JP2010255085A - Titanium plate and method for producing titanium plates - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a titanium plate which has satisfactory seizure resistance and crack resistance, thus has excellent press formability. <P>SOLUTION: In the titanium plate, the arithmetic mean roughness (Ra) lies in the range of 0.15 to 1.5 μm, the maximum height (Rz) lies in the range of 1.5 to 9.0 μm, skewness (Rsk) lies in the range of -3.0 to -0.5, the Vickers hardness at a measurement load of 0.098 N in the surface is higher than the Vickers hardness at a measurement load of 4.9 N, and a difference therebetween is ≤45. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a titanium plate used as a heat exchanger member, a consumer product such as a camera body and a kitchen device, a transport device member such as a motorcycle and an automobile, and an exterior material such as a home appliance, and a method of manufacturing the titanium plate.

  Titanium plates are excellent in corrosion resistance and are used in heat exchangers such as chemical, electric power and food production plants. In particular, a plate heat exchanger using a titanium plate increases the heat exchange efficiency by processing the titanium plate into a wave by press molding to increase the surface area. Therefore, the moldability for giving a deep corrugation is required. In addition, excellent formability is required for processing into camera casings, exterior products for home appliances, members for transportation equipment, and the like. Usually, the formability requires workability and lubricity of the plate itself.

  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 plate itself. A molding die and seizure occur in the molding process, which is a factor for lowering the molding limit. For this reason, it is generally said that for molded products that emphasize drawing, it is possible to improve moldability by preventing seizure with a tool, that is, by improving seizure resistance.

For example, Patent Document 1 describes a titanium thin plate having a titanium nitride layer with a thickness of 0.1 μm or more and 1.0 μm or less on the surface and a nitrogen diffusion layer under the titanium nitride layer. Patent Document 2 describes a titanium thin plate for forming, which has a nitrogen-enriched layer on the surface and has a thickness of 0.5 μm or more and 5 μm or less. Describes a titanium plate excellent in press moldability and surface gloss, characterized in that a TiC-containing layer is present on the surface layer of the base titanium and the thickness of the TiC-containing layer is 300 mm or more.
According to Patent Documents 1 to 3, it is described that seizure resistance and formability can be improved by forming a cured layer on the surface.

Patent Document 4 discloses that the surface of a titanium thin plate has a Vickers hardness with a load of 50 gf; HVS0.05 is 180 to 280, a Vickers hardness with a load of 200 gf; HVS0.2 is 170 or less, and JIS Z 2247 B An industrial pure titanium thin plate characterized in that the Erichsen value according to the law is 11.5 mm or more is described.
According to Patent Document 4, it is described that the surface hardness can be appropriately reduced as compared with the titanium plates of Patent Documents 1 to 3.

Further, in Patent Document 5, the arithmetic average roughness of the surface in the direction parallel to the rolling direction is 0.25 μm or more and 2.5 μm or less, and the test load is 0.098 N rather than the Vickers hardness due to the test load of 4.9 N on the surface. The titanium plate is characterized in that the Vickers hardness by 20 is higher than 20 and the Vickers hardness by test load 4.9N is 180 or less.
According to Patent Document 5, by increasing the roughness of the surface of the titanium plate to some extent, the amount of lubricant drawn between the titanium plate and the molding die during press molding is increased to prevent seizure, It describes that seizure flaws after press molding can be reduced.

In Patent Document 6, the content ratios of Fe, Ni, and Cr are 100 ppm ≦ Fe ≦ 700 ppm, 100 ppm ≦ Ni + Cr ≦ 700 ppm, and 200 ppm ≦ Fe + Ni + Cr ≦ 1100 ppm by weight ratio, and contain O (oxygen) A pure titanium material having a rate of 900 ppm or less and the balance of Ti and inevitable impurities is cold-rolled, and then annealed at a temperature of 600 to 850 ° C., so that the average crystal grain size of the pure titanium plate is 20 to 80 μm. And then pickling with an aqueous nitric hydrofluoric acid solution satisfying 2 wt% ≦ hydrofluoric acid ≦ 7 wt%, 4 wt% ≦ nitric acid ≦ 20 wt%, and 1 wt% ≦ nitric acid / hydrofluoric acid ≦ 5 wt%. A method for producing a pure titanium plate is described.
According to Patent Document 6, it is described that seizure hardly occurs during processing such as pressing, the formability of pressing is good, the surface is clean, and an inexpensive pure titanium plate can be manufactured. Has been.

  On the other hand, there is an Erichsen test (JIS B 7729) as a stretch forming evaluation that has been generally performed conventionally, and there are many known techniques defined in this Eriksen test. In the case of such a known technique, since the processing R is relatively large (punch φ20), the problem of surface cracking is difficult to manifest, and the formability can be improved by improving the surface seizure resistance. there were.

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. 2002-3968 Japanese Patent Laid-Open No. 10-30160

  However, in Patent Documents 1 to 3, since a hardened layer is formed on the surface, it is preferable to apply it to products that are subjected to processing that emphasizes seizure resistance. There is a problem that surface cracks easily occur and the moldability deteriorates.

  Patent Document 4 has a problem that the surface hardness is high and cracks are easily generated, and the surface form is not appropriate and seizure is likely to occur. That is, when it became a severe shape, there existed a problem that generation | occurrence | production of a crack could not be suppressed. Furthermore, when an oxide film is formed on the surface of the titanium plate to prevent seizure, there is a problem that the interference of light occurs depending on the thickness of the titanium plate and the design property is impaired.

  Since Patent Document 5 focuses on increasing the surface hardness in order to improve seizure resistance, there is a problem that surface cracks are likely to occur and the moldability is deteriorated. In addition, oil retention during press molding is improved by increasing the surface roughness. However, since the surface roughness is managed only by Ra, sufficient oil retention may not be achieved. In order to prevent sticking, it was necessary to form a relatively thick (that is, easy to break) oxide film. Further, in Patent Document 5, shot blasting is performed as a method for controlling the surface roughness. However, there is a problem in that the titanium plate is easily warped in the subsequent heat treatment, and the correction is required and productivity is poor. It was. Furthermore, cold rolling is also performed on the titanium plate using a rolling roll subjected to rough polishing, but when the surface of the titanium plate is adjusted to a rough surface by this method, the surface of the titanium plate is There are many sharp parts (convex parts). For this reason, the surface pressure of each sharp part rises, so it is easy to seize with the tool, and because the unevenness is aligned in one direction, once seizure occurs, seizure is not interrupted and defective products are generated. There was a problem that it was easy.

  Further, in Patent Document 6, the added element inhibits the growth of crystal grains, and a long heat treatment is required to obtain a desired particle size, so that productivity is lowered and a desired particle size is obtained. In some cases, the moldability itself was poor. In addition, since the grain boundary portion is preferentially dissolved in the pickling process after the elements are segregated at the grain boundary, many concave portions such as sharp notches are easily formed along the grain boundary. Therefore, when emphasis is placed on overhang forming or bending forming, there is a problem that cracking is likely to be the starting point, and formability is deteriorated.

  And in the conventionally known technology, it is understood that when the processing R is small and the forming depth is deep (like a deep and thin groove shape) like the plate heat exchanger member, cracking is likely to occur at the R portion. It was. This is because when a thick oxide film or nitride film is formed to improve seizure resistance, cracks tend to occur and the formability deteriorates. It turns out that it becomes the main factor which determines a limit.

  The present invention was made based on such a background, and provides a titanium plate that exhibits excellent press formability by having good seizure resistance and crack resistance, and a method for producing the titanium plate. Is an issue.

  In order to make the titanium surface difficult to break, it is effective to remove a hardened layer such as an oxide film. However, the titanium surface from which the hardened layer has been removed generally tends to seize with the surface of the molding die. When seizure occurs, it becomes a starting point of cracking, and even if it does not develop into cracking, titanium adheres to the molding die, so that it is necessary to polish the molding die and there is a problem that productivity is lowered. Therefore, it has been a problem to achieve both the removal of the cured layer and the seizure resistance.

  As a result of diligent research, the present inventors have demonstrated that the surface cracks are improved by improving the seizure resistance by maximizing the lubricating effect of the press oil during press molding by optimizing the shape of the surface irregularities. It has been found that it is possible to achieve both the prevention and the seizure prevention of the titanium plate and the molding die, thereby solving the above-mentioned problems, and the present invention has been completed.

(1) The titanium plate according to the present invention that has solved the above problems has an arithmetic average roughness (Ra) in the range of 0.15 to 1.5 μm and a maximum height (Rz) of 1.5 to 9.0 μm. The Vickers hardness at a measurement load of 0.098N on the surface is more than the Vickers hardness at a measurement load of 4.9N, and the degree of strain (Rsk) is in the range of -3.0 to -0.5. The difference is 45 or less.

  As described above, by setting the arithmetic average roughness (Ra) and the maximum height (Rz) to a specific numerical value range, it is possible to exhibit oil retention and make it difficult to induce cracking due to the notch effect. it can. Moreover, since it can prevent that the surface pressure to a smooth part raises by making distortion degree (Rsk) into a specific numerical value range, local plastic deformation and seizure can be prevented. And, the Vickers hardness at the measurement load of 0.098N on the surface is higher than the Vickers hardness at the measurement load of 4.9N, and the difference is set to 45 or less, that is, no hardened layer is formed on the surface. This makes it difficult for surface cracks to occur during molding.

(2) The titanium plate according to the present invention has a crystal grain size in the range of 20 to 80 μm in average slice length when a cross section cut by a cutting method defined in JIS G 0552 is observed with an optical microscope. preferable.
If the average section length of the crystal grain size in the case where the cross section cut by the cutting method specified in JIS G 0552 is observed with an optical microscope is in such a specific numerical range, the pickling process causes unevenness on the surface of the titanium plate. Since it becomes moderately rough, more excellent oil retention can be obtained.

(3) The titanium plate according to the present invention preferably has a plate thickness of 1.0 mm or less.
With such a plate thickness, it can be suitably used as a member for a heat exchanger.

(4) The method for producing a titanium plate according to the present invention includes an atmospheric annealing step in which the titanium plate after cold rolling is subjected to atmospheric annealing so that the crystal grain size is 20 to 80 μm, and the titanium plate after the atmospheric annealing step. Pickling in a pickling bath having a nitric acid / hydrofluoric acid ratio of 1 to 10 and a skin pass rolling the titanium plate after the pickling step with a rolling reduction of 0.2 to 1.0%. A rolling process.

  Thus, the crystal grain size can be made to a desired size by the atmospheric annealing process performed after cold rolling. And, by making each of the pickling step and skin pass rolling step performed on the titanium plate having a crystal grain size a desired size by the atmospheric annealing step as a specific condition, the unevenness of the titanium plate surface is in a desired state, that is, Desired arithmetic average roughness (Ra), maximum height (Rz), and degree of distortion (Rsk) can be obtained.

The titanium plate according to the present invention can exhibit excellent press formability by having good seizure resistance and crack resistance.
Moreover, according to the manufacturing method of the titanium plate which concerns on this invention, the titanium plate which exhibits the outstanding press-formability by having favorable seizure resistance and crack resistance can be manufactured.

It is a flowchart explaining the flow of the manufacturing method of the titanium plate which concerns on this invention. (A) is a top view which shows the shape of the shaping die for performing a moldability evaluation, (b) is the FF sectional view taken on the line of (a). (A) shows specimen No. 7 is a SEM image of the surface of FIG. 7 is a graph showing a roughness curve measured in a direction perpendicular to a rolling direction of 7. (A) shows specimen No. 10 is an SEM image of the surface of No. 10; It is a graph which shows the roughness curve measured to the orthogonal | vertical direction with respect to 10 rolling directions.

The gist of the present invention is to provide excellent formability by paying attention to the control of the form and hardness of the surface irregularities and making the titanium plate compatible with seizure resistance and crack resistance. The gist of the present invention is to provide a titanium plate manufacturing method for manufacturing such a titanium plate.
Here, the formability in the present invention refers to a general term for not only the workability of the plate material but also the lubricity with the press tool and the seizure resistance to the tool.

  The titanium plate according to the present invention has an arithmetic average roughness (Ra) in the range of 0.15 to 1.5 μm, a maximum height (Rz) in the range of 1.5 to 9.0 μm, and a strain ( Rsk) is in the range of -3.0 to -0.5, and the Vickers hardness at the measurement load of 0.098N on the surface is higher than the Vickers hardness at the measurement load of 4.9N, and the difference is 45 or less. It is trying to become. Arithmetic mean roughness (Ra), maximum height (Rz), and degree of distortion (Rsk) are based on JIS B 0601: 2001.

  The titanium plate according to the present invention basically has no hardened layer formed on the surface, and the surface was subjected to X-ray diffraction by a thin film method with an incident angle of 1 ° with an X-ray source of Cu-Kα. At this time, the peaks of TiC and TiN are hardly detected. Here, the hardened layer means a film intentionally formed by heat treatment under controlled atmosphere conditions, and examples thereof include an oxide film, a nitride film, a carbide film, and a film containing one or more of these. In addition, an oxide film formed by pickling treatment or a natural oxide film formed naturally by leaving it in the atmosphere at room temperature is called a passive film, but such a passive film is a cured layer. Not say. The thickness of the hardened layer is defined by Vickers hardness. This will be described later.

  And in the titanium plate which concerns on this invention, the recessed part 10 micrometers or more in diameter is formed discontinuously on the surface. The recess works as an oil reservoir and improves oil retention. Moreover, since the recessed part is formed discontinuously, even if seizure occurs in a certain convex part or a smooth part, seizure stops at the recessed part, and it can be prevented that the seizure develops into a large seizure. Moreover, since the depth of the recess is smaller than the diameter of the recess, the recess can be prevented from acting as a notch (notch effect), and the size (size, depth) and frequency of the recess. It has been clarified that the arithmetic average roughness (Ra), which is generally used as a management index, is insufficient to define the maximum height (Rz) that defines the depth of the recess, and the recess The degree of distortion (Rsk) that prescribes the frequency is defined as a management index, and these are defined in a specific numerical range. The size of the recess can be determined by observing the surface of the titanium plate with an SEM (scanning electron microscope).

As described above, by setting the arithmetic average roughness (Ra) and the maximum height (Rz) to a specific numerical value range, it is possible to exhibit oil retention and make it difficult to induce cracking due to the notch effect. it can. Moreover, since it can prevent that the surface pressure to a smooth part raises by making distortion degree (Rsk) into a specific numerical value range, local plastic deformation and seizure can be prevented. And, the Vickers hardness at the measurement load of 0.098N on the surface is higher than the Vickers hardness at the measurement load of 4.9N, and the difference is set to 45 or less, that is, no hardened layer is formed on the surface. This makes it difficult for surface cracks to occur during molding.
Hereinafter, the definition of these will be described in detail.

(composition)
The titanium plate according to the present invention is not limited to a titanium plate having a specific composition, but is preferably in the following composition range from the viewpoint of securing moldability of the base material.
O is suppressed to 1500 ppm or less, more preferably 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 suppressed to 300 ppm. The other balance is preferably Ti. These O, Fe, N, C, and H are general impurity elements (elements that are not actively added) contained in pure titanium, that is, inevitable impurities.

(Surface roughness)
In order to influence the average friction coefficient of the plate surface, the arithmetic average roughness (Ra) is defined. However, since the arithmetic average roughness (Ra) cannot express the depth of the recess, the maximum height (Rz ) Is also provided.
The arithmetic average roughness (Ra) and the maximum height (Rz) are quantified information only in the height direction (longitudinal direction) of the roughness, and include information on the shape in the horizontal direction (in-plane). Not. Therefore, the degree of distortion (Rsk) is defined in order to quantify the shape and distribution state of the concave portion on the surface.

(Arithmetic mean roughness (Ra))
As described above, the arithmetic average roughness (Ra) is specified in order to affect the average friction coefficient of the plate material surface.
If the arithmetic average roughness (Ra) is less than 0.15 μm, the oil retaining property cannot be exhibited. On the other hand, if the arithmetic average roughness (Ra) exceeds 1.5 μm, cracking due to a notch effect may be induced and formability may be deteriorated. Further, since the coefficient of friction increases, the flow of the plate material is hindered, and local deformation is likely to occur, so that cracking is likely to occur. Furthermore, it is not preferable because the press load is increased.
Therefore, the arithmetic average roughness (Ra) needs to be in the range of 0.15 to 1.5 μm. The arithmetic average roughness (Ra) is preferably in the range of 0.2 to 1.5 μm, and more preferably in the range of 0.2 to 1.0 μm.

(Maximum height (Rz))
The maximum height (Rz) defines the depth of the recess as described above.
If the maximum height (Rz) is less than 1.5 μm, the depth of the recesses is insufficient and good oil retention cannot be exhibited, and seizure is likely to occur during molding. On the other hand, if the maximum height (Rz) exceeds 9.0 μm, it can be the starting point of cracking due to the notch effect.
Therefore, the maximum height (Rz) needs to be in the range of 1.5 to 9.0 μm. The maximum height (Rz) is preferably in the range of 1.8 to 9.0 μm, and more preferably in the range of 1.8 to 6.0 μm.

(Strain (Rsk))
The degree of distortion (Rsk) corresponds to the frequency / area ratio of the recesses.
If the degree of strain (Rsk) is less than −3.0, the area of the smooth portion decreases and the surface pressure on the smooth portion increases, so that local plastic deformation and seizure are likely to occur. On the other hand, when the degree of distortion (Rsk) exceeds -0.5, even if the arithmetic average roughness (Ra) and the maximum height (Rz) are within a specified range, the surface has many convex portions or corner portions. There are many. For this reason, since the molding die slides on the convex portion or the corner portion at the time of molding, the surface pressure on the convex portion increases, and local plastic deformation and seizure of the surface easily occur. As a result, inflow of the plate material is hindered, tensile deformation occurs between two points where the inflow is hindered, and breakage easily occurs.
Accordingly, the degree of distortion (Rsk) needs to be in the range of -3.0 to -0.5. The degree of distortion (Rsk) is preferably in the range of -3.0 to -1.0.

  Here, the degree of distortion (Rsk) is a target parameter with respect to the center line of the amplitude distribution curve, and is calculated by the following equation (1).

  The degree of distortion (Rsk) is 0 when the probability density function obtained from the roughness curve is a normal distribution (targeted in the vertical direction), and is a negative (−) value when the concave portions are distributed on the smooth surface. When a convex portion is distributed on a smooth surface, a positive (+) value is taken.

  In order to achieve the surface form described above, in the titanium plate manufacturing method, it is necessary to control the crystal grain size and pickling conditions of the titanium plate, and to perform skin pass rolling with a light rolling reduction in a predetermined range. Details will be described later.

(Surface hardness)
When the hardened layer is formed on the titanium surface, the hardness is improved. However, it is easy to promote surface cracking by improving the hardness. In order not to promote the occurrence of cracks on the surface, the Vickers hardness at the measurement load of 0.098N and the Vickers hardness at the measurement load of 4.9N are measured, and the difference between them is less than a predetermined threshold value. Stipulated.

Here, the Vickers hardness at a measurement load of 0.098 N (10 g) can evaluate the hardness of the outermost surface, and the Vickers hardness at a measurement load of 4.9 N (200 g) is the hardness inside the material. Can be evaluated. Moreover, these differences can be taken and the formation degree of a hardened layer can be evaluated.
That is, when a hardened layer such as a nitride is formed on the surface, the difference in hardness exceeds 45, and surface cracking is likely to occur during molding, resulting in deterioration of moldability.
Therefore, the difference in Vickers hardness needs to be 45 or less. The difference in Vickers hardness is preferably 36 or less, more preferably 35 or less.

  In general, the Vickers hardness tends to be higher as the load is lower even if the material is homogeneous. For example, in a specimen according to an example of the present invention described later, when measured on a plate material in which a surface portion having a sufficient thickness (one side of 50 μm) is chemically removed, Vickers hardness at a measurement load of 0.098 N is obtained. The measured value of was an average 12 higher than the measured value of Vickers hardness at a measurement load of 4.9 N.

(Crystal grain size range)
The titanium plate according to the present invention preferably has a crystal grain size in the range of 20 to 80 μm in terms of an average slice length when a section cut by a cutting method defined in JIS G 0552 is observed with an optical microscope.
If the average slice length of the crystal grain size in the case of observing the cross section cut by the cutting method prescribed in JIS G 0552 with an optical microscope is in the range of 20 to 80 μm, the size of the crystal grain size is reflected by the pickling process. As a result, irregularities on the surface are formed, so that irregularities on the surface of the titanium plate become moderately rough, and excellent oil retention can be obtained.

If the average section length of the crystal grain size is less than 20 μm when the cross section cut by the cutting method specified in JIS G 0552 is observed with an optical microscope, the surface irregularities after the pickling process become shallow, which is desired. The roughness cannot be obtained.
On the other hand, when the average section length of the crystal grain size exceeds 80 μm when the cross section cut by the cutting method prescribed in JIS G 0552 is observed with an optical microscope, the irregularities formed on the surface even if the pickling process is performed. Since the distance between the recesses is too large, the desired roughness cannot be obtained. Therefore, excellent oil retention is not obtained and seizure is likely to occur. Furthermore, once seizure occurs, it becomes difficult to be interrupted.
Therefore, as described above, the average section length of the crystal grain size in the case where the cross section cut by the cutting method specified in JIS G 0552 is observed with an optical microscope needs to be in the range of 20 to 80 μm. In addition, when the cross section cut | disconnected by the prescription | regulation method prescribed | regulated to JISG0552 is observed with an optical microscope, it is preferable to make the average section length of a crystal grain diameter into the range of 20-65 micrometers, and set it as the range of 35-65 micrometers. Is more preferable.

  The thickness of the titanium plate according to the present invention can be appropriately determined according to handleability and usage, and is not particularly limited. When the titanium plate according to the present invention is suitably used as a member for a heat exchanger, for example, a heat radiating plate, the plate thickness is preferably 1.0 mm or less.

  In addition, the use of the titanium plate according to the present invention is not limited to the above-mentioned members for heat exchangers. For example, consumer products such as camera bodies and kitchen equipment, transport equipment members such as motorcycles and automobiles, and home appliances. It can also be used for exterior materials such as.

  The titanium plate according to the present invention has been described in detail above. According to such a titanium plate, the surface roughness is appropriately controlled by the arithmetic average roughness (Ra), the maximum height (Rz), and the degree of distortion (Rsk), so that excellent oil retention can be obtained. Therefore, as a result of maximizing the lubrication effect of the press oil during press molding, it becomes possible to obtain good seizure resistance. In addition, since the surface roughness is appropriately controlled in this way, the notch effect can be prevented and the occurrence of surface cracks can be prevented. Furthermore, since no hardened layer is formed on the surface of the titanium plate, it is possible to make it difficult for surface cracks to occur during molding. Therefore, the titanium plate according to the present invention can exhibit excellent press formability. Since the titanium plate according to the present invention has good seizure resistance, it is difficult for titanium to adhere to the molding die, and the frequency of polishing the molding die can be reduced. Therefore, productivity can be improved.

The titanium plate demonstrated above can be suitably manufactured with the manufacturing method of the titanium plate which concerns on this invention demonstrated below.
Here, before specifically explaining the method for producing a titanium plate according to the present invention, two typical production steps for a titanium plate after cold rolling are introduced.
The first is to perform vacuum annealing after cold rolling, and the second is to perform atmospheric annealing after cold rolling and then pickling.

  In the former case, a hardened layer is easily formed on the surface of the titanium plate during cold rolling and subsequent vacuum annealing. Even when the vacuum annealing atmosphere is an inert atmosphere and the oxygen and nitrogen partial pressures are lowered, if the lubricating oil during cold rolling remains on the titanium plate surface, titanium carbide is formed on the surface and hardened on the surface. A layer is formed. For this reason, there is a risk that a titanium plate that is susceptible to surface cracking during press formation may be produced.

In the latter case, since the surface hardened layer is removed from the pickled titanium plate, it is suitable for producing a titanium plate excellent in press formability. However, in the conventional control of the form of the titanium plate surface and the manufacturing method, the seizure resistance with the molding die is insufficient, and there is a possibility that seizure easily occurs.
In the present invention, on the basis of the latter manufacturing process, surface irregularities are formed so as to improve the oil retention of the lubricating oil, and the crystal grain size and pickling conditions are specified conditions to control the form, It was decided to carry out skin pass rolling under specific conditions after pickling. By doing in this way, seizure resistance can be improved without using a hardened layer.
Below, the manufacturing method of the titanium plate which concerns on this invention is demonstrated concretely.

As shown in FIG. 1, the manufacturing method of the titanium plate according to the present invention includes an atmospheric annealing step S1, a pickling step S2, and a skin pass rolling step S3, and each step is performed according to this procedure.
In addition, since the process up to the cold rolling does not greatly affect the surface form of the titanium plate according to the present invention, the casting process, the soaking process, the hot rough rolling process, What is necessary is just to perform a finishing process, a winding process, a cold rolling process, etc.
Below, each process of the manufacturing method of the titanium plate of this invention is demonstrated.

(Atmospheric annealing process)
The atmospheric annealing step S1 is a step of performing atmospheric annealing on the titanium plate after cold rolling so that the crystal grain size is 20 to 80 μm. When the crystal grain size of the titanium plate after cold rolling is set to 20 to 80 μm in the atmospheric annealing step S1, irregularities are formed on the surface with an appropriate size (depth) and distribution state by a subsequent pickling step S2. Will be able to. The depth of the concave portion on the surface affects the maximum height (Rz), and the distribution state of the concave portion affects the degree of distortion (Rsk).

In the atmospheric annealing step S1, continuous annealing (processing time is about 30 seconds to about 5 minutes) is performed. General atmospheric annealing is performed at 700 to 800 ° C., but in the present invention, in order to make the crystal grain size within a desired range, it is preferably 750 to 850 ° C. in terms of productivity.
The crystal grain size depends on the annealing temperature and the annealing time. If the crystal grain size is higher than the recrystallization temperature (600 ° C. or higher), the desired crystal grain is obtained by performing long-term atmospheric annealing even in a temperature range of less than 750 ° C. It is possible to obtain the diameter.

  When the atmospheric annealing step S1 is performed in the temperature range of 750 ° C. to 850 ° C., the crystal grain size can be increased as the annealing temperature is increased if the annealing time is constant. On the other hand, if the annealing temperature exceeds 850 ° C., the β phase precipitates during annealing, so that the crystal grains become fine after cooling, and if the treatment is performed for several minutes, there is a possibility that it becomes 20 μm or less. Therefore, the annealing temperature in the air annealing step S1 needs to be 850 ° C. or less.

(Pickling process)
The pickling step S2 is a step of pickling the titanium plate after the atmospheric annealing step S1 in a pickling bath having a nitric acid / hydrofluoric acid ratio of 1 or more and 10 or less. In the pickling step S2, when a pickling bath within the composition range described above is used, it is possible to remove about 20 μm on one side by a treatment for about 60 seconds at a liquid temperature of 65 ° C. By performing such pickling, irregularities can be formed in a desired form on the surface of the titanium plate, and the hardened layer formed on the surface can be removed. If it does in this way, the Vickers hardness in the measurement load 0.098N in the surface is higher than the Vickers hardness in the measurement load 4.9N, and the difference can be 45 or less.

  When the nitric acid / hydrofluoric acid ratio is less than 1, the surface irregularities become too fine (that is, many small and shallow irregularities are formed), and the oil retaining effect cannot be obtained. On the other hand, when the nitric acid / hydrofluoric acid ratio exceeds 10, the pickling speed becomes slow and it becomes difficult to remove the scale, and the pickling is performed smoothly. Therefore, since the unevenness | corrugation formed after pickling becomes small or an unevenness | corrugation is not formed, the outstanding oil retaining property cannot be obtained.

  The pickling temperature is not particularly limited. Since the pickling speed is changed by changing the temperature, the temperature may be set according to the pickling time determined from the configuration of the production line in the range of the bath temperature from room temperature to 70 ° C.

  The removal amount of the surface of the titanium plate by the pickling step S2 is preferably 1 μm or more on one side. The upper limit of the removal amount is not particularly limited, but is preferably 20 μm or less on one side from the viewpoint of productivity and yield.

(Skin pass rolling process)
Skin pass rolling step S3 is a step of performing skin pass rolling with a rolling reduction of 0.2 to 1.0% on the titanium plate after pickling step S2. The skin pass rolling step S3 can be performed at room temperature, whereby the convex portions formed on the surface can be leveled to obtain a titanium plate having appropriate smooth portions and concave portions. Thus, by providing an appropriate smooth portion on the surface, the local surface pressure can be lowered, and the friction coefficient can be reduced.
By performing this skin pass rolling step S3, the arithmetic average roughness (Ra) indicating the average friction coefficient of the titanium plate surface can be set in the range of 0.15 to 1.5 μm, and the depth of the concave portion is indicated. The maximum height (Rz) can be in the range of 1.5 to 9.0 μm, and the degree of distortion (Rsk) indicating the distribution state of the recesses can be in the range of −3.0 to −0.5. .

However, since the skin pass rolling itself is plastically deformed, the higher the reduction rate of the skin pass rolling, the smaller the elongation of the plate material and the smaller the surface recess area, so the degree of strain (Rsk) approaches 0 and the oil retaining property decreases. Resulting in. On the other hand, if the rolling reduction of skin pass rolling becomes too low, an appropriate smooth portion cannot be provided on the surface.
Therefore, the rolling reduction in the skin pass rolling step S3 needs to be 0.2 to 1.0%. In addition, it is preferable that the rolling reduction of skin pass rolling process S3 shall be 0.3-0.8%.

  According to the manufacturing method of the titanium plate concerning the present invention explained above, the titanium plate concerning the present invention mentioned above can be manufactured suitably.

  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.

  The effect of the present invention was verified using a titanium material corresponding to JIS-1 type. Needless to say, the effect of the present invention is the same as that of a titanium plate using a titanium material equivalent to the JIS-2 type and other grades of pure titanium material or titanium alloy material.

A cold rolled sheet of industrial pure titanium (JIS-1 type) was used. The chemical composition is O: 450 ppm, Fe: 250 ppm, N: 40 ppm, and the remainder is Ti and inevitable impurities.
First, a cold-rolled sheet that had been cold-rolled under normal conditions was air-annealed at a temperature of 750 to 850 ° C. The crystal grain size was controlled by the annealing conditions of this atmospheric annealing. The annealing conditions are shown in Table 1.

  Then, the test bodies 1-18 which formed the unevenness | corrugation of the surface by immersing a titanium plate in the hydrofluoric acid nitric acid liquid mixture of the density | concentration shown in Table 1 heated at 60 degreeC, and performing the pickling whose removal amount is 10 micrometers on one side. Obtained. Since the pickling speed varies depending on the nitric acid / hydrofluoric acid ratio, the pickling speed in the solution of each blending ratio was obtained by preliminary experiments, and the pickling time was set so as to obtain a predetermined removal amount.

  Moreover, the skin pass rolling of the rolling reduction shown in Table 1 was performed with respect to a part of test bodies 1-18. Skin pass rolling was performed under cold and lubricated conditions with tensile tension applied to both sides of the specimen. The manufacturing conditions are shown in Table 1 together with the evaluation results of the evaluation items described later.

For comparison, a test body that was subjected to vacuum annealing after cold rolling was prepared. The process up to the cold rolling step is as described above, and then the surface of the titanium plate was vacuum-annealed after degreasing and cleaning. As vacuum annealing, after the pressure in the chamber is once reduced to 1.3 × 10 ⁻³ Pa, the inside of the furnace is heated to 650 ° C., and oxygen gas is introduced until 6.7 × 10 ⁻³ Pa is reached. Cooling was performed after holding for a time. The obtained specimen was designated as specimen 19.

(Measurement of crystal grain size)
The crystal grain size was measured by cutting each test specimen by the cutting method specified in 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.

(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 for measurement with a measurement load of 4.9N, and an ultra micro Vickers hardness tester (AKASHI MVK-G3) is used for measurement with a measurement load of 0.098N. It was. Table 1 shows the measurement value of the measurement load of 4.9N and the difference between the measurement load of 0.098N and the measurement load of 4.9N.

(Measurement of surface roughness)
The surface roughness was measured using a surface roughness shape measuring machine (Surfcom 1400D manufactured by Tokyo Seimitsu Co., Ltd.) according to a method based on JIS B 0601: 2001. At this 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 defined as the surface roughness.

(Evaluation of formability)
The moldability was evaluated by performing press molding using a molding die simulating the heat exchanging portion of the plate heat exchanger for each specimen.
As shown in FIG. 2 (a), the shape of the molding die is such that the molding part is 100 mm × 100 mm, the pitch is 10 mm, the maximum height is 4 mm, and there are six twill lines, each twill line being at the apex, It has six types of R shapes of R = 0.4, 1.8, 0.8, 1.0, 1.4, and 0.6 in order from the top to the bottom of FIG.
Using this molding die, press molding was performed by an 80 ton hydraulic press. In press molding, press oil having a kinematic viscosity of 34 mm ² / s (40 ° C.) is applied to both surfaces of each test specimen, and the lower mold is set so that the rolling direction of each test specimen coincides with the vertical direction in FIG. After placing on the top and restraining the flange portion with a plate press, the pressing speed was 1 mm / s and the pressing depth was 3.8 mm.
The formability was evaluated by the number of cracks observed in each specimen after press molding. A specific evaluation method will be described below.

The presence or absence of cracks in the specimen was visually observed at 36 intersections between the ridge line portion shown in FIG. 2A and the dotted lines of the measurement positions A, B, C, C ′, D, and E. Note that the measurement position C ′ is a valley portion located between adjacent ridge line portions as shown in FIG.
For the measurement positions A, C, C ′, and E, which are the starting points of cracking, two points are given when no cracking or constriction is observed, one point when constriction is observed, and 0 points when cracking is observed, For measurement positions B and D, 1 point is given when no cracking or constriction is observed, 0.5 point when constriction is observed, 0 point when cracking is observed, and each point is the reciprocal of machining R The number of cracks was quantified and the total was obtained. After normalizing this total value as 100 when a case where no constriction is observed is observed, a function F (T, μ depending on temperature (T), lubricating oil viscosity (μ), and specimen thickness (t) is used. , T) and the function G (α, p) depending on the angle (α) and pitch (p) of the twill lines of the mold were calculated as the moldability score. Note that F and G take values from 0 to 1. The above formability score calculation method is represented by the following formula (2).

Formability score = F × G × ΣE (ij) / R (j) / (Σ _{A, C, C ', E} 2 / R (j) + Σ _{B, D} 1 / R (j)) × 100
... Formula (2)
Here, in Formula (2),
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, calculation was performed as E (ij) = 0.5 × (no cracking; 2, constriction; 1, cracking; 0).
Further, in this example, the temperature (T), the lubricating oil viscosity (μ), the test piece plate thickness (t), the angle (α) of the twill lines of the mold, and the pitch (p) were constant, so that F × G For convenience, the score was calculated as 1.

  Table 1 shows the moldability score of each specimen. As the moldability score, 70 points or more were regarded as good moldability, and less than 70 points were regarded as poor moldability.

  As shown in Table 1, the test bodies 1 to 7 had good moldability (Example). This seems to be because the oil-retaining property was improved because the surface roughness was formed in a good form, and the seizure resistance and crack resistance were improved.

  On the other hand, since the specimen 19 has a high surface hardness (Vickers hardness), surface cracking is likely to occur during molding, and as a result of an increased amount of cracking after molding, the moldability seems to have deteriorated ( Comparative example).

  Moreover, although the test bodies 8-11 and 15-17 had low surface hardness (Vickers hardness), they did not show the outstanding moldability (comparative example). This is because the surface roughness of the test specimen was not formed in a good form, and the oil retention was deteriorated due to at least one of the unevenness becoming shallow and the interval between the recesses becoming wide. It seems to be the cause.

  The test body 14 had a crystal grain size that satisfied the requirements of the present invention, but had poor moldability (Comparative Example). This is because the reduction ratio of the skin pass rolling performed after the pickling process was too high, and the good unevenness formed on the surface of the test body 14 in the pickling process was broken to become a smooth surface, and the oil retention was deteriorated. Seem. In addition, since the amount of plastic deformation applied before forming is large, the amount of plastic deformation in press forming is reduced, so that it seems that excellent formability cannot be obtained.

Since the pickling conditions of the test body 18 were not appropriate, the surface irregularities were reduced and the oil retaining property was deteriorated. As a result, the moldability seems to be deteriorated (Comparative Example).
And since the crystal grains of the test bodies 12 and 13 are too small, the unevenness | corrugation of the surface obtained by a pickling process became shallow, and as a result of having deteriorated oil retention property, it seems that the moldability deteriorated (comparative example). .

  Here, the SEM image and roughness curve of the surface of the test body 7 are shown in FIG. 3, and the SEM image and roughness curve of the surface of the test body 10 are shown in FIG.

As shown to Fig.3 (a), it turns out that the several recessed part is disperse | distributed to the smooth part on the surface of the test body 7. FIG. Such a dent acts as an oil reservoir, providing excellent oil retention, providing good seizure resistance and crack resistance despite the pickled surface, resulting in excellent moldability. It is thought that.
Moreover, as shown in FIG.3 (b), in the width | variety of 3 mm in the arbitrary positions of the surface of the test body 7, the recessed part is formed in the surface with a moderate distribution state, and a convex part is almost. It turns out that it is not formed.

On the other hand, as shown to Fig.4 (a), it turns out that the recessed part is hardly formed in the surface of the test body 10. FIG. Therefore, it is considered that the result of inferior moldability was obtained as a result of poor oil retention and poor seizure resistance and crack resistance.
Moreover, as shown in FIG.4 (b), in the width | variety of 3 mm in the arbitrary positions of the surface of the test body 10, it turns out that the recessed part is hardly formed and many convex parts are formed.

S1 Atmospheric annealing process S2 Pickling process S3 Skin pass rolling process

Claims (4)

Arithmetic mean roughness (Ra) is in the range of 0.15 to 1.5 μm,
The maximum height (Rz) is in the range of 1.5 to 9.0 μm,
The degree of strain (Rsk) is in the range of -3.0 to -0.5, and the Vickers hardness at the measurement load of 0.098N on the surface is higher than the Vickers hardness at the measurement load of 4.9N, and the difference Titanium plate characterized in that is 45 or less.   2. The titanium plate according to claim 1, wherein the crystal grain size in the case of observing with a light microscope a section cut by a cutting method defined in JIS G 0552 is in the range of 20 to 80 μm in average section length. .   The titanium plate according to claim 1 or 2, wherein a plate thickness is 1.0 mm or less. An atmospheric annealing step in which the titanium plate after cold rolling is subjected to atmospheric annealing so that the crystal grain size is 20 to 80 μm;
A pickling step of pickling the titanium plate after the atmospheric annealing step in a pickling bath having a nitric acid / hydrofluoric acid ratio of 1 to 10;
A skin pass rolling step in which the titanium plate after the pickling step is subjected to skin pass rolling with a rolling reduction of 0.2 to 1.0%;
The manufacturing method of the titanium plate characterized by the above-mentioned.