JP4928584B2 - Titanium plate, manufacturing method thereof, and manufacturing method of heat exchange member of plate heat exchanger - Google Patents

Abstract

Provided are a titanium plate which has satisfactory seizing resistance and crack resistance, whereby the plate exhibits excellent press formability, and a process for producing the titanium plate. The titanium plate (10) comprises a titanium base (1) and a hard layer (2) partly formed on the surface thereof. The hard layer (2) has been formed so that when the surface of the titanium plate (10) is viewed through an examination image bearing a plurality of squares (M) in which each side of each square (M) has a length (W) of 10 µm, then the average of all dimensions of the hard layer (2) that are measured along the lines (S) constituting the squares (M) and crossing the surface of the hard layer (2) is 5-200 µm per mm2 of the surface of the titanium plate (10). The process for producing the titanium plate (10) comprises a hard-layer formation step in which a hard layer (2) is formed on the surface of a titanium base (1) and a hard-layer removal step in which the hard layer (2) is partly removed.

Description

The present invention relates to a titanium plate excellent in press formability, a manufacturing method thereof, and a manufacturing method of a heat exchange member of a plate heat exchanger .

  Titanium plates are excellent in corrosion resistance, so heat exchanger parts for chemical / electric power and food production plants, consumer products such as camera bodies and kitchen equipment, transport equipment parts for motorcycles and automobiles, home appliances, etc. It is used for exterior materials. Among the heat exchangers, the plate heat exchanger increases the heat exchange efficiency by processing the titanium thin plate into a wave by press forming to increase the surface area, and requires a formability to make a deep wave. . Moreover, since it processes into the housing | casing of a camera, the exterior goods of household appliances, the member for transportation apparatuses, etc., the outstanding moldability (press moldability) is calculated | required. Formability requires workability and lubricity of the material itself and seizure resistance to the tool.

  Titanium plate is an active metal despite its high r-value (ratio of logarithmic strain in the plate width direction to logarithmic strain in the plate thickness direction during uniaxial tensile deformation) and high drawability of the material itself. In the molding process, seizure with the mold occurs, which becomes a factor of lowering the molding limit. For this reason, it is generally said that moldability can be improved by preventing seizure with a tool for molded products that place importance on drawing.

  Therefore, in order to prevent seizure with a tool and improve formability, for example, in Patent Documents 1 to 3, a hard layer such as a titanium nitride layer, a nitrogen-enriched layer, or a TiC-containing layer is formed on the surface. It has been proposed. However, a titanium plate with a hard layer specified in this document is preferable for application to products that emphasize seizure resistance. However, there is a problem that surface cracks easily occur and moldability deteriorates. Therefore, for example, Patent Document 4 proposes a titanium plate having a surface hardness that is appropriately lower than that of the titanium plate. Further, for example, in Patent Document 5, an impurity element segregating at a grain boundary is prescribed, and an unevenness is formed on the surface by defining conditions for annealing treatment and pickling treatment with nitric hydrofluoric acid. There has been proposed a method of manufacturing a titanium plate that prevents the seizure of the steel.

Japanese Patent Laid-Open No. 10-60620 Japanese Patent Laid-Open No. 10-204609 JP 2006-291362 A Japanese Patent No. 3600792 Japanese Patent Laid-Open No. 10-30160

However, the conventional titanium plate and its manufacturing method have the following problems.
The titanium plates described in Patent Documents 1 to 4 are often subjected to an Erichsen test (JIS B 7729) as an overhang forming evaluation. In this case, since the processing R is relatively large (punch φ20 mm), The problem of cracking is difficult to manifest and the formability may be improved by improving the seizure resistance of the surface. However, when forming into a shape with a small processing R and a deep forming depth (deep and thin groove shape) such as a plate heat exchanger member, cracks are likely to occur in the vicinity of the R portion, and the hard layer determines the forming limit. It became clear that it was a cause. That is, when a hard layer such as a thick oxide film or nitride film is formed in order to improve seizure resistance, it becomes clear that cracks tend to occur and the moldability is deteriorated.

  Moreover, although the titanium plate of patent document 4 has reduced the surface hardness moderately compared with the titanium plate of patent documents 1-3, when a deformation | transformation becomes a severe shape, it will generate | occur | produce a crack. There is a problem that it cannot be suppressed and cracking is likely to occur. The titanium plate described in Patent Document 5 has a problem that seizure is likely to occur in a process that requires a long sliding distance such as a drawing process because a hard layer is not formed on the surface.

The present invention has been made in view of the above-mentioned problems, and its purpose is to have excellent seizure resistance and crack resistance, so that a titanium plate that exhibits excellent press formability, a method for producing the same, and a plate. It is providing the manufacturing method of the heat exchange member of a heat exchanger .

The present inventors examined the following matters.
In order to make the titanium plate surface difficult to break, it is effective to remove the hard layer on the surface. However, the titanium plate surface from which the hard layer has been removed generally tends to seize with the mold surface. When seizure occurs, it becomes a starting point of cracking, and even when it does not develop into cracking, scratches are generated on the surface of the titanium plate, causing defects. In addition, since titanium adheres to the mold, it is necessary to polish the mold, and there is a problem that productivity is lowered. On the other hand, in order to suppress the occurrence of seizure on the surface of the titanium plate, it is effective to form a hard layer on the surface. However, since the hard layer has poor deformability, there is a problem that cracks are likely to occur. Therefore, it has been a problem to achieve both seizure resistance and crack resistance. Therefore, the present inventors partially formed a hard layer having excellent seizure resistance on the surface of the titanium plate, thereby preventing cracking during press molding and improving seizure resistance. The present inventors have found that both stickiness and crack resistance can be achieved, and have reached the present invention.

  That is, by forming a hard layer with excellent seizure resistance as a convex part on the surface of a titanium plate having excellent press formability (hereinafter referred to as formability as appropriate), seizure resistance and crack resistance are improved. I made them compatible. In this case, since the hard layer formed on the outermost surface at the time of press molding contacts the mold, seizure does not occur even if the sliding distance is long. On the other hand, although the hard layer is poor in deformability, the titanium plate of the present invention has a hard layer formed only partially on the surface, and the hard layer does not need to follow the macro deformation of the titanium plate and cracks. It is difficult to become the starting point of occurrence. In addition, the formability as used in the present invention is a general term for the workability of the material, the lubricity with the press tool, and the seizure resistance against the tool.

That is, a titanium plate according to the present invention is a titanium plate for a heat exchanging member of the plate heat exchanger the press molding is carried out, the surface of the titanium material, the hard layer is partially formed, the hard When observing the surface of the titanium plate on a plurality of grid-like observation images, the layer has an area per 1 mm ^{2 on} the surface of the titanium plate when each side of the grid is 10 μm. The total length of the hard layer at the position where the straight line constituting the grid crosses the surface of the hard layer (hereinafter referred to as the size of the hard layer as appropriate) is 5 to 200 μm. It is characterized by being.

  According to such a configuration, seizure resistance is improved by forming a hard layer, and crack resistance is improved by forming the hard layer partially as a convex portion with a predetermined size. .

  In the titanium plate according to the present invention, the total area ratio of the hard layer with respect to the entire surface of the titanium plate is preferably 20 to 90%.

  According to such a configuration, during press molding, the titanium material in the recess and the mold are hardly brought into contact with each other, seizure resistance is improved, and cracks are hardly generated during deformation.

  In the titanium plate according to the present invention, the arithmetic average roughness (Ra) of the surface of the titanium plate is preferably 0.15 to 1.5 μm. Moreover, it is preferable that the maximum height (Rz) of the surface of the titanium plate is 1.5 to 9.0 μm.

  According to such a configuration, the titanium material in the recess and the mold are hardly brought into contact with each other, the seizure resistance is improved, and the moldability is hardly deteriorated.

  The titanium plate manufacturing method according to the present invention is the above-described titanium plate manufacturing method, a hard layer forming step of forming a hard layer on the surface of the titanium material, and a hard layer partially removing the hard layer. And a removing step.

  According to such a manufacturing method, the titanium plate of the present invention can be manufactured by forming the hard layer on the surface of the titanium material and then partially removing the hard layer.

  In the method for producing a titanium plate according to the present invention, it is preferable that the hard layer is partially removed by dipping in a salt furnace heated to 350 ° C. or higher in the hard layer removing step.

  According to such a manufacturing method, by immersing the titanium plate in a salt furnace under predetermined conditions, the temperature rapidly increases, so that a rapid temperature change is given to the titanium plate, and fine cracks are formed in the entire hard layer. And the hard layer is partially peeled off.

  In the method for producing a titanium plate according to the present invention, in the hard layer removing step, nitric acid is contained in an amount of 5% by mass or more, hydrofluoric acid is contained in an amount of 1% by mass or more, and a mass ratio of the nitric acid to the hydrofluoric acid (hydrofluoric acid / It is preferable that the hard layer is partially removed by pickling in a pickling bath of 0.1 or more.

  According to such a manufacturing method, the hard layer is partially peeled off by pickling with a predetermined solution.

  In the method for producing a titanium plate according to the present invention, in the hard layer removing step, after being immersed in a salt furnace heated to 350 ° C. or higher, nitric acid is contained at 5% by mass or more, hydrofluoric acid is contained at 1% by mass or more, and It is preferable that the hard layer is partially removed by pickling in a pickling bath having a mass ratio of nitric acid to hydrofluoric acid (hydrofluoric acid / nitric acid) of 0.1 or more.

According to such a manufacturing method, even when a part of the hard layer remains on the surface of the titanium material after immersion in the salt furnace, the remaining hard layer is removed by pickling.
Moreover, the manufacturing method of the heat exchange member of the plate type heat exchanger which concerns on this invention is characterized by press-molding the said titanium plate.

Since the titanium plate according to the present invention has good seizure resistance and crack resistance, it is excellent in press formability.
The method for producing a titanium plate according to the present invention can produce a titanium plate excellent in press formability.

It is a schematic diagram which shows the titanium plate which concerns on this invention, (a) is a perspective view, (b) is XX sectional drawing of (a). It is a plane schematic diagram for demonstrating the size of the hard layer of the titanium plate which concerns on this invention. It is explanatory drawing for demonstrating the structure in which a titanium plate is cracked by a hard layer, (a) is explanatory drawing about the conventional titanium plate, (b) is explanatory drawing about the titanium plate which concerns on this invention. . In an Example, it is a schematic diagram which shows the shape of the shaping | molding die for performing a moldability evaluation, (a) is a top view, (b) is FF sectional drawing of (a). It is a SEM photograph of the surface of the test body in an Example.

  Next, with reference to the drawings, a titanium plate and a manufacturing method thereof according to the present invention will be described in detail.

≪Titanium plate≫
As shown in FIGS. 1 (a) and 1 (b), a titanium plate 10 according to the present invention has a hard layer 2 partially formed on the surface of a titanium material 1, and is formed partially. The size of the hard layer 2 is prescribed. Here, “surface” means both surfaces of the titanium material 1. Moreover, in FIG. 1 (a), (b), the hard layer 2 is shown in figure easily for convenience.
Each configuration will be described below.

<Composition>
Although this invention is not limited to the titanium plate of a specific composition, from a viewpoint of ensuring the moldability of the titanium raw material (base material) 1, what a titanium plate consists of titanium and an unavoidable impurity is preferable. Examples of inevitable impurities include general impurity elements (elements not actively added) contained in pure titanium, specifically, O, Fe, H, C, N, and the like. O is preferably 1500 ppm or less, and more preferably. Is suppressed to 1000 ppm or less, Fe is suppressed to 1500 ppm or less, more preferably 1000 ppm or less, H is suppressed to 130 ppm or less, C is suppressed to 800 ppm or less, and N is preferably suppressed to 300 ppm. As such a titanium plate, for example, a JIS-1 type cold rolled plate can be used.

<Hard layer>
In the titanium plate 10 of the present invention, the hard layer 2 is partially formed as a convex portion on the surface of the titanium material 1. And the remaining part of the surface consists of the titanium raw material 1, and forms the recessed part. Here, the hard layer 2 refers to a layer containing at least one of titanium oxide, titanium nitride, and titanium carbide, and indicates a hardness of about 10 GPa or more when measured with a nanoindenter. This hard layer 2 is clearly distinguished from a natural oxide film having a hardness of about 3 GPa by an equivalent method. That is, in the present invention, the natural oxide film is not included in the hard layer 2.

<Hard layer size: 5-200 μm>
As shown in FIG. 2, in the hard layer 2, when the surface of the titanium plate 10 is observed on a plurality of grid-like observation images, each side (length W of each side) of each grid M is 10 μm. In the area per 1 mm ^{2 on} the surface of the titanium plate 10, the lengths L ₁ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , L ₂ , The total average of L ₃ ... L ₈ ((L ₁ + L ₂ + L ₃ +... + L ₈ ) / 8) is set to 5 to 200 μm (in FIG. 2, the position where the straight line S and the hard layer 2 intersect). Is shown for 8 cases). That is, the size of the hard layer 2 is 5 to 200 μm in an area per 1 mm ² at any position on the surface of the titanium plate 10 (on an arbitrary observation image). In FIG. 2, for the sake of convenience, the size of the hard layer 2 is illustrated for easy explanation.

  The lower limit of the size of the hard layer 2 is not particularly limited as long as adhesion to the titanium part (titanium material 1) as a substrate is obtained, but a desired effect can be obtained if it is 5 μm or more. On the other hand, if it exceeds 200 μm, cracks starting from the hard layer 2 tend to occur during deformation by press molding, and the crack resistance decreases. Therefore, the size of the hard layer 2 is set to 5 to 200 μm. In addition, More preferably, it is 10-200 micrometers, More preferably, it is 20-150 micrometers.

  The size of the hard layer 2 is measured by, for example, using a scanning electron microscope to prepare a photograph of an area (area) of 1 mm × 1 mm on one side of the surface of the titanium plate 10 at a magnification of 100 times. A straight line S is drawn in an arbitrary direction, and image analysis is performed in such a manner that the straight line S is drawn in a lattice shape (a grid shape) with a lattice interval of 10 μm parallel and perpendicular to the straight line S. What is necessary is just to calculate by calculating the total average of each length that the straight line S crosses the surface of each formed hard layer 2.

Here, with reference to drawings, the mechanism in which a crack arises is demonstrated.
As shown in FIG. 3A, when the hard layer 2 is continuously formed on the surface of the titanium material 1 (that is, over the entire surface), the strain due to the load at the time of deformation by press molding is reduced. Since the distortion occurs in the entire area 2, the distortion becomes large and cracking is likely to occur (in FIGS. 3A and 3B, the length of the arrow indicates the magnitude of the distortion). On the other hand, when the hard layer 2 is formed discontinuously (that is, partially) on the surface of the titanium material 1 as shown in FIG. Since it occurs for each of the hard layers 2 that are partially formed, the strain applied to each of the hard layers 2 is reduced, and cracks are less likely to occur.
Thus, by forming the hard layer 2 partially in a predetermined size, the crack resistance can be improved, and the formability of the titanium plate 10 is improved.

  It is preferable that the titanium plate further defines the area ratio, surface roughness (arithmetic average roughness (Ra), maximum height (Rz)), surface hardness, crystal grain size, and the like of the hard layer 2 as predetermined.

<Area ratio of hard layer: 20 to 90%>
The area ratio of the hard layer 2 is preferably set to 20 to 90% with respect to the entire surface of the titanium plate 10 in order to improve crack resistance and to exhibit good seizure resistance of the titanium plate 10.
When the area ratio of the hard layer 2 is less than 20%, the titanium material 1 in the recess and the mold are likely to come into contact with each other during press molding, and there is a possibility that seizure may occur. On the other hand, if it exceeds 90%, there is a risk of becoming a base point of cracking during deformation. Therefore, the area ratio of the hard layer 2 is preferably 20 to 90%. In addition, More preferably, it is 35 to 80%.

  The area ratio of the hard layer 2 may be measured, for example, by preparing a photograph observed at a magnification of 100 times using a scanning electron microscope and analyzing the image.

<Arithmetic mean roughness (Ra): 0.15-1.5 μm>
The arithmetic average roughness (Ra) of the surface of the titanium plate 10 affects the average friction coefficient of the surface of the titanium plate 10. If the arithmetic average roughness (Ra) is less than 0.15 μm, the titanium material 1 in the recess and the mold are likely to come into contact with each other, and seizure is likely to occur during molding. On the other hand, if it exceeds 1.5 μm, cracking due to the notch effect may be induced to deteriorate the formability, and the press load is increased, which is not preferable. Accordingly, the arithmetic average roughness (Ra) is preferably 0.15 to 1.5 μm. In addition, More preferably, it is 0.2-1.5 micrometers, More preferably, it is 0.2-1.0 micrometer.

<Maximum height (Rz): 1.5 to 9.0 μm>
The maximum height (Rz) of the surface of the titanium plate 10 indicates the depth of the recess, and affects the formability. When the maximum height (Rz) is less than 1.5 μm, the depth of the recess is insufficient, and the titanium material 1 in the recess and the mold are likely to come into contact with each other, and seizure is likely to occur during molding. On the other hand, if it exceeds 9.0 μm, there is a possibility that it becomes a starting point of cracking due to the notch effect. Therefore, the maximum height (Rz) is preferably 1.5 to 9.0 μm. In addition, More preferably, it is 1.8-6.0 micrometers.

  The arithmetic average roughness (Ra) and the maximum height (Rz) may be measured by, for example, using a surface roughness shape measuring device by a method based on JIS B 0601: 2001. At that time, the measurement distance and the measurement speed are set to predetermined values, five points in parallel and perpendicular to the rolling direction are measured, and the average value is taken as the measurement value.

<Surface hardness>
In order to suppress the occurrence of seizure, the surface hardness of the titanium plate 10 has a difference between the Vickers hardness when the measurement load is 0.098N and the Vickers hardness when the measurement load is 4.9N is 40 to 900. It is preferable. The Vickers hardness is controlled by adjusting the conditions of cold rolling and heat treatment, which will be described later, and prescribing the surface state of the titanium plate 10 to a predetermined value.

  Here, the Vickers hardness at a measurement load of 0.098 N (10 g) can evaluate the hardness of the outermost surface of the titanium plate, and the Vickers hardness at a measurement load of 4.9 N (200 g) Hardness can be evaluated. Moreover, the formation degree of the hard layer 2 can be evaluated by taking these differences.

  When the hard layer 2 is formed on the surface of the titanium plate 10, the Vickers hardness increases in proportion to the thickness. The difference between the Vickers hardness at a measurement load of 0.098N and the Vickers hardness at a measurement load of 4.9N ([Vickers hardness at a measurement load of 0.098N] − [Vickers hardness at a measurement load of 4.9N) ]) Less than 40, seizure with the tool may occur. On the other hand, if it exceeds 900, surface cracks are likely to occur during molding, and moldability may deteriorate. Therefore, the difference between the Vickers hardness at a measurement load of 0.098N and the Vickers hardness at a measurement load of 4.9N is preferably 40 to 900. In addition, More preferably, it is 40-500.

  The measurement of Vickers hardness may be performed by, for example, a method based on JIS Z 2244 with the measurement surface being a titanium plate surface. At that time, the measurement load is 4.9 N and 0.098 N, 10 points are measured for each measurement load, and the average value is used as the measurement value. A micro Vickers hardness tester is used for measurement with a measurement load of 4.9 N, and an ultra micro Vickers hardness tester is used for measurement with a measurement load of 0.098 N. Then, the difference between the Vickers hardness at a measurement load of 4.9 N and the Vickers hardness at a measurement load of 0.098 N is calculated.

<Crystal grain size>
The titanium plate 10 preferably has a crystal grain size in the range of 20 to 80 μm in terms of average slice length when a cross section cut by a cutting method specified in JIS G 0552 is observed with an optical microscope. When the average section length of the crystal grain size is less than 20 μm, the work hardening index is low, and excellent stretch formability may not be obtained. On the other hand, when the average intercept length of the crystal grain size exceeds 80 μm, the material strength may be lowered. Therefore, the average intercept length of the crystal grain size is preferably within the above range from the viewpoint of formability and strength characteristics of the titanium plate 10. In addition, More preferably, it is 35-80 micrometers. The control of the crystal grain size is performed by the hot rolling and the heating temperature / cooling rate during cold rolling described later.

≪Titanium plate manufacturing method≫
Next, the manufacturing method of the titanium plate which concerns on this invention is demonstrated.
The method for manufacturing a titanium plate according to the present invention is a method for manufacturing the titanium plate 10 described above, and includes a hard layer forming step and a hard layer removing step.
Hereinafter, each step will be described.

<Hard layer forming process>
The hard layer forming step is a step of forming a hard layer on the surface of the titanium material.
In the hard layer forming step, first, a conventionally known method, for example, a raw material metal is melted and cast to form an ingot, which is hot-rolled and then cold-rolled to prepare a titanium material produced. Next, this titanium material is heat-treated to form a hard layer on the surface of the titanium material.

  The type and thickness of the hard layer can be controlled by the heat treatment atmosphere and temperature / time. The heat treatment temperature is preferably 600 to 800 ° C. If the heat treatment temperature is less than 600 ° C., there is a possibility that recrystallization of the structure after cold rolling does not occur sufficiently. On the other hand, when the temperature exceeds 800 ° C., the β phase is precipitated during the heat treatment, the crystal grains become fine after cooling, and the moldability deteriorates because the thickness of the hard layer becomes 20 μm or more even after treatment for several minutes. There is a fear. The treatment time may be adjusted in consideration of the heat treatment temperature. That is, a hard layer having a desired type and thickness can be obtained by controlling the heat treatment atmosphere and time at a predetermined temperature within this range. For example, titanium oxide having a thickness of about 100 nm can be obtained by performing heat treatment at 600 ° C. for 1 hour in the air. In the case of forming titanium nitride or titanium carbide, a hard layer having a similar structure can be formed by changing the atmosphere of the heat treatment. Further, the thickness of the hard layer may be in a range where good seizure resistance is obtained, and is preferably 5 to 250 nm.

  The titanium plate on which the hard layer is formed is cooled to room temperature (for example, about 20 ° C. ± 15 ° C.). In particular, as will be described later, when only the acid tip treatment is performed in the hard layer removing step, the substrate is cooled to room temperature at a rate of 100 ° C./min or higher. Examples of the cooling method after the heat treatment include furnace cooling, air cooling, water cooling, and the like, but the above cooling rate is necessarily satisfied when air cooling or water cooling is used. On the other hand, when salt furnace immersion is performed in the hard layer removal step, the titanium plate on which the hard layer is formed may be cooled at a rate of 100 ° C./min or higher, or may not be cooled at a rate of 100 ° C./min or higher. Also good.

<Hard layer removal process>
The hard layer removing step is a step of partially removing the hard layer.
That is, when the surface of the titanium plate is observed on a plurality of grid-like observation images, when each side of each grid is 10 μm, the grid is measured in the area per 1 mm ^{2 on} the surface of the titanium plate. It removes partially so that the total average of the length of a hard layer in the position where the straight line to construct crosses each surface of a hard layer may be 5-200 micrometers.
As a method of partially removing the hard layer, a method of partially removing the hard layer by immersing in a salt furnace heated to 350 ° C. or higher (salt furnace dipping treatment), 5% by mass or more of nitric acid, The hard layer is partially washed by pickling in a pickling bath containing 1% by mass or more of hydrofluoric acid and having a mass ratio of nitric acid to hydrofluoric acid (hydrofluoric acid / nitric acid) of 0.1 or more. A removal method (pickling treatment) can be used.

[Salt furnace immersion treatment]
After the heat treatment, the hard layer can be partially removed by immersing the titanium plate in a salt furnace heated to 350 ° C. or higher. Specifically, when the temperature rises rapidly by immersing in a salt furnace heated to 350 ° C. or higher for about 30 to 60 seconds, a rapid temperature change is given to the titanium plate, and fine cracks are formed in the entire hard layer. And the hard layer is partially peeled off. When the holding temperature of the salt furnace is less than 350 ° C., cracks do not enter sufficiently. Note that the holding temperature of the salt furnace is preferably 400 ° C. or higher, and the salt melting at 350 ° C. or higher may be selected. In this way, when removing the hard layer by immersion in a salt furnace, the size of cracks entering the hard layer changes depending on the degree of temperature change applied, but by immersing in a salt furnace at 350 ° C. or higher for a predetermined time, The layer size can be 5 to 200 μm .

  In addition, although a hard layer can be partially removed by salt furnace immersion treatment, you may perform pickling treatment after salt furnace immersion treatment. Thereby, even when a part of the hard layer remains on the surface of the titanium material, the remaining hard layer can be removed by pickling, so that the hard layer can be more reliably removed. In addition, since the titanium plate is immersed in the salt furnace, it is shielded from the atmosphere, and the unhard layer that appears on the surface is oxidized, and a new hard layer is not formed.

[Pickling treatment]
The hard layer can be partially removed by performing a pickling treatment after the heat treatment. In addition, although it is easy to perform above-mentioned salt furnace immersion before a pickling process, a desired surface state can be obtained even if it performs a pickling process directly after heat processing. When removing the hard layer only by pickling without immersion in the salt furnace, the thermal crack that occurs when the titanium plate is cooled after the formation of the hard layer (heat treatment) is the starting point from which the hard layer is removed by pickling. (Due to rapid cooling, the hard layer on the surface of the titanium plate tends to shrink, but the inside is slow to cool, so cracks occur on the surface). By cooling the titanium plate on which the hard layer is formed to room temperature at a rate of 100 ° C./min or more, it is possible to insert cracks in which the size of the hard layer remaining after the subsequent pickling treatment is 5 to 200 μm. Become.

  The solution used for the pickling treatment contains nitric acid at 5% by mass or more, hydrofluoric acid at 1% by mass or more, and the mass ratio of nitric acid to hydrofluoric acid (hydrofluoric acid / nitric acid) is 0.1 or more. And In any case, the pickling speed is slow and the productivity is poor under the condition below this value. In addition, when pickling directly after formation of a hard layer without immersion in a salt furnace, the hard layer can be partially peeled (removed) in a short time by increasing the acid concentration. For example, nitric acid: 7.5 mass%, hydrofluoric acid: 4.8 mass%, and mass ratio of nitric acid and hydrofluoric acid (hydrofluoric acid / nitric acid): 0.64. The pickling temperature is not particularly specified, but the bath temperature may be set within the range of room temperature to 70 ° C. according to the pickling time determined from the configuration of the production line (if the temperature is changed, pickling is performed). Speed changes).

  When the hard layer is removed by pickling, the hard layer is generally divided into a portion where the hard layer is easily removed and a portion where the hard layer is difficult to be removed. In the conventional titanium plate manufacturing method, all the hard layer was removed by increasing the pickling time, but by shortening the pickling time, a structure in which the hard layer partially remained can be formed. It becomes possible. The optimum pickling time varies depending on the thickness of the hard layer, the pickling temperature, and the composition of the pickling solution. If the pickling time is too long, the hard layer will be removed more than necessary, so it is necessary to adjust accordingly.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the scope of the present invention.
For example, in the removal of the hard layer, if it is a process that gives a sudden temperature change under the condition that a new hard layer is not generated on the surface of the titanium plate and can crack the hard layer, or peel it off, The method is not limited to immersion in a salt furnace, and for example, an oil bath or the like may be used.

In addition to salt furnace immersion treatment and pickling, the hard layer may be removed by shot blasting, and the hard layer is partially removed by a combination of two or more of salt furnace immersion, pickling and shot blasting. May be.
Furthermore, in addition to the method of partially removing the hard layer as described above, a method of partially forming the hard layer on the titanium plate surface may be used.

  Further, in carrying out the present invention, for example, a titanium material cleaning step for cleaning the titanium material, or unnecessary removal of dust and the like is not required between and before and after each step within a range that does not adversely affect each step. Other steps such as an object removing step and a titanium plate drying step for drying the titanium plate may be included.

  Next, the effect of the present invention will be described by comparing an example that satisfies the requirements of the present invention with a comparative example that does not satisfy the requirements of the present invention. In this test, a titanium material equivalent to JIS-1 type was used, but the effect of the present invention was to use a titanium material equivalent to JIS-2 type, and other grades of pure titanium material and titanium alloy material. Needless to say, the same effect can be achieved with a titanium plate.

As a raw material, an industrial pure titanium plate (JIS-1 type, cold rolled plate) was used. The chemical composition is O: 450 ppm, Fe: 250 ppm, N: 40 ppm, the balance: Ti and inevitable impurities. The titanium plate is obtained by subjecting a titanium raw material to a melting step, a casting step, a hot rolling step, and a cold rolling step that are well known to those skilled in the art.
This pure titanium plate was subjected to atmospheric annealing (heat treatment) at a predetermined temperature and for a predetermined time, and air-cooled to room temperature. Thereafter, a part is subjected to a salt furnace immersion treatment for 1 minute, and a part is subjected to a pickling treatment using a hydrofluoric acid nitric acid mixed solution having a predetermined concentration heated to 60 ° C. After the salt furnace immersion treatment for 1 minute, the pickling treatment was performed using a hydrofluoric acid nitric acid mixed solution having a predetermined concentration heated to 60 ° C. These conditions are shown in Table 1.

For comparison, a sample was prepared by vacuum annealing. The same industrial pure titanium plate as described above was used, the surface of the titanium plate was degreased and cleaned, and then vacuum annealing (heat treatment) was performed. As vacuum annealing, the pressure in the chamber was once reduced to 5 × 10 ⁻³ Pa and the interior of the furnace was heated to 650 ° C., then oxygen gas was introduced until a predetermined pressure was reached, and air cooling was performed to room temperature after 2 hours. . The pressure during the heat treatment was 5 × 10 ⁻³ Pa (No. 8 in Table 1).

  These titanium plates were measured for the following characteristics and evaluated for seizure resistance and formability.

(Measurement of hard layer size)
For the size of the hard layer, a photograph (see FIG. 5 (see FIG. 5 shows the test specimen) of a region (area) of 1 mm × 1 mm on one side of the surface of the titanium plate observed at a magnification of 100 times using a scanning electron microscope. No. 1)) was prepared, a straight line was drawn in an arbitrary direction on the surface, and further, parallel and perpendicular to the straight line, a straight line was drawn in a grid pattern with a grid interval of 10 μm. Image analysis was performed so as to obtain a state, and the total average of the lengths of the straight lines crossing the surface of each partially formed hard layer was calculated. In FIG. 5, the hard layer (titanium oxide) as the hard part and the titanium material as the soft part were distinguished from the difference in oxygen concentration in the EDX analysis.

(Measurement of hard layer area ratio)
For the area ratio of the hard layer, a photograph (see FIG. 5) observed at a magnification of 100 times using a scanning electron microscope is prepared, image analysis is performed on this photograph, and the total area of the hard layer with respect to the entire surface of the titanium plate The rate was measured.

(Measurement of surface roughness)
The arithmetic average roughness (Ra) and the maximum height (Rz) of each specimen were measured. For the measurement, a surface roughness shape measuring machine (Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd.) was used, and measurement was performed by a method based on JIS B 0601: 2001. At that time, the measurement distance was 7 mm, the measurement speed was 0.3 mm / sec, 5 points each in parallel and perpendicular to the rolling direction were measured, and the average value was taken as the measurement value.

(Measurement of Vickers hardness)
The measurement of Vickers hardness was carried out by a method based on JIS Z 2244 with the measurement surface as the surface of the test specimen. The measurement load was 4.9 N (200 g) and 0.098 N (10 g), 10 points were measured for each measurement load, and the average value was used as the measurement value. A micro Vickers hardness tester (MATSUZAWA SEIKI DMH-1) is used to measure a measurement load of 4.9N, and an ultra micro Vickers hardness tester (AKASHI MVK-G3) is used to measure a measurement load of 0.098N. It was. Further, the difference between the Vickers hardness at a measurement load of 4.9 N and the Vickers hardness at a measurement load of 0.098 N ([Vickers hardness at a measurement load of 0.098 N] − [Vickers hardness at a measurement load of 4.9 N) ]) Was calculated.

(Measurement of crystal grain size)
The crystal grain size was measured by cutting each test specimen by a method based on the cutting method of JIS G 0552 and measuring the crystal grain size when the cross-sectional structure was observed with an optical microscope. The crystal grains had an equiaxed shape.

(Evaluation of seizure resistance)
Each specimen was evaluated for seizure resistance. Using a surface property measuring device (TRIBOGEAR TYPE: 14FW) manufactured by HEIDON, a steel ball of φ9.525mm (material: SKD11, surface hardness: HRC60) is used as a counterpart material, and a predetermined thickness is placed on a titanium plate. Changes in the coefficient of friction when a constant load was applied and reciprocated 10 times were measured. The load applied was 10, 20, 50, 100 g, the reciprocating distance was 20 mm, and the speed was 120 mm / min. When the friction coefficient μ exceeded 0.15 for the first time, seizure was considered to occur, and the maximum load that kept the friction coefficient μ 0.15 or less after 10 reciprocations was defined as seizure resistance. When the seizure load is 50 g or more, seizure resistance is good, and when it is less than 50 g, seizure resistance is poor.

(Evaluation of formability)
The moldability was evaluated by performing a press test using a molding die simulating the heat exchange part of the plate heat exchanger for each test body. As shown in FIG. 4 (a), the shape of the molding die is a molded portion having a 100 mm × 100 mm pitch, a pitch of 10 mm, and a maximum height (Rz) of 4 mm. The apex has six types of R shapes of R = 0.4, 0.6, 0.8, 1.0, 1.4, and 1.8. As shown in FIG. 4B, the measurement position C is the peak side of the line passing through the mold center, and the measurement position C ′ is the valley side of the line passing through the mold center.

Using this molding die, press molding was performed with an 80-t hydraulic press. In press molding, press oil having a kinematic viscosity of 34 mm ² / s (temperature: 40 ° C.) is applied to both surfaces of each specimen cut to 160 mm × 160 mm, and the rolling direction of each specimen is the vertical direction in FIG. It arrange | positioned on a lower metal mold | die so that it might correspond, and it implemented on the conditions of press speed 1mm / s and indentation depth 3.6mm. And formability was evaluated by the number of cracks observed in each specimen after press molding. The specific evaluation method is as follows.

  The presence or absence of cracks in each specimen was visually observed at 36 intersection points of the ridge line portion and the dotted line (5 on the mountain side and 1 on the valley side) shown in FIG. For the measurement positions A, C, C ′, and E, which are the starting points of cracks, 2 points are given when no cracks are observed, 1 point when necking is observed, and 0 points when cracks are found. Scored. The other measurement positions B and D were scored with 1 point when no cracks were observed, 0.5 points when necking was observed, and 0 points when cracks were observed. Then, the number of points was multiplied by the reciprocal of processing R to quantify the state of cracking, and the total was obtained. This total value was normalized as 100 when no cracks were completely observed, and was calculated as a moldability score by the following formula (1). The method for calculating the moldability score is as follows.

Formability score = ΣE (ij) / R (j) / (ΣA _{, C, C ′, E} 2 / R (j) + ΣB _{, D} 1 / R (j)) × 100 (1) )
Here, in Formula (1),
In the case of A, C, C ′, E, E (ij) = 1.0 × (no cracking; 2, constriction; 1, cracking; 0)
In the case of B and D, it was calculated as E (ij) = 0.5 × (no crack; 2, constriction; 1, crack; 0).
A moldability score of 70 points or more was considered good moldability and less than 70 points was poor moldability.

  These results are shown in Table 1. In Table 1, those that cannot be measured are indicated by “−”.

As shown in Table 1, no. Since 1-6 satisfy | filled the range of this invention, the seizure resistance and the moldability were favorable.
On the other hand, no. Nos. 7, 9, and 10 had relatively good moldability, but were inferior in seizure resistance because a hard layer was not formed on the surface.
No. No. 8 was inferior in moldability because the hard layer produced during the vacuum annealing treatment was continuously formed on the surface.

  Here, the specimen No. An SEM photograph of the surface of No. 1 is shown in FIG. As shown in FIG. 5, it can be seen that irregularities are formed on the surface and the hard layer is formed as a convex portion. The hard layer formed as a convex part exhibits seizure resistance, and the titanium material that is the uncured part of the concave part exhibits high moldability, which is considered to have excellent seizure resistance and press formability. .

  As mentioned above, although the titanium plate which concerns on this invention, and its manufacturing method were shown in detail, showing embodiment and an Example, the meaning of this invention is not limited to an above-described content. Needless to say, the contents of the present invention can be widely modified and changed based on the above description.

1 titanium material 2 hard layer 10 of titanium plate S linear L ₁ ~L ₈ hard layer length M grid W length of squares of sides

Claims (9)

A titanium plate for a heat exchange member of a plate heat exchanger in which press molding is performed,
A hard layer is partially formed on the surface of the titanium material ,
When the surface of the titanium plate is observed on a plurality of grid-like observation images and each side of each grid is 10 μm, the hard layer is per 1 mm ^{2 on} the surface of the titanium plate. Titanium characterized in that, in terms of area, the total average length of the hard layer at a position where a straight line constituting the grid crosses each surface of the hard layer is 5 to 200 μm. Board.   2. The titanium plate according to claim 1, wherein the total area ratio of the hard layer with respect to the entire surface of the titanium plate is 20 to 90%.   3. The titanium plate according to claim 1, wherein an arithmetic average roughness (Ra) of a surface of the titanium plate is 0.15 to 1.5 μm.   4. The titanium plate according to claim 1, wherein a maximum height (Rz) of the surface of the titanium plate is 1.5 to 9.0 μm. 5. A method for producing a titanium plate according to any one of claims 1 to 4,
A hard layer forming step of forming a hard layer on the surface of the titanium material;
And a hard layer removing step of partially removing the hard layer.   The method for producing a titanium plate according to claim 5, wherein in the hard layer removing step, the hard layer is partially removed by immersing in a salt furnace heated to 350 ° C or higher.   In the hard layer removal step, the pickling bath contains 5% by mass or more nitric acid and 1% by mass or more hydrofluoric acid, and the mass ratio of nitric acid to hydrofluoric acid (hydrofluoric acid / nitric acid) is 0.1 or more. The method for producing a titanium plate according to claim 5, wherein the hard layer is partially removed by pickling inside.   In the hard layer removing step, after being immersed in a salt furnace heated to 350 ° C. or higher, nitric acid is contained in an amount of 5% by mass or more, hydrofluoric acid is contained in an amount of 1% by mass or more, and a mass ratio of the nitric acid and the hydrofluoric acid (hydrofluoric acid). The method for producing a titanium plate according to claim 5, wherein the hard layer is partially removed by pickling in a pickling bath of 0.1 or more acid / nitric acid). A method for manufacturing a heat exchange member of a plate heat exchanger, wherein the titanium plate according to any one of claims 1 to 4 is press-molded.