a).

  As described above, when the titanium plate is placed and pressed so that the rolling direction of the titanium plate and the apex direction of the V-shaped press pattern coincide with each other, cracks may occur at the apex. In order to solve the problem, the present inventors diligently experimented and researched.

  As a result, after prescribing the Fe content and the O content, the direction in which the hexagonal crystal is highly integrated on the titanium plate is aligned with the apex direction of the V-shaped press pattern obtained by press forming. By carrying out the molding, it was found that there was no cracking at the apex of the V-shaped press pattern during press molding, and it was possible to obtain a titanium plate with excellent press moldability, and the present invention was completed. It came to.

  Also, if the total elongation of the titanium plate in the direction where the degree of hexagonal crystal accumulation is high is 20% or more, cracks do not occur at the apex of the V-shaped press pattern during press forming, and the press formability is excellent. It was also confirmed that a titanium plate can be obtained more reliably.

  Furthermore, if the average crystal grain size of the α phase of the titanium plate is 10 to 200 μm, there is no crack at the top of the V-shaped press pattern at the time of press forming, and a titanium plate having excellent press formability is obtained. It was also confirmed that it can be obtained more reliably.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  The normal titanium plate 1 is manufactured by performing blasting and pickling treatment at any time between each process such as block rolling → hot rolling → intermediate annealing → cold rolling → final annealing. An object of the present invention is a method of forming a V-shaped press pattern 2 by press forming on the titanium plate 1 that has been rolled and annealed.

(Press pattern formation direction)
FIG. 1 is a schematic diagram showing an embodiment of the present invention. A V-shaped press pattern 2 is formed on a titanium plate 1 (FIG. 1 is a schematic diagram for explanation, see FIG. 3 for a detailed press pattern). ) Is exemplified. In the drawing, the A direction indicated by a double-headed arrow indicates a direction in which the α-phase (hexagonal) C-axis is highly integrated on the plate surface of the titanium plate 1, and the B direction is an orthogonal direction on the plate surface. Indicates. Moreover, the arrow shown by X shows the rolling direction at the time of rolling of the titanium plate 1, and a rolling direction and B direction correspond. That is, when the titanium plate 1 is rolled, the hexagonal C-axis accumulates in a direction (A direction) orthogonal to the rolling direction (B direction). Note that FIG. 1 is a schematic diagram, and an actual V-shaped press pattern 2 is a repetition of V-shaped irregularities, not three V-shaped lines.

  In the press forming method of the titanium plate of the present invention, the direction of the apex 3 of the V-shaped press pattern 2 formed on the titanium plate 1 is set to the α axis (hexagonal) C axis on the plate surface of the titanium plate 1. Is pressed in the direction A where the degree of integration is high. The press-formed titanium plate 1 has a lower yield strength in the B direction than in the A direction, so that the flow of the B direction plate increases and the formability is improved.

(Component composition)
In the present invention, the component composition of the titanium plate is also the main point of the invention. Next, the reason for defining the component composition will be described.

  Pure titanium contains a small amount of C, H, O, N, Fe, etc. as inevitable impurities, and the balance is Ti, but in the present invention, the content is relatively large among the inevitable impurities and mechanical. The upper limit of the content of Fe and O affecting the properties was specified.

  If the Fe content exceeds 0.15% by mass and increases too much, the strength becomes too high and the elongation in the A direction of the titanium plate decreases, and the press formability deteriorates. Therefore, the upper limit of the Fe content is 0.15% by mass. In addition, the upper limit with preferable content of Fe is 0.10 mass%, and a more preferable upper limit is 0.07 mass%.

  If the O content exceeds 0.15% by mass and increases too much, the strength becomes too high and the elongation in the A direction of the titanium plate decreases, and the press formability deteriorates. Therefore, the upper limit of the O content is 0.15% by mass. In addition, the upper limit with preferable content of O is 0.10 mass%, and a more preferable upper limit is 0.07 mass%.

(Total elongation in direction A)
In the present invention, it is preferable that the total elongation of the titanium plate in the A direction (the direction in which the degree of hexagonal C-axis integration is high) is 20% or more. If the total elongation in the A direction of the titanium plate is less than 20%, press formability deteriorates. The total elongation in the A direction of the titanium plate is more preferably 25% or more, and further preferably 30% or more.

(Average crystal grain size of α phase)
In the present invention, it is further preferable that the average crystal grain size of the α phase of the titanium plate is 10 to 200 μm. The larger the average crystal grain size of the α phase, the higher the frequency of deformation twins at the time of press forming, the total elongation of the titanium plate is increased, and the formability is improved. However, if the average crystal grain size becomes too large, it will cause rough skin after molding of the molded product.

  A more preferable lower limit of the average crystal grain size of the α phase is 20 μm, and a further preferable lower limit is 30 μm. On the other hand, a more preferable upper limit is 175 μm, and a more preferable upper limit is 150 μm.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and the present invention is implemented with appropriate modifications within a range that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

  In this example, first, a titanium ingot containing Fe and O at the contents shown in Table 1 was cast by CCIM (cold crucible induction melting method). The balance is Ti and unavoidable impurities such as C, H, N, and the like. The size of the ingot is a cylindrical shape of φ100 mm and is 10 kg. Using this ingot, the ingot rolling was performed, and then cooled to obtain a plate-like ingot rolled material having a thickness of 45 mm. Furthermore, hot rolling was performed, scale removal was performed, and a hot rolled sheet having a thickness of about 5 mm was obtained.

  Next, after performing an annealing treatment (intermediate annealing) in which air cooling was performed at 700 ° C. for 5 minutes in an atmospheric furnace, scale removal was performed. Next, after performing cold rolling at a cold rolling rate of 89%, an annealing process (final annealing) is performed by heating in an atmospheric furnace at 800 ° C. for 3 minutes and then air cooling, skin pass is performed, and scale removal To produce a titanium plate having a thickness of 0.3 mm.

  For these titanium plates after rolling and annealing, no. 1 to 3, the apex direction of the V-shaped press pattern formed on the titanium plate is directed to the direction in which the hexagonal C-axis has a high degree of integration, that is, the rolling vertical direction (A direction) perpendicular to the rolling direction. And press-molded. On the other hand, no. 4 and 5, the apex direction of the V-shaped press pattern formed on the titanium plate is pressed in the direction perpendicular to the direction in which the hexagonal C-axis is highly integrated, that is, in the rolling direction (B direction). Molded.

  Observation and measurement of the metal structure of each titanium plate after press forming and evaluation of press formability were performed as follows. Further, the total elongation and strength in the A direction (direction in which the degree of accumulation of the hexagonal C-axis was high) were also measured.

  In this example, a field emission scanning electron microscope (FESEM) (manufactured by JEOL Ltd., JSM5410) is equipped with a back-scattered electron diffraction image (Electron Back Scattering (Scattered) Pattern system). The metal structure was observed and measured by the crystal orientation analysis method. This measurement method was used because the EBSP method has higher resolution than other measurement methods and can perform measurement with high accuracy. First, the measurement principle will be described.

  In the EBSP method, an electron beam is irradiated onto a sample set in a lens barrel of FESEM to project EBSP on a screen. This is taken with a high-sensitivity camera and captured as an image on a computer. The orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. The calculated crystal orientation is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, data of tens of thousands to hundreds of thousands of points can be obtained at the end of measurement.

  Thus, the EBSP method has a wider field of view than the X-ray diffraction method or the electron beam diffraction method using a transmission electron microscope, and can provide various information on hundreds of crystal grains for several hours. There are advantages you can get within. In addition, since the specified region is scanned at a fixed interval instead of the measurement for each crystal grain, there is an advantage that each of the above-mentioned information regarding the above-described many measurement points covering the entire measurement region can be obtained. Details of the crystal orientation analysis method in which the EBSP system is mounted on these FESEMs are described in Kobe Steel Technical Report / Vol. 52 no. 2 (Sep. 2002) P66-70 and the like.

<Average crystal grain size of α phase>
Regarding the average crystal grain size of the α phase (crystal grains), among the crystal grains existing in a 1 mm × 1 mm plane of the titanium plate, the average crystal grain size of the top 100 α phases of the crystal grains is measured as described above. Obtained. As described above, this measurement is performed using a crystal orientation analysis method in which an EBSP system is mounted on an FESEM, and a texture parallel to the surface of the titanium plate and a 1/4 t portion texture in the plate thickness direction. It was carried out by measuring. Specifically, a sample was prepared in which the surface of the rolled surface of the titanium plate was mechanically polished and further subjected to electrolytic polishing following buffing to adjust the surface. Then, the measurement by EBSP was performed using FESEM (JEOL JSM 5410) by JEOL. As the EBSP measurement / analysis system, EBSP: OIM (Orientation Imaging Microscopy) manufactured by TSL was used.

  The measurement range of the titanium plate was 1 mm × 1 mm in the plane, and the measurement pitch was 1 μm in length and width. The average size of the α phase of the titanium plate is assumed to be 50 μm, and all α phases existing in the range of 1 mm × 1 mm can be observed and measured by this measurement. Of the α phase that could be measured in this range, the top 100 crystal grains with the largest size were extracted and observed, and the average crystal grain size of the α phase was determined from the formula (Σx) / 100. In this equation, x represents the crystal grain size of each α phase measured.

<Measurement of total elongation in A direction and tensile strength>
The total elongation in the A direction of the titanium plate was measured, and the tensile strength in the A direction of the titanium plate was also measured as a reference test.

  The total elongation in the A direction of the titanium plate was determined by preparing a No. 13 test piece defined in JISZ2201 from each manufactured titanium plate and performing a tensile test in accordance with JISZ2241 on this test piece. This total elongation was obtained by setting the gauge distance to 50 mm and measuring the gauge distance by abutting the test pieces after the tensile fracture in the tensile test.

  The tensile strength was obtained by measuring the tensile strength (TS) in the A direction after the tensile test. The test speed (strain speed in the tensile test) was 0.3 mm / min.

<Press formability>
As for press formability, as shown in FIG. 3, a titanium plate (test body) using a press mold that simulates press forming of a heat exchange portion of a plate heat exchanger provided with a V-shaped groove. The press molding was carried out and evaluated. As shown in FIG. 3, the press mold has a size of a molded part of 100 mm × 100 mm, and six parallel V-shaped parallel ridges with a pitch of 10 mm and a maximum height of 4 mm are formed on the surface. ing. The R shape of each ridge line portion is a total of R = 0.4, 1.8, 0.8, 1.0, 1.4, 0.6 in order from the top to the bottom of FIG. There are six types.

Using this molding die, press molding was performed by an 8 ton hydraulic press. Specifically, press oil having a kinematic viscosity of 34 mm ² / s (40 ° C) is applied to the front and back surfaces of each test specimen, each test specimen is placed on the upper surface of the lower mold, and the flange portion is restrained by a plate presser. After that, press molding was performed under the conditions of a press speed of 1 mm / s and an indentation depth of 3.8 mm. The press formability was evaluated by the number of cracks observed after press forming. A specific evaluation method will be described below.

  The presence or absence of cracks is visually observed at 36 points of intersection between the ridge line portion shown in FIG. 3A of each test body after press molding and the one-dot chain lines of measurement positions A, B, C, C ′, D, and E. Observed. Note that the measurement position C ′ is a valley portion located between adjacent ridge line portions, as shown in FIG.

  In this visual inspection, the measurement positions A, C, C ′, and E, which are the starting points of cracking, are 2 points if neither cracking nor constriction is observed, 1 point if constriction is recognized, 0 point if cracking is recognized, For other measurement positions B and D, 1 point is given if neither cracking nor constriction is observed, 0.5 point if constriction is recognized, 0 point if cracking is observed, and the reciprocal of machining R is added to each point. Multiply it and digitize the state of the cracks and determine the total. After normalizing the total value as 100 when the case where cracks are not completely observed and constriction is observed, the function F () depends on the temperature (T), the viscosity of the lubricating oil (μ), and the plate thickness (t) of the specimen. T, μ, t) and the function G (α, p) depending on the angle (α) and pitch (p) of the ridge line of the press mold were multiplied to calculate the formability score. Note that F and G are values from 0 to 1.

The calculation method of the above moldability score can be represented by the following formula.
Formability score = F × G × ΣE (ij) / R (j) / (ΣA, C, C ′, E2 / R (j) + ΣB, D 1 / R (j)) × 100
In this equation, in the case of A, C, C ′, E, E (ij) = 1.0 × (no cracking of the neck: 2, necking: 1, cracking 0), and in the case of B and D, E (ij) = 0.5 × (no cracking: 2, necking: 1, cracking 0). In this example, the temperature (T), the viscosity of the lubricating oil (μ), the thickness of the specimen (t), the angle of the ridge line of the press mold (α), and the pitch of the ridge line of the press mold (p ) Was constant, the moldability score was calculated with F × G as 1 for convenience.

  The calculated formability score was evaluated as being excellent in press formability, with ◎ being 75 points or more, ◯ being 50 points or more and less than 75 points, and x being less than 50 points.

  The test results are shown in Table 1.

  No. 1 and no. No. 2 is such that the Fe and O contents are both 0.15 mass% or less, and the apex direction of the V-shaped press pattern formed on the titanium plate is the direction in which the degree of accumulation of hexagonal C-axis is high, that is, rolling It is the invention example which carried out press molding toward the direction (A direction) orthogonal to a direction.

  In contrast, no. No. 3 is a comparative example in which the Fe and O contents exceed the upper limit. Nos. 4 and 5 press the apex direction of the V-shaped press pattern formed on the titanium plate in a direction perpendicular to the direction in which the hexagonal C-axis is highly integrated, that is, in the rolling direction (B direction). It is the comparative example which shape | molded.

  No. In the inventive examples 1 and 2, no cracks occurred in the press formability test. In the comparative example which does not satisfy any requirement among the requirements of 3 to 5 of the present invention, cracks occurred at the apex of the V-shaped press pattern in the press formability test. In other words, the press forming method satisfying the requirements of the present invention was subjected to press forming No. It can be said that the 1 and 2 titanium plates are titanium plates excellent in press formability.

  No. 1 and 2, the total elongation in the A direction is 20% or more and the average crystal grain size of the α phase is 10 to 200 μm. Even if these requirements are satisfied, a titanium plate having excellent press formability can be obtained. it can.

1 ... Titanium plate 2 ... Press pattern 3 ... Vertex

Claims (3)

A titanium plate containing 0.15% or less of Fe (not including 0%) and 0.15% or less (not including 0%) of O in mass% is press-molded to form a V-shape on the titanium plate. A press forming method of a titanium plate for forming a press pattern of
When the direction in which the degree of accumulation of the C axis of the α phase (hexagonal) of the titanium plate is high is the A direction, and the orthogonal direction is the B direction,
A press forming method of a titanium plate, wherein the press pattern is formed on the titanium plate with the apex direction of the V-shaped press pattern as the A direction.   2. The titanium plate press molding method according to claim 1, wherein the total elongation in the A direction of the titanium plate is 20% or more.   The titanium plate press forming method according to claim 1 or 2, wherein an average crystal grain size of the α phase of the titanium plate is 10 to 200 µm.

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